[PATCH] zlib-related bugs

the following diff addresses 3 zlib-related bugs in notmuch.
1) the second argument of gzerror() cannot be NULL, so replace it by a dummy
   &errnum.
2) gzerror() cannot be closed after gzclosed(), so just print the error value
   instead.
3) in gz_getline(), if gz_error sets its second argument to Z_STREAM_END then
   there was no error (only EOF).  Unfortunately the zlib manual is not very
   clear on the meaning of Z_STREAM_END, but I don't see how it could be an
   error.  I found this issue by using notmuch on OpenBSD, which has an old
   zlib.  I encountered other issues with notmuch on OpenBSD (e.g. there is no
   transparency mode in this older zlib, so notmuch dump output is always
   gzipped), but they do not seem to be bugs in notmuch.

diff --git a/notmuch-dump.c b/notmuch-dump.c
index 65e02639..5d4b2fa7 100644
--- a/notmuch-dump.c
+++ b/notmuch-dump.c
@@ -287,6 +287,7 @@ notmuch_database_dump (notmuch_database_t *notmuch,
     int outfd = -1;
 
     int ret = -1;
+    int errnum;
 
     if (output_file_name) {
        tempname = talloc_asprintf (notmuch, "%s.XXXXXX", output_file_name);
@@ -316,7 +317,7 @@ notmuch_database_dump (notmuch_database_t *notmuch,
 
     ret = gzflush (output, Z_FINISH);
     if (ret) {
-       fprintf (stderr, "Error flushing output: %s\n", gzerror (output, NULL));
+       fprintf (stderr, "Error flushing output: %s\n", gzerror (output, 
&errnum));
        goto DONE;
     }
 
@@ -332,7 +333,7 @@ notmuch_database_dump (notmuch_database_t *notmuch,
     ret = gzclose_w (output);
     if (ret) {
        fprintf (stderr, "Error closing %s: %s\n", name_for_error,
-                gzerror (output, NULL));
+                gzerror (output, &errnum));
        ret = EXIT_FAILURE;
        output = NULL;
        goto DONE;
diff --git a/notmuch-restore.c b/notmuch-restore.c
index 4b509d95..e2dc3d45 100644
--- a/notmuch-restore.c
+++ b/notmuch-restore.c
@@ -237,6 +237,7 @@ notmuch_restore_command (notmuch_config_t *config, int 
argc, char *argv[])
     int opt_index;
     int include = 0;
     int input_format = DUMP_FORMAT_AUTO;
+    int errnum;
 
     if (notmuch_database_open (notmuch_config_get_database_path (config),
                               NOTMUCH_DATABASE_MODE_READ_WRITE, &notmuch))
@@ -448,10 +449,13 @@ notmuch_restore_command (notmuch_config_t *config, int 
argc, char *argv[])
     if (notmuch)
        notmuch_database_destroy (notmuch);
 
-    if (input && gzclose_r (input)) {
-       fprintf (stderr, "Error closing %s: %s\n",
-                name_for_error, gzerror (input, NULL));
-       ret = EXIT_FAILURE;
+    if (input) {
+       errnum = gzclose_r (input);
+       if (errnum) {
+           fprintf (stderr, "Error closing %s: %d\n",
+                    name_for_error, errnum);
+           ret = EXIT_FAILURE;
+       }
     }
 
     return ret ? EXIT_FAILURE : EXIT_SUCCESS;
diff --git a/util/zlib-extra.c b/util/zlib-extra.c
index f691cccf..3800fa60 100644
--- a/util/zlib-extra.c
+++ b/util/zlib-extra.c
@@ -47,6 +47,7 @@ gz_getline (void *talloc_ctx, char **bufptr, ssize_t 
*bytes_read, gzFile stream)
            int zlib_status = 0;
            (void) gzerror (stream, &zlib_status);
            switch (zlib_status) {
+           case Z_STREAM_END:
            case Z_OK:
                /* no data read before EOF */
                if (offset == 0)
@@ -79,8 +80,9 @@ gz_getline (void *talloc_ctx, char **bufptr, ssize_t 
*bytes_read, gzFile stream)
 const char *
 gz_error_string (util_status_t status, gzFile file)
 {
+    int errnum;
     if (status == UTIL_GZERROR)
-       return gzerror (file, NULL);
+       return gzerror (file, &errnum);
     else
        return util_error_string (status);
 }
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