packfile: fix off-by-one error in decoding logic

[git/debian.git] / object-file.c

/*
 * GIT - The information manager from hell
 *
 * Copyright (C) Linus Torvalds, 2005
 *
 * This handles basic git object files - packing, unpacking,
 * creation etc.
 */
#include "cache.h"
#include "config.h"
#include "string-list.h"
#include "lockfile.h"
#include "delta.h"
#include "pack.h"
#include "blob.h"
#include "commit.h"
#include "run-command.h"
#include "tag.h"
#include "tree.h"
#include "tree-walk.h"
#include "refs.h"
#include "pack-revindex.h"
#include "hash-lookup.h"
#include "bulk-checkin.h"
#include "repository.h"
#include "replace-object.h"
#include "streaming.h"
#include "dir.h"
#include "list.h"
#include "mergesort.h"
#include "quote.h"
#include "packfile.h"
#include "object-store.h"
#include "promisor-remote.h"

/* The maximum size for an object header. */
#define MAX_HEADER_LEN 32


#define EMPTY_TREE_SHA1_BIN_LITERAL \
         "\x4b\x82\x5d\xc6\x42\xcb\x6e\xb9\xa0\x60" \
         "\xe5\x4b\xf8\xd6\x92\x88\xfb\xee\x49\x04"
#define EMPTY_TREE_SHA256_BIN_LITERAL \
        "\x6e\xf1\x9b\x41\x22\x5c\x53\x69\xf1\xc1" \
        "\x04\xd4\x5d\x8d\x85\xef\xa9\xb0\x57\xb5" \
        "\x3b\x14\xb4\xb9\xb9\x39\xdd\x74\xde\xcc" \
        "\x53\x21"

#define EMPTY_BLOB_SHA1_BIN_LITERAL \
        "\xe6\x9d\xe2\x9b\xb2\xd1\xd6\x43\x4b\x8b" \
        "\x29\xae\x77\x5a\xd8\xc2\xe4\x8c\x53\x91"
#define EMPTY_BLOB_SHA256_BIN_LITERAL \
        "\x47\x3a\x0f\x4c\x3b\xe8\xa9\x36\x81\xa2" \
        "\x67\xe3\xb1\xe9\xa7\xdc\xda\x11\x85\x43" \
        "\x6f\xe1\x41\xf7\x74\x91\x20\xa3\x03\x72" \
        "\x18\x13"

static const struct object_id empty_tree_oid = {
        .hash = EMPTY_TREE_SHA1_BIN_LITERAL,
        .algo = GIT_HASH_SHA1,
};
static const struct object_id empty_blob_oid = {
        .hash = EMPTY_BLOB_SHA1_BIN_LITERAL,
        .algo = GIT_HASH_SHA1,
};
static const struct object_id null_oid_sha1 = {
        .hash = {0},
        .algo = GIT_HASH_SHA1,
};
static const struct object_id empty_tree_oid_sha256 = {
        .hash = EMPTY_TREE_SHA256_BIN_LITERAL,
        .algo = GIT_HASH_SHA256,
};
static const struct object_id empty_blob_oid_sha256 = {
        .hash = EMPTY_BLOB_SHA256_BIN_LITERAL,
        .algo = GIT_HASH_SHA256,
};
static const struct object_id null_oid_sha256 = {
        .hash = {0},
        .algo = GIT_HASH_SHA256,
};

static void git_hash_sha1_init(git_hash_ctx *ctx)
{
        git_SHA1_Init(&ctx->sha1);
}

static void git_hash_sha1_clone(git_hash_ctx *dst, const git_hash_ctx *src)
{
        git_SHA1_Clone(&dst->sha1, &src->sha1);
}

static void git_hash_sha1_update(git_hash_ctx *ctx, const void *data, size_t len)
{
        git_SHA1_Update(&ctx->sha1, data, len);
}

static void git_hash_sha1_final(unsigned char *hash, git_hash_ctx *ctx)
{
        git_SHA1_Final(hash, &ctx->sha1);
}

static void git_hash_sha1_final_oid(struct object_id *oid, git_hash_ctx *ctx)
{
        git_SHA1_Final(oid->hash, &ctx->sha1);
        memset(oid->hash + GIT_SHA1_RAWSZ, 0, GIT_MAX_RAWSZ - GIT_SHA1_RAWSZ);
        oid->algo = GIT_HASH_SHA1;
}


static void git_hash_sha256_init(git_hash_ctx *ctx)
{
        git_SHA256_Init(&ctx->sha256);
}

static void git_hash_sha256_clone(git_hash_ctx *dst, const git_hash_ctx *src)
{
        git_SHA256_Clone(&dst->sha256, &src->sha256);
}

static void git_hash_sha256_update(git_hash_ctx *ctx, const void *data, size_t len)
{
        git_SHA256_Update(&ctx->sha256, data, len);
}

static void git_hash_sha256_final(unsigned char *hash, git_hash_ctx *ctx)
{
        git_SHA256_Final(hash, &ctx->sha256);
}

static void git_hash_sha256_final_oid(struct object_id *oid, git_hash_ctx *ctx)
{
        git_SHA256_Final(oid->hash, &ctx->sha256);
        /*
         * This currently does nothing, so the compiler should optimize it out,
         * but keep it in case we extend the hash size again.
         */
        memset(oid->hash + GIT_SHA256_RAWSZ, 0, GIT_MAX_RAWSZ - GIT_SHA256_RAWSZ);
        oid->algo = GIT_HASH_SHA256;
}

static void git_hash_unknown_init(git_hash_ctx *ctx)
{
        BUG("trying to init unknown hash");
}

static void git_hash_unknown_clone(git_hash_ctx *dst, const git_hash_ctx *src)
{
        BUG("trying to clone unknown hash");
}

static void git_hash_unknown_update(git_hash_ctx *ctx, const void *data, size_t len)
{
        BUG("trying to update unknown hash");
}

static void git_hash_unknown_final(unsigned char *hash, git_hash_ctx *ctx)
{
        BUG("trying to finalize unknown hash");
}

static void git_hash_unknown_final_oid(struct object_id *oid, git_hash_ctx *ctx)
{
        BUG("trying to finalize unknown hash");
}


const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = {
        {
                NULL,
                0x00000000,
                0,
                0,
                0,
                git_hash_unknown_init,
                git_hash_unknown_clone,
                git_hash_unknown_update,
                git_hash_unknown_final,
                git_hash_unknown_final_oid,
                NULL,
                NULL,
                NULL,
        },
        {
                "sha1",
                /* "sha1", big-endian */
                0x73686131,
                GIT_SHA1_RAWSZ,
                GIT_SHA1_HEXSZ,
                GIT_SHA1_BLKSZ,
                git_hash_sha1_init,
                git_hash_sha1_clone,
                git_hash_sha1_update,
                git_hash_sha1_final,
                git_hash_sha1_final_oid,
                &empty_tree_oid,
                &empty_blob_oid,
                &null_oid_sha1,
        },
        {
                "sha256",
                /* "s256", big-endian */
                0x73323536,
                GIT_SHA256_RAWSZ,
                GIT_SHA256_HEXSZ,
                GIT_SHA256_BLKSZ,
                git_hash_sha256_init,
                git_hash_sha256_clone,
                git_hash_sha256_update,
                git_hash_sha256_final,
                git_hash_sha256_final_oid,
                &empty_tree_oid_sha256,
                &empty_blob_oid_sha256,
                &null_oid_sha256,
        }
};

const struct object_id *null_oid(void)
{
        return the_hash_algo->null_oid;
}

const char *empty_tree_oid_hex(void)
{
        static char buf[GIT_MAX_HEXSZ + 1];
        return oid_to_hex_r(buf, the_hash_algo->empty_tree);
}

const char *empty_blob_oid_hex(void)
{
        static char buf[GIT_MAX_HEXSZ + 1];
        return oid_to_hex_r(buf, the_hash_algo->empty_blob);
}

int hash_algo_by_name(const char *name)
{
        int i;
        if (!name)
                return GIT_HASH_UNKNOWN;
        for (i = 1; i < GIT_HASH_NALGOS; i++)
                if (!strcmp(name, hash_algos[i].name))
                        return i;
        return GIT_HASH_UNKNOWN;
}

int hash_algo_by_id(uint32_t format_id)
{
        int i;
        for (i = 1; i < GIT_HASH_NALGOS; i++)
                if (format_id == hash_algos[i].format_id)
                        return i;
        return GIT_HASH_UNKNOWN;
}

int hash_algo_by_length(int len)
{
        int i;
        for (i = 1; i < GIT_HASH_NALGOS; i++)
                if (len == hash_algos[i].rawsz)
                        return i;
        return GIT_HASH_UNKNOWN;
}

