odb/transaction: add transaction interface to write packfiles

In git-receive-pack(1), the incoming packfile is written to the ODB via
`unpack()`, which spawns git-index-pack(1) or git-unpack-objects(1)
directly. With pluggable object databases, an alternative backend may
need to handle writing packfile data differently though.

Introduce `odb_transaction_write_pack()` as a generic interface to
handle writing a packfile to a transaction and use the logic from
`unpack()` as the "files" backend implementation. Note that when storing
the objects as a packfile, git-index-pack(1) also writes a ".keep"
lockfile next to it to prevent a concurrent repack from removing the new
pack prior to reference updates being performed. The "files" transaction
backend is responsible for managing these ".keep" files and removes them
post-commit once the transaction is finalized.

Call sites in git-receive-pack(1) are updated accordingly.

Signed-off-by: Justin Tobler <jltobler@gmail.com>

Author: jltobler

builtin/receive-pack.c

@@ -15,15 +15,13 @@
 #include "gpg-interface.h"
 #include "hex.h"
 #include "hook.h"
-#include "lockfile.h"
 #include "object.h"
 #include "object-file.h"
 #include "object-name.h"
 #include "odb.h"
 #include "oid-array.h"
 #include "oidset.h"
 #include "pack.h"
-#include "packfile.h"
 #include "parse-options.h"
 #include "pkt-line.h"
 #include "protocol.h"
@@ -2292,162 +2290,11 @@ static void read_push_options(struct packet_reader *reader,
 	}
 }
 
