index-pack: --verify

Given an existing .pack file and the .idx file that describes it,
this new mode of operation reads and re-index the packfile and makes
sure the existing .idx file matches the result byte-for-byte.

All the objects in the .pack file are validated during this operation as
well.  Unlike verify-pack, which visits each object described in the .idx
file in the SHA-1 order, index-pack efficiently exploits the delta-chain
to avoid rebuilding the objects that are used as the base of deltified
objects over and over again while validating the objects, resulting in
much quicker verification of the .pack file and its .idx file.

This version however cannot verify a .pack/.idx pair with a handcrafted v2
index that uses 64-bit offset representation for offsets that would fit
within 31-bit. You can create such an .idx file by giving a custom offset
to --index-version option to the command.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/index-pack.c

@@ -11,7 +11,7 @@
 #include "exec_cmd.h"
 
 static const char index_pack_usage[] =
-"git index-pack [-v] [-o <index-file>] [ --keep | --keep=<msg> ] [--strict] (<pack-file> | --stdin [--fix-thin] [<pack-file>])";
+"git index-pack [-v] [-o <index-file>] [--keep | --keep=<msg>] [--verify] [--strict] (<pack-file> | --stdin [--fix-thin] [<pack-file>])";
 
 struct object_entry
 {
@@ -891,9 +891,32 @@ static int git_index_pack_config(const char *k, const char *v, void *cb)
 	return git_default_config(k, v, cb);
 }
 
+static void read_idx_option(struct pack_idx_option *opts, const char *pack_name)
+{
+	struct packed_git *p = add_packed_git(pack_name, strlen(pack_name), 1);
+
+	if (!p)
+		die("Cannot open existing pack file '%s'", pack_name);
+	if (open_pack_index(p))
+		die("Cannot open existing pack idx file for '%s'", pack_name);
+
+	/* Read the attributes from the existing idx file */
+	opts->version = p->index_version;
+
+	/*
+	 * Get rid of the idx file as we do not need it anymore.
+	 * NEEDSWORK: extract this bit from free_pack_by_name() in
+	 * sha1_file.c, perhaps?  It shouldn't matter very much as we
+	 * know we haven't installed this pack (hence we never have
+	 * read anything from it).
+	 */
+	close_pack_index(p);
+	free(p);
+}
+
 int cmd_index_pack(int argc, const char **argv, const char *prefix)
 {
-	int i, fix_thin_pack = 0;
+	int i, fix_thin_pack = 0, verify = 0;
 	const char *curr_pack, *curr_index;
 	const char *index_name = NULL, *pack_name = NULL;
 	const char *keep_name = NULL, *keep_msg = NULL;
@@ -922,6 +945,8 @@ int cmd_index_pack(int argc, const char **argv, const char *prefix)
 				fix_thin_pack = 1;
 			} else if (!strcmp(arg, "--strict")) {
 				strict = 1;
+			} else if (!strcmp(arg, "--verify")) {
+				verify = 1;
 			} else if (!strcmp(arg, "--keep")) {
 				keep_msg = "";
 			} else if (!prefixcmp(arg, "--keep=")) {
@@ -988,6 +1013,12 @@ int cmd_index_pack(int argc, const char **argv, const char *prefix)
 		strcpy(keep_name_buf + len - 5, ".keep");
 		keep_name = keep_name_buf;
 	}
+	if (verify) {
+		if (!index_name)
+			die("--verify with no packfile name given");
+		read_idx_option(&opts, index_name);
+		opts.flags |= WRITE_IDX_VERIFY;
+	}
 
 	curr_pack = open_pack_file(pack_name);
 	parse_pack_header();
@@ -1038,10 +1069,13 @@ int cmd_index_pack(int argc, const char **argv, const char *prefix)
 	curr_index = write_idx_file(index_name, idx_objects, nr_objects, &opts, pack_sha1);
 	free(idx_objects);
 
-	final(pack_name, curr_pack,
-		index_name, curr_index,
-		keep_name, keep_msg,
-		pack_sha1);
+	if (!verify)
+		final(pack_name, curr_pack,
+		      index_name, curr_index,
+		      keep_name, keep_msg,
+		      pack_sha1);
+	else
+		close(input_fd);
 	free(objects);
 	free(index_name_buf);
 	free(keep_name_buf);

csum-file.c

@@ -11,8 +11,20 @@
 #include "progress.h"
 #include "csum-file.h"
 
-static void flush(struct sha1file *f, void * buf, unsigned int count)
+static void flush(struct sha1file *f, void *buf, unsigned int count)
 {
+	if (0 <= f->check_fd && count)  {
+		unsigned char check_buffer[8192];
+		ssize_t ret = read_in_full(f->check_fd, check_buffer, count);
+
+		if (ret < 0)
+			die_errno("%s: sha1 file read error", f->name);
+		if (ret < count)
+			die("%s: sha1 file truncated", f->name);
+		if (memcmp(buf, check_buffer, count))
+			die("sha1 file '%s' validation error", f->name);
+	}
+
 	for (;;) {
 		int ret = xwrite(f->fd, buf, count);
 		if (ret > 0) {
@@ -59,6 +71,17 @@ int sha1close(struct sha1file *f, unsigned char *result, unsigned int flags)
 		fd = 0;
 	} else
 		fd = f->fd;
+	if (0 <= f->check_fd) {
+		char discard;
+		int cnt = read_in_full(f->check_fd, &discard, 1);
+		if (cnt < 0)
+			die_errno("%s: error when reading the tail of sha1 file",
+				  f->name);
+		if (cnt)
+			die("%s: sha1 file has trailing garbage", f->name);
+		if (close(f->check_fd))
+			die_errno("%s: sha1 file error on close", f->name);
+	}
 	free(f);
 	return fd;
 }
@@ -101,10 +124,31 @@ struct sha1file *sha1fd(int fd, const char *name)
 	return sha1fd_throughput(fd, name, NULL);
 }
 
