t2028: tighten grep expression to make "move worktree" test more robust

[alt-git.git] / connect.c

#include "git-compat-util.h"
#include "cache.h"
#include "config.h"
#include "pkt-line.h"
#include "quote.h"
#include "refs.h"
#include "run-command.h"
#include "remote.h"
#include "connect.h"
#include "url.h"
#include "string-list.h"
#include "sha1-array.h"
#include "transport.h"
#include "strbuf.h"
#include "protocol.h"

static char *server_capabilities;
static const char *parse_feature_value(const char *, const char *, int *);

static int check_ref(const char *name, unsigned int flags)
{
        if (!flags)
                return 1;

        if (!skip_prefix(name, "refs/", &name))
                return 0;

        /* REF_NORMAL means that we don't want the magic fake tag refs */
        if ((flags & REF_NORMAL) && check_refname_format(name, 0))
                return 0;

        /* REF_HEADS means that we want regular branch heads */
        if ((flags & REF_HEADS) && starts_with(name, "heads/"))
                return 1;

        /* REF_TAGS means that we want tags */
        if ((flags & REF_TAGS) && starts_with(name, "tags/"))
                return 1;

        /* All type bits clear means that we are ok with anything */
        return !(flags & ~REF_NORMAL);
}

int check_ref_type(const struct ref *ref, int flags)
{
        return check_ref(ref->name, flags);
}

static void die_initial_contact(int unexpected)
{
        if (unexpected)
                die(_("The remote end hung up upon initial contact"));
        else
                die(_("Could not read from remote repository.\n\n"
                      "Please make sure you have the correct access rights\n"
                      "and the repository exists."));
}

static void parse_one_symref_info(struct string_list *symref, const char *val, int len)
{
        char *sym, *target;
        struct string_list_item *item;

        if (!len)
                return; /* just "symref" */
        /* e.g. "symref=HEAD:refs/heads/master" */
        sym = xmemdupz(val, len);
        target = strchr(sym, ':');
        if (!target)
                /* just "symref=something" */
                goto reject;
        *(target++) = '\0';
        if (check_refname_format(sym, REFNAME_ALLOW_ONELEVEL) ||
            check_refname_format(target, REFNAME_ALLOW_ONELEVEL))
                /* "symref=bogus:pair */
                goto reject;
        item = string_list_append_nodup(symref, sym);
        item->util = target;
        return;
reject:
        free(sym);
        return;
}

static void annotate_refs_with_symref_info(struct ref *ref)
{
        struct string_list symref = STRING_LIST_INIT_DUP;
        const char *feature_list = server_capabilities;

        while (feature_list) {
                int len;
                const char *val;

                val = parse_feature_value(feature_list, "symref", &len);
                if (!val)
                        break;
                parse_one_symref_info(&symref, val, len);
                feature_list = val + 1;
        }
        string_list_sort(&symref);

        for (; ref; ref = ref->next) {
                struct string_list_item *item;
                item = string_list_lookup(&symref, ref->name);
                if (!item)
                        continue;
                ref->symref = xstrdup((char *)item->util);
        }
        string_list_clear(&symref, 0);
}

/*
 * Read one line of a server's ref advertisement into packet_buffer.
 */
static int read_remote_ref(int in, char **src_buf, size_t *src_len,
                           int *responded)
{
        int len = packet_read(in, src_buf, src_len,
                              packet_buffer, sizeof(packet_buffer),
                              PACKET_READ_GENTLE_ON_EOF |
                              PACKET_READ_CHOMP_NEWLINE);
        const char *arg;
        if (len < 0)
                die_initial_contact(*responded);
        if (len > 4 && skip_prefix(packet_buffer, "ERR ", &arg))
                die("remote error: %s", arg);

        *responded = 1;

        return len;
}

#define EXPECTING_PROTOCOL_VERSION 0
#define EXPECTING_FIRST_REF 1
#define EXPECTING_REF 2
#define EXPECTING_SHALLOW 3

