git/builtin/receive-pack.c

#include "builtin.h"
#include "lockfile.h"
#include "pack.h"
#include "refs.h"
#include "pkt-line.h"
#include "sideband.h"
#include "run-command.h"
#include "exec_cmd.h"
#include "commit.h"
#include "object.h"
#include "remote.h"
#include "connect.h"
#include "transport.h"
#include "string-list.h"
#include "sha1-array.h"
#include "connected.h"
#include "argv-array.h"
#include "version.h"
#include "tag.h"
#include "gpg-interface.h"
#include "sigchain.h"

static const char receive_pack_usage[] = "git receive-pack <git-dir>";

enum deny_action {
	DENY_UNCONFIGURED,
	DENY_IGNORE,
	DENY_WARN,
	DENY_REFUSE
};

static int deny_deletes;
static int deny_non_fast_forwards;
static enum deny_action deny_current_branch = DENY_UNCONFIGURED;
static enum deny_action deny_delete_current = DENY_UNCONFIGURED;
static int receive_fsck_objects = -1;
static int transfer_fsck_objects = -1;
static int receive_unpack_limit = -1;
static int transfer_unpack_limit = -1;
static int unpack_limit = 100;
static int report_status;
static int use_sideband;
static int quiet;
static int prefer_ofs_delta = 1;
static int auto_update_server_info;
static int auto_gc = 1;
static int fix_thin = 1;
static int stateless_rpc;
static const char *service_dir;
static const char *head_name;
static void *head_name_to_free;
static int sent_capabilities;
static int shallow_update;
static const char *alt_shallow_file;
static struct strbuf push_cert = STRBUF_INIT;
static unsigned char push_cert_sha1[20];
static struct signature_check sigcheck;
static const char *push_cert_nonce;
static const char *cert_nonce_seed;

static const char *NONCE_UNSOLICITED = "UNSOLICITED";
static const char *NONCE_BAD = "BAD";
static const char *NONCE_MISSING = "MISSING";
static const char *NONCE_OK = "OK";
static const char *NONCE_SLOP = "SLOP";
static const char *nonce_status;
static long nonce_stamp_slop;
static unsigned long nonce_stamp_slop_limit;

static enum deny_action parse_deny_action(const char *var, const char *value)
{
	if (value) {
		if (!strcasecmp(value, "ignore"))
			return DENY_IGNORE;
		if (!strcasecmp(value, "warn"))
			return DENY_WARN;
		if (!strcasecmp(value, "refuse"))
			return DENY_REFUSE;
	}
	if (git_config_bool(var, value))
		return DENY_REFUSE;
	return DENY_IGNORE;
}

static int receive_pack_config(const char *var, const char *value, void *cb)
{
	int status = parse_hide_refs_config(var, value, "receive");

	if (status)
		return status;

	if (strcmp(var, "receive.denydeletes") == 0) {
		deny_deletes = git_config_bool(var, value);
		return 0;
	}

	if (strcmp(var, "receive.denynonfastforwards") == 0) {
		deny_non_fast_forwards = git_config_bool(var, value);
		return 0;
	}

	if (strcmp(var, "receive.unpacklimit") == 0) {
		receive_unpack_limit = git_config_int(var, value);
		return 0;
	}

	if (strcmp(var, "transfer.unpacklimit") == 0) {
		transfer_unpack_limit = git_config_int(var, value);
		return 0;
	}

	if (strcmp(var, "receive.fsckobjects") == 0) {
		receive_fsck_objects = git_config_bool(var, value);
		return 0;
	}

	if (strcmp(var, "transfer.fsckobjects") == 0) {
		transfer_fsck_objects = git_config_bool(var, value);
		return 0;
	}

	if (!strcmp(var, "receive.denycurrentbranch")) {
		deny_current_branch = parse_deny_action(var, value);
		return 0;
	}

	if (strcmp(var, "receive.denydeletecurrent") == 0) {
		deny_delete_current = parse_deny_action(var, value);
		return 0;
	}

	if (strcmp(var, "repack.usedeltabaseoffset") == 0) {
		prefer_ofs_delta = git_config_bool(var, value);
		return 0;
	}

	if (strcmp(var, "receive.updateserverinfo") == 0) {
		auto_update_server_info = git_config_bool(var, value);
		return 0;
	}

	if (strcmp(var, "receive.autogc") == 0) {
		auto_gc = git_config_bool(var, value);
		return 0;
	}

	if (strcmp(var, "receive.shallowupdate") == 0) {
		shallow_update = git_config_bool(var, value);
		return 0;
	}

	if (strcmp(var, "receive.certnonceseed") == 0)
		return git_config_string(&cert_nonce_seed, var, value);

	if (strcmp(var, "receive.certnonceslop") == 0) {
		nonce_stamp_slop_limit = git_config_ulong(var, value);
		return 0;
	}

	return git_default_config(var, value, cb);
}

static void show_ref(const char *path, const unsigned char *sha1)
{
	if (ref_is_hidden(path))
		return;

	if (sent_capabilities) {
		packet_write(1, "%s %s\n", sha1_to_hex(sha1), path);
	} else {
		struct strbuf cap = STRBUF_INIT;

		strbuf_addstr(&cap,
			      "report-status delete-refs side-band-64k quiet");
		if (prefer_ofs_delta)
			strbuf_addstr(&cap, " ofs-delta");
		if (push_cert_nonce)
			strbuf_addf(&cap, " push-cert=%s", push_cert_nonce);
		strbuf_addf(&cap, " agent=%s", git_user_agent_sanitized());
		packet_write(1, "%s %s%c%s\n",
			     sha1_to_hex(sha1), path, 0, cap.buf);
		strbuf_release(&cap);
		sent_capabilities = 1;
	}
}

static int show_ref_cb(const char *path, const unsigned char *sha1, int flag, void *unused)
{
	path = strip_namespace(path);
	/*
	 * Advertise refs outside our current namespace as ".have"
	 * refs, so that the client can use them to minimize data
	 * transfer but will otherwise ignore them. This happens to
	 * cover ".have" that are thrown in by add_one_alternate_ref()
	 * to mark histories that are complete in our alternates as
	 * well.
	 */
	if (!path)
		path = ".have";
	show_ref(path, sha1);
	return 0;
}

