[PATCH] Subject: [PATCH] Add some documentation.

[git/jrn.git] / sha1_file.c

/*
 * GIT - The information manager from hell
 *
 * Copyright (C) Linus Torvalds, 2005
 *
 * This handles basic git sha1 object files - packing, unpacking,
 * creation etc.
 */
#include <sys/types.h>
#include <dirent.h>
#include "cache.h"
#include "delta.h"
#include "pack.h"

#ifndef O_NOATIME
#if defined(__linux__) && (defined(__i386__) || defined(__PPC__))
#define O_NOATIME 01000000
#else
#define O_NOATIME 0
#endif
#endif

static unsigned int sha1_file_open_flag = O_NOATIME;

static unsigned hexval(char c)
{
        if (c >= '0' && c <= '9')
                return c - '0';
        if (c >= 'a' && c <= 'f')
                return c - 'a' + 10;
        if (c >= 'A' && c <= 'F')
                return c - 'A' + 10;
        return ~0;
}

int get_sha1_hex(const char *hex, unsigned char *sha1)
{
        int i;
        for (i = 0; i < 20; i++) {
                unsigned int val = (hexval(hex[0]) << 4) | hexval(hex[1]);
                if (val & ~0xff)
                        return -1;
                *sha1++ = val;
                hex += 2;
        }
        return 0;
}

static char *git_dir, *git_object_dir, *git_index_file, *git_refs_dir,
        *git_graft_file;
static void setup_git_env(void)
{
        git_dir = gitenv(GIT_DIR_ENVIRONMENT);
        if (!git_dir)
                git_dir = DEFAULT_GIT_DIR_ENVIRONMENT;
        git_object_dir = gitenv(DB_ENVIRONMENT);
        if (!git_object_dir) {
                git_object_dir = xmalloc(strlen(git_dir) + 9);
                sprintf(git_object_dir, "%s/objects", git_dir);
        }
        git_refs_dir = xmalloc(strlen(git_dir) + 6);
        sprintf(git_refs_dir, "%s/refs", git_dir);
        git_index_file = gitenv(INDEX_ENVIRONMENT);
        if (!git_index_file) {
                git_index_file = xmalloc(strlen(git_dir) + 7);
                sprintf(git_index_file, "%s/index", git_dir);
        }
        git_graft_file = gitenv(GRAFT_ENVIRONMENT);
        if (!git_graft_file)
                git_graft_file = strdup(git_path("info/grafts"));
}

char *get_object_directory(void)
{
        if (!git_object_dir)
                setup_git_env();
        return git_object_dir;
}

char *get_refs_directory(void)
{
        if (!git_refs_dir)
                setup_git_env();
        return git_refs_dir;
}

char *get_index_file(void)
{
        if (!git_index_file)
                setup_git_env();
        return git_index_file;
}

char *get_graft_file(void)
{
        if (!git_graft_file)
                setup_git_env();
        return git_graft_file;
}

int safe_create_leading_directories(char *path)
{
        char *pos = path;

        while (pos) {
                pos = strchr(pos, '/');
                if (!pos)
                        break;
                *pos = 0;
                if (mkdir(path, 0777) < 0)
                        if (errno != EEXIST) {
                                *pos = '/';
                                return -1;
                        }
                *pos++ = '/';
        }
        return 0;
}

char * sha1_to_hex(const unsigned char *sha1)
{
        static char buffer[50];
        static const char hex[] = "0123456789abcdef";
        char *buf = buffer;
        int i;

        for (i = 0; i < 20; i++) {
                unsigned int val = *sha1++;
                *buf++ = hex[val >> 4];
                *buf++ = hex[val & 0xf];
        }
        return buffer;
}

static void fill_sha1_path(char *pathbuf, const unsigned char *sha1)
{
        int i;
        for (i = 0; i < 20; i++) {
                static char hex[] = "0123456789abcdef";
                unsigned int val = sha1[i];
                char *pos = pathbuf + i*2 + (i > 0);
                *pos++ = hex[val >> 4];
                *pos = hex[val & 0xf];
        }
}

/*
 * NOTE! This returns a statically allocated buffer, so you have to be
 * careful about using it. Do a "strdup()" if you need to save the
 * filename.
 *
 * Also note that this returns the location for creating.  Reading
 * SHA1 file can happen from any alternate directory listed in the
 * DB_ENVIRONMENT environment variable if it is not found in
 * the primary object database.
 */
char *sha1_file_name(const unsigned char *sha1)
{
        static char *name, *base;

        if (!base) {
                const char *sha1_file_directory = get_object_directory();
                int len = strlen(sha1_file_directory);
                base = xmalloc(len + 60);
                memcpy(base, sha1_file_directory, len);
                memset(base+len, 0, 60);
                base[len] = '/';
                base[len+3] = '/';
                name = base + len + 1;
        }
        fill_sha1_path(name, sha1);
        return base;
}

char *sha1_pack_name(const unsigned char *sha1)
{
        static const char hex[] = "0123456789abcdef";
        static char *name, *base, *buf;
        int i;

        if (!base) {
                const char *sha1_file_directory = get_object_directory();
                int len = strlen(sha1_file_directory);
                base = xmalloc(len + 60);
                sprintf(base, "%s/pack/pack-1234567890123456789012345678901234567890.pack", sha1_file_directory);
                name = base + len + 11;
        }

