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From: "Eric W. Biederman" <ebiederm@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org,
	"brian m. carlson" <sandals@crustytoothpaste.net>,
	"Eric W . Biederman" <ebiederm@xmission.com>
Subject: [PATCH 15/30] object-file-convert: add a function to convert trees between algorithms
Date: Wed, 27 Sep 2023 14:55:22 -0500	[thread overview]
Message-ID: <20230927195537.1682-15-ebiederm@gmail.com> (raw)
In-Reply-To: <87jzsbjt0a.fsf@gmail.froward.int.ebiederm.org>

From: "brian m. carlson" <sandals@crustytoothpaste.net>

In the future, we're going to want to provide SHA-256 repositories that
have compatibility support for SHA-1 as well.  In order to do so, we'll
need to be able to convert tree objects from SHA-256 to SHA-1 by writing
a tree with each SHA-256 object ID mapped to a SHA-1 object ID.

We implement a function, convert_tree_object, that takes an existing
tree buffer and writes it to a new strbuf, converting between
algorithms.  Let's make this function generic, because while we only
need it to convert from the main algorithm to the compatibility
algorithm now, we may need to do the other way around in the future,
such as for transport.

We avoid reusing the code in decode_tree_entry because that code
normalizes data, and we don't want that here.  We want to produce a
complete round trip of data, so if, for example, the old entry had a
wrongly zero-padded mode, we'd want to preserve that when converting to
ensure a stable hash value.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 object-file-convert.c | 51 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 50 insertions(+), 1 deletion(-)

diff --git a/object-file-convert.c b/object-file-convert.c
index 4d62ed192bf0..a9e7a208a707 100644
--- a/object-file-convert.c
+++ b/object-file-convert.c
@@ -1,8 +1,10 @@
 #include "git-compat-util.h"
 #include "gettext.h"
 #include "strbuf.h"
+#include "hex.h"
 #include "repository.h"
 #include "hash-ll.h"
+#include "hash.h"
 #include "object.h"
 #include "loose.h"
 #include "object-file-convert.h"
@@ -36,6 +38,51 @@ int repo_oid_to_algop(struct repository *repo, const struct object_id *src,
 	return 0;
 }
 
+static int decode_tree_entry_raw(struct object_id *oid, const char **path,
+				 size_t *len, const struct git_hash_algo *algo,
+				 const char *buf, unsigned long size)
+{
+	uint16_t mode;
+	const unsigned hashsz = algo->rawsz;
+
+	if (size < hashsz + 3 || buf[size - (hashsz + 1)]) {
+		return -1;
+	}
+
+	*path = parse_mode(buf, &mode);
+	if (!*path || !**path)
+		return -1;
+	*len = strlen(*path) + 1;
+
+	oidread_algop(oid, (const unsigned char *)*path + *len, algo);
+	return 0;
+}
+
+static int convert_tree_object(struct strbuf *out,
+			       const struct git_hash_algo *from,
+			       const struct git_hash_algo *to,
+			       const char *buffer, size_t size)
+{
+	const char *p = buffer, *end = buffer + size;
+
+	while (p < end) {
+		struct object_id entry_oid, mapped_oid;
+		const char *path = NULL;
+		size_t pathlen;
+
+		if (decode_tree_entry_raw(&entry_oid, &path, &pathlen, from, p,
+					  end - p))
+			return error(_("failed to decode tree entry"));
+		if (repo_oid_to_algop(the_repository, &entry_oid, to, &mapped_oid))
+			return error(_("failed to map tree entry for %s"), oid_to_hex(&entry_oid));
+		strbuf_add(out, p, path - p);
+		strbuf_add(out, path, pathlen);
+		strbuf_add(out, mapped_oid.hash, to->rawsz);
+		p = path + pathlen + from->rawsz;
+	}
+	return 0;
+}
+
 int convert_object_file(struct strbuf *outbuf,
 			const struct git_hash_algo *from,
 			const struct git_hash_algo *to,
@@ -50,8 +97,10 @@ int convert_object_file(struct strbuf *outbuf,
 		die("Refusing noop object file conversion");
 
 	switch (type) {
-	case OBJ_COMMIT:
 	case OBJ_TREE:
+		ret = convert_tree_object(outbuf, from, to, buf, len);
+		break;
+	case OBJ_COMMIT:
 	case OBJ_TAG:
 	default:
 		/* Not implemented yet, so fail. */
-- 
2.41.0


  parent reply	other threads:[~2023-09-27 19:56 UTC|newest]