static void show_one_alternate_sha1(const unsigned char sha1[20], void *unused)
{
	show_ref(".have", sha1);
}

static void collect_one_alternate_ref(const struct ref *ref, void *data)
{
	struct sha1_array *sa = data;
	sha1_array_append(sa, ref->old_sha1);
}

static void write_head_info(void)
{
	struct sha1_array sa = SHA1_ARRAY_INIT;
	for_each_alternate_ref(collect_one_alternate_ref, &sa);
	sha1_array_for_each_unique(&sa, show_one_alternate_sha1, NULL);
	sha1_array_clear(&sa);
	for_each_ref(show_ref_cb, NULL);
	if (!sent_capabilities)
		show_ref("capabilities^{}", null_sha1);

	advertise_shallow_grafts(1);

	/* EOF */
	packet_flush(1);
}

struct command {
	struct command *next;
	const char *error_string;
	unsigned int skip_update:1,
		     did_not_exist:1;
	int index;
	unsigned char old_sha1[20];
	unsigned char new_sha1[20];
	char ref_name[FLEX_ARRAY]; /* more */
};

static void rp_error(const char *err, ...) __attribute__((format (printf, 1, 2)));
static void rp_warning(const char *err, ...) __attribute__((format (printf, 1, 2)));

static void report_message(const char *prefix, const char *err, va_list params)
{
	int sz = strlen(prefix);
	char msg[4096];

	strncpy(msg, prefix, sz);
	sz += vsnprintf(msg + sz, sizeof(msg) - sz, err, params);
	if (sz > (sizeof(msg) - 1))
		sz = sizeof(msg) - 1;
	msg[sz++] = '\n';

	if (use_sideband)
		send_sideband(1, 2, msg, sz, use_sideband);
	else
		xwrite(2, msg, sz);
}

static void rp_warning(const char *err, ...)
{
	va_list params;
	va_start(params, err);
	report_message("warning: ", err, params);
	va_end(params);
}

static void rp_error(const char *err, ...)
{
	va_list params;
	va_start(params, err);
	report_message("error: ", err, params);
	va_end(params);
}

static int copy_to_sideband(int in, int out, void *arg)
{
	char data[128];
	while (1) {
		ssize_t sz = xread(in, data, sizeof(data));
		if (sz <= 0)
			break;
		send_sideband(1, 2, data, sz, use_sideband);
	}
	close(in);
	return 0;
}

#define HMAC_BLOCK_SIZE 64

static void hmac_sha1(unsigned char *out,
		      const char *key_in, size_t key_len,
		      const char *text, size_t text_len)
{
	unsigned char key[HMAC_BLOCK_SIZE];
	unsigned char k_ipad[HMAC_BLOCK_SIZE];
	unsigned char k_opad[HMAC_BLOCK_SIZE];
	int i;
	git_SHA_CTX ctx;

	/* RFC 2104 2. (1) */
	memset(key, '\0', HMAC_BLOCK_SIZE);
	if (HMAC_BLOCK_SIZE < key_len) {
		git_SHA1_Init(&ctx);
		git_SHA1_Update(&ctx, key_in, key_len);
		git_SHA1_Final(key, &ctx);
	} else {
		memcpy(key, key_in, key_len);
	}

	/* RFC 2104 2. (2) & (5) */
	for (i = 0; i < sizeof(key); i++) {
		k_ipad[i] = key[i] ^ 0x36;
		k_opad[i] = key[i] ^ 0x5c;
	}

	/* RFC 2104 2. (3) & (4) */
	git_SHA1_Init(&ctx);
	git_SHA1_Update(&ctx, k_ipad, sizeof(k_ipad));
	git_SHA1_Update(&ctx, text, text_len);
	git_SHA1_Final(out, &ctx);

	/* RFC 2104 2. (6) & (7) */
	git_SHA1_Init(&ctx);
	git_SHA1_Update(&ctx, k_opad, sizeof(k_opad));
	git_SHA1_Update(&ctx, out, 20);
	git_SHA1_Final(out, &ctx);
}

static char *prepare_push_cert_nonce(const char *path, unsigned long stamp)
{
	struct strbuf buf = STRBUF_INIT;
	unsigned char sha1[20];

	strbuf_addf(&buf, "%s:%lu", path, stamp);
	hmac_sha1(sha1, buf.buf, buf.len, cert_nonce_seed, strlen(cert_nonce_seed));;
	strbuf_release(&buf);

	/* RFC 2104 5. HMAC-SHA1-80 */
	strbuf_addf(&buf, "%lu-%.*s", stamp, 20, sha1_to_hex(sha1));
	return strbuf_detach(&buf, NULL);
}

/*
 * NEEDSWORK: reuse find_commit_header() from jk/commit-author-parsing
 * after dropping "_commit" from its name and possibly moving it out
 * of commit.c
 */
static char *find_header(const char *msg, size_t len, const char *key)
{
	int key_len = strlen(key);
	const char *line = msg;

	while (line && line < msg + len) {
		const char *eol = strchrnul(line, '\n');

		if ((msg + len <= eol) || line == eol)
			return NULL;
		if (line + key_len < eol &&
		    !memcmp(line, key, key_len) && line[key_len] == ' ') {
			int offset = key_len + 1;
			return xmemdupz(line + offset, (eol - line) - offset);
		}
		line = *eol ? eol + 1 : NULL;
	}
	return NULL;
}

static const char *check_nonce(const char *buf, size_t len)
{
	char *nonce = find_header(buf, len, "nonce");
	unsigned long stamp, ostamp;
	char *bohmac, *expect = NULL;
	const char *retval = NONCE_BAD;

	if (!nonce) {
		retval = NONCE_MISSING;
		goto leave;
	} else if (!push_cert_nonce) {
		retval = NONCE_UNSOLICITED;
		goto leave;
	} else if (!strcmp(push_cert_nonce, nonce)) {
		retval = NONCE_OK;
		goto leave;
	}

	if (!stateless_rpc) {
		/* returned nonce MUST match what we gave out earlier */
		retval = NONCE_BAD;
		goto leave;
	}