/* Returns 1 if packet_buffer is a protocol version pkt-line, 0 otherwise. */
static int process_protocol_version(void)
{
        switch (determine_protocol_version_client(packet_buffer)) {
        case protocol_v1:
                return 1;
        case protocol_v0:
                return 0;
        default:
                die("server is speaking an unknown protocol");
        }
}

static void process_capabilities(int *len)
{
        int nul_location = strlen(packet_buffer);
        if (nul_location == *len)
                return;
        server_capabilities = xstrdup(packet_buffer + nul_location + 1);
        *len = nul_location;
}

static int process_dummy_ref(void)
{
        struct object_id oid;
        const char *name;

        if (parse_oid_hex(packet_buffer, &oid, &name))
                return 0;
        if (*name != ' ')
                return 0;
        name++;

        return !oidcmp(&null_oid, &oid) && !strcmp(name, "capabilities^{}");
}

static void check_no_capabilities(int len)
{
        if (strlen(packet_buffer) != len)
                warning("Ignoring capabilities after first line '%s'",
                        packet_buffer + strlen(packet_buffer));
}

static int process_ref(int len, struct ref ***list, unsigned int flags,
                       struct oid_array *extra_have)
{
        struct object_id old_oid;
        const char *name;

        if (parse_oid_hex(packet_buffer, &old_oid, &name))
                return 0;
        if (*name != ' ')
                return 0;
        name++;

        if (extra_have && !strcmp(name, ".have")) {
                oid_array_append(extra_have, &old_oid);
        } else if (!strcmp(name, "capabilities^{}")) {
                die("protocol error: unexpected capabilities^{}");
        } else if (check_ref(name, flags)) {
                struct ref *ref = alloc_ref(name);
                oidcpy(&ref->old_oid, &old_oid);
                **list = ref;
                *list = &ref->next;
        }
        check_no_capabilities(len);
        return 1;
}

static int process_shallow(int len, struct oid_array *shallow_points)
{
        const char *arg;
        struct object_id old_oid;

        if (!skip_prefix(packet_buffer, "shallow ", &arg))
                return 0;

        if (get_oid_hex(arg, &old_oid))
                die("protocol error: expected shallow sha-1, got '%s'", arg);
        if (!shallow_points)
                die("repository on the other end cannot be shallow");
        oid_array_append(shallow_points, &old_oid);
        check_no_capabilities(len);
        return 1;
}

/*
 * Read all the refs from the other end
 */
struct ref **get_remote_heads(int in, char *src_buf, size_t src_len,
                              struct ref **list, unsigned int flags,
                              struct oid_array *extra_have,
                              struct oid_array *shallow_points)
{
        struct ref **orig_list = list;

        /*
         * A hang-up after seeing some response from the other end
         * means that it is unexpected, as we know the other end is
         * willing to talk to us.  A hang-up before seeing any
         * response does not necessarily mean an ACL problem, though.
         */
        int responded = 0;
        int len;
        int state = EXPECTING_PROTOCOL_VERSION;

        *list = NULL;

        while ((len = read_remote_ref(in, &src_buf, &src_len, &responded))) {
                switch (state) {
                case EXPECTING_PROTOCOL_VERSION:
                        if (process_protocol_version()) {
                                state = EXPECTING_FIRST_REF;
                                break;
                        }
                        state = EXPECTING_FIRST_REF;
                        /* fallthrough */
                case EXPECTING_FIRST_REF:
                        process_capabilities(&len);
                        if (process_dummy_ref()) {
                                state = EXPECTING_SHALLOW;
                                break;
                        }
                        state = EXPECTING_REF;
                        /* fallthrough */
                case EXPECTING_REF:
                        if (process_ref(len, &list, flags, extra_have))
                                break;
                        state = EXPECTING_SHALLOW;
                        /* fallthrough */
                case EXPECTING_SHALLOW:
                        if (process_shallow(len, shallow_points))
                                break;
                        die("protocol error: unexpected '%s'", packet_buffer);
                default:
                        die("unexpected state %d", state);
                }
        }

        annotate_refs_with_symref_info(*orig_list);

        return list;
}

static const char *parse_feature_value(const char *feature_list, const char *feature, int *lenp)
{
        int len;

        if (!feature_list)
                return NULL;

