[PATCH] commit.c: Replace starts_with() with skip_prefix()

[PATCH] commit.c: Replace starts_with() with skip_prefix()

[Karthik Nayak]

Replace with skip_prefix(), which uses the inbuilt function
strcmp() to compare.

Other Places were this can be implemented:
commit.c : line 1117
commit.c : line 1197

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 commit.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/commit.c b/commit.c
index 6bf4fe0..1e181cf 100644
--- a/commit.c
+++ b/commit.c
@@ -552,6 +552,7 @@ static void record_author_date(struct author_date_slab *author_date,
 	char *buffer = NULL;
 	struct ident_split ident;
 	char *date_end;
+	char *flag_sp; /* stores return value of skip_prefix() */
 	unsigned long date;
 
 	if (!commit->buffer) {
@@ -566,7 +567,7 @@ static void record_author_date(struct author_date_slab *author_date,
 	     buf;
 	     buf = line_end + 1) {
 		line_end = strchrnul(buf, '\n');
-		if (!starts_with(buf, "author ")) {
+		if ((flag_sp = skip_prefix(buf, "author ")) == NULL) {
 			if (!line_end[0] || line_end[1] == '\n')
 				return; /* end of header */
 			continue;
-- 
1.9.0.138.g2de3478

Re: [PATCH] commit.c: Replace starts_with() with skip_prefix()

[Eric Sunshine]

Thanks for the submission. Some commentary below to expose you to the
review process on this project...

On Mon, Mar 3, 2014 at 2:47 AM, Karthik Nayak <karthik.188@gmail.com> wrote:
> Replace with skip_prefix(), which uses the inbuilt function
> strcmp() to compare.

Explaining the purpose of the change is indeed important, however,
this description misses the mark. See below.

> Other Places were this can be implemented:
> commit.c : line 1117
> commit.c : line 1197

Bonus points if you actually follow through with this.

> Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
> ---
>  commit.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/commit.c b/commit.c
> index 6bf4fe0..1e181cf 100644
> --- a/commit.c
> +++ b/commit.c
> @@ -552,6 +552,7 @@ static void record_author_date(struct author_date_slab *author_date,
>         char *buffer = NULL;
>         struct ident_split ident;
>         char *date_end;
> +       char *flag_sp; /* stores return value of skip_prefix() */

It's not clear why this variable is needed. It's only assigned (below)
but never referenced. Also, the name conveys little or no meaning. If
you need a comment to explain the purpose of the variable, that's
probably a good indication that it's poorly named.

>         unsigned long date;
>
>         if (!commit->buffer) {
> @@ -566,7 +567,7 @@ static void record_author_date(struct author_date_slab *author_date,
>              buf;
>              buf = line_end + 1) {
>                 line_end = strchrnul(buf, '\n');
> -               if (!starts_with(buf, "author ")) {
> +               if ((flag_sp = skip_prefix(buf, "author ")) == NULL) {

Unfortunately, this change makes the code more difficult to read.
Let's review the GSoC microproject:

    Rewrite commit.c:record_author_date() to use skip_prefix().
    Are there other places in this file where skip_prefix() would
    be **more readable** than starts_with()?

Note the part I **highlighted**. This is a good clue that use of
skip_prefix() can be used to simplify the code. Examine
record_author_date() more carefully and see if you can identify how to
do so.

>                         if (!line_end[0] || line_end[1] == '\n')
>                                 return; /* end of header */
>                         continue;
> --
> 1.9.0.138.g2de3478

Re: [PATCH] commit.c: Replace starts_with() with skip_prefix()

[karthik nayak]

Hello Eric,
Thanks for Pointing out everything, i had a thorough look and fixed a
couple of things.
Here is an Updated Patch.
- Removed unnecessary code and variables.
- Replaced all instances of starts_with() with skip_prefix()

Replace starts_with() with skip_prefix() for better reading purposes.
Also to replace "buf + strlen(author )" by skip_prefix(), which is
saved in a new "const char" variable "buf_skipprefix".