/*
 * This is meant to hold a *small* number of objects that you would
 * want read_object_file() to be able to return, but yet you do not want
 * to write them into the object store (e.g. a browse-only
 * application).
 */
static struct cached_object {
        struct object_id oid;
        enum object_type type;
        void *buf;
        unsigned long size;
} *cached_objects;
static int cached_object_nr, cached_object_alloc;

static struct cached_object empty_tree = {
        { EMPTY_TREE_SHA1_BIN_LITERAL },
        OBJ_TREE,
        "",
        0
};

static struct cached_object *find_cached_object(const struct object_id *oid)
{
        int i;
        struct cached_object *co = cached_objects;

        for (i = 0; i < cached_object_nr; i++, co++) {
                if (oideq(&co->oid, oid))
                        return co;
        }
        if (oideq(oid, the_hash_algo->empty_tree))
                return &empty_tree;
        return NULL;
}


static int get_conv_flags(unsigned flags)
{
        if (flags & HASH_RENORMALIZE)
                return CONV_EOL_RENORMALIZE;
        else if (flags & HASH_WRITE_OBJECT)
                return global_conv_flags_eol | CONV_WRITE_OBJECT;
        else
                return 0;
}


int mkdir_in_gitdir(const char *path)
{
        if (mkdir(path, 0777)) {
                int saved_errno = errno;
                struct stat st;
                struct strbuf sb = STRBUF_INIT;

                if (errno != EEXIST)
                        return -1;
                /*
                 * Are we looking at a path in a symlinked worktree
                 * whose original repository does not yet have it?
                 * e.g. .git/rr-cache pointing at its original
                 * repository in which the user hasn't performed any
                 * conflict resolution yet?
                 */
                if (lstat(path, &st) || !S_ISLNK(st.st_mode) ||
                    strbuf_readlink(&sb, path, st.st_size) ||
                    !is_absolute_path(sb.buf) ||
                    mkdir(sb.buf, 0777)) {
                        strbuf_release(&sb);
                        errno = saved_errno;
                        return -1;
                }
                strbuf_release(&sb);
        }
        return adjust_shared_perm(path);
}

static enum scld_error safe_create_leading_directories_1(char *path, int share)
{
        char *next_component = path + offset_1st_component(path);
        enum scld_error ret = SCLD_OK;

        while (ret == SCLD_OK && next_component) {
                struct stat st;
                char *slash = next_component, slash_character;

                while (*slash && !is_dir_sep(*slash))
                        slash++;

                if (!*slash)
                        break;

                next_component = slash + 1;
                while (is_dir_sep(*next_component))
                        next_component++;
                if (!*next_component)
                        break;

                slash_character = *slash;
                *slash = '\0';
                if (!stat(path, &st)) {
                        /* path exists */
                        if (!S_ISDIR(st.st_mode)) {
                                errno = ENOTDIR;
                                ret = SCLD_EXISTS;
                        }
                } else if (mkdir(path, 0777)) {
                        if (errno == EEXIST &&
                            !stat(path, &st) && S_ISDIR(st.st_mode))
                                ; /* somebody created it since we checked */
                        else if (errno == ENOENT)
                                /*
                                 * Either mkdir() failed because
                                 * somebody just pruned the containing
                                 * directory, or stat() failed because
                                 * the file that was in our way was
                                 * just removed.  Either way, inform
                                 * the caller that it might be worth
                                 * trying again:
                                 */
                                ret = SCLD_VANISHED;
                        else
                                ret = SCLD_FAILED;
                } else if (share && adjust_shared_perm(path)) {
                        ret = SCLD_PERMS;
                }
                *slash = slash_character;
        }
        return ret;
}

enum scld_error safe_create_leading_directories(char *path)
{
        return safe_create_leading_directories_1(path, 1);
}

enum scld_error safe_create_leading_directories_no_share(char *path)
{
        return safe_create_leading_directories_1(path, 0);
}

enum scld_error safe_create_leading_directories_const(const char *path)
{
        int save_errno;
        /* path points to cache entries, so xstrdup before messing with it */
        char *buf = xstrdup(path);
        enum scld_error result = safe_create_leading_directories(buf);

        save_errno = errno;
        free(buf);
        errno = save_errno;
        return result;
}

int raceproof_create_file(const char *path, create_file_fn fn, void *cb)
{
        /*
         * The number of times we will try to remove empty directories
         * in the way of path. This is only 1 because if another
         * process is racily creating directories that conflict with
         * us, we don't want to fight against them.
         */
        int remove_directories_remaining = 1;

        /*
         * The number of times that we will try to create the
         * directories containing path. We are willing to attempt this
         * more than once, because another process could be trying to
         * clean up empty directories at the same time as we are
         * trying to create them.
         */
        int create_directories_remaining = 3;

        /* A scratch copy of path, filled lazily if we need it: */
        struct strbuf path_copy = STRBUF_INIT;

        int ret, save_errno;

        /* Sanity check: */
        assert(*path);

retry_fn:
        ret = fn(path, cb);
        save_errno = errno;
        if (!ret)
                goto out;

        if (errno == EISDIR && remove_directories_remaining-- > 0) {
                /*
                 * A directory is in the way. Maybe it is empty; try
                 * to remove it:
                 */
                if (!path_copy.len)
                        strbuf_addstr(&path_copy, path);

                if (!remove_dir_recursively(&path_copy, REMOVE_DIR_EMPTY_ONLY))
                        goto retry_fn;
        } else if (errno == ENOENT && create_directories_remaining-- > 0) {
                /*
                 * Maybe the containing directory didn't exist, or
                 * maybe it was just deleted by a process that is
                 * racing with us to clean up empty directories. Try
                 * to create it:
                 */
                enum scld_error scld_result;

                if (!path_copy.len)
                        strbuf_addstr(&path_copy, path);

                do {
                        scld_result = safe_create_leading_directories(path_copy.buf);
                        if (scld_result == SCLD_OK)
                                goto retry_fn;
                } while (scld_result == SCLD_VANISHED && create_directories_remaining-- > 0);
        }

out:
        strbuf_release(&path_copy);
        errno = save_errno;
        return ret;
}

static void fill_loose_path(struct strbuf *buf, const struct object_id *oid)
{
        int i;
        for (i = 0; i < the_hash_algo->rawsz; i++) {
                static char hex[] = "0123456789abcdef";
                unsigned int val = oid->hash[i];
                strbuf_addch(buf, hex[val >> 4]);
                strbuf_addch(buf, hex[val & 0xf]);
                if (!i)
                        strbuf_addch(buf, '/');
        }
}

static const char *odb_loose_path(struct object_directory *odb,
                                  struct strbuf *buf,
                                  const struct object_id *oid)
{
        strbuf_reset(buf);
        strbuf_addstr(buf, odb->path);
        strbuf_addch(buf, '/');
        fill_loose_path(buf, oid);
        return buf->buf;
}

const char *loose_object_path(struct repository *r, struct strbuf *buf,
                              const struct object_id *oid)
{
        return odb_loose_path(r->objects->odb, buf, oid);
}

/*
 * Return non-zero iff the path is usable as an alternate object database.
 */
static int alt_odb_usable(struct raw_object_store *o,
                          struct strbuf *path,
                          const char *normalized_objdir, khiter_t *pos)
{
        int r;

        /* Detect cases where alternate disappeared */
        if (!is_directory(path->buf)) {
                error(_("object directory %s does not exist; "
                        "check .git/objects/info/alternates"),
                      path->buf);
                return 0;
        }

        /*
         * Prevent the common mistake of listing the same
         * thing twice, or object directory itself.
         */
        if (!o->odb_by_path) {
                khiter_t p;

                o->odb_by_path = kh_init_odb_path_map();
                assert(!o->odb->next);
                p = kh_put_odb_path_map(o->odb_by_path, o->odb->path, &r);
                assert(r == 1); /* never used */
                kh_value(o->odb_by_path, p) = o->odb;
        }
        if (fspatheq(path->buf, normalized_objdir))
                return 0;
        *pos = kh_put_odb_path_map(o->odb_by_path, path->buf, &r);
        /* r: 0 = exists, 1 = never used, 2 = deleted */
        return r == 0 ? 0 : 1;
}

/*
 * Prepare alternate object database registry.
 *
 * The variable alt_odb_list points at the list of struct
 * object_directory.  The elements on this list come from
 * non-empty elements from colon separated ALTERNATE_DB_ENVIRONMENT
 * environment variable, and $GIT_OBJECT_DIRECTORY/info/alternates,
 * whose contents is similar to that environment variable but can be
 * LF separated.  Its base points at a statically allocated buffer that
 * contains "/the/directory/corresponding/to/.git/objects/...", while
 * its name points just after the slash at the end of ".git/objects/"
 * in the example above, and has enough space to hold all hex characters
 * of the object ID, an extra slash for the first level indirection, and
 * the terminating NUL.
 */
static void read_info_alternates(struct repository *r,
                                 const char *relative_base,
                                 int depth);
static int link_alt_odb_entry(struct repository *r, const struct strbuf *entry,
        const char *relative_base, int depth, const char *normalized_objdir)
{
        struct object_directory *ent;
        struct strbuf pathbuf = STRBUF_INIT;
        khiter_t pos;

        if (!is_absolute_path(entry->buf) && relative_base) {
                strbuf_realpath(&pathbuf, relative_base, 1);
                strbuf_addch(&pathbuf, '/');
        }
        strbuf_addbuf(&pathbuf, entry);

        if (strbuf_normalize_path(&pathbuf) < 0 && relative_base) {
                error(_("unable to normalize alternate object path: %s"),
                      pathbuf.buf);
                strbuf_release(&pathbuf);
                return -1;
        }

        /*
         * The trailing slash after the directory name is given by
         * this function at the end. Remove duplicates.
         */
        while (pathbuf.len && pathbuf.buf[pathbuf.len - 1] == '/')
                strbuf_setlen(&pathbuf, pathbuf.len - 1);

        if (!alt_odb_usable(r->objects, &pathbuf, normalized_objdir, &pos)) {
                strbuf_release(&pathbuf);
                return -1;
        }

        CALLOC_ARRAY(ent, 1);
        /* pathbuf.buf is already in r->objects->odb_by_path */
        ent->path = strbuf_detach(&pathbuf, NULL);

        /* add the alternate entry */
        *r->objects->odb_tail = ent;
        r->objects->odb_tail = &(ent->next);
        ent->next = NULL;
        assert(r->objects->odb_by_path);
        kh_value(r->objects->odb_by_path, pos) = ent;