        len = strlen(feature);
        while (*feature_list) {
                const char *found = strstr(feature_list, feature);
                if (!found)
                        return NULL;
                if (feature_list == found || isspace(found[-1])) {
                        const char *value = found + len;
                        /* feature with no value (e.g., "thin-pack") */
                        if (!*value || isspace(*value)) {
                                if (lenp)
                                        *lenp = 0;
                                return value;
                        }
                        /* feature with a value (e.g., "agent=git/1.2.3") */
                        else if (*value == '=') {
                                value++;
                                if (lenp)
                                        *lenp = strcspn(value, " \t\n");
                                return value;
                        }
                        /*
                         * otherwise we matched a substring of another feature;
                         * keep looking
                         */
                }
                feature_list = found + 1;
        }
        return NULL;
}

int parse_feature_request(const char *feature_list, const char *feature)
{
        return !!parse_feature_value(feature_list, feature, NULL);
}

const char *server_feature_value(const char *feature, int *len)
{
        return parse_feature_value(server_capabilities, feature, len);
}

int server_supports(const char *feature)
{
        return !!server_feature_value(feature, NULL);
}

enum protocol {
        PROTO_LOCAL = 1,
        PROTO_FILE,
        PROTO_SSH,
        PROTO_GIT
};

int url_is_local_not_ssh(const char *url)
{
        const char *colon = strchr(url, ':');
        const char *slash = strchr(url, '/');
        return !colon || (slash && slash < colon) ||
                has_dos_drive_prefix(url);
}

static const char *prot_name(enum protocol protocol)
{
        switch (protocol) {
                case PROTO_LOCAL:
                case PROTO_FILE:
                        return "file";
                case PROTO_SSH:
                        return "ssh";
                case PROTO_GIT:
                        return "git";
                default:
                        return "unknown protocol";
        }
}

static enum protocol get_protocol(const char *name)
{
        if (!strcmp(name, "ssh"))
                return PROTO_SSH;
        if (!strcmp(name, "git"))
                return PROTO_GIT;
        if (!strcmp(name, "git+ssh")) /* deprecated - do not use */
                return PROTO_SSH;
        if (!strcmp(name, "ssh+git")) /* deprecated - do not use */
                return PROTO_SSH;
        if (!strcmp(name, "file"))
                return PROTO_FILE;
        die("I don't handle protocol '%s'", name);
}

static char *host_end(char **hoststart, int removebrackets)
{
        char *host = *hoststart;
        char *end;
        char *start = strstr(host, "@[");
        if (start)
                start++; /* Jump over '@' */
        else
                start = host;
        if (start[0] == '[') {
                end = strchr(start + 1, ']');
                if (end) {
                        if (removebrackets) {
                                *end = 0;
                                memmove(start, start + 1, end - start);
                                end++;
                        }
                } else
                        end = host;
        } else
                end = host;
        return end;
}

#define STR_(s) # s
#define STR(s)  STR_(s)

static void get_host_and_port(char **host, const char **port)
{
        char *colon, *end;
        end = host_end(host, 1);
        colon = strchr(end, ':');
        if (colon) {
                long portnr = strtol(colon + 1, &end, 10);
                if (end != colon + 1 && *end == '\0' && 0 <= portnr && portnr < 65536) {
                        *colon = 0;
                        *port = colon + 1;
                } else if (!colon[1]) {
                        *colon = 0;
                }
        }
}

static void enable_keepalive(int sockfd)
{
        int ka = 1;

        if (setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE, &ka, sizeof(ka)) < 0)
                fprintf(stderr, "unable to set SO_KEEPALIVE on socket: %s\n",
                        strerror(errno));
}

#ifndef NO_IPV6

static const char *ai_name(const struct addrinfo *ai)
{
        static char addr[NI_MAXHOST];
        if (getnameinfo(ai->ai_addr, ai->ai_addrlen, addr, sizeof(addr), NULL, 0,
                        NI_NUMERICHOST) != 0)
                xsnprintf(addr, sizeof(addr), "(unknown)");

        return addr;
}

/*
 * Returns a connected socket() fd, or else die()s.
 */
static int git_tcp_connect_sock(char *host, int flags)
{
        struct strbuf error_message = STRBUF_INIT;
        int sockfd = -1;
        const char *port = STR(DEFAULT_GIT_PORT);
        struct addrinfo hints, *ai0, *ai;
        int gai;
        int cnt = 0;

        get_host_and_port(&host, &port);
        if (!*port)
                port = "<none>";