	/*
	 * In stateless mode, we may be receiving a nonce issued by
	 * another instance of the server that serving the same
	 * repository, and the timestamps may not match, but the
	 * nonce-seed and dir should match, so we can recompute and
	 * report the time slop.
	 *
	 * In addition, when a nonce issued by another instance has
	 * timestamp within receive.certnonceslop seconds, we pretend
	 * as if we issued that nonce when reporting to the hook.
	 */

	/* nonce is concat(<seconds-since-epoch>, "-", <hmac>) */
	if (*nonce <= '0' || '9' < *nonce) {
		retval = NONCE_BAD;
		goto leave;
	}
	stamp = strtoul(nonce, &bohmac, 10);
	if (bohmac == nonce || bohmac[0] != '-') {
		retval = NONCE_BAD;
		goto leave;
	}

	expect = prepare_push_cert_nonce(service_dir, stamp);
	if (strcmp(expect, nonce)) {
		/* Not what we would have signed earlier */
		retval = NONCE_BAD;
		goto leave;
	}

	/*
	 * By how many seconds is this nonce stale?  Negative value
	 * would mean it was issued by another server with its clock
	 * skewed in the future.
	 */
	ostamp = strtoul(push_cert_nonce, NULL, 10);
	nonce_stamp_slop = (long)ostamp - (long)stamp;

	if (nonce_stamp_slop_limit &&
	    abs(nonce_stamp_slop) <= nonce_stamp_slop_limit) {
		/*
		 * Pretend as if the received nonce (which passes the
		 * HMAC check, so it is not a forged by third-party)
		 * is what we issued.
		 */
		free((void *)push_cert_nonce);
		push_cert_nonce = xstrdup(nonce);
		retval = NONCE_OK;
	} else {
		retval = NONCE_SLOP;
	}

leave:
	free(nonce);
	free(expect);
	return retval;
}

static void prepare_push_cert_sha1(struct child_process *proc)
{
	static int already_done;
	struct argv_array env = ARGV_ARRAY_INIT;

	if (!push_cert.len)
		return;

	if (!already_done) {
		struct strbuf gpg_output = STRBUF_INIT;
		struct strbuf gpg_status = STRBUF_INIT;
		int bogs /* beginning_of_gpg_sig */;

		already_done = 1;
		if (write_sha1_file(push_cert.buf, push_cert.len, "blob", push_cert_sha1))
			hashclr(push_cert_sha1);

		memset(&sigcheck, '\0', sizeof(sigcheck));
		sigcheck.result = 'N';

		bogs = parse_signature(push_cert.buf, push_cert.len);
		if (verify_signed_buffer(push_cert.buf, bogs,
					 push_cert.buf + bogs, push_cert.len - bogs,
					 &gpg_output, &gpg_status) < 0) {
			; /* error running gpg */
		} else {
			sigcheck.payload = push_cert.buf;
			sigcheck.gpg_output = gpg_output.buf;
			sigcheck.gpg_status = gpg_status.buf;
			parse_gpg_output(&sigcheck);
		}

		strbuf_release(&gpg_output);
		strbuf_release(&gpg_status);
		nonce_status = check_nonce(push_cert.buf, bogs);
	}
	if (!is_null_sha1(push_cert_sha1)) {
		argv_array_pushf(&env, "GIT_PUSH_CERT=%s", sha1_to_hex(push_cert_sha1));
		argv_array_pushf(&env, "GIT_PUSH_CERT_SIGNER=%s",
				 sigcheck.signer ? sigcheck.signer : "");
		argv_array_pushf(&env, "GIT_PUSH_CERT_KEY=%s",
				 sigcheck.key ? sigcheck.key : "");
		argv_array_pushf(&env, "GIT_PUSH_CERT_STATUS=%c", sigcheck.result);
		if (push_cert_nonce) {
			argv_array_pushf(&env, "GIT_PUSH_CERT_NONCE=%s", push_cert_nonce);
			argv_array_pushf(&env, "GIT_PUSH_CERT_NONCE_STATUS=%s", nonce_status);
			if (nonce_status == NONCE_SLOP)
				argv_array_pushf(&env, "GIT_PUSH_CERT_NONCE_SLOP=%ld",
						 nonce_stamp_slop);
		}
		proc->env = env.argv;
	}
}

typedef int (*feed_fn)(void *, const char **, size_t *);
static int run_and_feed_hook(const char *hook_name, feed_fn feed, void *feed_state)
{
	struct child_process proc = CHILD_PROCESS_INIT;
	struct async muxer;
	const char *argv[2];
	int code;

	argv[0] = find_hook(hook_name);
	if (!argv[0])
		return 0;

	argv[1] = NULL;

	proc.argv = argv;
	proc.in = -1;
	proc.stdout_to_stderr = 1;

	prepare_push_cert_sha1(&proc);

	if (use_sideband) {
		memset(&muxer, 0, sizeof(muxer));
		muxer.proc = copy_to_sideband;
		muxer.in = -1;
		code = start_async(&muxer);
		if (code)
			return code;
		proc.err = muxer.in;
	}

	code = start_command(&proc);
	if (code) {
		if (use_sideband)
			finish_async(&muxer);
		return code;
	}

	sigchain_push(SIGPIPE, SIG_IGN);

	while (1) {
		const char *buf;
		size_t n;
		if (feed(feed_state, &buf, &n))
			break;
		if (write_in_full(proc.in, buf, n) != n)
			break;
	}
	close(proc.in);
	if (use_sideband)
		finish_async(&muxer);

	sigchain_pop(SIGPIPE);

	return finish_command(&proc);
}

struct receive_hook_feed_state {
	struct command *cmd;
	int skip_broken;
	struct strbuf buf;
};

static int feed_receive_hook(void *state_, const char **bufp, size_t *sizep)
{
	struct receive_hook_feed_state *state = state_;
	struct command *cmd = state->cmd;