        /* recursively add alternates */
        read_info_alternates(r, ent->path, depth + 1);

        return 0;
}

static const char *parse_alt_odb_entry(const char *string,
                                       int sep,
                                       struct strbuf *out)
{
        const char *end;

        strbuf_reset(out);

        if (*string == '#') {
                /* comment; consume up to next separator */
                end = strchrnul(string, sep);
        } else if (*string == '"' && !unquote_c_style(out, string, &end)) {
                /*
                 * quoted path; unquote_c_style has copied the
                 * data for us and set "end". Broken quoting (e.g.,
                 * an entry that doesn't end with a quote) falls
                 * back to the unquoted case below.
                 */
        } else {
                /* normal, unquoted path */
                end = strchrnul(string, sep);
                strbuf_add(out, string, end - string);
        }

        if (*end)
                end++;
        return end;
}

static void link_alt_odb_entries(struct repository *r, const char *alt,
                                 int sep, const char *relative_base, int depth)
{
        struct strbuf objdirbuf = STRBUF_INIT;
        struct strbuf entry = STRBUF_INIT;

        if (!alt || !*alt)
                return;

        if (depth > 5) {
                error(_("%s: ignoring alternate object stores, nesting too deep"),
                                relative_base);
                return;
        }

        strbuf_add_absolute_path(&objdirbuf, r->objects->odb->path);
        if (strbuf_normalize_path(&objdirbuf) < 0)
                die(_("unable to normalize object directory: %s"),
                    objdirbuf.buf);

        while (*alt) {
                alt = parse_alt_odb_entry(alt, sep, &entry);
                if (!entry.len)
                        continue;
                link_alt_odb_entry(r, &entry,
                                   relative_base, depth, objdirbuf.buf);
        }
        strbuf_release(&entry);
        strbuf_release(&objdirbuf);
}

static void read_info_alternates(struct repository *r,
                                 const char *relative_base,
                                 int depth)
{
        char *path;
        struct strbuf buf = STRBUF_INIT;

        path = xstrfmt("%s/info/alternates", relative_base);
        if (strbuf_read_file(&buf, path, 1024) < 0) {
                warn_on_fopen_errors(path);
                free(path);
                return;
        }

        link_alt_odb_entries(r, buf.buf, '\n', relative_base, depth);
        strbuf_release(&buf);
        free(path);
}

void add_to_alternates_file(const char *reference)
{
        struct lock_file lock = LOCK_INIT;
        char *alts = git_pathdup("objects/info/alternates");
        FILE *in, *out;
        int found = 0;

        hold_lock_file_for_update(&lock, alts, LOCK_DIE_ON_ERROR);
        out = fdopen_lock_file(&lock, "w");
        if (!out)
                die_errno(_("unable to fdopen alternates lockfile"));

        in = fopen(alts, "r");
        if (in) {
                struct strbuf line = STRBUF_INIT;

                while (strbuf_getline(&line, in) != EOF) {
                        if (!strcmp(reference, line.buf)) {
                                found = 1;
                                break;
                        }
                        fprintf_or_die(out, "%s\n", line.buf);
                }

                strbuf_release(&line);
                fclose(in);
        }
        else if (errno != ENOENT)
                die_errno(_("unable to read alternates file"));

        if (found) {
                rollback_lock_file(&lock);
        } else {
                fprintf_or_die(out, "%s\n", reference);
                if (commit_lock_file(&lock))
                        die_errno(_("unable to move new alternates file into place"));
                if (the_repository->objects->loaded_alternates)
                        link_alt_odb_entries(the_repository, reference,
                                             '\n', NULL, 0);
        }
        free(alts);
}

void add_to_alternates_memory(const char *reference)
{
        /*
         * Make sure alternates are initialized, or else our entry may be
         * overwritten when they are.
         */
        prepare_alt_odb(the_repository);

        link_alt_odb_entries(the_repository, reference,
                             '\n', NULL, 0);
}

/*
 * Compute the exact path an alternate is at and returns it. In case of
 * error NULL is returned and the human readable error is added to `err`
 * `path` may be relative and should point to $GIT_DIR.
 * `err` must not be null.
 */
char *compute_alternate_path(const char *path, struct strbuf *err)
{
        char *ref_git = NULL;
        const char *repo;
        int seen_error = 0;

        ref_git = real_pathdup(path, 0);
        if (!ref_git) {
                seen_error = 1;
                strbuf_addf(err, _("path '%s' does not exist"), path);
                goto out;
        }

        repo = read_gitfile(ref_git);
        if (!repo)
                repo = read_gitfile(mkpath("%s/.git", ref_git));
        if (repo) {
                free(ref_git);
                ref_git = xstrdup(repo);
        }

        if (!repo && is_directory(mkpath("%s/.git/objects", ref_git))) {
                char *ref_git_git = mkpathdup("%s/.git", ref_git);
                free(ref_git);
                ref_git = ref_git_git;
        } else if (!is_directory(mkpath("%s/objects", ref_git))) {
                struct strbuf sb = STRBUF_INIT;
                seen_error = 1;
                if (get_common_dir(&sb, ref_git)) {
                        strbuf_addf(err,
                                    _("reference repository '%s' as a linked "
                                      "checkout is not supported yet."),
                                    path);
                        goto out;
                }

                strbuf_addf(err, _("reference repository '%s' is not a "
                                        "local repository."), path);
                goto out;
        }

        if (!access(mkpath("%s/shallow", ref_git), F_OK)) {
                strbuf_addf(err, _("reference repository '%s' is shallow"),
                            path);
                seen_error = 1;
                goto out;
        }

        if (!access(mkpath("%s/info/grafts", ref_git), F_OK)) {
                strbuf_addf(err,
                            _("reference repository '%s' is grafted"),
                            path);
                seen_error = 1;
                goto out;
        }

out:
        if (seen_error) {
                FREE_AND_NULL(ref_git);
        }

        return ref_git;
}

static void fill_alternate_refs_command(struct child_process *cmd,
                                        const char *repo_path)
{
        const char *value;

        if (!git_config_get_value("core.alternateRefsCommand", &value)) {
                cmd->use_shell = 1;

                strvec_push(&cmd->args, value);
                strvec_push(&cmd->args, repo_path);
        } else {
                cmd->git_cmd = 1;

                strvec_pushf(&cmd->args, "--git-dir=%s", repo_path);
                strvec_push(&cmd->args, "for-each-ref");
                strvec_push(&cmd->args, "--format=%(objectname)");

                if (!git_config_get_value("core.alternateRefsPrefixes", &value)) {
                        strvec_push(&cmd->args, "--");
                        strvec_split(&cmd->args, value);
                }
        }

        cmd->env = local_repo_env;
        cmd->out = -1;
}

static void read_alternate_refs(const char *path,
                                alternate_ref_fn *cb,
                                void *data)
{
        struct child_process cmd = CHILD_PROCESS_INIT;
        struct strbuf line = STRBUF_INIT;
        FILE *fh;

        fill_alternate_refs_command(&cmd, path);

        if (start_command(&cmd))
                return;

        fh = xfdopen(cmd.out, "r");
        while (strbuf_getline_lf(&line, fh) != EOF) {
                struct object_id oid;
                const char *p;

                if (parse_oid_hex(line.buf, &oid, &p) || *p) {
                        warning(_("invalid line while parsing alternate refs: %s"),
                                line.buf);
                        break;
                }

                cb(&oid, data);
        }

        fclose(fh);
        finish_command(&cmd);
        strbuf_release(&line);
}

struct alternate_refs_data {
        alternate_ref_fn *fn;
        void *data;
};

static int refs_from_alternate_cb(struct object_directory *e,
                                  void *data)
{
        struct strbuf path = STRBUF_INIT;
        size_t base_len;
        struct alternate_refs_data *cb = data;

        if (!strbuf_realpath(&path, e->path, 0))
                goto out;
        if (!strbuf_strip_suffix(&path, "/objects"))
                goto out;
        base_len = path.len;

        /* Is this a git repository with refs? */
        strbuf_addstr(&path, "/refs");
        if (!is_directory(path.buf))
                goto out;
        strbuf_setlen(&path, base_len);

        read_alternate_refs(path.buf, cb->fn, cb->data);

out:
        strbuf_release(&path);
        return 0;
}

void for_each_alternate_ref(alternate_ref_fn fn, void *data)
{
        struct alternate_refs_data cb;
        cb.fn = fn;
        cb.data = data;
        foreach_alt_odb(refs_from_alternate_cb, &cb);
}

int foreach_alt_odb(alt_odb_fn fn, void *cb)
{
        struct object_directory *ent;
        int r = 0;

        prepare_alt_odb(the_repository);
        for (ent = the_repository->objects->odb->next; ent; ent = ent->next) {
                r = fn(ent, cb);
                if (r)
                        break;
        }
        return r;
}

void prepare_alt_odb(struct repository *r)
{
        if (r->objects->loaded_alternates)
                return;

        link_alt_odb_entries(r, r->objects->alternate_db, PATH_SEP, NULL, 0);

        read_info_alternates(r, r->objects->odb->path, 0);
        r->objects->loaded_alternates = 1;
}

/* Returns 1 if we have successfully freshened the file, 0 otherwise. */
static int freshen_file(const char *fn)
{
        return !utime(fn, NULL);
}

