[PATCH] apply: improve error messages when reading patch

From: Phillip Wood via GitGitGadget <gitgitgadget@gmail.com>
Date: Jun 26, 2023, 09:37 UTC
Message-ID: <pull.1552.git.1687772253869.gitgitgadget@gmail.com>

From: Phillip Wood <phillip.wood@dunelm.org.uk>

Commit f1c0e3946e (apply: reject patches larger than ~1 GiB, 2022-10-25) added a limit on the size of patch that apply will process to avoid integer overflows. The implementation re-used the existing error message for when we are unable to read the patch. This is unfortunate because (a) it does not signal to the user that the patch is being rejected because it is too large and (b) it uses error_errno() without setting errno.

This patch adds a specific error message for the case when a patch is too large. It also updates the existing message to make it clearer that it is the patch that cannot be read rather than any other file and marks both messages for translation. The "git apply" prefix is also dropped to match most of the rest of the error messages in apply.c (there are still a few error messages that prefixed with "git apply" and are not marked for translation after this patch). The test added in f1c0e3946e is updated accordingly.

Reported-by: Premek Vysoky <Premek.Vysoky@microsoft.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
    apply: improve error messages when reading patch
    
    I haven't changed it but I found the test a bit confusing as it
    superficially looks like it is generating a valid patch that is too
    large, but it isn't actually a valid patch because the changed line is
    lacking a leading '+' and a trailing '\n'. As we are checking for the
    error message that does not matter but it might be clearer to just do
    
    sz=$((1024 * 1024 * 1023)) &&
    test-tool genzeros $sz | test_must_fail git apply &&
    grep "patch too large" err
    
    
    if we don't care about the patch being valid. Alternatively we could
    create a valid patch with
    
    sz=$((1024 * 1024 * 1023)) &&
    {
        cat <<-\EOF &&
        diff --git a/file b/file
        new file mode 100644
        --- /dev/null
        +++ b/file
        @@ -0,0 +1 @@
        EOF
        printf "+%${sz}s\n" x
    } | test_must_fail git apply 2>err &&
    grep "patch too large" err

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1552%2Fphillipwood%2Fapply-error-message-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1552/phillipwood/apply-error-message-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1552

 apply.c                    | 7 ++++---
 t/t4141-apply-too-large.sh | 2 +-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/apply.c b/apply.c
index 6212ab3a1b3..21c7f92ada8 100644
--- a/apply.c
+++ b/apply.c
@@ -410,9 +410,10 @@ static void say_patch_name(FILE *output, const char *fmt, struct patch *patch)
 
 static int read_patch_file(struct strbuf *sb, int fd)
 {
-	if (strbuf_read(sb, fd, 0) < 0 || sb->len >= MAX_APPLY_SIZE)
-		return error_errno("git apply: failed to read");
-
+	if (strbuf_read(sb, fd, 0) < 0)
+		return error_errno(_("failed to read patch"));
+	else if (sb->len >= MAX_APPLY_SIZE)
+		return error(_("patch too large"));
 	/*
 	 * Make sure that we have some slop in the buffer
 	 * so that we can do speculative "memcmp" etc, and
diff --git a/t/t4141-apply-too-large.sh b/t/t4141-apply-too-large.sh
index 58742d4fc5d..20cc1209f62 100755
--- a/t/t4141-apply-too-large.sh
+++ b/t/t4141-apply-too-large.sh
@@ -17,7 +17,7 @@ test_expect_success EXPENSIVE 'git apply rejects patches that are too large' '
 		EOF
 		test-tool genzeros
 	} | test_copy_bytes $sz | test_must_fail git apply 2>err &&
-	grep "git apply: failed to read" err
+	grep "patch too large" err
 '
 
 test_done

base-commit: fe86abd7511a9a6862d5706c6fa1d9b57a63ba09

-- 
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