	while (cmd &&
	       state->skip_broken && (cmd->error_string || cmd->did_not_exist))
		cmd = cmd->next;
	if (!cmd)
		return -1; /* EOF */
	strbuf_reset(&state->buf);
	strbuf_addf(&state->buf, "%s %s %s\n",
		    sha1_to_hex(cmd->old_sha1), sha1_to_hex(cmd->new_sha1),
		    cmd->ref_name);
	state->cmd = cmd->next;
	if (bufp) {
		*bufp = state->buf.buf;
		*sizep = state->buf.len;
	}
	return 0;
}

static int run_receive_hook(struct command *commands, const char *hook_name,
			    int skip_broken)
{
	struct receive_hook_feed_state state;
	int status;

	strbuf_init(&state.buf, 0);
	state.cmd = commands;
	state.skip_broken = skip_broken;
	if (feed_receive_hook(&state, NULL, NULL))
		return 0;
	state.cmd = commands;
	status = run_and_feed_hook(hook_name, feed_receive_hook, &state);
	strbuf_release(&state.buf);
	return status;
}

static int run_update_hook(struct command *cmd)
{
	const char *argv[5];
	struct child_process proc = CHILD_PROCESS_INIT;
	int code;

	argv[0] = find_hook("update");
	if (!argv[0])
		return 0;

	argv[1] = cmd->ref_name;
	argv[2] = sha1_to_hex(cmd->old_sha1);
	argv[3] = sha1_to_hex(cmd->new_sha1);
	argv[4] = NULL;

	proc.no_stdin = 1;
	proc.stdout_to_stderr = 1;
	proc.err = use_sideband ? -1 : 0;
	proc.argv = argv;

	code = start_command(&proc);
	if (code)
		return code;
	if (use_sideband)
		copy_to_sideband(proc.err, -1, NULL);
	return finish_command(&proc);
}

static int is_ref_checked_out(const char *ref)
{
	if (is_bare_repository())
		return 0;

	if (!head_name)
		return 0;
	return !strcmp(head_name, ref);
}

static char *refuse_unconfigured_deny_msg[] = {
	"By default, updating the current branch in a non-bare repository",
	"is denied, because it will make the index and work tree inconsistent",
	"with what you pushed, and will require 'git reset --hard' to match",
	"the work tree to HEAD.",
	"",
	"You can set 'receive.denyCurrentBranch' configuration variable to",
	"'ignore' or 'warn' in the remote repository to allow pushing into",
	"its current branch; however, this is not recommended unless you",
	"arranged to update its work tree to match what you pushed in some",
	"other way.",
	"",
	"To squelch this message and still keep the default behaviour, set",
	"'receive.denyCurrentBranch' configuration variable to 'refuse'."
};

static void refuse_unconfigured_deny(void)
{
	int i;
	for (i = 0; i < ARRAY_SIZE(refuse_unconfigured_deny_msg); i++)
		rp_error("%s", refuse_unconfigured_deny_msg[i]);
}

static char *refuse_unconfigured_deny_delete_current_msg[] = {
	"By default, deleting the current branch is denied, because the next",
	"'git clone' won't result in any file checked out, causing confusion.",
	"",
	"You can set 'receive.denyDeleteCurrent' configuration variable to",
	"'warn' or 'ignore' in the remote repository to allow deleting the",
	"current branch, with or without a warning message.",
	"",
	"To squelch this message, you can set it to 'refuse'."
};

static void refuse_unconfigured_deny_delete_current(void)
{
	int i;
	for (i = 0;
	     i < ARRAY_SIZE(refuse_unconfigured_deny_delete_current_msg);
	     i++)
		rp_error("%s", refuse_unconfigured_deny_delete_current_msg[i]);
}

static int command_singleton_iterator(void *cb_data, unsigned char sha1[20]);
static int update_shallow_ref(struct command *cmd, struct shallow_info *si)
{
	static struct lock_file shallow_lock;
	struct sha1_array extra = SHA1_ARRAY_INIT;
	const char *alt_file;
	uint32_t mask = 1 << (cmd->index % 32);
	int i;

	trace_printf_key(&trace_shallow,
			 "shallow: update_shallow_ref %s\n", cmd->ref_name);
	for (i = 0; i < si->shallow->nr; i++)
		if (si->used_shallow[i] &&
		    (si->used_shallow[i][cmd->index / 32] & mask) &&
		    !delayed_reachability_test(si, i))
			sha1_array_append(&extra, si->shallow->sha1[i]);

	setup_alternate_shallow(&shallow_lock, &alt_file, &extra);
	if (check_shallow_connected(command_singleton_iterator,
				    0, cmd, alt_file)) {
		rollback_lock_file(&shallow_lock);
		sha1_array_clear(&extra);
		return -1;
	}

	commit_lock_file(&shallow_lock);

	/*
	 * Make sure setup_alternate_shallow() for the next ref does
	 * not lose these new roots..
	 */
	for (i = 0; i < extra.nr; i++)
		register_shallow(extra.sha1[i]);

	si->shallow_ref[cmd->index] = 0;
	sha1_array_clear(&extra);
	return 0;
}

static const char *update(struct command *cmd, struct shallow_info *si)
{
	const char *name = cmd->ref_name;
	struct strbuf namespaced_name_buf = STRBUF_INIT;
	const char *namespaced_name;
	unsigned char *old_sha1 = cmd->old_sha1;
	unsigned char *new_sha1 = cmd->new_sha1;