        buf = name;

        for (i = 0; i < 20; i++) {
                unsigned int val = *sha1++;
                *buf++ = hex[val >> 4];
                *buf++ = hex[val & 0xf];
        }
        
        return base;
}

char *sha1_pack_index_name(const unsigned char *sha1)
{
        static const char hex[] = "0123456789abcdef";
        static char *name, *base, *buf;
        int i;

        if (!base) {
                const char *sha1_file_directory = get_object_directory();
                int len = strlen(sha1_file_directory);
                base = xmalloc(len + 60);
                sprintf(base, "%s/pack/pack-1234567890123456789012345678901234567890.idx", sha1_file_directory);
                name = base + len + 11;
        }

        buf = name;

        for (i = 0; i < 20; i++) {
                unsigned int val = *sha1++;
                *buf++ = hex[val >> 4];
                *buf++ = hex[val & 0xf];
        }
        
        return base;
}

struct alternate_object_database *alt_odb_list;
static struct alternate_object_database **alt_odb_tail;

/*
 * Prepare alternate object database registry.
 *
 * The variable alt_odb_list points at the list of struct
 * alternate_object_database.  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 exactly in the same format as that environment
 * variable.  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 40-byte hex
 * SHA1, an extra slash for the first level indirection, and the
 * terminating NUL.
 */
static void link_alt_odb_entries(const char *alt, const char *ep, int sep)
{
        const char *cp, *last;
        struct alternate_object_database *ent;

        last = alt;
        while (last < ep) {
                cp = last;
                if (cp < ep && *cp == '#') {
                        while (cp < ep && *cp != sep)
                                cp++;
                        last = cp + 1;
                        continue;
                }
                for ( ; cp < ep && *cp != sep; cp++)
                        ;
                if (last != cp) {
                        /* 43 = 40-byte + 2 '/' + terminating NUL */
                        int pfxlen = cp - last;
                        int entlen = pfxlen + 43;

                        ent = xmalloc(sizeof(*ent) + entlen);
                        *alt_odb_tail = ent;
                        alt_odb_tail = &(ent->next);
                        ent->next = NULL;

                        memcpy(ent->base, last, pfxlen);
                        ent->name = ent->base + pfxlen + 1;
                        ent->base[pfxlen] = ent->base[pfxlen + 3] = '/';
                        ent->base[entlen-1] = 0;
                }
                while (cp < ep && *cp == sep)
                        cp++;
                last = cp;
        }
}

void prepare_alt_odb(void)
{
        char path[PATH_MAX];
        char *map;
        int fd;
        struct stat st;
        char *alt = gitenv(ALTERNATE_DB_ENVIRONMENT) ? : "";

        sprintf(path, "%s/info/alternates", get_object_directory());
        if (alt_odb_tail)
                return;
        alt_odb_tail = &alt_odb_list;
        link_alt_odb_entries(alt, alt + strlen(alt), ':');

        fd = open(path, O_RDONLY);
        if (fd < 0)
                return;
        if (fstat(fd, &st) || (st.st_size == 0)) {
                close(fd);
                return;
        }
        map = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
        close(fd);
        if (map == MAP_FAILED)
                return;

        link_alt_odb_entries(map, map + st.st_size, '\n');
        munmap(map, st.st_size);
}

static char *find_sha1_file(const unsigned char *sha1, struct stat *st)
{
        char *name = sha1_file_name(sha1);
        struct alternate_object_database *alt;

        if (!stat(name, st))
                return name;
        prepare_alt_odb();
        for (alt = alt_odb_list; alt; alt = alt->next) {
                name = alt->name;
                fill_sha1_path(name, sha1);
                if (!stat(alt->base, st))
                        return alt->base;
        }
        return NULL;
}

#define PACK_MAX_SZ (1<<26)
static int pack_used_ctr;
static unsigned long pack_mapped;
struct packed_git *packed_git;

static int check_packed_git_idx(const char *path, unsigned long *idx_size_,
                                void **idx_map_)
{
        void *idx_map;
        unsigned int *index;
        unsigned long idx_size;
        int nr, i;
        int fd = open(path, O_RDONLY);
        struct stat st;
        if (fd < 0)
                return -1;
        if (fstat(fd, &st)) {
                close(fd);
                return -1;
        }
        idx_size = st.st_size;
        idx_map = mmap(NULL, idx_size, PROT_READ, MAP_PRIVATE, fd, 0);
        close(fd);
        if (idx_map == MAP_FAILED)
                return -1;

        index = idx_map;
        *idx_map_ = idx_map;
        *idx_size_ = idx_size;

        /* check index map */
        if (idx_size < 4*256 + 20 + 20)
                return error("index file too small");
        nr = 0;
        for (i = 0; i < 256; i++) {
                unsigned int n = ntohl(index[i]);
                if (n < nr)
                        return error("non-monotonic index");
                nr = n;
        }

