Am 12.02.2019 um 08:20 schrieb René Scharfe:
> That command currently prints the pax comment in tar archives if it
> looks like a SHA1 hash based on its length.  It should continue to do
> so, and _also_ show longer hashes.  Your change makes it _only_ show
> those longer hashes.
>
> So it could check for all known valid hash lengths in turn, or accept
> any payload length between 40 and the_hash_algo->hexsz, or loosen up
> totally and show comments of any length.

How about the following patch, as a preparation?

-- >8 --
From: Rene Scharfe <l....@web.de>
Subject: [PATCH] get-tar-commit-id: parse comment record

Parse pax comment records properly and get rid of magic numbers for
acceptable comment length.  This simplifies a later change to handle
longer hashes.

Signed-off-by: Rene Scharfe <l....@web.de>
---
 builtin/get-tar-commit-id.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/builtin/get-tar-commit-id.c b/builtin/get-tar-commit-id.c
index 2706fcfaf2..312e44ed05 100644
--- a/builtin/get-tar-commit-id.c
+++ b/builtin/get-tar-commit-id.c
@@ -21,6 +21,8 @@ int cmd_get_tar_commit_id(int argc, const char **argv, const 
char *prefix)
        char *content = buffer + RECORDSIZE;
        const char *comment;
        ssize_t n;
+       long len;
+       char *end;

        if (argc != 1)
                usage(builtin_get_tar_commit_id_usage);
@@ -32,10 +34,17 @@ int cmd_get_tar_commit_id(int argc, const char **argv, 
const char *prefix)
                die_errno("git get-tar-commit-id: EOF before reading tar 
header");
        if (header->typeflag[0] != 'g')
                return 1;
-       if (!skip_prefix(content, "52 comment=", &comment))
+
+       len = strtol(content, &end, 10);
+       if (errno == ERANGE || end == content || len < 0)
+               return 1;
+       if (!skip_prefix(end, " comment=", &comment))
+               return 1;
+       len -= comment - content;
+       if (len != GIT_SHA1_HEXSZ + 1)
                return 1;

-       if (write_in_full(1, comment, 41) < 0)
+       if (write_in_full(1, comment, len) < 0)
                die_errno("git get-tar-commit-id: write error");

        return 0;
--
2.20.1

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