/*
 * All of the check_and_freshen functions return 1 if the file exists and was
 * freshened (if freshening was requested), 0 otherwise. If they return
 * 0, you should not assume that it is safe to skip a write of the object (it
 * either does not exist on disk, or has a stale mtime and may be subject to
 * pruning).
 */
int check_and_freshen_file(const char *fn, int freshen)
{
        if (access(fn, F_OK))
                return 0;
        if (freshen && !freshen_file(fn))
                return 0;
        return 1;
}

static int check_and_freshen_odb(struct object_directory *odb,
                                 const struct object_id *oid,
                                 int freshen)
{
        static struct strbuf path = STRBUF_INIT;
        odb_loose_path(odb, &path, oid);
        return check_and_freshen_file(path.buf, freshen);
}

static int check_and_freshen_local(const struct object_id *oid, int freshen)
{
        return check_and_freshen_odb(the_repository->objects->odb, oid, freshen);
}

static int check_and_freshen_nonlocal(const struct object_id *oid, int freshen)
{
        struct object_directory *odb;

        prepare_alt_odb(the_repository);
        for (odb = the_repository->objects->odb->next; odb; odb = odb->next) {
                if (check_and_freshen_odb(odb, oid, freshen))
                        return 1;
        }
        return 0;
}

static int check_and_freshen(const struct object_id *oid, int freshen)
{
        return check_and_freshen_local(oid, freshen) ||
               check_and_freshen_nonlocal(oid, freshen);
}

int has_loose_object_nonlocal(const struct object_id *oid)
{
        return check_and_freshen_nonlocal(oid, 0);
}

static int has_loose_object(const struct object_id *oid)
{
        return check_and_freshen(oid, 0);
}

static void mmap_limit_check(size_t length)
{
        static size_t limit = 0;
        if (!limit) {
                limit = git_env_ulong("GIT_MMAP_LIMIT", 0);
                if (!limit)
                        limit = SIZE_MAX;
        }
        if (length > limit)
                die(_("attempting to mmap %"PRIuMAX" over limit %"PRIuMAX),
                    (uintmax_t)length, (uintmax_t)limit);
}

void *xmmap_gently(void *start, size_t length,
                  int prot, int flags, int fd, off_t offset)
{
        void *ret;

        mmap_limit_check(length);
        ret = mmap(start, length, prot, flags, fd, offset);
        if (ret == MAP_FAILED && !length)
                ret = NULL;
        return ret;
}

const char *mmap_os_err(void)
{
        static const char blank[] = "";
#if defined(__linux__)
        if (errno == ENOMEM) {
                /* this continues an existing error message: */
                static const char enomem[] =
", check sys.vm.max_map_count and/or RLIMIT_DATA";
                return enomem;
        }
#endif /* OS-specific bits */
        return blank;
}

void *xmmap(void *start, size_t length,
        int prot, int flags, int fd, off_t offset)
{
        void *ret = xmmap_gently(start, length, prot, flags, fd, offset);
        if (ret == MAP_FAILED)
                die_errno(_("mmap failed%s"), mmap_os_err());
        return ret;
}

/*
 * With an in-core object data in "map", rehash it to make sure the
 * object name actually matches "oid" to detect object corruption.
 * With "map" == NULL, try reading the object named with "oid" using
 * the streaming interface and rehash it to do the same.
 */
int check_object_signature(struct repository *r, const struct object_id *oid,
                           void *map, unsigned long size, const char *type)
{
        struct object_id real_oid;
        enum object_type obj_type;
        struct git_istream *st;
        git_hash_ctx c;
        char hdr[MAX_HEADER_LEN];
        int hdrlen;

        if (map) {
                hash_object_file(r->hash_algo, map, size, type, &real_oid);
                return !oideq(oid, &real_oid) ? -1 : 0;
        }

        st = open_istream(r, oid, &obj_type, &size, NULL);
        if (!st)
                return -1;

        /* Generate the header */
        hdrlen = xsnprintf(hdr, sizeof(hdr), "%s %"PRIuMAX , type_name(obj_type), (uintmax_t)size) + 1;

        /* Sha1.. */
        r->hash_algo->init_fn(&c);
        r->hash_algo->update_fn(&c, hdr, hdrlen);
        for (;;) {
                char buf[1024 * 16];
                ssize_t readlen = read_istream(st, buf, sizeof(buf));

                if (readlen < 0) {
                        close_istream(st);
                        return -1;
                }
                if (!readlen)
                        break;
                r->hash_algo->update_fn(&c, buf, readlen);
        }
        r->hash_algo->final_oid_fn(&real_oid, &c);
        close_istream(st);
        return !oideq(oid, &real_oid) ? -1 : 0;
}

int git_open_cloexec(const char *name, int flags)
{
        int fd;
        static int o_cloexec = O_CLOEXEC;

        fd = open(name, flags | o_cloexec);
        if ((o_cloexec & O_CLOEXEC) && fd < 0 && errno == EINVAL) {
                /* Try again w/o O_CLOEXEC: the kernel might not support it */
                o_cloexec &= ~O_CLOEXEC;
                fd = open(name, flags | o_cloexec);
        }

#if defined(F_GETFD) && defined(F_SETFD) && defined(FD_CLOEXEC)
        {
                static int fd_cloexec = FD_CLOEXEC;

                if (!o_cloexec && 0 <= fd && fd_cloexec) {
                        /* Opened w/o O_CLOEXEC?  try with fcntl(2) to add it */
                        int flags = fcntl(fd, F_GETFD);
                        if (fcntl(fd, F_SETFD, flags | fd_cloexec))
                                fd_cloexec = 0;
                }
        }
#endif
        return fd;
}

/*
 * Find "oid" as a loose object in the local repository or in an alternate.
 * Returns 0 on success, negative on failure.
 *
 * The "path" out-parameter will give the path of the object we found (if any).
 * Note that it may point to static storage and is only valid until another
 * call to stat_loose_object().
 */
static int stat_loose_object(struct repository *r, const struct object_id *oid,
                             struct stat *st, const char **path)
{
        struct object_directory *odb;
        static struct strbuf buf = STRBUF_INIT;

        prepare_alt_odb(r);
        for (odb = r->objects->odb; odb; odb = odb->next) {
                *path = odb_loose_path(odb, &buf, oid);
                if (!lstat(*path, st))
                        return 0;
        }

        return -1;
}

/*
 * Like stat_loose_object(), but actually open the object and return the
 * descriptor. See the caveats on the "path" parameter above.
 */
static int open_loose_object(struct repository *r,
                             const struct object_id *oid, const char **path)
{
        int fd;
        struct object_directory *odb;
        int most_interesting_errno = ENOENT;
        static struct strbuf buf = STRBUF_INIT;

        prepare_alt_odb(r);
        for (odb = r->objects->odb; odb; odb = odb->next) {
                *path = odb_loose_path(odb, &buf, oid);
                fd = git_open(*path);
                if (fd >= 0)
                        return fd;

                if (most_interesting_errno == ENOENT)
                        most_interesting_errno = errno;
        }
        errno = most_interesting_errno;
        return -1;
}

static int quick_has_loose(struct repository *r,
                           const struct object_id *oid)
{
        struct object_directory *odb;

        prepare_alt_odb(r);
        for (odb = r->objects->odb; odb; odb = odb->next) {
                if (oidtree_contains(odb_loose_cache(odb, oid), oid))
                        return 1;
        }
        return 0;
}

/*
 * Map the loose object at "path" if it is not NULL, or the path found by
 * searching for a loose object named "oid".
 */
static void *map_loose_object_1(struct repository *r, const char *path,
                             const struct object_id *oid, unsigned long *size)
{
        void *map;
        int fd;

        if (path)
                fd = git_open(path);
        else
                fd = open_loose_object(r, oid, &path);
        map = NULL;
        if (fd >= 0) {
                struct stat st;

                if (!fstat(fd, &st)) {
                        *size = xsize_t(st.st_size);
                        if (!*size) {
                                /* mmap() is forbidden on empty files */
                                error(_("object file %s is empty"), path);
                                close(fd);
                                return NULL;
                        }
                        map = xmmap(NULL, *size, PROT_READ, MAP_PRIVATE, fd, 0);
                }
                close(fd);
        }
        return map;
}

void *map_loose_object(struct repository *r,
                       const struct object_id *oid,
                       unsigned long *size)
{
        return map_loose_object_1(r, NULL, oid, size);
}

static int unpack_loose_short_header(git_zstream *stream,
                                     unsigned char *map, unsigned long mapsize,
                                     void *buffer, unsigned long bufsiz)
{
        int ret;

        /* Get the data stream */
        memset(stream, 0, sizeof(*stream));
        stream->next_in = map;
        stream->avail_in = mapsize;
        stream->next_out = buffer;
        stream->avail_out = bufsiz;

        git_inflate_init(stream);
        obj_read_unlock();
        ret = git_inflate(stream, 0);
        obj_read_lock();

        return ret;
}

int unpack_loose_header(git_zstream *stream,
                        unsigned char *map, unsigned long mapsize,
                        void *buffer, unsigned long bufsiz)
{
        int status = unpack_loose_short_header(stream, map, mapsize,
                                               buffer, bufsiz);

        if (status < Z_OK)
                return status;

        /* Make sure we have the terminating NUL */
        if (!memchr(buffer, '\0', stream->next_out - (unsigned char *)buffer))
                return -1;
        return 0;
}

static int unpack_loose_header_to_strbuf(git_zstream *stream, unsigned char *map,
                                         unsigned long mapsize, void *buffer,
                                         unsigned long bufsiz, struct strbuf *header)
{
        int status;

        status = unpack_loose_short_header(stream, map, mapsize, buffer, bufsiz);
        if (status < Z_OK)
                return -1;

        /*
         * Check if entire header is unpacked in the first iteration.
         */
        if (memchr(buffer, '\0', stream->next_out - (unsigned char *)buffer))
                return 0;

        /*
         * buffer[0..bufsiz] was not large enough.  Copy the partial
         * result out to header, and then append the result of further
         * reading the stream.
         */
        strbuf_add(header, buffer, stream->next_out - (unsigned char *)buffer);
        stream->next_out = buffer;
        stream->avail_out = bufsiz;

        do {
                obj_read_unlock();
                status = git_inflate(stream, 0);
                obj_read_lock();
                strbuf_add(header, buffer, stream->next_out - (unsigned char *)buffer);
                if (memchr(buffer, '\0', stream->next_out - (unsigned char *)buffer))
                        return 0;
                stream->next_out = buffer;
                stream->avail_out = bufsiz;
        } while (status != Z_STREAM_END);
        return -1;
}

static void *unpack_loose_rest(git_zstream *stream,
                               void *buffer, unsigned long size,
                               const struct object_id *oid)
{
        int bytes = strlen(buffer) + 1;
        unsigned char *buf = xmallocz(size);
        unsigned long n;
        int status = Z_OK;

        n = stream->total_out - bytes;
        if (n > size)
                n = size;
        memcpy(buf, (char *) buffer + bytes, n);
        bytes = n;
        if (bytes <= size) {
                /*
                 * The above condition must be (bytes <= size), not
                 * (bytes < size).  In other words, even though we
                 * expect no more output and set avail_out to zero,
                 * the input zlib stream may have bytes that express
                 * "this concludes the stream", and we *do* want to
                 * eat that input.
                 *
                 * Otherwise we would not be able to test that we
                 * consumed all the input to reach the expected size;
                 * we also want to check that zlib tells us that all
                 * went well with status == Z_STREAM_END at the end.
                 */
                stream->next_out = buf + bytes;
                stream->avail_out = size - bytes;
                while (status == Z_OK) {
                        obj_read_unlock();
                        status = git_inflate(stream, Z_FINISH);
                        obj_read_lock();
                }
        }
        if (status == Z_STREAM_END && !stream->avail_in) {
                git_inflate_end(stream);
                return buf;
        }

        if (status < 0)
                error(_("corrupt loose object '%s'"), oid_to_hex(oid));
        else if (stream->avail_in)
                error(_("garbage at end of loose object '%s'"),
                      oid_to_hex(oid));
        free(buf);
        return NULL;
}