	/* only refs/... are allowed */
	if (!starts_with(name, "refs/") || check_refname_format(name + 5, 0)) {
		rp_error("refusing to create funny ref '%s' remotely", name);
		return "funny refname";
	}

	strbuf_addf(&namespaced_name_buf, "%s%s", get_git_namespace(), name);
	namespaced_name = strbuf_detach(&namespaced_name_buf, NULL);

	if (is_ref_checked_out(namespaced_name)) {
		switch (deny_current_branch) {
		case DENY_IGNORE:
			break;
		case DENY_WARN:
			rp_warning("updating the current branch");
			break;
		case DENY_REFUSE:
		case DENY_UNCONFIGURED:
			rp_error("refusing to update checked out branch: %s", name);
			if (deny_current_branch == DENY_UNCONFIGURED)
				refuse_unconfigured_deny();
			return "branch is currently checked out";
		}
	}

	if (!is_null_sha1(new_sha1) && !has_sha1_file(new_sha1)) {
		error("unpack should have generated %s, "
		      "but I can't find it!", sha1_to_hex(new_sha1));
		return "bad pack";
	}

	if (!is_null_sha1(old_sha1) && is_null_sha1(new_sha1)) {
		if (deny_deletes && starts_with(name, "refs/heads/")) {
			rp_error("denying ref deletion for %s", name);
			return "deletion prohibited";
		}

		if (!strcmp(namespaced_name, head_name)) {
			switch (deny_delete_current) {
			case DENY_IGNORE:
				break;
			case DENY_WARN:
				rp_warning("deleting the current branch");
				break;
			case DENY_REFUSE:
			case DENY_UNCONFIGURED:
				if (deny_delete_current == DENY_UNCONFIGURED)
					refuse_unconfigured_deny_delete_current();
				rp_error("refusing to delete the current branch: %s", name);
				return "deletion of the current branch prohibited";
			}
		}
	}

	if (deny_non_fast_forwards && !is_null_sha1(new_sha1) &&
	    !is_null_sha1(old_sha1) &&
	    starts_with(name, "refs/heads/")) {
		struct object *old_object, *new_object;
		struct commit *old_commit, *new_commit;

		old_object = parse_object(old_sha1);
		new_object = parse_object(new_sha1);

		if (!old_object || !new_object ||
		    old_object->type != OBJ_COMMIT ||
		    new_object->type != OBJ_COMMIT) {
			error("bad sha1 objects for %s", name);
			return "bad ref";
		}
		old_commit = (struct commit *)old_object;
		new_commit = (struct commit *)new_object;
		if (!in_merge_bases(old_commit, new_commit)) {
			rp_error("denying non-fast-forward %s"
				 " (you should pull first)", name);
			return "non-fast-forward";
		}
	}
	if (run_update_hook(cmd)) {
		rp_error("hook declined to update %s", name);
		return "hook declined";
	}

	if (is_null_sha1(new_sha1)) {
		if (!parse_object(old_sha1)) {
			old_sha1 = NULL;
			if (ref_exists(name)) {
				rp_warning("Allowing deletion of corrupt ref.");
			} else {
				rp_warning("Deleting a non-existent ref.");
				cmd->did_not_exist = 1;
			}
		}
		if (delete_ref(namespaced_name, old_sha1, 0)) {
			rp_error("failed to delete %s", name);
			return "failed to delete";
		}
		return NULL; /* good */
	}
	else {
		struct strbuf err = STRBUF_INIT;
		struct ref_transaction *transaction;

		if (shallow_update && si->shallow_ref[cmd->index] &&
		    update_shallow_ref(cmd, si))
			return "shallow error";

		transaction = ref_transaction_begin(&err);
		if (!transaction ||
		    ref_transaction_update(transaction, namespaced_name,
					   new_sha1, old_sha1, 0, 1, "push",
					   &err) ||
		    ref_transaction_commit(transaction, &err)) {
			ref_transaction_free(transaction);

			rp_error("%s", err.buf);
			strbuf_release(&err);
			return "failed to update ref";
		}

		ref_transaction_free(transaction);
		strbuf_release(&err);
		return NULL; /* good */
	}
}

static void run_update_post_hook(struct command *commands)
{
	struct command *cmd;
	int argc;
	const char **argv;
	struct child_process proc = CHILD_PROCESS_INIT;
	char *hook;

	hook = find_hook("post-update");
	for (argc = 0, cmd = commands; cmd; cmd = cmd->next) {
		if (cmd->error_string || cmd->did_not_exist)
			continue;
		argc++;
	}
	if (!argc || !hook)
		return;

	argv = xmalloc(sizeof(*argv) * (2 + argc));
	argv[0] = hook;

	for (argc = 1, cmd = commands; cmd; cmd = cmd->next) {
		if (cmd->error_string || cmd->did_not_exist)
			continue;
		argv[argc] = xstrdup(cmd->ref_name);
		argc++;
	}
	argv[argc] = NULL;

	proc.no_stdin = 1;
	proc.stdout_to_stderr = 1;
	proc.err = use_sideband ? -1 : 0;
	proc.argv = argv;

	if (!start_command(&proc)) {
		if (use_sideband)
			copy_to_sideband(proc.err, -1, NULL);
		finish_command(&proc);
	}
}

static void check_aliased_update(struct command *cmd, struct string_list *list)
{
	struct strbuf buf = STRBUF_INIT;
	const char *dst_name;
	struct string_list_item *item;
	struct command *dst_cmd;
	unsigned char sha1[20];
	char cmd_oldh[41], cmd_newh[41], dst_oldh[41], dst_newh[41];
	int flag;

	strbuf_addf(&buf, "%s%s", get_git_namespace(), cmd->ref_name);
	dst_name = resolve_ref_unsafe(buf.buf, 0, sha1, &flag);
	strbuf_release(&buf);

	if (!(flag & REF_ISSYMREF))
		return;

	dst_name = strip_namespace(dst_name);
	if (!dst_name) {
		rp_error("refusing update to broken symref '%s'", cmd->ref_name);
		cmd->skip_update = 1;
		cmd->error_string = "broken symref";
		return;
	}

	if ((item = string_list_lookup(list, dst_name)) == NULL)
		return;

	cmd->skip_update = 1;

	dst_cmd = (struct command *) item->util;

	if (!hashcmp(cmd->old_sha1, dst_cmd->old_sha1) &&
	    !hashcmp(cmd->new_sha1, dst_cmd->new_sha1))
		return;

	dst_cmd->skip_update = 1;