+struct sha1file *sha1fd_check(const char *name)
+{
+	int sink, check;
+	struct sha1file *f;
+
+	sink = open("/dev/null", O_WRONLY);
+	if (sink < 0)
+		return NULL;
+	check = open(name, O_RDONLY);
+	if (check < 0) {
+		int saved_errno = errno;
+		close(sink);
+		errno = saved_errno;
+		return NULL;
+	}
+	f = sha1fd(sink, name);
+	f->check_fd = check;
+	return f;
+}
+
 struct sha1file *sha1fd_throughput(int fd, const char *name, struct progress *tp)
 {
 	struct sha1file *f = xmalloc(sizeof(*f));
 	f->fd = fd;
+	f->check_fd = -1;
 	f->offset = 0;
 	f->total = 0;
 	f->tp = tp;

csum-file.h

@@ -6,6 +6,7 @@ struct progress;
 /* A SHA1-protected file */
 struct sha1file {
 	int fd;
+	int check_fd;
 	unsigned int offset;
 	git_SHA_CTX ctx;
 	off_t total;
@@ -21,6 +22,7 @@ struct sha1file {
 #define CSUM_FSYNC	2
 
 extern struct sha1file *sha1fd(int fd, const char *name);
+extern struct sha1file *sha1fd_check(const char *name);
 extern struct sha1file *sha1fd_throughput(int fd, const char *name, struct progress *tp);
 extern int sha1close(struct sha1file *, unsigned char *, unsigned int);
 extern int sha1write(struct sha1file *, void *, unsigned int);

pack-write.c

@@ -47,17 +47,22 @@ const char *write_idx_file(const char *index_name, struct pack_idx_entry **objec
 	else
 		sorted_by_sha = list = last = NULL;
 
-	if (!index_name) {
-		static char tmpfile[PATH_MAX];
-		fd = odb_mkstemp(tmpfile, sizeof(tmpfile), "pack/tmp_idx_XXXXXX");
-		index_name = xstrdup(tmpfile);
+	if (opts->flags & WRITE_IDX_VERIFY) {
+		assert(index_name);
+		f = sha1fd_check(index_name);
 	} else {
-		unlink(index_name);
-		fd = open(index_name, O_CREAT|O_EXCL|O_WRONLY, 0600);
+		if (!index_name) {
+			static char tmpfile[PATH_MAX];
+			fd = odb_mkstemp(tmpfile, sizeof(tmpfile), "pack/tmp_idx_XXXXXX");
+			index_name = xstrdup(tmpfile);
+		} else {
+			unlink(index_name);
+			fd = open(index_name, O_CREAT|O_EXCL|O_WRONLY, 0600);
+		}
+		if (fd < 0)
+			die_errno("unable to create '%s'", index_name);
+		f = sha1fd(fd, index_name);
 	}
-	if (fd < 0)
-		die_errno("unable to create '%s'", index_name);
-	f = sha1fd(fd, index_name);
 
 	/* if last object's offset is >= 2^31 we should use index V2 */
 	index_version = (last_obj_offset >> 31) ? 2 : opts->version;
@@ -142,7 +147,8 @@ const char *write_idx_file(const char *index_name, struct pack_idx_entry **objec
 	}
 
 	sha1write(f, sha1, 20);
-	sha1close(f, NULL, CSUM_FSYNC);
+	sha1close(f, NULL, ((opts->flags & WRITE_IDX_VERIFY)
+			    ? CSUM_CLOSE : CSUM_FSYNC));
 	git_SHA1_Final(sha1, &ctx);
 	return index_name;
 }

pack.h

@@ -35,6 +35,10 @@ struct pack_header {
 #define PACK_IDX_SIGNATURE 0xff744f63	/* "\377tOc" */
 
 struct pack_idx_option {
+	unsigned flags;
+	/* flag bits */
+#define WRITE_IDX_VERIFY 01
+
 	uint32_t version;
 	uint32_t off32_limit;
 };

t/t5302-pack-index.sh

@@ -65,6 +65,14 @@ test_expect_success \
     'cmp "test-1-${pack1}.idx" "1.idx" &&
      cmp "test-2-${pack2}.idx" "2.idx"'
 
+test_expect_success 'index-pack --verify on index version 1' '
+	git index-pack --verify "test-1-${pack1}.pack"
+'
+
+test_expect_success 'index-pack --verify on index version 2' '
+	git index-pack --verify "test-2-${pack2}.pack"
+'
+
 test_expect_success \
     'index v2: force some 64-bit offsets with pack-objects' \
     'pack3=$(git pack-objects --index-version=2,0x40000 test-3 <obj-list)'
@@ -93,6 +101,16 @@ test_expect_success OFF64_T \
     '64-bit offsets: index-pack result should match pack-objects one' \
     'cmp "test-3-${pack3}.idx" "3.idx"'
 
+test_expect_success OFF64_T 'index-pack --verify on 64-bit offset v2 (cheat)' '
+	# This cheats by knowing which lower offset should still be encoded
+	# in 64-bit representation.
+	git index-pack --verify --index-version=2,0x40000 "test-3-${pack3}.pack"
+'
+
+test_expect_failure OFF64_T 'index-pack --verify on 64-bit offset v2' '
+	git index-pack --verify "test-3-${pack3}.pack"
+'
+
 # returns the object number for given object in given pack index
 index_obj_nr()
 {