        /*
         * Total size:
         *  - 256 index entries 4 bytes each
         *  - 24-byte entries * nr (20-byte sha1 + 4-byte offset)
         *  - 20-byte SHA1 of the packfile
         *  - 20-byte SHA1 file checksum
         */
        if (idx_size != 4*256 + nr * 24 + 20 + 20)
                return error("wrong index file size");

        return 0;
}

static int unuse_one_packed_git(void)
{
        struct packed_git *p, *lru = NULL;

        for (p = packed_git; p; p = p->next) {
                if (p->pack_use_cnt || !p->pack_base)
                        continue;
                if (!lru || p->pack_last_used < lru->pack_last_used)
                        lru = p;
        }
        if (!lru)
                return 0;
        munmap(lru->pack_base, lru->pack_size);
        lru->pack_base = NULL;
        return 1;
}

void unuse_packed_git(struct packed_git *p)
{
        p->pack_use_cnt--;
}

int use_packed_git(struct packed_git *p)
{
        if (!p->pack_size) {
                struct stat st;
                // We created the struct before we had the pack
                stat(p->pack_name, &st);
                if (!S_ISREG(st.st_mode))
                        die("packfile %s not a regular file", p->pack_name);
                p->pack_size = st.st_size;
        }
        if (!p->pack_base) {
                int fd;
                struct stat st;
                void *map;

                pack_mapped += p->pack_size;
                while (PACK_MAX_SZ < pack_mapped && unuse_one_packed_git())
                        ; /* nothing */
                fd = open(p->pack_name, O_RDONLY);
                if (fd < 0)
                        die("packfile %s cannot be opened", p->pack_name);
                if (fstat(fd, &st)) {
                        close(fd);
                        die("packfile %s cannot be opened", p->pack_name);
                }
                if (st.st_size != p->pack_size)
                        die("packfile %s size mismatch.", p->pack_name);
                map = mmap(NULL, p->pack_size, PROT_READ, MAP_PRIVATE, fd, 0);
                close(fd);
                if (map == MAP_FAILED)
                        die("packfile %s cannot be mapped.", p->pack_name);
                p->pack_base = map;

                /* Check if the pack file matches with the index file.
                 * this is cheap.
                 */
                if (memcmp((char*)(p->index_base) + p->index_size - 40,
                           p->pack_base + p->pack_size - 20, 20)) {
                              
                        die("packfile %s does not match index.", p->pack_name);
                }
        }
        p->pack_last_used = pack_used_ctr++;
        p->pack_use_cnt++;
        return 0;
}

struct packed_git *add_packed_git(char *path, int path_len)
{
        struct stat st;
        struct packed_git *p;
        unsigned long idx_size;
        void *idx_map;

        if (check_packed_git_idx(path, &idx_size, &idx_map))
                return NULL;

        /* do we have a corresponding .pack file? */
        strcpy(path + path_len - 4, ".pack");
        if (stat(path, &st) || !S_ISREG(st.st_mode)) {
                munmap(idx_map, idx_size);
                return NULL;
        }
        /* ok, it looks sane as far as we can check without
         * actually mapping the pack file.
         */
        p = xmalloc(sizeof(*p) + path_len + 2);
        strcpy(p->pack_name, path);
        p->index_size = idx_size;
        p->pack_size = st.st_size;
        p->index_base = idx_map;
        p->next = NULL;
        p->pack_base = NULL;
        p->pack_last_used = 0;
        p->pack_use_cnt = 0;
        return p;
}

struct packed_git *parse_pack_index(unsigned char *sha1)
{
        char *path = sha1_pack_index_name(sha1);
        return parse_pack_index_file(sha1, path);
}

struct packed_git *parse_pack_index_file(unsigned char *sha1, char *idx_path)
{
        struct packed_git *p;
        unsigned long idx_size;
        void *idx_map;
        char *path;

        if (check_packed_git_idx(idx_path, &idx_size, &idx_map))
                return NULL;

        path = sha1_pack_name(sha1);

        p = xmalloc(sizeof(*p) + strlen(path) + 2);
        strcpy(p->pack_name, path);
        p->index_size = idx_size;
        p->pack_size = 0;
        p->index_base = idx_map;
        p->next = NULL;
        p->pack_base = NULL;
        p->pack_last_used = 0;
        p->pack_use_cnt = 0;
        memcpy(p->sha1, sha1, 20);
        return p;
}

void install_packed_git(struct packed_git *pack)
{
        pack->next = packed_git;
        packed_git = pack;
}

static void prepare_packed_git_one(char *objdir)
{
        char path[PATH_MAX];
        int len;
        DIR *dir;
        struct dirent *de;

        sprintf(path, "%s/pack", objdir);
        len = strlen(path);
        dir = opendir(path);
        if (!dir)
                return;
        path[len++] = '/';
        while ((de = readdir(dir)) != NULL) {
                int namelen = strlen(de->d_name);
                struct packed_git *p;

                if (strcmp(de->d_name + namelen - 4, ".idx"))
                        continue;

                /* we have .idx.  Is it a file we can map? */
                strcpy(path + len, de->d_name);
                p = add_packed_git(path, len + namelen);
                if (!p)
                        continue;
                p->next = packed_git;
                packed_git = p;
        }
        closedir(dir);
}

void prepare_packed_git(void)
{
        static int run_once = 0;
        struct alternate_object_database *alt;

        if (run_once)
                return;
        prepare_packed_git_one(get_object_directory());
        prepare_alt_odb();
        for (alt = alt_odb_list; alt; alt = alt->next) {
                alt->name[0] = 0;
                prepare_packed_git_one(alt->base);
        }
        run_once = 1;
}

int check_sha1_signature(const unsigned char *sha1, void *map, unsigned long size, const char *type)
{
        char header[100];
        unsigned char real_sha1[20];
        SHA_CTX c;