        memset(&hints, 0, sizeof(hints));
        if (flags & CONNECT_IPV4)
                hints.ai_family = AF_INET;
        else if (flags & CONNECT_IPV6)
                hints.ai_family = AF_INET6;
        hints.ai_socktype = SOCK_STREAM;
        hints.ai_protocol = IPPROTO_TCP;

        if (flags & CONNECT_VERBOSE)
                fprintf(stderr, "Looking up %s ... ", host);

        gai = getaddrinfo(host, port, &hints, &ai);
        if (gai)
                die("Unable to look up %s (port %s) (%s)", host, port, gai_strerror(gai));

        if (flags & CONNECT_VERBOSE)
                fprintf(stderr, "done.\nConnecting to %s (port %s) ... ", host, port);

        for (ai0 = ai; ai; ai = ai->ai_next, cnt++) {
                sockfd = socket(ai->ai_family,
                                ai->ai_socktype, ai->ai_protocol);
                if ((sockfd < 0) ||
                    (connect(sockfd, ai->ai_addr, ai->ai_addrlen) < 0)) {
                        strbuf_addf(&error_message, "%s[%d: %s]: errno=%s\n",
                                    host, cnt, ai_name(ai), strerror(errno));
                        if (0 <= sockfd)
                                close(sockfd);
                        sockfd = -1;
                        continue;
                }
                if (flags & CONNECT_VERBOSE)
                        fprintf(stderr, "%s ", ai_name(ai));
                break;
        }

        freeaddrinfo(ai0);

        if (sockfd < 0)
                die("unable to connect to %s:\n%s", host, error_message.buf);

        enable_keepalive(sockfd);

        if (flags & CONNECT_VERBOSE)
                fprintf(stderr, "done.\n");

        strbuf_release(&error_message);

        return sockfd;
}

#else /* NO_IPV6 */

/*
 * Returns a connected socket() fd, or else die()s.
 */
static int git_tcp_connect_sock(char *host, int flags)
{
        struct strbuf error_message = STRBUF_INIT;
        int sockfd = -1;
        const char *port = STR(DEFAULT_GIT_PORT);
        char *ep;
        struct hostent *he;
        struct sockaddr_in sa;
        char **ap;
        unsigned int nport;
        int cnt;

        get_host_and_port(&host, &port);

        if (flags & CONNECT_VERBOSE)
                fprintf(stderr, "Looking up %s ... ", host);

        he = gethostbyname(host);
        if (!he)
                die("Unable to look up %s (%s)", host, hstrerror(h_errno));
        nport = strtoul(port, &ep, 10);
        if ( ep == port || *ep ) {
                /* Not numeric */
                struct servent *se = getservbyname(port,"tcp");
                if ( !se )
                        die("Unknown port %s", port);
                nport = se->s_port;
        }

        if (flags & CONNECT_VERBOSE)
                fprintf(stderr, "done.\nConnecting to %s (port %s) ... ", host, port);

        for (cnt = 0, ap = he->h_addr_list; *ap; ap++, cnt++) {
                memset(&sa, 0, sizeof sa);
                sa.sin_family = he->h_addrtype;
                sa.sin_port = htons(nport);
                memcpy(&sa.sin_addr, *ap, he->h_length);

                sockfd = socket(he->h_addrtype, SOCK_STREAM, 0);
                if ((sockfd < 0) ||
                    connect(sockfd, (struct sockaddr *)&sa, sizeof sa) < 0) {
                        strbuf_addf(&error_message, "%s[%d: %s]: errno=%s\n",
                                host,
                                cnt,
                                inet_ntoa(*(struct in_addr *)&sa.sin_addr),
                                strerror(errno));
                        if (0 <= sockfd)
                                close(sockfd);
                        sockfd = -1;
                        continue;
                }
                if (flags & CONNECT_VERBOSE)
                        fprintf(stderr, "%s ",
                                inet_ntoa(*(struct in_addr *)&sa.sin_addr));
                break;
        }

        if (sockfd < 0)
                die("unable to connect to %s:\n%s", host, error_message.buf);

        enable_keepalive(sockfd);

        if (flags & CONNECT_VERBOSE)
                fprintf(stderr, "done.\n");

        return sockfd;
}

#endif /* NO_IPV6 */


/*
 * Dummy child_process returned by git_connect() if the transport protocol
 * does not need fork(2).
 */
static struct child_process no_fork = CHILD_PROCESS_INIT;