/*
 * We used to just use "sscanf()", but that's actually way
 * too permissive for what we want to check. So do an anal
 * object header parse by hand.
 */
static int parse_loose_header_extended(const char *hdr, struct object_info *oi,
                                       unsigned int flags)
{
        const char *type_buf = hdr;
        unsigned long size;
        int type, type_len = 0;

        /*
         * The type can be of any size but is followed by
         * a space.
         */
        for (;;) {
                char c = *hdr++;
                if (!c)
                        return -1;
                if (c == ' ')
                        break;
                type_len++;
        }

        type = type_from_string_gently(type_buf, type_len, 1);
        if (oi->type_name)
                strbuf_add(oi->type_name, type_buf, type_len);
        /*
         * Set type to 0 if its an unknown object and
         * we're obtaining the type using '--allow-unknown-type'
         * option.
         */
        if ((flags & OBJECT_INFO_ALLOW_UNKNOWN_TYPE) && (type < 0))
                type = 0;
        else if (type < 0)
                die(_("invalid object type"));
        if (oi->typep)
                *oi->typep = type;

        /*
         * The length must follow immediately, and be in canonical
         * decimal format (ie "010" is not valid).
         */
        size = *hdr++ - '0';
        if (size > 9)
                return -1;
        if (size) {
                for (;;) {
                        unsigned long c = *hdr - '0';
                        if (c > 9)
                                break;
                        hdr++;
                        size = size * 10 + c;
                }
        }

        if (oi->sizep)
                *oi->sizep = size;

        /*
         * The length must be followed by a zero byte
         */
        return *hdr ? -1 : type;
}

int parse_loose_header(const char *hdr, unsigned long *sizep)
{
        struct object_info oi = OBJECT_INFO_INIT;

        oi.sizep = sizep;
        return parse_loose_header_extended(hdr, &oi, 0);
}

static int loose_object_info(struct repository *r,
                             const struct object_id *oid,
                             struct object_info *oi, int flags)
{
        int status = 0;
        unsigned long mapsize;
        void *map;
        git_zstream stream;
        char hdr[MAX_HEADER_LEN];
        struct strbuf hdrbuf = STRBUF_INIT;
        unsigned long size_scratch;

        if (oi->delta_base_oid)
                oidclr(oi->delta_base_oid);

        /*
         * If we don't care about type or size, then we don't
         * need to look inside the object at all. Note that we
         * do not optimize out the stat call, even if the
         * caller doesn't care about the disk-size, since our
         * return value implicitly indicates whether the
         * object even exists.
         */
        if (!oi->typep && !oi->type_name && !oi->sizep && !oi->contentp) {
                const char *path;
                struct stat st;
                if (!oi->disk_sizep && (flags & OBJECT_INFO_QUICK))
                        return quick_has_loose(r, oid) ? 0 : -1;
                if (stat_loose_object(r, oid, &st, &path) < 0)
                        return -1;
                if (oi->disk_sizep)
                        *oi->disk_sizep = st.st_size;
                return 0;
        }

        map = map_loose_object(r, oid, &mapsize);
        if (!map)
                return -1;

        if (!oi->sizep)
                oi->sizep = &size_scratch;

        if (oi->disk_sizep)
                *oi->disk_sizep = mapsize;
        if ((flags & OBJECT_INFO_ALLOW_UNKNOWN_TYPE)) {
                if (unpack_loose_header_to_strbuf(&stream, map, mapsize, hdr, sizeof(hdr), &hdrbuf) < 0)
                        status = error(_("unable to unpack %s header with --allow-unknown-type"),
                                       oid_to_hex(oid));
        } else if (unpack_loose_header(&stream, map, mapsize, hdr, sizeof(hdr)) < 0)
                status = error(_("unable to unpack %s header"),
                               oid_to_hex(oid));
        if (status < 0)
                ; /* Do nothing */
        else if (hdrbuf.len) {
                if ((status = parse_loose_header_extended(hdrbuf.buf, oi, flags)) < 0)
                        status = error(_("unable to parse %s header with --allow-unknown-type"),
                                       oid_to_hex(oid));
        } else if ((status = parse_loose_header_extended(hdr, oi, flags)) < 0)
                status = error(_("unable to parse %s header"), oid_to_hex(oid));

        if (status >= 0 && oi->contentp) {
                *oi->contentp = unpack_loose_rest(&stream, hdr,
                                                  *oi->sizep, oid);
                if (!*oi->contentp) {
                        git_inflate_end(&stream);
                        status = -1;
                }
        } else
                git_inflate_end(&stream);

        munmap(map, mapsize);
        if (status && oi->typep)
                *oi->typep = status;
        if (oi->sizep == &size_scratch)
                oi->sizep = NULL;
        strbuf_release(&hdrbuf);
        oi->whence = OI_LOOSE;
        return (status < 0) ? status : 0;
}

int obj_read_use_lock = 0;
pthread_mutex_t obj_read_mutex;

void enable_obj_read_lock(void)
{
        if (obj_read_use_lock)
                return;

        obj_read_use_lock = 1;
        init_recursive_mutex(&obj_read_mutex);
}

void disable_obj_read_lock(void)
{
        if (!obj_read_use_lock)
                return;

        obj_read_use_lock = 0;
        pthread_mutex_destroy(&obj_read_mutex);
}

int fetch_if_missing = 1;

static int do_oid_object_info_extended(struct repository *r,
                                       const struct object_id *oid,
                                       struct object_info *oi, unsigned flags)
{
        static struct object_info blank_oi = OBJECT_INFO_INIT;
        struct cached_object *co;
        struct pack_entry e;
        int rtype;
        const struct object_id *real = oid;
        int already_retried = 0;


        if (flags & OBJECT_INFO_LOOKUP_REPLACE)
                real = lookup_replace_object(r, oid);

        if (is_null_oid(real))
                return -1;

        if (!oi)
                oi = &blank_oi;

        co = find_cached_object(real);
        if (co) {
                if (oi->typep)
                        *(oi->typep) = co->type;
                if (oi->sizep)
                        *(oi->sizep) = co->size;
                if (oi->disk_sizep)
                        *(oi->disk_sizep) = 0;
                if (oi->delta_base_oid)
                        oidclr(oi->delta_base_oid);
                if (oi->type_name)
                        strbuf_addstr(oi->type_name, type_name(co->type));
                if (oi->contentp)
                        *oi->contentp = xmemdupz(co->buf, co->size);
                oi->whence = OI_CACHED;
                return 0;
        }

        while (1) {
                if (find_pack_entry(r, real, &e))
                        break;

                if (flags & OBJECT_INFO_IGNORE_LOOSE)
                        return -1;

                /* Most likely it's a loose object. */
                if (!loose_object_info(r, real, oi, flags))
                        return 0;

                /* Not a loose object; someone else may have just packed it. */
                if (!(flags & OBJECT_INFO_QUICK)) {
                        reprepare_packed_git(r);
                        if (find_pack_entry(r, real, &e))
                                break;
                }

                /* Check if it is a missing object */
                if (fetch_if_missing && repo_has_promisor_remote(r) &&
                    !already_retried &&
                    !(flags & OBJECT_INFO_SKIP_FETCH_OBJECT)) {
                        /*
                         * TODO Investigate checking promisor_remote_get_direct()
                         * TODO return value and stopping on error here.
                         */
                        promisor_remote_get_direct(r, real, 1);
                        already_retried = 1;
                        continue;
                }

                return -1;
        }

        if (oi == &blank_oi)
                /*
                 * We know that the caller doesn't actually need the
                 * information below, so return early.
                 */
                return 0;
        rtype = packed_object_info(r, e.p, e.offset, oi);
        if (rtype < 0) {
                mark_bad_packed_object(e.p, real->hash);
                return do_oid_object_info_extended(r, real, oi, 0);
        } else if (oi->whence == OI_PACKED) {
                oi->u.packed.offset = e.offset;
                oi->u.packed.pack = e.p;
                oi->u.packed.is_delta = (rtype == OBJ_REF_DELTA ||
                                         rtype == OBJ_OFS_DELTA);
        }

        return 0;
}

int oid_object_info_extended(struct repository *r, const struct object_id *oid,
                             struct object_info *oi, unsigned flags)
{
        int ret;
        obj_read_lock();
        ret = do_oid_object_info_extended(r, oid, oi, flags);
        obj_read_unlock();
        return ret;
}


/* returns enum object_type or negative */
int oid_object_info(struct repository *r,
                    const struct object_id *oid,
                    unsigned long *sizep)
{
        enum object_type type;
        struct object_info oi = OBJECT_INFO_INIT;

        oi.typep = &type;
        oi.sizep = sizep;
        if (oid_object_info_extended(r, oid, &oi,
                                      OBJECT_INFO_LOOKUP_REPLACE) < 0)
                return -1;
        return type;
}

static void *read_object(struct repository *r,
                         const struct object_id *oid, enum object_type *type,
                         unsigned long *size)
{
        struct object_info oi = OBJECT_INFO_INIT;
        void *content;
        oi.typep = type;
        oi.sizep = size;
        oi.contentp = &content;

        if (oid_object_info_extended(r, oid, &oi, 0) < 0)
                return NULL;
        return content;
}

int pretend_object_file(void *buf, unsigned long len, enum object_type type,
                        struct object_id *oid)
{
        struct cached_object *co;

        hash_object_file(the_hash_algo, buf, len, type_name(type), oid);
        if (has_object_file_with_flags(oid, OBJECT_INFO_QUICK | OBJECT_INFO_SKIP_FETCH_OBJECT) ||
            find_cached_object(oid))
                return 0;
        ALLOC_GROW(cached_objects, cached_object_nr + 1, cached_object_alloc);
        co = &cached_objects[cached_object_nr++];
        co->size = len;
        co->type = type;
        co->buf = xmalloc(len);
        memcpy(co->buf, buf, len);
        oidcpy(&co->oid, oid);
        return 0;
}