-static const char *parse_pack_header(struct pack_header *hdr, int pack_fd)
-{
-	switch (read_pack_header(pack_fd, 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 struct tempfile *pack_lockfile;
-
-static void push_header_arg(struct strvec *args, struct pack_header *hdr)
-{
-	strvec_pushf(args, "--pack_header=%"PRIu32",%"PRIu32,
-		     ntohl(hdr->hdr_version), ntohl(hdr->hdr_entries));
-}
-
-static unsigned int get_unpack_limit(struct repository *repo)
-{
-	unsigned int limit = 100;
-
-	repo_config_get_uint(repo, "transfer.unpacklimit", &limit);
-	repo_config_get_uint(repo, "receive.unpacklimit", &limit);
-
-	return limit;
-}
-
-struct unpack_opts {
-	const char *fsck_msg_types;
-	const char *shallow_file;
-	off_t max_input_size;
-	int fsck_objects;
-	int reject_thin;
-	int err_fd;
-	int quiet;
-};
-
-static int unpack(struct odb_transaction *transaction, int pack_fd,
-		  struct strbuf *err_msg, const struct unpack_opts *opts)
-{
-	struct pack_header hdr;
-	const char *hdr_err;
-	int status;
-	struct child_process child = CHILD_PROCESS_INIT;
-	int err_fd = opts->err_fd;
-
-	hdr_err = parse_pack_header(&hdr, pack_fd);
-	if (hdr_err) {
-		if (err_fd > 0)
-			close(err_fd);
-		strbuf_addstr(err_msg, hdr_err);
-		return -1;
-	}
-
-	if (opts->shallow_file) {
-		strvec_push(&child.args, "--shallow-file");
-		strvec_push(&child.args, opts->shallow_file);
-	}
-
-	odb_transaction_env(transaction, &child.env);
-
-	if (ntohl(hdr.hdr_entries) < get_unpack_limit(the_repository)) {
-		strvec_push(&child.args, "unpack-objects");
-		push_header_arg(&child.args, &hdr);
-		if (opts->quiet)
-			strvec_push(&child.args, "-q");
-		if (opts->fsck_objects)
-			strvec_pushf(&child.args, "--strict%s",
-				     opts->fsck_msg_types);
-		if (opts->max_input_size)
-			strvec_pushf(&child.args, "--max-input-size=%"PRIuMAX,
-				     (uintmax_t)opts->max_input_size);
-		child.no_stdout = 1;
-		child.in = pack_fd;
-		child.err = err_fd;
-		child.git_cmd = 1;
-		status = run_command(&child);
-		if (status) {
-			strbuf_addstr(err_msg, "unpack-objects abnormal exit");
-			return -1;
-		}
-	} else {
-		char hostname[HOST_NAME_MAX + 1];
-		char *lockfile;
-
-		strvec_pushl(&child.args, "index-pack", "--stdin", NULL);
-		push_header_arg(&child.args, &hdr);
-
-		if (xgethostname(hostname, sizeof(hostname)))
-			xsnprintf(hostname, sizeof(hostname), "localhost");
-		strvec_pushf(&child.args,
-			     "--keep=receive-pack %"PRIuMAX" on %s",
-			     (uintmax_t)getpid(),
-			     hostname);
-
-		if (!opts->quiet && err_fd)
-			strvec_push(&child.args, "--show-resolving-progress");
-		if (err_fd)
-			strvec_push(&child.args, "--report-end-of-input");
-		if (opts->fsck_objects)
-			strvec_pushf(&child.args, "--strict%s",
-				     opts->fsck_msg_types);
-		if (!opts->reject_thin)
-			strvec_push(&child.args, "--fix-thin");
-		if (opts->max_input_size)
-			strvec_pushf(&child.args, "--max-input-size=%"PRIuMAX,
-				     (uintmax_t)opts->max_input_size);
-		child.out = -1;
-		child.in = pack_fd;
-		child.err = err_fd;
-		child.git_cmd = 1;
-		status = start_command(&child);
-		if (status) {
-			strbuf_addstr(err_msg, "index-pack fork failed");
-			return -1;
-		}
-
-		/*
-		 * The lockfile filepath is expected to be the final location of
-		 * the ".keep" file after being migrated to the main ODB source.
-		 * This ensures the lockfile can be found and removed later
-		 * after the ODB transaction has been committed.
-		 */
-		lockfile = index_pack_lockfile(transaction->source, child.out, NULL);
-		if (lockfile) {
-			pack_lockfile = register_tempfile(lockfile);
-			free(lockfile);
-		}
-		close(child.out);
-
-		status = finish_command(&child);
-		if (status) {
-			strbuf_addstr(err_msg, "index-pack abnormal exit");
-			return -1;
-		}
-		odb_reprepare(the_repository->objects);
-	}
-	return 0;
-}
-
 static int unpack_with_sideband(struct odb_transaction *transaction,
 				const char *shallow_file,
 				struct strbuf *err_msg)
 {
-	struct unpack_opts opts = {
+	struct odb_transaction_write_pack_opts opts = {
 		.fsck_objects = (receive_fsck_objects >= 0
 				 ? receive_fsck_objects
 				 : transfer_fsck_objects >= 0
@@ -2463,7 +2310,7 @@ static int unpack_with_sideband(struct odb_transaction *transaction,
 	int ret;
 
 	if (!use_sideband)
-		return unpack(transaction, 0, err_msg, &opts);
+		return odb_transaction_write_pack(transaction, 0, err_msg, &opts);
 
 	use_keepalive = KEEPALIVE_AFTER_NUL;
 	memset(&muxer, 0, sizeof(muxer));
@@ -2473,7 +2320,7 @@ static int unpack_with_sideband(struct odb_transaction *transaction,
 		return 0;
 
 	opts.err_fd = muxer.in;
-	ret = unpack(transaction, 0, err_msg, &opts);
+	ret = odb_transaction_write_pack(transaction, 0, err_msg, &opts);
 
 	finish_async(&muxer);
 	return ret;
@@ -2749,7 +2596,6 @@ int cmd_receive_pack(int argc,
 				 &push_options);
 		if (odb_transaction_finalize(transaction))
 			strbuf_addstr(&unpack_status, "unable to finalize object transaction");
-		delete_tempfile(&pack_lockfile);
 		sigchain_push(SIGPIPE, SIG_IGN);
 		if (report_status_v2)
 			report_v2(commands, &unpack_status);