Thread overview: 104+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-27 19:49 [PATCH 00/30] Initial support for multiple hash functions Eric W. Biederman
2023-09-27 19:55 ` [PATCH 01/30] object-file-convert: Stubs for converting from one object format to another Eric W. Biederman
2023-09-27 20:42   ` Eric Sunshine
2023-10-02  1:22     ` Eric W. Biederman
2023-10-02  2:27       ` Eric Sunshine
2023-09-27 19:55 ` [PATCH 02/30] oid-array: Teach oid-array to handle multiple kinds of oids Eric W. Biederman
2023-09-27 23:20   ` Eric Sunshine
2023-09-27 19:55 ` [PATCH 03/30] object-names: Support input of oids in any supported hash Eric W. Biederman
2023-09-27 23:29   ` Eric Sunshine
2023-10-02  1:54     ` Eric W. Biederman
2023-09-27 19:55 ` [PATCH 04/30] repository: add a compatibility hash algorithm Eric W. Biederman
2023-09-27 19:55 ` [PATCH 05/30] loose: add a mapping between SHA-1 and SHA-256 for loose objects Eric W. Biederman
2023-09-28  7:14   ` Eric Sunshine
2023-10-02  2:11     ` Eric W. Biederman
2023-10-02  2:36       ` Eric Sunshine
2023-09-27 19:55 ` [PATCH 06/30] loose: Compatibilty short name support Eric W. Biederman
2023-09-27 19:55 ` [PATCH 07/30] object-file: Update the loose object map when writing loose objects Eric W. Biederman
2023-09-27 19:55 ` [PATCH 08/30] object-file: Add a compat_oid_in parameter to write_object_file_flags Eric W. Biederman
2023-09-27 19:55 ` [PATCH 09/30] commit: write commits for both hashes Eric W. Biederman
2023-09-27 19:55 ` [PATCH 10/30] commit: Convert mergetag before computing the signature of a commit Eric W. Biederman
2023-09-27 19:55 ` [PATCH 11/30] commit: Export add_header_signature to support handling signatures on tags Eric W. Biederman
2023-09-27 19:55 ` [PATCH 12/30] tag: sign both hashes Eric W. Biederman
2023-09-27 19:55 ` [PATCH 13/30] cache: add a function to read an OID of a specific algorithm Eric W. Biederman
2023-09-27 19:55 ` [PATCH 14/30] object: Factor out parse_mode out of fast-import and tree-walk into in object.h Eric W. Biederman
2023-09-27 19:55 ` Eric W. Biederman [this message]
2023-09-27 19:55 ` [PATCH 16/30] object-file-convert: convert tag objects when writing Eric W. Biederman
2023-09-27 19:55 ` [PATCH 17/30] object-file-convert: Don't leak when converting tag objects Eric W. Biederman
2023-09-27 19:55 ` [PATCH 18/30] object-file-convert: convert commit objects when writing Eric W. Biederman
2023-09-27 19:55 ` [PATCH 19/30] object-file-convert: Convert commits that embed signed tags Eric W. Biederman
2023-09-27 19:55 ` [PATCH 20/30] object-file: Update object_info_extended to reencode objects Eric W. Biederman
2023-09-27 19:55 ` [PATCH 21/30] repository: Implement extensions.compatObjectFormat Eric W. Biederman
2023-09-27 21:39   ` Junio C Hamano
2023-09-28 20:18     ` Junio C Hamano
2023-09-29  0:50       ` Eric Biederman
2023-09-29 16:59       ` Eric W. Biederman
2023-09-29 18:48         ` Junio C Hamano
2023-10-02  0:48           ` Eric W. Biederman
2023-10-02  1:31     ` Eric W. Biederman
2023-09-27 19:55 ` [PATCH 22/30] rev-parse: Add an --output-object-format parameter Eric W. Biederman
2023-09-27 19:55 ` [PATCH 23/30] builtin/cat-file: Let the oid determine the output algorithm Eric W. Biederman
2023-09-27 19:55 ` [PATCH 24/30] tree-walk: init_tree_desc take an oid to get the hash algorithm Eric W. Biederman
2023-09-27 19:55 ` [PATCH 25/30] object-file: Handle compat objects in check_object_signature Eric W. Biederman
2023-09-27 19:55 ` [PATCH 26/30] builtin/ls-tree: Let the oid determine the output algorithm Eric W. Biederman
2023-09-27 19:55 ` [PATCH 27/30] test-lib: Compute the compatibility hash so tests may use it Eric W. Biederman
2023-09-27 19:55 ` [PATCH 28/30] t1006: Rename sha1 to oid Eric W. Biederman
2023-09-27 19:55 ` [PATCH 29/30] t1006: Test oid compatibility with cat-file Eric W. Biederman
2023-09-27 19:55 ` [PATCH 30/30] t1016-compatObjectFormat: Add tests to verify the conversion between objects Eric W. Biederman
2023-09-27 21:31 ` [PATCH 00/30] Initial support for multiple hash functions Junio C Hamano
2023-10-02  2:39 ` [PATCH v2 00/30] initial " Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 01/30] object-file-convert: stubs for converting from one object format to another Eric W. Biederman
2024-02-08  8:23     ` Linus Arver
2024-02-15 11:21     ` Patrick Steinhardt