/*
 * This function dies on corrupt objects; the callers who want to
 * deal with them should arrange to call read_object() and give error
 * messages themselves.
 */
void *read_object_file_extended(struct repository *r,
                                const struct object_id *oid,
                                enum object_type *type,
                                unsigned long *size,
                                int lookup_replace)
{
        void *data;
        const struct packed_git *p;
        const char *path;
        struct stat st;
        const struct object_id *repl = lookup_replace ?
                lookup_replace_object(r, oid) : oid;

        errno = 0;
        data = read_object(r, repl, type, size);
        if (data)
                return data;

        obj_read_lock();
        if (errno && errno != ENOENT)
                die_errno(_("failed to read object %s"), oid_to_hex(oid));

        /* die if we replaced an object with one that does not exist */
        if (repl != oid)
                die(_("replacement %s not found for %s"),
                    oid_to_hex(repl), oid_to_hex(oid));

        if (!stat_loose_object(r, repl, &st, &path))
                die(_("loose object %s (stored in %s) is corrupt"),
                    oid_to_hex(repl), path);

        if ((p = has_packed_and_bad(r, repl->hash)) != NULL)
                die(_("packed object %s (stored in %s) is corrupt"),
                    oid_to_hex(repl), p->pack_name);
        obj_read_unlock();

        return NULL;
}

void *read_object_with_reference(struct repository *r,
                                 const struct object_id *oid,
                                 const char *required_type_name,
                                 unsigned long *size,
                                 struct object_id *actual_oid_return)
{
        enum object_type type, required_type;
        void *buffer;
        unsigned long isize;
        struct object_id actual_oid;

        required_type = type_from_string(required_type_name);
        oidcpy(&actual_oid, oid);
        while (1) {
                int ref_length = -1;
                const char *ref_type = NULL;

                buffer = repo_read_object_file(r, &actual_oid, &type, &isize);
                if (!buffer)
                        return NULL;
                if (type == required_type) {
                        *size = isize;
                        if (actual_oid_return)
                                oidcpy(actual_oid_return, &actual_oid);
                        return buffer;
                }
                /* Handle references */
                else if (type == OBJ_COMMIT)
                        ref_type = "tree ";
                else if (type == OBJ_TAG)
                        ref_type = "object ";
                else {
                        free(buffer);
                        return NULL;
                }
                ref_length = strlen(ref_type);

                if (ref_length + the_hash_algo->hexsz > isize ||
                    memcmp(buffer, ref_type, ref_length) ||
                    get_oid_hex((char *) buffer + ref_length, &actual_oid)) {
                        free(buffer);
                        return NULL;
                }
                free(buffer);
                /* Now we have the ID of the referred-to object in
                 * actual_oid.  Check again. */
        }
}

static void write_object_file_prepare(const struct git_hash_algo *algo,
                                      const void *buf, unsigned long len,
                                      const char *type, struct object_id *oid,
                                      char *hdr, int *hdrlen)
{
        git_hash_ctx c;

        /* Generate the header */
        *hdrlen = xsnprintf(hdr, *hdrlen, "%s %"PRIuMAX , type, (uintmax_t)len)+1;

        /* Sha1.. */
        algo->init_fn(&c);
        algo->update_fn(&c, hdr, *hdrlen);
        algo->update_fn(&c, buf, len);
        algo->final_oid_fn(oid, &c);
}

/*
 * Move the just written object into its final resting place.
 */
int finalize_object_file(const char *tmpfile, const char *filename)
{
        int ret = 0;

        if (object_creation_mode == OBJECT_CREATION_USES_RENAMES)
                goto try_rename;
        else if (link(tmpfile, filename))
                ret = errno;

        /*
         * Coda hack - coda doesn't like cross-directory links,
         * so we fall back to a rename, which will mean that it
         * won't be able to check collisions, but that's not a
         * big deal.
         *
         * The same holds for FAT formatted media.
         *
         * When this succeeds, we just return.  We have nothing
         * left to unlink.
         */
        if (ret && ret != EEXIST) {
        try_rename:
                if (!rename(tmpfile, filename))
                        goto out;
                ret = errno;
        }
        unlink_or_warn(tmpfile);
        if (ret) {
                if (ret != EEXIST) {
                        return error_errno(_("unable to write file %s"), filename);
                }
                /* FIXME!!! Collision check here ? */
        }

out:
        if (adjust_shared_perm(filename))
                return error(_("unable to set permission to '%s'"), filename);
        return 0;
}

static int write_buffer(int fd, const void *buf, size_t len)
{
        if (write_in_full(fd, buf, len) < 0)
                return error_errno(_("file write error"));
        return 0;
}

int hash_object_file(const struct git_hash_algo *algo, const void *buf,
                     unsigned long len, const char *type,
                     struct object_id *oid)
{
        char hdr[MAX_HEADER_LEN];
        int hdrlen = sizeof(hdr);
        write_object_file_prepare(algo, buf, len, type, oid, hdr, &hdrlen);
        return 0;
}

/* Finalize a file on disk, and close it. */
static void close_loose_object(int fd)
{
        if (fsync_object_files)
                fsync_or_die(fd, "loose object file");
        if (close(fd) != 0)
                die_errno(_("error when closing loose object file"));
}

/* Size of directory component, including the ending '/' */
static inline int directory_size(const char *filename)
{
        const char *s = strrchr(filename, '/');
        if (!s)
                return 0;
        return s - filename + 1;
}

/*
 * This creates a temporary file in the same directory as the final
 * 'filename'
 *
 * We want to avoid cross-directory filename renames, because those
 * can have problems on various filesystems (FAT, NFS, Coda).
 */
static int create_tmpfile(struct strbuf *tmp, const char *filename)
{
        int fd, dirlen = directory_size(filename);

        strbuf_reset(tmp);
        strbuf_add(tmp, filename, dirlen);
        strbuf_addstr(tmp, "tmp_obj_XXXXXX");
        fd = git_mkstemp_mode(tmp->buf, 0444);
        if (fd < 0 && dirlen && errno == ENOENT) {
                /*
                 * Make sure the directory exists; note that the contents
                 * of the buffer are undefined after mkstemp returns an
                 * error, so we have to rewrite the whole buffer from
                 * scratch.
                 */
                strbuf_reset(tmp);
                strbuf_add(tmp, filename, dirlen - 1);
                if (mkdir(tmp->buf, 0777) && errno != EEXIST)
                        return -1;
                if (adjust_shared_perm(tmp->buf))
                        return -1;

                /* Try again */
                strbuf_addstr(tmp, "/tmp_obj_XXXXXX");
                fd = git_mkstemp_mode(tmp->buf, 0444);
        }
        return fd;
}

static int write_loose_object(const struct object_id *oid, char *hdr,
                              int hdrlen, const void *buf, unsigned long len,
                              time_t mtime)
{
        int fd, ret;
        unsigned char compressed[4096];
        git_zstream stream;
        git_hash_ctx c;
        struct object_id parano_oid;
        static struct strbuf tmp_file = STRBUF_INIT;
        static struct strbuf filename = STRBUF_INIT;

        loose_object_path(the_repository, &filename, oid);

        fd = create_tmpfile(&tmp_file, filename.buf);
        if (fd < 0) {
                if (errno == EACCES)
                        return error(_("insufficient permission for adding an object to repository database %s"), get_object_directory());
                else
                        return error_errno(_("unable to create temporary file"));
        }

        /* Set it up */
        git_deflate_init(&stream, zlib_compression_level);
        stream.next_out = compressed;
        stream.avail_out = sizeof(compressed);
        the_hash_algo->init_fn(&c);

        /* First header.. */
        stream.next_in = (unsigned char *)hdr;
        stream.avail_in = hdrlen;
        while (git_deflate(&stream, 0) == Z_OK)
                ; /* nothing */
        the_hash_algo->update_fn(&c, hdr, hdrlen);

        /* Then the data itself.. */
        stream.next_in = (void *)buf;
        stream.avail_in = len;
        do {
                unsigned char *in0 = stream.next_in;
                ret = git_deflate(&stream, Z_FINISH);
                the_hash_algo->update_fn(&c, in0, stream.next_in - in0);
                if (write_buffer(fd, compressed, stream.next_out - compressed) < 0)
                        die(_("unable to write loose object file"));
                stream.next_out = compressed;
                stream.avail_out = sizeof(compressed);
        } while (ret == Z_OK);

        if (ret != Z_STREAM_END)
                die(_("unable to deflate new object %s (%d)"), oid_to_hex(oid),
                    ret);
        ret = git_deflate_end_gently(&stream);
        if (ret != Z_OK)
                die(_("deflateEnd on object %s failed (%d)"), oid_to_hex(oid),
                    ret);
        the_hash_algo->final_oid_fn(&parano_oid, &c);
        if (!oideq(oid, &parano_oid))
                die(_("confused by unstable object source data for %s"),
                    oid_to_hex(oid));

        close_loose_object(fd);

        if (mtime) {
                struct utimbuf utb;
                utb.actime = mtime;
                utb.modtime = mtime;
                if (utime(tmp_file.buf, &utb) < 0)
                        warning_errno(_("failed utime() on %s"), tmp_file.buf);
        }

        return finalize_object_file(tmp_file.buf, filename.buf);
}

static int freshen_loose_object(const struct object_id *oid)
{
        return check_and_freshen(oid, 1);
}

static int freshen_packed_object(const struct object_id *oid)
{
        struct pack_entry e;
        if (!find_pack_entry(the_repository, oid, &e))
                return 0;
        if (e.p->freshened)
                return 1;
        if (!freshen_file(e.p->pack_name))
                return 0;
        e.p->freshened = 1;
        return 1;
}

int write_object_file(const void *buf, unsigned long len, const char *type,
                      struct object_id *oid)
{
        char hdr[MAX_HEADER_LEN];
        int hdrlen = sizeof(hdr);

