[PATCH] GSoC Miniproject 15. Rewrite fsck.c:fsck_commit()

modified fsck.c:fsck_commit(). Replaced memcmp() with starts_with() function.
starts_with() seems much more relevant than memcmp(). It uses one less argument
and its return value makes more sense.
skip_prefix() is not used as it uses strcmp() internally which seems unnecessarily
for current task. The current task can be easily done by providing offsets to the
buffer pointer (the way it is implemented currently).

Signed-off-by: Ashwin Jha <redacted>
---
 fsck.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/fsck.c b/fsck.c
index 64bf279..82e1640 100644
--- a/fsck.c
+++ b/fsck.c

@@ -6,6 +6,7 @@
 #include "commit.h"
 #include "tag.h"
 #include "fsck.h"
+#include "strbuf.h"
 
 static int fsck_walk_tree(struct tree *tree, fsck_walk_func walk, void *data)
 {

@@ -290,12 +291,12 @@ static int fsck_commit(struct commit *commit, fsck_error error_func)
 	int parents = 0;
 	int err;
 
-	if (memcmp(buffer, "tree ", 5))
+	if (!starts_with(buffer, "tree "))
 		return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'tree' line");
 	if (get_sha1_hex(buffer+5, tree_sha1) || buffer[45] != '\n')
 		return error_func(&commit->object, FSCK_ERROR, "invalid 'tree' line format - bad sha1");
 	buffer += 46;
-	while (!memcmp(buffer, "parent ", 7)) {
+	while (starts_with(buffer, "parent ")) {
 		if (get_sha1_hex(buffer+7, sha1) || buffer[47] != '\n')
 			return error_func(&commit->object, FSCK_ERROR, "invalid 'parent' line format - bad sha1");
 		buffer += 48;

@@ -322,15 +323,15 @@ 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))
+	if (!starts_with(buffer, "author "))
 		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 ")))
+	if (!starts_with(buffer, "committer "))
 		return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'committer' line");
-	buffer += strlen("committer ");
+	buffer += 10;
 	err = fsck_ident(&buffer, &commit->object, error_func);
 	if (err)
 		return err;

-- 
1.7.9.5

Thanks for the submission. Comments below to give you a feel for the
Git review process...

On Thu, Mar 20, 2014 at 9:54 PM, Ashwin Jha [off-list ref] wrote:

Subject: [PATCH] GSoC Miniproject 15. Rewrite fsck.c:fsck_commit()

The subject becomes part of the permanent Git history, but the fact
that this is a GSoC submission won't be meaningful to anyone months or
years from now. You can mention GSoC inside [...], however, as in
[PATCH GSoC], since that gets stripped off the subject automatically
when the patch is applied. Use the commentary section after the "---"
line just below your sign-off to explain that this is microproject 15.

The subject itself should concisely summarize the change. "Rewrite
fsck.c:fsck_commit()" doesn't say much. You might say instead:

    Subject: fsk_commit: replace memcmp() with starts_with()

modified fsck.c:fsck_commit(). Replaced memcmp() with starts_with() function.

Capitalize start of sentence.

Use imperative mood: "modify" rather than "modified"; "Replace" rather
than "Replaced".

starts_with() seems much more relevant than memcmp(). It uses one less argument
and its return value makes more sense.

As a justification, "uses one less argument" falls flat, and really
has nothing to do with the decision to make the change. The bit about
the return value is a slightly better but is still weak. You might
instead justify the change by pointing out that the name starts_with()
does a better job of conveying the intention of the code, which is to
check the string for a prefix, than does memcmp().

skip_prefix() is not used as it uses strcmp() internally which seems unnecessarily
for current task. The current task can be easily done by providing offsets to the
buffer pointer (the way it is implemented currently).

Not sure what this means. What is the "current task", and what is
implemented where currently?

One of the benefits of starts_with() and skip_prefix() is that they
allow you to eliminate magic numbers, such as 5 in the memcmp()
invocation. However, if you look a couple lines below, you see in the
expression 'buffer+5' that the magic number is still present. In fact,
the code becomes less clear with your change because the 5 in
'buffer+5' is much more mysterious without the preceding
memcmp(foo,"bar",5). It is possible to eliminate this magic number,
but starts_with() is not the answer.

                return error_func(&commit->object, FSCK_ERROR, "invalid 'tree' line format - bad sha1");
        buffer += 46;
-       while (!memcmp(buffer, "parent ", 7)) {
+       while (starts_with(buffer, "parent ")) {
                if (get_sha1_hex(buffer+7, sha1) || buffer[47] != '\n')

Ditto here with magic number 7 in 'buffer+7'.

And again with 7.

        err = fsck_ident(&buffer, &commit->object, error_func);
        if (err)
                return err;
-       if (memcmp(buffer, "committer ", strlen("committer ")))
+       if (!starts_with(buffer, "committer "))
                return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'committer' line");
-       buffer += strlen("committer ");
+       buffer += 10;

Again with 10 (newly introduced).

        err = fsck_ident(&buffer, &commit->object, error_func);
        if (err)
                return err;
--
1.7.9.5

-------- Original Message --------
Subject: 	[PATCH] GSoC Miniproject 15. Rewrite fsck.c:fsck_commit()
Date: 	Fri, 21 Mar 2014 07:24:46 +0530
From: 	Ashwin Jha <redacted>
To: 	git@vger.kernel.org
CC: 	Ashwin Jha <redacted>



modified fsck.c:fsck_commit(). Replaced memcmp() with starts_with() function.
starts_with() seems much more relevant than memcmp(). It uses one less argument
and its return value makes more sense.
skip_prefix() is not used as it uses strcmp() internally which seems unnecessarily
for current task. The current task can be easily done by providing offsets to the
buffer pointer (the way it is implemented currently).

Signed-off-by: Ashwin Jha <redacted>
---
  fsck.c |   11 ++++++-----
  1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/fsck.c b/fsck.c
index 64bf279..82e1640 100644
--- a/fsck.c
+++ b/fsck.c

@@ -6,6 +6,7 @@
  #include "commit.h"
  #include "tag.h"
  #include "fsck.h"
+#include "strbuf.h"
  
  static int fsck_walk_tree(struct tree *tree, fsck_walk_func walk, void *data)
  {

@@ -290,12 +291,12 @@ static int fsck_commit(struct commit *commit, fsck_error error_func)
  	int parents = 0;
  	int err;
  
-	if (memcmp(buffer, "tree ", 5))
+	if (!starts_with(buffer, "tree "))
  		return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'tree' line");
  	if (get_sha1_hex(buffer+5, tree_sha1) || buffer[45] != '\n')
  		return error_func(&commit->object, FSCK_ERROR, "invalid 'tree' line format - bad sha1");
  	buffer += 46;
-	while (!memcmp(buffer, "parent ", 7)) {
+	while (starts_with(buffer, "parent ")) {
  		if (get_sha1_hex(buffer+7, sha1) || buffer[47] != '\n')
  			return error_func(&commit->object, FSCK_ERROR, "invalid 'parent' line format - bad sha1");
  		buffer += 48;

@@ -322,15 +323,15 @@ 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))
+	if (!starts_with(buffer, "author "))
  		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 ")))
+	if (!starts_with(buffer, "committer "))
  		return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'committer' line");
-	buffer += strlen("committer ");
+	buffer += 10;
  	err = fsck_ident(&buffer, &commit->object, error_func);
  	if (err)
  		return err;

-- 
1.7.9.5