int git_connection_is_socket(struct child_process *conn)
{
        return conn == &no_fork;
}

static struct child_process *git_tcp_connect(int fd[2], char *host, int flags)
{
        int sockfd = git_tcp_connect_sock(host, flags);

        fd[0] = sockfd;
        fd[1] = dup(sockfd);

        return &no_fork;
}


static char *git_proxy_command;

static int git_proxy_command_options(const char *var, const char *value,
                void *cb)
{
        if (!strcmp(var, "core.gitproxy")) {
                const char *for_pos;
                int matchlen = -1;
                int hostlen;
                const char *rhost_name = cb;
                int rhost_len = strlen(rhost_name);

                if (git_proxy_command)
                        return 0;
                if (!value)
                        return config_error_nonbool(var);
                /* [core]
                 * ;# matches www.kernel.org as well
                 * gitproxy = netcatter-1 for kernel.org
                 * gitproxy = netcatter-2 for sample.xz
                 * gitproxy = netcatter-default
                 */
                for_pos = strstr(value, " for ");
                if (!for_pos)
                        /* matches everybody */
                        matchlen = strlen(value);
                else {
                        hostlen = strlen(for_pos + 5);
                        if (rhost_len < hostlen)
                                matchlen = -1;
                        else if (!strncmp(for_pos + 5,
                                          rhost_name + rhost_len - hostlen,
                                          hostlen) &&
                                 ((rhost_len == hostlen) ||
                                  rhost_name[rhost_len - hostlen -1] == '.'))
                                matchlen = for_pos - value;
                        else
                                matchlen = -1;
                }
                if (0 <= matchlen) {
                        /* core.gitproxy = none for kernel.org */
                        if (matchlen == 4 &&
                            !memcmp(value, "none", 4))
                                matchlen = 0;
                        git_proxy_command = xmemdupz(value, matchlen);
                }
                return 0;
        }

        return git_default_config(var, value, cb);
}

static int git_use_proxy(const char *host)
{
        git_proxy_command = getenv("GIT_PROXY_COMMAND");
        git_config(git_proxy_command_options, (void*)host);
        return (git_proxy_command && *git_proxy_command);
}

static struct child_process *git_proxy_connect(int fd[2], char *host)
{
        const char *port = STR(DEFAULT_GIT_PORT);
        struct child_process *proxy;

        get_host_and_port(&host, &port);

        if (looks_like_command_line_option(host))
                die("strange hostname '%s' blocked", host);
        if (looks_like_command_line_option(port))
                die("strange port '%s' blocked", port);

        proxy = xmalloc(sizeof(*proxy));
        child_process_init(proxy);
        argv_array_push(&proxy->args, git_proxy_command);
        argv_array_push(&proxy->args, host);
        argv_array_push(&proxy->args, port);
        proxy->in = -1;
        proxy->out = -1;
        if (start_command(proxy))
                die("cannot start proxy %s", git_proxy_command);
        fd[0] = proxy->out; /* read from proxy stdout */
        fd[1] = proxy->in;  /* write to proxy stdin */
        return proxy;
}

static char *get_port(char *host)
{
        char *end;
        char *p = strchr(host, ':');

        if (p) {
                long port = strtol(p + 1, &end, 10);
                if (end != p + 1 && *end == '\0' && 0 <= port && port < 65536) {
                        *p = '\0';
                        return p+1;
                }
        }

        return NULL;
}

/*
 * Extract protocol and relevant parts from the specified connection URL.
 * The caller must free() the returned strings.
 */
static enum protocol parse_connect_url(const char *url_orig, char **ret_host,
                                       char **ret_path)
{
        char *url;
        char *host, *path;
        char *end;
        int separator = '/';
        enum protocol protocol = PROTO_LOCAL;

        if (is_url(url_orig))
                url = url_decode(url_orig);
        else
                url = xstrdup(url_orig);

        host = strstr(url, "://");
        if (host) {
                *host = '\0';
                protocol = get_protocol(url);
                host += 3;
        } else {
                host = url;
                if (!url_is_local_not_ssh(url)) {
                        protocol = PROTO_SSH;
                        separator = ':';
                }
        }