	strcpy(cmd_oldh, find_unique_abbrev(cmd->old_sha1, DEFAULT_ABBREV));
	strcpy(cmd_newh, find_unique_abbrev(cmd->new_sha1, DEFAULT_ABBREV));
	strcpy(dst_oldh, find_unique_abbrev(dst_cmd->old_sha1, DEFAULT_ABBREV));
	strcpy(dst_newh, find_unique_abbrev(dst_cmd->new_sha1, DEFAULT_ABBREV));
	rp_error("refusing inconsistent update between symref '%s' (%s..%s) and"
		 " its target '%s' (%s..%s)",
		 cmd->ref_name, cmd_oldh, cmd_newh,
		 dst_cmd->ref_name, dst_oldh, dst_newh);

	cmd->error_string = dst_cmd->error_string =
		"inconsistent aliased update";
}

static void check_aliased_updates(struct command *commands)
{
	struct command *cmd;
	struct string_list ref_list = STRING_LIST_INIT_NODUP;

	for (cmd = commands; cmd; cmd = cmd->next) {
		struct string_list_item *item =
			string_list_append(&ref_list, cmd->ref_name);
		item->util = (void *)cmd;
	}
	sort_string_list(&ref_list);

	for (cmd = commands; cmd; cmd = cmd->next) {
		if (!cmd->error_string)
			check_aliased_update(cmd, &ref_list);
	}

	string_list_clear(&ref_list, 0);
}

static int command_singleton_iterator(void *cb_data, unsigned char sha1[20])
{
	struct command **cmd_list = cb_data;
	struct command *cmd = *cmd_list;

	if (!cmd || is_null_sha1(cmd->new_sha1))
		return -1; /* end of list */
	*cmd_list = NULL; /* this returns only one */
	hashcpy(sha1, cmd->new_sha1);
	return 0;
}

static void set_connectivity_errors(struct command *commands,
				    struct shallow_info *si)
{
	struct command *cmd;

	for (cmd = commands; cmd; cmd = cmd->next) {
		struct command *singleton = cmd;
		if (shallow_update && si->shallow_ref[cmd->index])
			/* to be checked in update_shallow_ref() */
			continue;
		if (!check_everything_connected(command_singleton_iterator,
						0, &singleton))
			continue;
		cmd->error_string = "missing necessary objects";
	}
}

struct iterate_data {
	struct command *cmds;
	struct shallow_info *si;
};

static int iterate_receive_command_list(void *cb_data, unsigned char sha1[20])
{
	struct iterate_data *data = cb_data;
	struct command **cmd_list = &data->cmds;
	struct command *cmd = *cmd_list;

	for (; cmd; cmd = cmd->next) {
		if (shallow_update && data->si->shallow_ref[cmd->index])
			/* to be checked in update_shallow_ref() */
			continue;
		if (!is_null_sha1(cmd->new_sha1) && !cmd->skip_update) {
			hashcpy(sha1, cmd->new_sha1);
			*cmd_list = cmd->next;
			return 0;
		}
	}
	*cmd_list = NULL;
	return -1; /* end of list */
}

static void reject_updates_to_hidden(struct command *commands)
{
	struct command *cmd;

	for (cmd = commands; cmd; cmd = cmd->next) {
		if (cmd->error_string || !ref_is_hidden(cmd->ref_name))
			continue;
		if (is_null_sha1(cmd->new_sha1))
			cmd->error_string = "deny deleting a hidden ref";
		else
			cmd->error_string = "deny updating a hidden ref";
	}
}

static void execute_commands(struct command *commands,
			     const char *unpacker_error,
			     struct shallow_info *si)
{
	int checked_connectivity;
	struct command *cmd;
	unsigned char sha1[20];
	struct iterate_data data;

	if (unpacker_error) {
		for (cmd = commands; cmd; cmd = cmd->next)
			cmd->error_string = "unpacker error";
		return;
	}

	data.cmds = commands;
	data.si = si;
	if (check_everything_connected(iterate_receive_command_list, 0, &data))
		set_connectivity_errors(commands, si);

	reject_updates_to_hidden(commands);

	if (run_receive_hook(commands, "pre-receive", 0)) {
		for (cmd = commands; cmd; cmd = cmd->next) {
			if (!cmd->error_string)
				cmd->error_string = "pre-receive hook declined";
		}
		return;
	}

	check_aliased_updates(commands);

	free(head_name_to_free);
	head_name = head_name_to_free = resolve_refdup("HEAD", 0, sha1, NULL);

	checked_connectivity = 1;
	for (cmd = commands; cmd; cmd = cmd->next) {
		if (cmd->error_string)
			continue;

		if (cmd->skip_update)
			continue;

		cmd->error_string = update(cmd, si);
		if (shallow_update && !cmd->error_string &&
		    si->shallow_ref[cmd->index]) {
			error("BUG: connectivity check has not been run on ref %s",
			      cmd->ref_name);
			checked_connectivity = 0;
		}
	}

	if (shallow_update && !checked_connectivity)
		error("BUG: run 'git fsck' for safety.\n"
		      "If there are errors, try to remove "
		      "the reported refs above");
}

static struct command **queue_command(struct command **tail,
				      const char *line,
				      int linelen)
{
	unsigned char old_sha1[20], new_sha1[20];
	struct command *cmd;
	const char *refname;
	int reflen;

	if (linelen < 83 ||
	    line[40] != ' ' ||
	    line[81] != ' ' ||
	    get_sha1_hex(line, old_sha1) ||
	    get_sha1_hex(line + 41, new_sha1))
		die("protocol error: expected old/new/ref, got '%s'", line);

	refname = line + 82;
	reflen = linelen - 82;
	cmd = xcalloc(1, sizeof(struct command) + reflen + 1);
	hashcpy(cmd->old_sha1, old_sha1);
	hashcpy(cmd->new_sha1, new_sha1);
	memcpy(cmd->ref_name, refname, reflen);
	cmd->ref_name[reflen] = '\0';
	*tail = cmd;
	return &cmd->next;
}

static void queue_commands_from_cert(struct command **tail,
				     struct strbuf *push_cert)
{
	const char *boc, *eoc;

	if (*tail)
		die("protocol error: got both push certificate and unsigned commands");

	boc = strstr(push_cert->buf, "\n\n");
	if (!boc)
		die("malformed push certificate %.*s", 100, push_cert->buf);
	else
		boc += 2;
	eoc = push_cert->buf + parse_signature(push_cert->buf, push_cert->len);

