On Tue, Mar 28, 2017 at 03:46:18PM -0400, Jeff King wrote:
> As a result, the data we feed to the sha1 computation may be
> truncated, and it's possible that a commit with a very long
> filename could erroneously collide in the patch-id space
> with another commit. For instance, if one commit modified
> "really-long-filename/foo" and another modified "bar" in the
> same directory.
>
> In practice this is unlikely. Because the filenames are
> repeated, and because there's a single cutoff at the end of
> the buffer, the offending filename would have to be on the
> order of four times larger than PATH_MAX.
>
> But it's easy to fix by moving to a strbuf.
The other obvious solution is to avoid formatting the string entirely,
and just feed the pieces to the sha1 computation. Unfortunately that
still involves formatting the modes (into a fixed-size buffer!) since we
need the sha1 of their string representations.
That patch is below for reference. I'm not sure if it's more readable or
not.
---
diff --git a/diff.c b/diff.c
index a628ac3a9..435c734f4 100644
--- a/diff.c
+++ b/diff.c
@@ -4570,6 +4570,19 @@ static void patch_id_consume(void *priv, char *line,
unsigned long len)
data->patchlen += new_len;
}
+static void patch_id_add_string(git_SHA_CTX *ctx, const char *str)
+{
+ git_SHA1_Update(ctx, str, strlen(str));
+}
+
+static void patch_id_add_mode(git_SHA_CTX *ctx, unsigned mode)
+{
+ /* large enough for 2^32 in octal */
+ char buf[12];
+ int len = xsnprintf(buf, sizeof(buf), "%06o", mode);
+ git_SHA1_Update(ctx, buf, len);
+}
+
/* returns 0 upon success, and writes result into sha1 */
static int diff_get_patch_id(struct diff_options *options, unsigned char
*sha1, int diff_header_only)
{
@@ -4577,7 +4590,6 @@ static int diff_get_patch_id(struct diff_options
*options, unsigned char *sha1,
int i;
git_SHA_CTX ctx;
struct patch_id_t data;
- char buffer[PATH_MAX * 4 + 20];
git_SHA1_Init(&ctx);
memset(&data, 0, sizeof(struct patch_id_t));
@@ -4609,36 +4621,30 @@ static int diff_get_patch_id(struct diff_options
*options, unsigned char *sha1,
len1 = remove_space(p->one->path, strlen(p->one->path));
len2 = remove_space(p->two->path, strlen(p->two->path));
- if (p->one->mode == 0)
- len1 = snprintf(buffer, sizeof(buffer),
- "diff--gita/%.*sb/%.*s"
- "newfilemode%06o"
- "---/dev/null"
- "+++b/%.*s",
- len1, p->one->path,
- len2, p->two->path,
- p->two->mode,
- len2, p->two->path);
- else if (p->two->mode == 0)
- len1 = snprintf(buffer, sizeof(buffer),
- "diff--gita/%.*sb/%.*s"
- "deletedfilemode%06o"
- "---a/%.*s"
- "+++/dev/null",
- len1, p->one->path,
- len2, p->two->path,
- p->one->mode,
- len1, p->one->path);
- else
- len1 = snprintf(buffer, sizeof(buffer),
- "diff--gita/%.*sb/%.*s"
- "---a/%.*s"
- "+++b/%.*s",
- len1, p->one->path,
- len2, p->two->path,
- len1, p->one->path,
- len2, p->two->path);
- git_SHA1_Update(&ctx, buffer, len1);
+ patch_id_add_string(&ctx, "diff--git");
+ patch_id_add_string(&ctx, "a/");
+ git_SHA1_Update(&ctx, p->one->path, len1);
+ patch_id_add_string(&ctx, "b/");
+ git_SHA1_Update(&ctx, p->two->path, len2);
+
+ if (p->one->mode == 0) {
+ patch_id_add_string(&ctx, "newfilemode");
+ patch_id_add_mode(&ctx, p->two->mode);
+ patch_id_add_string(&ctx, "---/dev/null");
+ patch_id_add_string(&ctx, "+++b/");
+ git_SHA1_Update(&ctx, p->two->path, len2);
+ } else if (p->two->mode == 0) {
+ patch_id_add_string(&ctx, "deletedfilemode");
+ patch_id_add_mode(&ctx, p->one->mode);
+ patch_id_add_string(&ctx, "---a/");
+ git_SHA1_Update(&ctx, p->one->path, len1);
+ patch_id_add_string(&ctx, "+++/dev/null");
+ } else {
+ patch_id_add_string(&ctx, "---a/");
+ git_SHA1_Update(&ctx, p->one->path, len1);
+ patch_id_add_string(&ctx, "+++b/");
+ git_SHA1_Update(&ctx, p->two->path, len2);
+ }
if (diff_header_only)
continue;