        SHA1_Init(&c);
        SHA1_Update(&c, header, 1+sprintf(header, "%s %lu", type, size));
        SHA1_Update(&c, map, size);
        SHA1_Final(real_sha1, &c);
        return memcmp(sha1, real_sha1, 20) ? -1 : 0;
}

static void *map_sha1_file_internal(const unsigned char *sha1,
                                    unsigned long *size)
{
        struct stat st;
        void *map;
        int fd;
        char *filename = find_sha1_file(sha1, &st);

        if (!filename) {
                return NULL;
        }

        fd = open(filename, O_RDONLY | sha1_file_open_flag);
        if (fd < 0) {
                /* See if it works without O_NOATIME */
                switch (sha1_file_open_flag) {
                default:
                        fd = open(filename, O_RDONLY);
                        if (fd >= 0)
                                break;
                /* Fallthrough */
                case 0:
                        return NULL;
                }

                /* If it failed once, it will probably fail again.
                 * Stop using O_NOATIME
                 */
                sha1_file_open_flag = 0;
        }
        map = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
        close(fd);
        if (map == MAP_FAILED)
                return NULL;
        *size = st.st_size;
        return map;
}

int unpack_sha1_header(z_stream *stream, void *map, unsigned long mapsize, void *buffer, unsigned long size)
{
        /* Get the data stream */
        memset(stream, 0, sizeof(*stream));
        stream->next_in = map;
        stream->avail_in = mapsize;
        stream->next_out = buffer;
        stream->avail_out = size;

        inflateInit(stream);
        return inflate(stream, 0);
}

static void *unpack_sha1_rest(z_stream *stream, void *buffer, unsigned long size)
{
        int bytes = strlen(buffer) + 1;
        unsigned char *buf = xmalloc(1+size);

        memcpy(buf, buffer + bytes, stream->total_out - bytes);
        bytes = stream->total_out - bytes;
        if (bytes < size) {
                stream->next_out = buf + bytes;
                stream->avail_out = size - bytes;
                while (inflate(stream, Z_FINISH) == Z_OK)
                        /* nothing */;
        }
        buf[size] = 0;
        inflateEnd(stream);
        return buf;
}

/*
 * 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.
 */
int parse_sha1_header(char *hdr, char *type, unsigned long *sizep)
{
        int i;
        unsigned long size;

        /*
         * The type can be at most ten bytes (including the 
         * terminating '\0' that we add), and is followed by
         * a space. 
         */
        i = 10;
        for (;;) {
                char c = *hdr++;
                if (c == ' ')
                        break;
                if (!--i)
                        return -1;
                *type++ = c;
        }
        *type = 0;

        /*
         * 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;
                }
        }
        *sizep = size;

        /*
         * The length must be followed by a zero byte
         */
        return *hdr ? -1 : 0;
}

void * unpack_sha1_file(void *map, unsigned long mapsize, char *type, unsigned long *size)
{
        int ret;
        z_stream stream;
        char hdr[8192];

        ret = unpack_sha1_header(&stream, map, mapsize, hdr, sizeof(hdr));
        if (ret < Z_OK || parse_sha1_header(hdr, type, size) < 0)
                return NULL;

        return unpack_sha1_rest(&stream, hdr, *size);
}

/* forward declaration for a mutually recursive function */
static int packed_object_info(struct pack_entry *entry,
                              char *type, unsigned long *sizep);

static int packed_delta_info(unsigned char *base_sha1,
                             unsigned long delta_size,
                             unsigned long left,
                             char *type,
                             unsigned long *sizep,
                             struct packed_git *p)
{
        struct pack_entry base_ent;

        if (left < 20)
                die("truncated pack file");

        /* The base entry _must_ be in the same pack */
        if (!find_pack_entry_one(base_sha1, &base_ent, p))
                die("failed to find delta-pack base object %s",
                    sha1_to_hex(base_sha1));

        /* We choose to only get the type of the base object and
         * ignore potentially corrupt pack file that expects the delta
         * based on a base with a wrong size.  This saves tons of
         * inflate() calls.
         */

        if (packed_object_info(&base_ent, type, NULL))
                die("cannot get info for delta-pack base");

        if (sizep) {
                const unsigned char *data;
                unsigned char delta_head[64];
                unsigned long result_size;
                z_stream stream;
                int st;

                memset(&stream, 0, sizeof(stream));

                data = stream.next_in = base_sha1 + 20;
                stream.avail_in = left - 20;
                stream.next_out = delta_head;
                stream.avail_out = sizeof(delta_head);

                inflateInit(&stream);
                st = inflate(&stream, Z_FINISH);
                inflateEnd(&stream);
                if ((st != Z_STREAM_END) &&
                    stream.total_out != sizeof(delta_head))
                        die("delta data unpack-initial failed");