        /*
         * Don't do destructive transforms as protocol code does
         * '[]' unwrapping in get_host_and_port()
         */
        end = host_end(&host, 0);

        if (protocol == PROTO_LOCAL)
                path = end;
        else if (protocol == PROTO_FILE && has_dos_drive_prefix(end))
                path = end; /* "file://$(pwd)" may be "file://C:/projects/repo" */
        else
                path = strchr(end, separator);

        if (!path || !*path)
                die("No path specified. See 'man git-pull' for valid url syntax");

        /*
         * null-terminate hostname and point path to ~ for URL's like this:
         *    ssh://host.xz/~user/repo
         */

        end = path; /* Need to \0 terminate host here */
        if (separator == ':')
                path++; /* path starts after ':' */
        if (protocol == PROTO_GIT || protocol == PROTO_SSH) {
                if (path[1] == '~')
                        path++;
        }

        path = xstrdup(path);
        *end = '\0';

        *ret_host = xstrdup(host);
        *ret_path = path;
        free(url);
        return protocol;
}

static const char *get_ssh_command(void)
{
        const char *ssh;

        if ((ssh = getenv("GIT_SSH_COMMAND")))
                return ssh;

        if (!git_config_get_string_const("core.sshcommand", &ssh))
                return ssh;

        return NULL;
}

enum ssh_variant {
        VARIANT_AUTO,
        VARIANT_SIMPLE,
        VARIANT_SSH,
        VARIANT_PLINK,
        VARIANT_PUTTY,
        VARIANT_TORTOISEPLINK,
};

static void override_ssh_variant(enum ssh_variant *ssh_variant)
{
        const char *variant = getenv("GIT_SSH_VARIANT");

        if (!variant && git_config_get_string_const("ssh.variant", &variant))
                return;

        if (!strcmp(variant, "auto"))
                *ssh_variant = VARIANT_AUTO;
        else if (!strcmp(variant, "plink"))
                *ssh_variant = VARIANT_PLINK;
        else if (!strcmp(variant, "putty"))
                *ssh_variant = VARIANT_PUTTY;
        else if (!strcmp(variant, "tortoiseplink"))
                *ssh_variant = VARIANT_TORTOISEPLINK;
        else if (!strcmp(variant, "simple"))
                *ssh_variant = VARIANT_SIMPLE;
        else
                *ssh_variant = VARIANT_SSH;
}

static enum ssh_variant determine_ssh_variant(const char *ssh_command,
                                              int is_cmdline)
{
        enum ssh_variant ssh_variant = VARIANT_AUTO;
        const char *variant;
        char *p = NULL;

        override_ssh_variant(&ssh_variant);

        if (ssh_variant != VARIANT_AUTO)
                return ssh_variant;

        if (!is_cmdline) {
                p = xstrdup(ssh_command);
                variant = basename(p);
        } else {
                const char **ssh_argv;

                p = xstrdup(ssh_command);
                if (split_cmdline(p, &ssh_argv) > 0) {
                        variant = basename((char *)ssh_argv[0]);
                        /*
                         * At this point, variant points into the buffer
                         * referenced by p, hence we do not need ssh_argv
                         * any longer.
                         */
                        free(ssh_argv);
                } else {
                        free(p);
                        return ssh_variant;
                }
        }

        if (!strcasecmp(variant, "ssh") ||
            !strcasecmp(variant, "ssh.exe"))
                ssh_variant = VARIANT_SSH;
        else if (!strcasecmp(variant, "plink") ||
                 !strcasecmp(variant, "plink.exe"))
                ssh_variant = VARIANT_PLINK;
        else if (!strcasecmp(variant, "tortoiseplink") ||
                 !strcasecmp(variant, "tortoiseplink.exe"))
                ssh_variant = VARIANT_TORTOISEPLINK;

        free(p);
        return ssh_variant;
}

/*
 * Open a connection using Git's native protocol.
 *
 * The caller is responsible for freeing hostandport, but this function may
 * modify it (for example, to truncate it to remove the port part).
 */
static struct child_process *git_connect_git(int fd[2], char *hostandport,
                                             const char *path, const char *prog,
                                             int flags)
{
        struct child_process *conn;
        struct strbuf request = STRBUF_INIT;
        /*
         * Set up virtual host information based on where we will
         * connect, unless the user has overridden us in
         * the environment.
         */
        char *target_host = getenv("GIT_OVERRIDE_VIRTUAL_HOST");
        if (target_host)
                target_host = xstrdup(target_host);
        else
                target_host = xstrdup(hostandport);

        transport_check_allowed("git");