2023-10-02  2:40   ` [PATCH v2 02/30] oid-array: teach oid-array to handle multiple kinds of oids Eric W. Biederman
2024-02-13  8:16     ` Linus Arver
2024-02-15  6:22       ` Eric W. Biederman
2024-02-16  0:16         ` Linus Arver
2024-02-16  4:48           ` Eric W. Biederman
2024-02-17  1:59             ` Linus Arver
2024-02-13  8:31     ` Kristoffer Haugsbakk
2024-02-15  6:24       ` Eric W. Biederman
2024-02-15 11:21     ` Patrick Steinhardt
2023-10-02  2:40   ` [PATCH v2 03/30] object-names: support input of oids in any supported hash Eric W. Biederman
2024-02-13  9:33     ` Linus Arver
2024-02-15 11:21     ` Patrick Steinhardt
2023-10-02  2:40   ` [PATCH v2 04/30] repository: add a compatibility hash algorithm Eric W. Biederman
2024-02-13 10:02     ` Linus Arver
2024-02-15 11:22     ` Patrick Steinhardt
2023-10-02  2:40   ` [PATCH v2 05/30] loose: add a mapping between SHA-1 and SHA-256 for loose objects Eric W. Biederman
2024-02-14  7:20     ` Linus Arver
2024-02-15  5:33       ` Eric W. Biederman
2024-02-15 11:22     ` Patrick Steinhardt
2023-10-02  2:40   ` [PATCH v2 06/30] loose: compatibilty short name support Eric W. Biederman
2024-02-15 11:22     ` Patrick Steinhardt
2023-10-02  2:40   ` [PATCH v2 07/30] object-file: update the loose object map when writing loose objects Eric W. Biederman
2024-02-15 11:22     ` Patrick Steinhardt
2023-10-02  2:40   ` [PATCH v2 08/30] object-file: add a compat_oid_in parameter to write_object_file_flags Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 09/30] commit: write commits for both hashes Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 10/30] commit: convert mergetag before computing the signature of a commit Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 11/30] commit: export add_header_signature to support handling signatures on tags Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 12/30] tag: sign both hashes Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 13/30] cache: add a function to read an OID of a specific algorithm Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 14/30] object: factor out parse_mode out of fast-import and tree-walk into in object.h Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 15/30] object-file-convert: add a function to convert trees between algorithms Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 16/30] object-file-convert: convert tag objects when writing Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 17/30] object-file-convert: don't leak when converting tag objects Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 18/30] object-file-convert: convert commit objects when writing Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 19/30] object-file-convert: convert commits that embed signed tags Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 20/30] object-file: update object_info_extended to reencode objects Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 21/30] repository: implement extensions.compatObjectFormat Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 22/30] rev-parse: add an --output-object-format parameter Eric W. Biederman
2024-02-08 16:25     ` Jean-Noël Avila
2023-10-02  2:40   ` [PATCH v2 23/30] builtin/cat-file: let the oid determine the output algorithm Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 24/30] tree-walk: init_tree_desc take an oid to get the hash algorithm Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 25/30] object-file: handle compat objects in check_object_signature Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 26/30] builtin/ls-tree: let the oid determine the output algorithm Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 27/30] test-lib: compute the compatibility hash so tests may use it Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 28/30] t1006: rename sha1 to oid Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 29/30] t1006: test oid compatibility with cat-file Eric W. Biederman
2023-10-02  2:40   ` [PATCH v2 30/30] t1016-compatObjectFormat: add tests to verify the conversion between objects Eric W. Biederman
2024-02-07 22:18   ` [PATCH v2 00/30] initial support for multiple hash functions Junio C Hamano
2024-02-08  0:24     ` Linus Arver
2024-02-08  6:11       ` Patrick Steinhardt
2024-02-14  7:36       ` Linus Arver
2024-02-15 11:27   ` Patrick Steinhardt

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