                /* Examine the initial part of the delta to figure out
                 * the result size.
                 */
                data = delta_head;
                get_delta_hdr_size(&data); /* ignore base size */

                /* Read the result size */
                result_size = get_delta_hdr_size(&data);
                *sizep = result_size;
        }
        return 0;
}

static unsigned long unpack_object_header(struct packed_git *p, unsigned long offset,
        enum object_type *type, unsigned long *sizep)
{
        unsigned shift;
        unsigned char *pack, c;
        unsigned long size;

        if (offset >= p->pack_size)
                die("object offset outside of pack file");

        pack =  p->pack_base + offset;
        c = *pack++;
        offset++;
        *type = (c >> 4) & 7;
        size = c & 15;
        shift = 4;
        while (c & 0x80) {
                if (offset >= p->pack_size)
                        die("object offset outside of pack file");
                c = *pack++;
                offset++;
                size += (c & 0x7f) << shift;
                shift += 7;
        }
        *sizep = size;
        return offset;
}

void packed_object_info_detail(struct pack_entry *e,
                               char *type,
                               unsigned long *size,
                               unsigned long *store_size,
                               int *delta_chain_length,
                               unsigned char *base_sha1)
{
        struct packed_git *p = e->p;
        unsigned long offset, left;
        unsigned char *pack;
        enum object_type kind;

        offset = unpack_object_header(p, e->offset, &kind, size);
        pack = p->pack_base + offset;
        left = p->pack_size - offset;
        if (kind != OBJ_DELTA)
                *delta_chain_length = 0;
        else {
                int chain_length = 0;
                memcpy(base_sha1, pack, 20);
                do {
                        struct pack_entry base_ent;
                        unsigned long junk;

                        find_pack_entry_one(pack, &base_ent, p);
                        offset = unpack_object_header(p, base_ent.offset,
                                                      &kind, &junk);
                        pack = p->pack_base + offset;
                        chain_length++;
                } while (kind == OBJ_DELTA);
                *delta_chain_length = chain_length;
        }
        switch (kind) {
        case OBJ_COMMIT:
                strcpy(type, "commit");
                break;
        case OBJ_TREE:
                strcpy(type, "tree");
                break;
        case OBJ_BLOB:
                strcpy(type, "blob");
                break;
        case OBJ_TAG:
                strcpy(type, "tag");
                break;
        default:
                die("corrupted pack file");
        }
        *store_size = 0; /* notyet */
}

static int packed_object_info(struct pack_entry *entry,
                              char *type, unsigned long *sizep)
{
        struct packed_git *p = entry->p;
        unsigned long offset, size, left;
        unsigned char *pack;
        enum object_type kind;
        int retval;

        if (use_packed_git(p))
                die("cannot map packed file");

        offset = unpack_object_header(p, entry->offset, &kind, &size);
        pack = p->pack_base + offset;
        left = p->pack_size - offset;

        switch (kind) {
        case OBJ_DELTA:
                retval = packed_delta_info(pack, size, left, type, sizep, p);
                unuse_packed_git(p);
                return retval;
        case OBJ_COMMIT:
                strcpy(type, "commit");
                break;
        case OBJ_TREE:
                strcpy(type, "tree");
                break;
        case OBJ_BLOB:
                strcpy(type, "blob");
                break;
        case OBJ_TAG:
                strcpy(type, "tag");
                break;
        default:
                die("corrupted pack file");
        }
        if (sizep)
                *sizep = size;
        unuse_packed_git(p);
        return 0;
}

/* forward declaration for a mutually recursive function */
static void *unpack_entry(struct pack_entry *, char *, unsigned long *);

static void *unpack_delta_entry(unsigned char *base_sha1,
                                unsigned long delta_size,
                                unsigned long left,
                                char *type,
                                unsigned long *sizep,
                                struct packed_git *p)
{
        struct pack_entry base_ent;
        void *data, *delta_data, *result, *base;
        unsigned long data_size, result_size, base_size;
        z_stream stream;
        int st;

        if (left < 20)
                die("truncated pack file");
        data = base_sha1 + 20;
        data_size = left - 20;
        delta_data = xmalloc(delta_size);

        memset(&stream, 0, sizeof(stream));

        stream.next_in = data;
        stream.avail_in = data_size;
        stream.next_out = delta_data;
        stream.avail_out = delta_size;

        inflateInit(&stream);
        st = inflate(&stream, Z_FINISH);
        inflateEnd(&stream);
        if ((st != Z_STREAM_END) || stream.total_out != delta_size)
                die("delta data unpack failed");