	while (boc < eoc) {
		const char *eol = memchr(boc, '\n', eoc - boc);
		tail = queue_command(tail, boc, eol ? eol - boc : eoc - eol);
		boc = eol ? eol + 1 : eoc;
	}
}

static struct command *read_head_info(struct sha1_array *shallow)
{
	struct command *commands = NULL;
	struct command **p = &commands;
	for (;;) {
		char *line;
		int len, linelen;

		line = packet_read_line(0, &len);
		if (!line)
			break;

		if (len == 48 && starts_with(line, "shallow ")) {
			unsigned char sha1[20];
			if (get_sha1_hex(line + 8, sha1))
				die("protocol error: expected shallow sha, got '%s'",
				    line + 8);
			sha1_array_append(shallow, sha1);
			continue;
		}

		linelen = strlen(line);
		if (linelen < len) {
			const char *feature_list = line + linelen + 1;
			if (parse_feature_request(feature_list, "report-status"))
				report_status = 1;
			if (parse_feature_request(feature_list, "side-band-64k"))
				use_sideband = LARGE_PACKET_MAX;
			if (parse_feature_request(feature_list, "quiet"))
				quiet = 1;
		}

		if (!strcmp(line, "push-cert")) {
			int true_flush = 0;
			char certbuf[1024];

			for (;;) {
				len = packet_read(0, NULL, NULL,
						  certbuf, sizeof(certbuf), 0);
				if (!len) {
					true_flush = 1;
					break;
				}
				if (!strcmp(certbuf, "push-cert-end\n"))
					break; /* end of cert */
				strbuf_addstr(&push_cert, certbuf);
			}

			if (true_flush)
				break;
			continue;
		}

		p = queue_command(p, line, linelen);
	}

	if (push_cert.len)
		queue_commands_from_cert(p, &push_cert);

	return commands;
}

static const char *parse_pack_header(struct pack_header *hdr)
{
	switch (read_pack_header(0, hdr)) {
	case PH_ERROR_EOF:
		return "eof before pack header was fully read";

	case PH_ERROR_PACK_SIGNATURE:
		return "protocol error (pack signature mismatch detected)";

	case PH_ERROR_PROTOCOL:
		return "protocol error (pack version unsupported)";

	default:
		return "unknown error in parse_pack_header";

	case 0:
		return NULL;
	}
}

static const char *pack_lockfile;

static const char *unpack(int err_fd, struct shallow_info *si)
{
	struct pack_header hdr;
	struct argv_array av = ARGV_ARRAY_INIT;
	const char *hdr_err;
	int status;
	char hdr_arg[38];
	struct child_process child = CHILD_PROCESS_INIT;
	int fsck_objects = (receive_fsck_objects >= 0
			    ? receive_fsck_objects
			    : transfer_fsck_objects >= 0
			    ? transfer_fsck_objects
			    : 0);

	hdr_err = parse_pack_header(&hdr);
	if (hdr_err) {
		if (err_fd > 0)
			close(err_fd);
		return hdr_err;
	}
	snprintf(hdr_arg, sizeof(hdr_arg),
			"--pack_header=%"PRIu32",%"PRIu32,
			ntohl(hdr.hdr_version), ntohl(hdr.hdr_entries));

	if (si->nr_ours || si->nr_theirs) {
		alt_shallow_file = setup_temporary_shallow(si->shallow);
		argv_array_pushl(&av, "--shallow-file", alt_shallow_file, NULL);
	}

	if (ntohl(hdr.hdr_entries) < unpack_limit) {
		argv_array_pushl(&av, "unpack-objects", hdr_arg, NULL);
		if (quiet)
			argv_array_push(&av, "-q");
		if (fsck_objects)
			argv_array_push(&av, "--strict");
		child.argv = av.argv;
		child.no_stdout = 1;
		child.err = err_fd;
		child.git_cmd = 1;
		status = run_command(&child);
		if (status)
			return "unpack-objects abnormal exit";
	} else {
		int s;
		char keep_arg[256];

		s = sprintf(keep_arg, "--keep=receive-pack %"PRIuMAX" on ", (uintmax_t) getpid());
		if (gethostname(keep_arg + s, sizeof(keep_arg) - s))
			strcpy(keep_arg + s, "localhost");

		argv_array_pushl(&av, "index-pack",
				 "--stdin", hdr_arg, keep_arg, NULL);
		if (fsck_objects)
			argv_array_push(&av, "--strict");
		if (fix_thin)
			argv_array_push(&av, "--fix-thin");
		child.argv = av.argv;
		child.out = -1;
		child.err = err_fd;
		child.git_cmd = 1;
		status = start_command(&child);
		if (status)
			return "index-pack fork failed";
		pack_lockfile = index_pack_lockfile(child.out);
		close(child.out);
		status = finish_command(&child);
		if (status)
			return "index-pack abnormal exit";
		reprepare_packed_git();
	}
	return NULL;
}

static const char *unpack_with_sideband(struct shallow_info *si)
{
	struct async muxer;
	const char *ret;

	if (!use_sideband)
		return unpack(0, si);

	memset(&muxer, 0, sizeof(muxer));
	muxer.proc = copy_to_sideband;
	muxer.in = -1;
	if (start_async(&muxer))
		return NULL;

	ret = unpack(muxer.in, si);

	finish_async(&muxer);
	return ret;
}

static void prepare_shallow_update(struct command *commands,
				   struct shallow_info *si)
{
	int i, j, k, bitmap_size = (si->ref->nr + 31) / 32;

	si->used_shallow = xmalloc(sizeof(*si->used_shallow) *
				   si->shallow->nr);
	assign_shallow_commits_to_refs(si, si->used_shallow, NULL);

	si->need_reachability_test =
		xcalloc(si->shallow->nr, sizeof(*si->need_reachability_test));
	si->reachable =
		xcalloc(si->shallow->nr, sizeof(*si->reachable));
	si->shallow_ref = xcalloc(si->ref->nr, sizeof(*si->shallow_ref));

	for (i = 0; i < si->nr_ours; i++)
		si->need_reachability_test[si->ours[i]] = 1;

	for (i = 0; i < si->shallow->nr; i++) {
		if (!si->used_shallow[i])
			continue;
		for (j = 0; j < bitmap_size; j++) {
			if (!si->used_shallow[i][j])
				continue;
			si->need_reachability_test[i]++;
			for (k = 0; k < 32; k++)
				if (si->used_shallow[i][j] & (1 << k))
					si->shallow_ref[j * 32 + k]++;
		}