        /*
         * These underlying connection commands die() if they
         * cannot connect.
         */
        if (git_use_proxy(hostandport))
                conn = git_proxy_connect(fd, hostandport);
        else
                conn = git_tcp_connect(fd, hostandport, flags);
        /*
         * Separate original protocol components prog and path
         * from extended host header with a NUL byte.
         *
         * Note: Do not add any other headers here!  Doing so
         * will cause older git-daemon servers to crash.
         */
        strbuf_addf(&request,
                    "%s %s%chost=%s%c",
                    prog, path, 0,
                    target_host, 0);

        /* If using a new version put that stuff here after a second null byte */
        if (get_protocol_version_config() > 0) {
                strbuf_addch(&request, '\0');
                strbuf_addf(&request, "version=%d%c",
                            get_protocol_version_config(), '\0');
        }

        packet_write(fd[1], request.buf, request.len);

        free(target_host);
        strbuf_release(&request);
        return conn;
}

/*
 * Append the appropriate environment variables to `env` and options to
 * `args` for running ssh in Git's SSH-tunneled transport.
 */
static void push_ssh_options(struct argv_array *args, struct argv_array *env,
                             enum ssh_variant variant, const char *port,
                             int flags)
{
        if (variant == VARIANT_SSH &&
            get_protocol_version_config() > 0) {
                argv_array_push(args, "-o");
                argv_array_push(args, "SendEnv=" GIT_PROTOCOL_ENVIRONMENT);
                argv_array_pushf(env, GIT_PROTOCOL_ENVIRONMENT "=version=%d",
                                 get_protocol_version_config());
        }

        if (flags & CONNECT_IPV4) {
                switch (variant) {
                case VARIANT_AUTO:
                        BUG("VARIANT_AUTO passed to push_ssh_options");
                case VARIANT_SIMPLE:
                        die("ssh variant 'simple' does not support -4");
                case VARIANT_SSH:
                case VARIANT_PLINK:
                case VARIANT_PUTTY:
                case VARIANT_TORTOISEPLINK:
                        argv_array_push(args, "-4");
                }
        } else if (flags & CONNECT_IPV6) {
                switch (variant) {
                case VARIANT_AUTO:
                        BUG("VARIANT_AUTO passed to push_ssh_options");
                case VARIANT_SIMPLE:
                        die("ssh variant 'simple' does not support -6");
                case VARIANT_SSH:
                case VARIANT_PLINK:
                case VARIANT_PUTTY:
                case VARIANT_TORTOISEPLINK:
                        argv_array_push(args, "-6");
                }
        }

        if (variant == VARIANT_TORTOISEPLINK)
                argv_array_push(args, "-batch");

        if (port) {
                switch (variant) {
                case VARIANT_AUTO:
                        BUG("VARIANT_AUTO passed to push_ssh_options");
                case VARIANT_SIMPLE:
                        die("ssh variant 'simple' does not support setting port");
                case VARIANT_SSH:
                        argv_array_push(args, "-p");
                        break;
                case VARIANT_PLINK:
                case VARIANT_PUTTY:
                case VARIANT_TORTOISEPLINK:
                        argv_array_push(args, "-P");
                }

                argv_array_push(args, port);
        }
}

/* Prepare a child_process for use by Git's SSH-tunneled transport. */
static void fill_ssh_args(struct child_process *conn, const char *ssh_host,
                          const char *port, int flags)
{
        const char *ssh;
        enum ssh_variant variant;

        if (looks_like_command_line_option(ssh_host))
                die("strange hostname '%s' blocked", ssh_host);

        ssh = get_ssh_command();
        if (ssh) {
                variant = determine_ssh_variant(ssh, 1);
        } else {
                /*
                 * GIT_SSH is the no-shell version of
                 * GIT_SSH_COMMAND (and must remain so for
                 * historical compatibility).
                 */
                conn->use_shell = 0;

                ssh = getenv("GIT_SSH");
                if (!ssh)
                        ssh = "ssh";
                variant = determine_ssh_variant(ssh, 0);
        }

        if (variant == VARIANT_AUTO) {
                struct child_process detect = CHILD_PROCESS_INIT;

                detect.use_shell = conn->use_shell;
                detect.no_stdin = detect.no_stdout = detect.no_stderr = 1;

                argv_array_push(&detect.args, ssh);
                argv_array_push(&detect.args, "-G");
                push_ssh_options(&detect.args, &detect.env_array,
                                 VARIANT_SSH, port, flags);
                argv_array_push(&detect.args, ssh_host);

                variant = run_command(&detect) ? VARIANT_SIMPLE : VARIANT_SSH;
        }

        argv_array_push(&conn->args, ssh);
        push_ssh_options(&conn->args, &conn->env_array, variant, port, flags);
        argv_array_push(&conn->args, ssh_host);
}