        /* The base entry _must_ be in the same pack */
        if (!find_pack_entry_one(base_sha1, &base_ent, p))
                die("failed to find delta-pack base object %s",
                    sha1_to_hex(base_sha1));
        base = unpack_entry_gently(&base_ent, type, &base_size);
        if (!base)
                die("failed to read delta-pack base object %s",
                    sha1_to_hex(base_sha1));
        result = patch_delta(base, base_size,
                             delta_data, delta_size,
                             &result_size);
        if (!result)
                die("failed to apply delta");
        free(delta_data);
        free(base);
        *sizep = result_size;
        return result;
}

static void *unpack_non_delta_entry(unsigned char *data,
                                    unsigned long size,
                                    unsigned long left)
{
        int st;
        z_stream stream;
        unsigned char *buffer;

        buffer = xmalloc(size + 1);
        buffer[size] = 0;
        memset(&stream, 0, sizeof(stream));
        stream.next_in = data;
        stream.avail_in = left;
        stream.next_out = buffer;
        stream.avail_out = size;

        inflateInit(&stream);
        st = inflate(&stream, Z_FINISH);
        inflateEnd(&stream);
        if ((st != Z_STREAM_END) || stream.total_out != size) {
                free(buffer);
                return NULL;
        }

        return buffer;
}

static void *unpack_entry(struct pack_entry *entry,
                          char *type, unsigned long *sizep)
{
        struct packed_git *p = entry->p;
        void *retval;

        if (use_packed_git(p))
                die("cannot map packed file");
        retval = unpack_entry_gently(entry, type, sizep);
        unuse_packed_git(p);
        if (!retval)
                die("corrupted pack file");
        return retval;
}

/* The caller is responsible for use_packed_git()/unuse_packed_git() pair */
void *unpack_entry_gently(struct pack_entry *entry,
                          char *type, unsigned long *sizep)
{
        struct packed_git *p = entry->p;
        unsigned long offset, size, left;
        unsigned char *pack;
        enum object_type kind;
        void *retval;

        offset = unpack_object_header(p, entry->offset, &kind, &size);
        pack = p->pack_base + offset;
        left = p->pack_size - offset;
        switch (kind) {
        case OBJ_DELTA:
                retval = unpack_delta_entry(pack, size, left, type, sizep, p);
                return retval;
        case OBJ_COMMIT:
                strcpy(type, "commit");
                break;
        case OBJ_TREE:
                strcpy(type, "tree");
                break;
        case OBJ_BLOB:
                strcpy(type, "blob");
                break;
        case OBJ_TAG:
                strcpy(type, "tag");
                break;
        default:
                return NULL;
        }
        *sizep = size;
        retval = unpack_non_delta_entry(pack, size, left);
        return retval;
}

int num_packed_objects(const struct packed_git *p)
{
        /* See check_packed_git_idx() */
        return (p->index_size - 20 - 20 - 4*256) / 24;
}

int nth_packed_object_sha1(const struct packed_git *p, int n,
                           unsigned char* sha1)
{
        void *index = p->index_base + 256;
        if (n < 0 || num_packed_objects(p) <= n)
                return -1;
        memcpy(sha1, (index + 24 * n + 4), 20);
        return 0;
}

int find_pack_entry_one(const unsigned char *sha1,
                        struct pack_entry *e, struct packed_git *p)
{
        unsigned int *level1_ofs = p->index_base;
        int hi = ntohl(level1_ofs[*sha1]);
        int lo = ((*sha1 == 0x0) ? 0 : ntohl(level1_ofs[*sha1 - 1]));
        void *index = p->index_base + 256;

        do {
                int mi = (lo + hi) / 2;
                int cmp = memcmp(index + 24 * mi + 4, sha1, 20);
                if (!cmp) {
                        e->offset = ntohl(*((int*)(index + 24 * mi)));
                        memcpy(e->sha1, sha1, 20);
                        e->p = p;
                        return 1;
                }
                if (cmp > 0)
                        hi = mi;
                else
                        lo = mi+1;
        } while (lo < hi);
        return 0;
}

static int find_pack_entry(const unsigned char *sha1, struct pack_entry *e)
{
        struct packed_git *p;
        prepare_packed_git();

        for (p = packed_git; p; p = p->next) {
                if (find_pack_entry_one(sha1, e, p))
                        return 1;
        }
        return 0;
}

struct packed_git *find_sha1_pack(const unsigned char *sha1, 
                                  struct packed_git *packs)
{
        struct packed_git *p;
        struct pack_entry e;

        for (p = packs; p; p = p->next) {
                if (find_pack_entry_one(sha1, &e, p))
                        return p;
        }
        return NULL;
        
}

int sha1_object_info(const unsigned char *sha1, char *type, unsigned long *sizep)
{
        int status;
        unsigned long mapsize, size;
        void *map;
        z_stream stream;
        char hdr[128];

        map = map_sha1_file_internal(sha1, &mapsize);
        if (!map) {
                struct pack_entry e;

                if (!find_pack_entry(sha1, &e))
                        return error("unable to find %s", sha1_to_hex(sha1));
                return packed_object_info(&e, type, sizep);
        }
        if (unpack_sha1_header(&stream, map, mapsize, hdr, sizeof(hdr)) < 0)
                status = error("unable to unpack %s header",
                               sha1_to_hex(sha1));
        if (parse_sha1_header(hdr, type, &size) < 0)
                status = error("unable to parse %s header", sha1_to_hex(sha1));
        else {
                status = 0;
                if (sizep)
                        *sizep = size;
        }
        inflateEnd(&stream);
        munmap(map, mapsize);
        return status;
}

static void *read_packed_sha1(const unsigned char *sha1, char *type, unsigned long *size)
{
        struct pack_entry e;

        if (!find_pack_entry(sha1, &e)) {
                error("cannot read sha1_file for %s", sha1_to_hex(sha1));
                return NULL;
        }
        return unpack_entry(&e, type, size);
}