        /* Normally if we have it in the pack then we do not bother writing
         * it out into .git/objects/??/?{38} file.
         */
        write_object_file_prepare(the_hash_algo, buf, len, type, oid, hdr,
                                  &hdrlen);
        if (freshen_packed_object(oid) || freshen_loose_object(oid))
                return 0;
        return write_loose_object(oid, hdr, hdrlen, buf, len, 0);
}

int hash_object_file_literally(const void *buf, unsigned long len,
                               const char *type, struct object_id *oid,
                               unsigned flags)
{
        char *header;
        int hdrlen, status = 0;

        /* type string, SP, %lu of the length plus NUL must fit this */
        hdrlen = strlen(type) + MAX_HEADER_LEN;
        header = xmalloc(hdrlen);
        write_object_file_prepare(the_hash_algo, buf, len, type, oid, header,
                                  &hdrlen);

        if (!(flags & HASH_WRITE_OBJECT))
                goto cleanup;
        if (freshen_packed_object(oid) || freshen_loose_object(oid))
                goto cleanup;
        status = write_loose_object(oid, header, hdrlen, buf, len, 0);

cleanup:
        free(header);
        return status;
}

int force_object_loose(const struct object_id *oid, time_t mtime)
{
        void *buf;
        unsigned long len;
        enum object_type type;
        char hdr[MAX_HEADER_LEN];
        int hdrlen;
        int ret;

        if (has_loose_object(oid))
                return 0;
        buf = read_object(the_repository, oid, &type, &len);
        if (!buf)
                return error(_("cannot read object for %s"), oid_to_hex(oid));
        hdrlen = xsnprintf(hdr, sizeof(hdr), "%s %"PRIuMAX , type_name(type), (uintmax_t)len) + 1;
        ret = write_loose_object(oid, hdr, hdrlen, buf, len, mtime);
        free(buf);

        return ret;
}

int has_object(struct repository *r, const struct object_id *oid,
               unsigned flags)
{
        int quick = !(flags & HAS_OBJECT_RECHECK_PACKED);
        unsigned object_info_flags = OBJECT_INFO_SKIP_FETCH_OBJECT |
                (quick ? OBJECT_INFO_QUICK : 0);

        if (!startup_info->have_repository)
                return 0;
        return oid_object_info_extended(r, oid, NULL, object_info_flags) >= 0;
}

int repo_has_object_file_with_flags(struct repository *r,
                                    const struct object_id *oid, int flags)
{
        if (!startup_info->have_repository)
                return 0;
        return oid_object_info_extended(r, oid, NULL, flags) >= 0;
}

int repo_has_object_file(struct repository *r,
                         const struct object_id *oid)
{
        return repo_has_object_file_with_flags(r, oid, 0);
}

static void check_tree(const void *buf, size_t size)
{
        struct tree_desc desc;
        struct name_entry entry;

        init_tree_desc(&desc, buf, size);
        while (tree_entry(&desc, &entry))
                /* do nothing
                 * tree_entry() will die() on malformed entries */
                ;
}

static void check_commit(const void *buf, size_t size)
{
        struct commit c;
        memset(&c, 0, sizeof(c));
        if (parse_commit_buffer(the_repository, &c, buf, size, 0))
                die(_("corrupt commit"));
}

static void check_tag(const void *buf, size_t size)
{
        struct tag t;
        memset(&t, 0, sizeof(t));
        if (parse_tag_buffer(the_repository, &t, buf, size))
                die(_("corrupt tag"));
}

static int index_mem(struct index_state *istate,
                     struct object_id *oid, void *buf, size_t size,
                     enum object_type type,
                     const char *path, unsigned flags)
{
        int ret, re_allocated = 0;
        int write_object = flags & HASH_WRITE_OBJECT;

        if (!type)
                type = OBJ_BLOB;

        /*
         * Convert blobs to git internal format
         */
        if ((type == OBJ_BLOB) && path) {
                struct strbuf nbuf = STRBUF_INIT;
                if (convert_to_git(istate, path, buf, size, &nbuf,
                                   get_conv_flags(flags))) {
                        buf = strbuf_detach(&nbuf, &size);
                        re_allocated = 1;
                }
        }
        if (flags & HASH_FORMAT_CHECK) {
                if (type == OBJ_TREE)
                        check_tree(buf, size);
                if (type == OBJ_COMMIT)
                        check_commit(buf, size);
                if (type == OBJ_TAG)
                        check_tag(buf, size);
        }

        if (write_object)
                ret = write_object_file(buf, size, type_name(type), oid);
        else
                ret = hash_object_file(the_hash_algo, buf, size,
                                       type_name(type), oid);
        if (re_allocated)
                free(buf);
        return ret;
}

static int index_stream_convert_blob(struct index_state *istate,
                                     struct object_id *oid,
                                     int fd,
                                     const char *path,
                                     unsigned flags)
{
        int ret;
        const int write_object = flags & HASH_WRITE_OBJECT;
        struct strbuf sbuf = STRBUF_INIT;

        assert(path);
        assert(would_convert_to_git_filter_fd(istate, path));

        convert_to_git_filter_fd(istate, path, fd, &sbuf,
                                 get_conv_flags(flags));

        if (write_object)
                ret = write_object_file(sbuf.buf, sbuf.len, type_name(OBJ_BLOB),
                                        oid);
        else
                ret = hash_object_file(the_hash_algo, sbuf.buf, sbuf.len,
                                       type_name(OBJ_BLOB), oid);
        strbuf_release(&sbuf);
        return ret;
}

static int index_pipe(struct index_state *istate, struct object_id *oid,
                      int fd, enum object_type type,
                      const char *path, unsigned flags)
{
        struct strbuf sbuf = STRBUF_INIT;
        int ret;

        if (strbuf_read(&sbuf, fd, 4096) >= 0)
                ret = index_mem(istate, oid, sbuf.buf, sbuf.len, type, path, flags);
        else
                ret = -1;
        strbuf_release(&sbuf);
        return ret;
}

#define SMALL_FILE_SIZE (32*1024)

static int index_core(struct index_state *istate,
                      struct object_id *oid, int fd, size_t size,
                      enum object_type type, const char *path,
                      unsigned flags)
{
        int ret;

        if (!size) {
                ret = index_mem(istate, oid, "", size, type, path, flags);
        } else if (size <= SMALL_FILE_SIZE) {
                char *buf = xmalloc(size);
                ssize_t read_result = read_in_full(fd, buf, size);
                if (read_result < 0)
                        ret = error_errno(_("read error while indexing %s"),
                                          path ? path : "<unknown>");
                else if (read_result != size)
                        ret = error(_("short read while indexing %s"),
                                    path ? path : "<unknown>");
                else
                        ret = index_mem(istate, oid, buf, size, type, path, flags);
                free(buf);
        } else {
                void *buf = xmmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
                ret = index_mem(istate, oid, buf, size, type, path, flags);
                munmap(buf, size);
        }
        return ret;
}

/*
 * This creates one packfile per large blob unless bulk-checkin
 * machinery is "plugged".
 *
 * This also bypasses the usual "convert-to-git" dance, and that is on
 * purpose. We could write a streaming version of the converting
 * functions and insert that before feeding the data to fast-import
 * (or equivalent in-core API described above). However, that is
 * somewhat complicated, as we do not know the size of the filter
 * result, which we need to know beforehand when writing a git object.
 * Since the primary motivation for trying to stream from the working
 * tree file and to avoid mmaping it in core is to deal with large
 * binary blobs, they generally do not want to get any conversion, and
 * callers should avoid this code path when filters are requested.
 */
static int index_stream(struct object_id *oid, int fd, size_t size,
                        enum object_type type, const char *path,
                        unsigned flags)
{
        return index_bulk_checkin(oid, fd, size, type, path, flags);
}

int index_fd(struct index_state *istate, struct object_id *oid,
             int fd, struct stat *st,
             enum object_type type, const char *path, unsigned flags)
{
        int ret;

        /*
         * Call xsize_t() only when needed to avoid potentially unnecessary
         * die() for large files.
         */
        if (type == OBJ_BLOB && path && would_convert_to_git_filter_fd(istate, path))
                ret = index_stream_convert_blob(istate, oid, fd, path, flags);
        else if (!S_ISREG(st->st_mode))
                ret = index_pipe(istate, oid, fd, type, path, flags);
        else if (st->st_size <= big_file_threshold || type != OBJ_BLOB ||
                 (path && would_convert_to_git(istate, path)))
                ret = index_core(istate, oid, fd, xsize_t(st->st_size),
                                 type, path, flags);
        else
                ret = index_stream(oid, fd, xsize_t(st->st_size), type, path,
                                   flags);
        close(fd);
        return ret;
}

int index_path(struct index_state *istate, struct object_id *oid,
               const char *path, struct stat *st, unsigned flags)
{
        int fd;
        struct strbuf sb = STRBUF_INIT;
        int rc = 0;

        switch (st->st_mode & S_IFMT) {
        case S_IFREG:
                fd = open(path, O_RDONLY);
                if (fd < 0)
                        return error_errno("open(\"%s\")", path);
                if (index_fd(istate, oid, fd, st, OBJ_BLOB, path, flags) < 0)
                        return error(_("%s: failed to insert into database"),
                                     path);
                break;
        case S_IFLNK:
                if (strbuf_readlink(&sb, path, st->st_size))
                        return error_errno("readlink(\"%s\")", path);
                if (!(flags & HASH_WRITE_OBJECT))
                        hash_object_file(the_hash_algo, sb.buf, sb.len,
                                         blob_type, oid);
                else if (write_object_file(sb.buf, sb.len, blob_type, oid))
                        rc = error(_("%s: failed to insert into database"), path);
                strbuf_release(&sb);
                break;
        case S_IFDIR:
                return resolve_gitlink_ref(path, "HEAD", oid);
        default:
                return error(_("%s: unsupported file type"), path);
        }
        return rc;
}