/*
 * This returns the dummy child_process `no_fork` if the transport protocol
 * does not need fork(2), or a struct child_process object if it does.  Once
 * done, finish the connection with finish_connect() with the value returned
 * from this function (it is safe to call finish_connect() with NULL to
 * support the former case).
 *
 * If it returns, the connect is successful; it just dies on errors (this
 * will hopefully be changed in a libification effort, to return NULL when
 * the connection failed).
 */
struct child_process *git_connect(int fd[2], const char *url,
                                  const char *prog, int flags)
{
        char *hostandport, *path;
        struct child_process *conn;
        enum protocol protocol;

        /* Without this we cannot rely on waitpid() to tell
         * what happened to our children.
         */
        signal(SIGCHLD, SIG_DFL);

        protocol = parse_connect_url(url, &hostandport, &path);
        if ((flags & CONNECT_DIAG_URL) && (protocol != PROTO_SSH)) {
                printf("Diag: url=%s\n", url ? url : "NULL");
                printf("Diag: protocol=%s\n", prot_name(protocol));
                printf("Diag: hostandport=%s\n", hostandport ? hostandport : "NULL");
                printf("Diag: path=%s\n", path ? path : "NULL");
                conn = NULL;
        } else if (protocol == PROTO_GIT) {
                conn = git_connect_git(fd, hostandport, path, prog, flags);
        } else {
                struct strbuf cmd = STRBUF_INIT;
                const char *const *var;

                conn = xmalloc(sizeof(*conn));
                child_process_init(conn);

                if (looks_like_command_line_option(path))
                        die("strange pathname '%s' blocked", path);

                strbuf_addstr(&cmd, prog);
                strbuf_addch(&cmd, ' ');
                sq_quote_buf(&cmd, path);

                /* remove repo-local variables from the environment */
                for (var = local_repo_env; *var; var++)
                        argv_array_push(&conn->env_array, *var);

                conn->use_shell = 1;
                conn->in = conn->out = -1;
                if (protocol == PROTO_SSH) {
                        char *ssh_host = hostandport;
                        const char *port = NULL;
                        transport_check_allowed("ssh");
                        get_host_and_port(&ssh_host, &port);

                        if (!port)
                                port = get_port(ssh_host);

                        if (flags & CONNECT_DIAG_URL) {
                                printf("Diag: url=%s\n", url ? url : "NULL");
                                printf("Diag: protocol=%s\n", prot_name(protocol));
                                printf("Diag: userandhost=%s\n", ssh_host ? ssh_host : "NULL");
                                printf("Diag: port=%s\n", port ? port : "NONE");
                                printf("Diag: path=%s\n", path ? path : "NULL");

                                free(hostandport);
                                free(path);
                                free(conn);
                                strbuf_release(&cmd);
                                return NULL;
                        }
                        fill_ssh_args(conn, ssh_host, port, flags);
                } else {
                        transport_check_allowed("file");
                        if (get_protocol_version_config() > 0) {
                                argv_array_pushf(&conn->env_array, GIT_PROTOCOL_ENVIRONMENT "=version=%d",
                                                 get_protocol_version_config());
                        }
                }
                argv_array_push(&conn->args, cmd.buf);

                if (start_command(conn))
                        die("unable to fork");

                fd[0] = conn->out; /* read from child's stdout */
                fd[1] = conn->in;  /* write to child's stdin */
                strbuf_release(&cmd);
        }
        free(hostandport);
        free(path);
        return conn;
}

int finish_connect(struct child_process *conn)
{
        int code;
        if (!conn || git_connection_is_socket(conn))
                return 0;

        code = finish_command(conn);
        free(conn);
        return code;
}