void * read_sha1_file(const unsigned char *sha1, char *type, unsigned long *size)
{
        unsigned long mapsize;
        void *map, *buf;
        struct pack_entry e;

        if (find_pack_entry(sha1, &e))
                return read_packed_sha1(sha1, type, size);
        map = map_sha1_file_internal(sha1, &mapsize);
        if (map) {
                buf = unpack_sha1_file(map, mapsize, type, size);
                munmap(map, mapsize);
                return buf;
        }
        return NULL;
}

void *read_object_with_reference(const unsigned char *sha1,
                                 const char *required_type,
                                 unsigned long *size,
                                 unsigned char *actual_sha1_return)
{
        char type[20];
        void *buffer;
        unsigned long isize;
        unsigned char actual_sha1[20];

        memcpy(actual_sha1, sha1, 20);
        while (1) {
                int ref_length = -1;
                const char *ref_type = NULL;

                buffer = read_sha1_file(actual_sha1, type, &isize);
                if (!buffer)
                        return NULL;
                if (!strcmp(type, required_type)) {
                        *size = isize;
                        if (actual_sha1_return)
                                memcpy(actual_sha1_return, actual_sha1, 20);
                        return buffer;
                }
                /* Handle references */
                else if (!strcmp(type, "commit"))
                        ref_type = "tree ";
                else if (!strcmp(type, "tag"))
                        ref_type = "object ";
                else {
                        free(buffer);
                        return NULL;
                }
                ref_length = strlen(ref_type);

                if (memcmp(buffer, ref_type, ref_length) ||
                    get_sha1_hex(buffer + ref_length, actual_sha1)) {
                        free(buffer);
                        return NULL;
                }
                free(buffer);
                /* Now we have the ID of the referred-to object in
                 * actual_sha1.  Check again. */
        }
}

char *write_sha1_file_prepare(void *buf,
                              unsigned long len,
                              const char *type,
                              unsigned char *sha1,
                              unsigned char *hdr,
                              int *hdrlen)
{
        SHA_CTX c;

        /* Generate the header */
        *hdrlen = sprintf((char *)hdr, "%s %lu", type, len)+1;

        /* Sha1.. */
        SHA1_Init(&c);
        SHA1_Update(&c, hdr, *hdrlen);
        SHA1_Update(&c, buf, len);
        SHA1_Final(sha1, &c);

        return sha1_file_name(sha1);
}

int write_sha1_file(void *buf, unsigned long len, const char *type, unsigned char *returnsha1)
{
        int size;
        unsigned char *compressed;
        z_stream stream;
        unsigned char sha1[20];
        char *filename;
        static char tmpfile[PATH_MAX];
        unsigned char hdr[50];
        int fd, hdrlen, ret;

        /* Normally if we have it in the pack then we do not bother writing
         * it out into .git/objects/??/?{38} file.
         */
        filename = write_sha1_file_prepare(buf, len, type, sha1, hdr, &hdrlen);
        if (returnsha1)
                memcpy(returnsha1, sha1, 20);
        if (has_sha1_file(sha1))
                return 0;
        fd = open(filename, O_RDONLY);
        if (fd >= 0) {
                /*
                 * FIXME!!! We might do collision checking here, but we'd
                 * need to uncompress the old file and check it. Later.
                 */
                close(fd);
                return 0;
        }

        if (errno != ENOENT) {
                fprintf(stderr, "sha1 file %s: %s", filename, strerror(errno));
                return -1;
        }

        snprintf(tmpfile, sizeof(tmpfile), "%s/obj_XXXXXX", get_object_directory());

        fd = mkstemp(tmpfile);
        if (fd < 0) {
                fprintf(stderr, "unable to create temporary sha1 filename %s: %s", tmpfile, strerror(errno));
                return -1;
        }

        /* Set it up */
        memset(&stream, 0, sizeof(stream));
        deflateInit(&stream, Z_BEST_COMPRESSION);
        size = deflateBound(&stream, len+hdrlen);
        compressed = xmalloc(size);

        /* Compress it */
        stream.next_out = compressed;
        stream.avail_out = size;

        /* First header.. */
        stream.next_in = hdr;
        stream.avail_in = hdrlen;
        while (deflate(&stream, 0) == Z_OK)
                /* nothing */;

        /* Then the data itself.. */
        stream.next_in = buf;
        stream.avail_in = len;
        while (deflate(&stream, Z_FINISH) == Z_OK)
                /* nothing */;
        deflateEnd(&stream);
        size = stream.total_out;

        if (write(fd, compressed, size) != size)
                die("unable to write file");
        fchmod(fd, 0444);
        close(fd);
        free(compressed);

        ret = link(tmpfile, filename);
        if (ret < 0) {
                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.
                 *
                 * When this succeeds, we just return 0. We have nothing
                 * left to unlink.
                 */
                if (ret == EXDEV && !rename(tmpfile, filename))
                        return 0;
        }
        unlink(tmpfile);
        if (ret) {
                if (ret != EEXIST) {
                        fprintf(stderr, "unable to write sha1 filename %s: %s", filename, strerror(ret));
                        return -1;
                }
                /* FIXME!!! Collision check here ? */
        }

        return 0;
}

int write_sha1_to_fd(int fd, const unsigned char *sha1)
{
        ssize_t size;
        unsigned long objsize;
        int posn = 0;
        void *map = map_sha1_file_internal(sha1, &objsize);
        void *buf = map;
        void *temp_obj = NULL;
        z_stream stream;

        if (!buf) {
                unsigned char *unpacked;
                unsigned long len;
                char type[20];
                char hdr[50];
                int hdrlen;
                // need to unpack and recompress it by itself
                unpacked = read_packed_sha1(sha1, type, &len);

                hdrlen = sprintf(hdr, "%s %lu", type, len) + 1;