int read_pack_header(int fd, struct pack_header *header)
{
        if (read_in_full(fd, header, sizeof(*header)) != sizeof(*header))
                /* "eof before pack header was fully read" */
                return PH_ERROR_EOF;

        if (header->hdr_signature != htonl(PACK_SIGNATURE))
                /* "protocol error (pack signature mismatch detected)" */
                return PH_ERROR_PACK_SIGNATURE;
        if (!pack_version_ok(header->hdr_version))
                /* "protocol error (pack version unsupported)" */
                return PH_ERROR_PROTOCOL;
        return 0;
}

void assert_oid_type(const struct object_id *oid, enum object_type expect)
{
        enum object_type type = oid_object_info(the_repository, oid, NULL);
        if (type < 0)
                die(_("%s is not a valid object"), oid_to_hex(oid));
        if (type != expect)
                die(_("%s is not a valid '%s' object"), oid_to_hex(oid),
                    type_name(expect));
}

int for_each_file_in_obj_subdir(unsigned int subdir_nr,
                                struct strbuf *path,
                                each_loose_object_fn obj_cb,
                                each_loose_cruft_fn cruft_cb,
                                each_loose_subdir_fn subdir_cb,
                                void *data)
{
        size_t origlen, baselen;
        DIR *dir;
        struct dirent *de;
        int r = 0;
        struct object_id oid;

        if (subdir_nr > 0xff)
                BUG("invalid loose object subdirectory: %x", subdir_nr);

        origlen = path->len;
        strbuf_complete(path, '/');
        strbuf_addf(path, "%02x", subdir_nr);

        dir = opendir(path->buf);
        if (!dir) {
                if (errno != ENOENT)
                        r = error_errno(_("unable to open %s"), path->buf);
                strbuf_setlen(path, origlen);
                return r;
        }

        oid.hash[0] = subdir_nr;
        strbuf_addch(path, '/');
        baselen = path->len;

        while ((de = readdir_skip_dot_and_dotdot(dir))) {
                size_t namelen;

                namelen = strlen(de->d_name);
                strbuf_setlen(path, baselen);
                strbuf_add(path, de->d_name, namelen);
                if (namelen == the_hash_algo->hexsz - 2 &&
                    !hex_to_bytes(oid.hash + 1, de->d_name,
                                  the_hash_algo->rawsz - 1)) {
                        oid_set_algo(&oid, the_hash_algo);
                        if (obj_cb) {
                                r = obj_cb(&oid, path->buf, data);
                                if (r)
                                        break;
                        }
                        continue;
                }

                if (cruft_cb) {
                        r = cruft_cb(de->d_name, path->buf, data);
                        if (r)
                                break;
                }
        }
        closedir(dir);

        strbuf_setlen(path, baselen - 1);
        if (!r && subdir_cb)
                r = subdir_cb(subdir_nr, path->buf, data);

        strbuf_setlen(path, origlen);

        return r;
}

int for_each_loose_file_in_objdir_buf(struct strbuf *path,
                            each_loose_object_fn obj_cb,
                            each_loose_cruft_fn cruft_cb,
                            each_loose_subdir_fn subdir_cb,
                            void *data)
{
        int r = 0;
        int i;

        for (i = 0; i < 256; i++) {
                r = for_each_file_in_obj_subdir(i, path, obj_cb, cruft_cb,
                                                subdir_cb, data);
                if (r)
                        break;
        }

        return r;
}

int for_each_loose_file_in_objdir(const char *path,
                                  each_loose_object_fn obj_cb,
                                  each_loose_cruft_fn cruft_cb,
                                  each_loose_subdir_fn subdir_cb,
                                  void *data)
{
        struct strbuf buf = STRBUF_INIT;
        int r;

        strbuf_addstr(&buf, path);
        r = for_each_loose_file_in_objdir_buf(&buf, obj_cb, cruft_cb,
                                              subdir_cb, data);
        strbuf_release(&buf);

        return r;
}

int for_each_loose_object(each_loose_object_fn cb, void *data,
                          enum for_each_object_flags flags)
{
        struct object_directory *odb;

        prepare_alt_odb(the_repository);
        for (odb = the_repository->objects->odb; odb; odb = odb->next) {
                int r = for_each_loose_file_in_objdir(odb->path, cb, NULL,
                                                      NULL, data);
                if (r)
                        return r;

                if (flags & FOR_EACH_OBJECT_LOCAL_ONLY)
                        break;
        }

        return 0;
}

static int append_loose_object(const struct object_id *oid, const char *path,
                               void *data)
{
        oidtree_insert(data, oid);
        return 0;
}

struct oidtree *odb_loose_cache(struct object_directory *odb,
                                  const struct object_id *oid)
{
        int subdir_nr = oid->hash[0];
        struct strbuf buf = STRBUF_INIT;
        size_t word_bits = bitsizeof(odb->loose_objects_subdir_seen[0]);
        size_t word_index = subdir_nr / word_bits;
        size_t mask = 1u << (subdir_nr % word_bits);
        uint32_t *bitmap;

        if (subdir_nr < 0 ||
            subdir_nr >= bitsizeof(odb->loose_objects_subdir_seen))
                BUG("subdir_nr out of range");

        bitmap = &odb->loose_objects_subdir_seen[word_index];
        if (*bitmap & mask)
                return odb->loose_objects_cache;
        if (!odb->loose_objects_cache) {
                ALLOC_ARRAY(odb->loose_objects_cache, 1);
                oidtree_init(odb->loose_objects_cache);
        }
        strbuf_addstr(&buf, odb->path);
        for_each_file_in_obj_subdir(subdir_nr, &buf,
                                    append_loose_object,
                                    NULL, NULL,
                                    odb->loose_objects_cache);
        *bitmap |= mask;
        strbuf_release(&buf);
        return odb->loose_objects_cache;
}

void odb_clear_loose_cache(struct object_directory *odb)
{
        oidtree_clear(odb->loose_objects_cache);
        FREE_AND_NULL(odb->loose_objects_cache);
        memset(&odb->loose_objects_subdir_seen, 0,
               sizeof(odb->loose_objects_subdir_seen));
}

static int check_stream_oid(git_zstream *stream,
                            const char *hdr,
                            unsigned long size,
                            const char *path,
                            const struct object_id *expected_oid)
{
        git_hash_ctx c;
        struct object_id real_oid;
        unsigned char buf[4096];
        unsigned long total_read;
        int status = Z_OK;

        the_hash_algo->init_fn(&c);
        the_hash_algo->update_fn(&c, hdr, stream->total_out);

        /*
         * We already read some bytes into hdr, but the ones up to the NUL
         * do not count against the object's content size.
         */
        total_read = stream->total_out - strlen(hdr) - 1;

        /*
         * This size comparison must be "<=" to read the final zlib packets;
         * see the comment in unpack_loose_rest for details.
         */
        while (total_read <= size &&
               (status == Z_OK ||
                (status == Z_BUF_ERROR && !stream->avail_out))) {
                stream->next_out = buf;
                stream->avail_out = sizeof(buf);
                if (size - total_read < stream->avail_out)
                        stream->avail_out = size - total_read;
                status = git_inflate(stream, Z_FINISH);
                the_hash_algo->update_fn(&c, buf, stream->next_out - buf);
                total_read += stream->next_out - buf;
        }
        git_inflate_end(stream);

        if (status != Z_STREAM_END) {
                error(_("corrupt loose object '%s'"), oid_to_hex(expected_oid));
                return -1;
        }
        if (stream->avail_in) {
                error(_("garbage at end of loose object '%s'"),
                      oid_to_hex(expected_oid));
                return -1;
        }

        the_hash_algo->final_oid_fn(&real_oid, &c);
        if (!oideq(expected_oid, &real_oid)) {
                error(_("hash mismatch for %s (expected %s)"), path,
                      oid_to_hex(expected_oid));
                return -1;
        }

        return 0;
}

int read_loose_object(const char *path,
                      const struct object_id *expected_oid,
                      enum object_type *type,
                      unsigned long *size,
                      void **contents)
{
        int ret = -1;
        void *map = NULL;
        unsigned long mapsize;
        git_zstream stream;
        char hdr[MAX_HEADER_LEN];

        *contents = NULL;

        map = map_loose_object_1(the_repository, path, NULL, &mapsize);
        if (!map) {
                error_errno(_("unable to mmap %s"), path);
                goto out;
        }

        if (unpack_loose_header(&stream, map, mapsize, hdr, sizeof(hdr)) < 0) {
                error(_("unable to unpack header of %s"), path);
                goto out;
        }

        *type = parse_loose_header(hdr, size);
        if (*type < 0) {
                error(_("unable to parse header of %s"), path);
                git_inflate_end(&stream);
                goto out;
        }

        if (*type == OBJ_BLOB && *size > big_file_threshold) {
                if (check_stream_oid(&stream, hdr, *size, path, expected_oid) < 0)
                        goto out;
        } else {
                *contents = unpack_loose_rest(&stream, hdr, *size, expected_oid);
                if (!*contents) {
                        error(_("unable to unpack contents of %s"), path);
                        git_inflate_end(&stream);
                        goto out;
                }
                if (check_object_signature(the_repository, expected_oid,
                                           *contents, *size,
                                           type_name(*type))) {
                        error(_("hash mismatch for %s (expected %s)"), path,
                              oid_to_hex(expected_oid));
                        free(*contents);
                        goto out;
                }
        }

        ret = 0; /* everything checks out */

out:
        if (map)
                munmap(map, mapsize);
        return ret;
}