Using --no-name with pipes by default for reproducibility (a patch included)

[Karel Klic]

Hi,

a Fedora user recently complained [1] about metadata (--name enabled by 
default) breaking checksums with no obvious advantage.

$ echo "foo" | gzip | sha1sum; sleep 1; echo "foo" | gzip | sha1sum
b1803d7287d7001ab13aa8ca598248b837f61944  -
3100bbc82e16778390147936310432407235f45e  -

While --name might be useful when compressing a file, I think it should 
not be enabled by default for pipes, so we get

$ echo "foo" | gzip | sha1sum; sleep 1; echo "foo" | gzip | sha1sum
505705216e4b4ed1f80dc55fb97d5e7f8a48d84f  -
505705216e4b4ed1f80dc55fb97d5e7f8a48d84f  -

Is there a reason why --name is enabled by default for pipes?

The user suggests that --name is less useful than having the possibility 
of comparing checksums even when compressing a file, so it should be 
disabled by default.

Best regards,
Karel Klic

[1] https://bugzilla.redhat.com/show_bug.cgi?id=615824

Here is a patch: Do not store file name and mtime by default when 
compressing data from a pipe.

diff -up gzip-1.4/gzip.c.no_time gzip-1.4/gzip.c
--- gzip-1.4/gzip.c.no_time     2010-07-26 17:53:26.524902628 +0200
+++ gzip-1.4/gzip.c     2010-07-26 17:56:20.954778912 +0200
@@ -518,14 +518,15 @@ int main (int argc, char **argv)
        }
     } /* loop on all arguments */

-    /* By default, save name and timestamp on compression but do not
-     * restore them on decompression.
-     */
-    if (no_time < 0) no_time = decompress;
-    if (no_name < 0) no_name = decompress;
-
     file_count = argc - optind;

+    /* By default, save name and timestamp on compression except when
+     * reading data from stdin, and do not restore them on
+     * decompression.
+     */
+    if (no_time < 0) no_time = decompress || (file_count == 0);
+    if (no_name < 0) no_name = decompress || (file_count == 0);
+
 #if O_BINARY
 #else
     if (ascii && !quiet) {