                /* Set it up */
                memset(&stream, 0, sizeof(stream));
                deflateInit(&stream, Z_BEST_COMPRESSION);
                size = deflateBound(&stream, len + hdrlen);
                temp_obj = buf = xmalloc(size);

                /* Compress it */
                stream.next_out = buf;
                stream.avail_out = size;
                
                /* First header.. */
                stream.next_in = (void *)hdr;
                stream.avail_in = hdrlen;
                while (deflate(&stream, 0) == Z_OK)
                        /* nothing */;

                /* Then the data itself.. */
                stream.next_in = unpacked;
                stream.avail_in = len;
                while (deflate(&stream, Z_FINISH) == Z_OK)
                        /* nothing */;
                deflateEnd(&stream);
                free(unpacked);
                
                objsize = stream.total_out;
        }

        do {
                size = write(fd, buf + posn, objsize - posn);
                if (size <= 0) {
                        if (!size) {
                                fprintf(stderr, "write closed");
                        } else {
                                perror("write ");
                        }
                        return -1;
                }
                posn += size;
        } while (posn < objsize);

        if (map)
                munmap(map, objsize);
        if (temp_obj)
                free(temp_obj);

        return 0;
}

int write_sha1_from_fd(const unsigned char *sha1, int fd, char *buffer,
                       size_t bufsize, size_t *bufposn)
{
        char *filename = sha1_file_name(sha1);

        int local;
        z_stream stream;
        unsigned char real_sha1[20];
        unsigned char discard[4096];
        int ret;
        SHA_CTX c;

        local = open(filename, O_WRONLY | O_CREAT | O_EXCL, 0666);

        if (local < 0)
                return error("Couldn't open %s\n", filename);

        memset(&stream, 0, sizeof(stream));

        inflateInit(&stream);

        SHA1_Init(&c);

        do {
                ssize_t size;
                if (*bufposn) {
                        stream.avail_in = *bufposn;
                        stream.next_in = (unsigned char *) buffer;
                        do {
                                stream.next_out = discard;
                                stream.avail_out = sizeof(discard);
                                ret = inflate(&stream, Z_SYNC_FLUSH);
                                SHA1_Update(&c, discard, sizeof(discard) -
                                            stream.avail_out);
                        } while (stream.avail_in && ret == Z_OK);
                        write(local, buffer, *bufposn - stream.avail_in);
                        memmove(buffer, buffer + *bufposn - stream.avail_in,
                                stream.avail_in);
                        *bufposn = stream.avail_in;
                        if (ret != Z_OK)
                                break;
                }
                size = read(fd, buffer + *bufposn, bufsize - *bufposn);
                if (size <= 0) {
                        close(local);
                        unlink(filename);
                        if (!size)
                                return error("Connection closed?");
                        perror("Reading from connection");
                        return -1;
                }
                *bufposn += size;
        } while (1);
        inflateEnd(&stream);

        close(local);
        SHA1_Final(real_sha1, &c);
        if (ret != Z_STREAM_END) {
                unlink(filename);
                return error("File %s corrupted", sha1_to_hex(sha1));
        }
        if (memcmp(sha1, real_sha1, 20)) {
                unlink(filename);
                return error("File %s has bad hash\n", sha1_to_hex(sha1));
        }
        
        return 0;
}

int has_pack_index(const unsigned char *sha1)
{
        struct stat st;
        if (stat(sha1_pack_index_name(sha1), &st))
                return 0;
        return 1;
}

int has_pack_file(const unsigned char *sha1)
{
        struct stat st;
        if (stat(sha1_pack_name(sha1), &st))
                return 0;
        return 1;
}

int has_sha1_pack(const unsigned char *sha1)
{
        struct pack_entry e;
        return find_pack_entry(sha1, &e);
}

int has_sha1_file(const unsigned char *sha1)
{
        struct stat st;
        struct pack_entry e;

        if (find_pack_entry(sha1, &e))
                return 1;
        return find_sha1_file(sha1, &st) ? 1 : 0;
}

int index_fd(unsigned char *sha1, int fd, struct stat *st, int write_object, const char *type)
{
        unsigned long size = st->st_size;
        void *buf;
        int ret;
        unsigned char hdr[50];
        int hdrlen;

        buf = "";
        if (size)
                buf = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
        close(fd);
        if (buf == MAP_FAILED)
                return -1;

        if (!type)
                type = "blob";
        if (write_object)
                ret = write_sha1_file(buf, size, type, sha1);
        else {
                write_sha1_file_prepare(buf, size, type, sha1, hdr, &hdrlen);
                ret = 0;
        }
        if (size)
                munmap(buf, size);
        return ret;
}