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[PATCH v3 07/21] read_packed_refs(): make parsing of the header line more robust

From
Michael Haggerty <mhagger@alum.mit.edu>
Date
Sep 25, 2017, 08:00 UTC
Message-ID
<10a0edfa6de813c3bf6045a2d99bc0f06571bc10.1506325610.git.mhagger@alum.mit.edu>
In-Reply-To
<cover.1506325610.git.mhagger@alum.mit.edu>

The old code parsed the traits in the `packed-refs` header by looking for the string " trait " (i.e., the name of the trait with a space on either side) in the header line. This is fragile, because if any other implementation of Git forgets to write the trailing space, the last trait would silently be ignored (and the error might never be noticed).

So instead, use `string_list_split_in_place()` to split the traits into tokens then use `unsorted_string_list_has_string()` to look for the tokens we are interested in. This means that we can read the traits correctly even if the header line is missing a trailing space (or indeed, if it is missing the space after the colon, or if it has multiple spaces somewhere).

However, older Git clients (and perhaps other Git implementations) still require the surrounding spaces, so we still have to output the header with a trailing space.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
 refs/packed-backend.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 141f02b9c8..a45e3ff92f 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -257,25 +257,30 @@ static struct packed_ref_cache *read_packed_refs(struct packed_ref_store *refs)
 
 	/* If the file has a header line, process it: */
 	if (pos < eof && *pos == '#') {
-		const char *traits;
+		char *p;
+		struct string_list traits = STRING_LIST_INIT_NODUP;
 
 		eol = memchr(pos, '\n', eof - pos);
 		if (!eol)
 			die_unterminated_line(refs->path, pos, eof - pos);
 
-		strbuf_add(&line, pos, eol + 1 - pos);
+		strbuf_add(&line, pos, eol - pos);
 
-		if (!skip_prefix(line.buf, "# pack-refs with:", &traits))
+		if (!skip_prefix(line.buf, "# pack-refs with:", (const char **)&p))
 			die_invalid_line(refs->path, pos, eof - pos);
 
-		if (strstr(traits, " fully-peeled "))
+		string_list_split_in_place(&traits, p, ' ', -1);
+
+		if (unsorted_string_list_has_string(&traits, "fully-peeled"))
 			peeled = PEELED_FULLY;
-		else if (strstr(traits, " peeled "))
+		else if (unsorted_string_list_has_string(&traits, "peeled"))
 			peeled = PEELED_TAGS;
 		/* perhaps other traits later as well */
 
 		/* The "+ 1" is for the LF character. */
 		pos = eol + 1;
+
+		string_list_clear(&traits, 0);
 		strbuf_reset(&line);
 	}
 
@@ -610,7 +615,11 @@ int packed_refs_is_locked(struct ref_store *ref_store)
 
 /*
  * The packed-refs header line that we write out.  Perhaps other
- * traits will be added later.  The trailing space is required.
+ * traits will be added later.
+ *
+ * Note that earlier versions of Git used to parse these traits by
+ * looking for " trait " in the line. For this reason, the space after
+ * the colon and the trailing space are required.
  */
 static const char PACKED_REFS_HEADER[] =
 	"# pack-refs with: peeled fully-peeled \n";

-- 
2.14.1
Previous: Michael HaggertyNext: Michael Haggerty
Message 8 of 24 in “Read `packed-refs` using mmap()”
  1. 00/21 Read `packed-refs` using mmap()Michael Haggerty, Sep 25, 2017
  2. 01/21 ref_iterator: keep track of whether the iterator output is orderedMichael Haggerty, Sep 25, 2017
  3. 02/21 prefix_ref_iterator: break when we leave the prefixMichael Haggerty, Sep 25, 2017
  4. 03/21 packed_ref_cache: add a backlink to the associated `packed_ref_store`Michael Haggerty, Sep 25, 2017
  5. 04/21 die_unterminated_line(), die_invalid_line(): new functionsMichael Haggerty, Sep 25, 2017
  6. 05/21 read_packed_refs(): use mmap to read the `packed-refs` fileMichael Haggerty, Sep 25, 2017
  7. 06/21 read_packed_refs(): only check for a header at the top of the fileMichael Haggerty, Sep 25, 2017
  8. 07/21 read_packed_refs(): make parsing of the header line more robustMichael Haggerty, Sep 25, 2017
  9. 09/21 packed_ref_cache: remember the file-wide peeling stateMichael Haggerty, Sep 25, 2017
  10. 08/21 read_packed_refs(): read references with minimal copyingMichael Haggerty, Sep 25, 2017
  11. 10/21 mmapped_ref_iterator: add iterator over a packed-refs fileMichael Haggerty, Sep 25, 2017
  12. 12/21 packed-backend.c: reorder some definitionsMichael Haggerty, Sep 25, 2017
  13. 13/21 packed_ref_cache: keep the `packed-refs` file mmapped if possibleMichael Haggerty, Sep 25, 2017
  14. 14/21 read_packed_refs(): ensure that references are ordered when readMichael Haggerty, Sep 25, 2017
  15. 11/21 mmapped_ref_iterator_advance(): no peeled value for broken refsMichael Haggerty, Sep 25, 2017
  16. 15/21 packed_ref_iterator_begin(): iterate using `mmapped_ref_iterator`Michael Haggerty, Sep 25, 2017
  17. 16/21 packed_read_raw_ref(): read the reference from the mmapped bufferMichael Haggerty, Sep 25, 2017
  18. 17/21 ref_store: implement `refs_peel_ref()` genericallyMichael Haggerty, Sep 25, 2017
  19. 18/21 packed_ref_store: get rid of the `ref_cache` entirelyMichael Haggerty, Sep 25, 2017
  20. 20/21 mmapped_ref_iterator: inline into `packed_ref_iterator`Michael Haggerty, Sep 25, 2017
  21. 19/21 ref_cache: remove support for storing peeled valuesMichael Haggerty, Sep 25, 2017
  22. 21/21 packed-backend.c: rename a bunch of things and update commentsMichael Haggerty, Sep 25, 2017
  23. Jeff KingSep 25, 2017
  24. Junio C HamanoSep 29, 2017

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