		/*
		 * true for those associated with some refs and belong
		 * in "ours" list aka "step 7 not done yet"
		 */
		si->need_reachability_test[i] =
			si->need_reachability_test[i] > 1;
	}

	/*
	 * keep hooks happy by forcing a temporary shallow file via
	 * env variable because we can't add --shallow-file to every
	 * command. check_everything_connected() will be done with
	 * true .git/shallow though.
	 */
	setenv(GIT_SHALLOW_FILE_ENVIRONMENT, alt_shallow_file, 1);
}

static void update_shallow_info(struct command *commands,
				struct shallow_info *si,
				struct sha1_array *ref)
{
	struct command *cmd;
	int *ref_status;
	remove_nonexistent_theirs_shallow(si);
	if (!si->nr_ours && !si->nr_theirs) {
		shallow_update = 0;
		return;
	}

	for (cmd = commands; cmd; cmd = cmd->next) {
		if (is_null_sha1(cmd->new_sha1))
			continue;
		sha1_array_append(ref, cmd->new_sha1);
		cmd->index = ref->nr - 1;
	}
	si->ref = ref;

	if (shallow_update) {
		prepare_shallow_update(commands, si);
		return;
	}

	ref_status = xmalloc(sizeof(*ref_status) * ref->nr);
	assign_shallow_commits_to_refs(si, NULL, ref_status);
	for (cmd = commands; cmd; cmd = cmd->next) {
		if (is_null_sha1(cmd->new_sha1))
			continue;
		if (ref_status[cmd->index]) {
			cmd->error_string = "shallow update not allowed";
			cmd->skip_update = 1;
		}
	}
	free(ref_status);
}

static void report(struct command *commands, const char *unpack_status)
{
	struct command *cmd;
	struct strbuf buf = STRBUF_INIT;

	packet_buf_write(&buf, "unpack %s\n",
			 unpack_status ? unpack_status : "ok");
	for (cmd = commands; cmd; cmd = cmd->next) {
		if (!cmd->error_string)
			packet_buf_write(&buf, "ok %s\n",
					 cmd->ref_name);
		else
			packet_buf_write(&buf, "ng %s %s\n",
					 cmd->ref_name, cmd->error_string);
	}
	packet_buf_flush(&buf);

	if (use_sideband)
		send_sideband(1, 1, buf.buf, buf.len, use_sideband);
	else
		write_or_die(1, buf.buf, buf.len);
	strbuf_release(&buf);
}

static int delete_only(struct command *commands)
{
	struct command *cmd;
	for (cmd = commands; cmd; cmd = cmd->next) {
		if (!is_null_sha1(cmd->new_sha1))
			return 0;
	}
	return 1;
}

int cmd_receive_pack(int argc, const char **argv, const char *prefix)
{
	int advertise_refs = 0;
	int i;
	struct command *commands;
	struct sha1_array shallow = SHA1_ARRAY_INIT;
	struct sha1_array ref = SHA1_ARRAY_INIT;
	struct shallow_info si;

	packet_trace_identity("receive-pack");

	argv++;
	for (i = 1; i < argc; i++) {
		const char *arg = *argv++;

		if (*arg == '-') {
			if (!strcmp(arg, "--quiet")) {
				quiet = 1;
				continue;
			}

			if (!strcmp(arg, "--advertise-refs")) {
				advertise_refs = 1;
				continue;
			}
			if (!strcmp(arg, "--stateless-rpc")) {
				stateless_rpc = 1;
				continue;
			}
			if (!strcmp(arg, "--reject-thin-pack-for-testing")) {
				fix_thin = 0;
				continue;
			}

			usage(receive_pack_usage);
		}
		if (service_dir)
			usage(receive_pack_usage);
		service_dir = arg;
	}
	if (!service_dir)
		usage(receive_pack_usage);

	setup_path();

	if (!enter_repo(service_dir, 0))
		die("'%s' does not appear to be a git repository", service_dir);

	git_config(receive_pack_config, NULL);
	if (cert_nonce_seed)
		push_cert_nonce = prepare_push_cert_nonce(service_dir, time(NULL));

	if (0 <= transfer_unpack_limit)
		unpack_limit = transfer_unpack_limit;
	else if (0 <= receive_unpack_limit)
		unpack_limit = receive_unpack_limit;

	if (advertise_refs || !stateless_rpc) {
		write_head_info();
	}
	if (advertise_refs)
		return 0;

	if ((commands = read_head_info(&shallow)) != NULL) {
		const char *unpack_status = NULL;

		prepare_shallow_info(&si, &shallow);
		if (!si.nr_ours && !si.nr_theirs)
			shallow_update = 0;
		if (!delete_only(commands)) {
			unpack_status = unpack_with_sideband(&si);
			update_shallow_info(commands, &si, &ref);
		}
		execute_commands(commands, unpack_status, &si);
		if (pack_lockfile)
			unlink_or_warn(pack_lockfile);
		if (report_status)
			report(commands, unpack_status);
		run_receive_hook(commands, "post-receive", 1);
		run_update_post_hook(commands);
		if (auto_gc) {
			const char *argv_gc_auto[] = {
				"gc", "--auto", "--quiet", NULL,
			};
			int opt = RUN_GIT_CMD | RUN_COMMAND_STDOUT_TO_STDERR;
			run_command_v_opt(argv_gc_auto, opt);
		}
		if (auto_update_server_info)
			update_server_info(0);
		clear_shallow_info(&si);
	}
	if (use_sideband)
		packet_flush(1);
	sha1_array_clear(&shallow);
	sha1_array_clear(&ref);
	free((void *)push_cert_nonce);
	return 0;
}