Re: [PATCH] Modify fsck_commit. Replace memcmp by skip_prefix

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Thanks for your comments, Tanay and Eric.

Regarding the [PATCH v2], I will keep this in mind for the subsequent patches.

On 03/23/2014 02:10 PM, Eric Sunshine wrote:
Thanks for the resubmission. Comments below...

On Sat, Mar 22, 2014 at 11:12 AM, Ashwin Jha <ajha.dev@xxxxxxxxx> wrote:
Subject: [PATCH] Modify fsck_commit. Replace memcmp by skip_prefix
In his review, Tanay already mentioned indicating a resubmission via
[PATCH vN]. Additionally, specify the module or function being
modified, followed by a colon and space. On this project, it is
customary to forego capitalization in the subject (and only the
subject). So, you might write:

     Subject: [PATCH v2] fsck_commit: replace memcmp() by skip_prefix()

Replace memcmp by skip_prefix as it serves the dual
purpose of checking the string for a prefix as well
as skipping that prefix.
Good.

Signed-off-by: Ashwin Jha <ajha.dev@xxxxxxxxx>
---
Tanay mentioned this already: Below the "---" line under your sign-off
is where you should, as a courtesy to reviewers, explain what changed
since the previous attempt. Also, provide a link to the previous
version, like this [1].

[1]: http://git.661346.n2.nabble.com/PATCH-GSoC-Miniproject-15-Rewrite-fsck-c-fsck-commit-td7606180.html

  fsck.c |   25 ++++++++++++++-----------
  1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/fsck.c b/fsck.c
index 64bf279..021b3fc 100644
--- a/fsck.c
+++ b/fsck.c
@@ -6,6 +6,7 @@
  #include "commit.h"
  #include "tag.h"
  #include "fsck.h"
+#include "git-compat-util.h"

  static int fsck_walk_tree(struct tree *tree, fsck_walk_func walk, void *data)
  {
@@ -284,21 +285,23 @@ static int fsck_ident(char **ident, struct object *obj, fsck_error error_func)

  static int fsck_commit(struct commit *commit, fsck_error error_func)
  {
-       char *buffer = commit->buffer;
+       char *next_parent, *buffer = commit->buffer;
The name 'next_parent' doesn't seem correct. After invoking
skip_prefix(), this variable will point at the hex representation of
the parent's SHA1, so a better name might be 'parent_id'.

         unsigned char tree_sha1[20], sha1[20];
         struct commit_graft *graft;
         int parents = 0;
         int err;

-       if (memcmp(buffer, "tree ", 5))
+       buffer = (char *)skip_prefix(buffer, "tree ");
These casts are ugly. It should be possible to get rid of all of them.
Hint: Does this function modify the memory referenced by 'buffer'?
(The answer is very slightly involved, though not difficult. A proper
fix would involve turning this submission into a 2-patch series: one a
preparatory patch, and the other this patch without the casts.)
Eric, certainly this function does not modify the memory referenced by 'buffer'.
So, 'buffer' should be declared as a const char *.
But, what about the argument to fsck_ident(). First argument required is a char **.
Now, the compiler will correctly give a warning for incorrect argument type.

I have seen the code of fsck_ident(), and it is nowhere modifying the memory referenced by buffer. So, I know that this will not cause any problem. But, still it will be a bad practice to do away with
warnings.

And can you explain me a bit about a 2-patch series.

Once again thanks for your help.
+       if (buffer == NULL)

On this project, it is customary to say !buffer. Ditto for the
remaining instances.

                 return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'tree' line");
-       if (get_sha1_hex(buffer+5, tree_sha1) || buffer[45] != '\n')
+       if (get_sha1_hex(buffer, tree_sha1) || buffer[40] != '\n')
                 return error_func(&commit->object, FSCK_ERROR, "invalid 'tree' line format - bad sha1");
-       buffer += 46;
-       while (!memcmp(buffer, "parent ", 7)) {
-               if (get_sha1_hex(buffer+7, sha1) || buffer[47] != '\n')
+       buffer += 41;
+       while ((next_parent = (char *)skip_prefix(buffer, "parent ")) != NULL) {
Likewise, on this project, it is customary to omit the '!= NULL'.

+               buffer = next_parent;
+               if (get_sha1_hex(buffer, sha1) || buffer[40] != '\n')
                         return error_func(&commit->object, FSCK_ERROR, "invalid 'parent' line format - bad sha1");
-               buffer += 48;
+               buffer += 41;
                 parents++;
         }
         graft = lookup_commit_graft(commit->object.sha1);
@@ -322,15 +325,15 @@ static int fsck_commit(struct commit *commit, fsck_error error_func)
                 if (p || parents)
                         return error_func(&commit->object, FSCK_ERROR, "parent objects missing");
         }
-       if (memcmp(buffer, "author ", 7))
+       buffer = (char *)skip_prefix(buffer, "author ");
+       if (buffer == NULL)
                 return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'author' line");
-       buffer += 7;
         err = fsck_ident(&buffer, &commit->object, error_func);
         if (err)
                 return err;
-       if (memcmp(buffer, "committer ", strlen("committer ")))
+       buffer = (char *)skip_prefix(buffer, "committer ");
+       if (buffer == NULL)
                 return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'committer' line");
-       buffer += strlen("committer ");
         err = fsck_ident(&buffer, &commit->object, error_func);
         if (err)
                 return err;
Other than the minor points mentioned above, the patch looks good. Thanks.

--
1.7.9.5
Regards,
Ashwin
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