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 commit.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/commit.c b/commit.c
index 6bf4fe0..e5dc2e2 100644
--- a/commit.c
+++ b/commit.c
@@ -552,6 +552,7 @@ static void record_author_date(struct
author_date_slab *author_date,
  char *buffer = NULL;
  struct ident_split ident;
  char *date_end;
+ const char *buf_skipprefix;
  unsigned long date;

  if (!commit->buffer) {
@@ -562,18 +563,20 @@ static void record_author_date(struct
author_date_slab *author_date,
  return;
  }

+ buf_skipprefix = skip_prefix(buf, "author ");
+
  for (buf = commit->buffer ? commit->buffer : buffer;
      buf;
      buf = line_end + 1) {
  line_end = strchrnul(buf, '\n');
- if (!starts_with(buf, "author ")) {
+ if (!buf_skipprefix) {
  if (!line_end[0] || line_end[1] == '\n')
  return; /* end of header */
  continue;
  }
  if (split_ident_line(&ident,
-     buf + strlen("author "),
-     line_end - (buf + strlen("author "))) ||
+ buf_skipprefix,
+ line_end - buf_skipprefix) ||
     !ident.date_begin || !ident.date_end)
  goto fail_exit; /* malformed "author" line */
  break;
@@ -1113,7 +1116,7 @@ int parse_signed_commit(const unsigned char *sha1,
  next = next ? next + 1 : tail;
  if (in_signature && line[0] == ' ')
  sig = line + 1;
- else if (starts_with(line, gpg_sig_header) &&
+ else if (skip_prefix(line, gpg_sig_header) &&
  line[gpg_sig_header_len] == ' ')
  sig = line + gpg_sig_header_len + 1;
  if (sig) {
@@ -1193,7 +1196,7 @@ static void parse_gpg_output(struct signature_check *sigc)
  for (i = 0; i < ARRAY_SIZE(sigcheck_gpg_status); i++) {
  const char *found, *next;

- if (starts_with(buf, sigcheck_gpg_status[i].check + 1)) {
+ if (skip_prefix(buf, sigcheck_gpg_status[i].check + 1)) {
  /* At the very beginning of the buffer */
  found = buf + strlen(sigcheck_gpg_status[i].check + 1);
  } else {
-- 
1.9.0.138.g2de3478

Re: [PATCH] commit.c: Replace starts_with() with skip_prefix()

[Eric Sunshine]

On Mon, Mar 3, 2014 at 10:23 AM, karthik nayak <karthik.188@gmail.com> wrote:
> Hello Eric,
> Thanks for Pointing out everything, i had a thorough look and fixed a
> couple of things.
> Here is an Updated Patch.
> - Removed unnecessary code and variables.
> - Replaced all instances of starts_with() with skip_prefix()

This commentary is important for the on-going email discussion but
does not belong in the commit message for the permanent project
history, so place it below the "---" line just under your sign-off.

Explaining what changed since the last attempt, as you do here, is a
good thing. To further ease the review process, supply a link to the
previous attempt, like this [1].

[1]: http://thread.gmane.org/gmane.comp.version-control.git/243194

> Replace starts_with() with skip_prefix() for better reading purposes.
> Also to replace "buf + strlen(author )" by skip_prefix(), which is
> saved in a new "const char" variable "buf_skipprefix".

The second sentence is really the meat of this change, and not at all
incidental as "Also" implies. You should use it (or a refinement of
it) as your commit message. The first sentence doesn't particularly
add much and can easily be dropped.

> Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
> ---
>  commit.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/commit.c b/commit.c
> index 6bf4fe0..e5dc2e2 100644
> --- a/commit.c
> +++ b/commit.c
> @@ -552,6 +552,7 @@ static void record_author_date(struct
> author_date_slab *author_date,
>   char *buffer = NULL;
>   struct ident_split ident;
>   char *date_end;
> + const char *buf_skipprefix;

Read this response by Junio [2] to another GSoC candidate which
explains why this is a poor variable name and how to craft a better
one.

[2]: http://thread.gmane.org/gmane.comp.version-control.git/243231/focus=243259

>   unsigned long date;
>
>   if (!commit->buffer) {
> @@ -562,18 +563,20 @@ static void record_author_date(struct
> author_date_slab *author_date,
>   return;
>   }
>
> + buf_skipprefix = skip_prefix(buf, "author ");

Unfortunately, your patch is badly whitespace-damaged as if it was
pasted into the mailer and mangled. (Your first submission did not
have this problem.) If you can, use "git send-email" to avoid such
corruption.

> +
>   for (buf = commit->buffer ? commit->buffer : buffer;
>       buf;
>       buf = line_end + 1) {
>   line_end = strchrnul(buf, '\n');
> - if (!starts_with(buf, "author ")) {
> + if (!buf_skipprefix) {
>   if (!line_end[0] || line_end[1] == '\n')
>   return; /* end of header */
>   continue;
>   }
>   if (split_ident_line(&ident,
> -     buf + strlen("author "),
> -     line_end - (buf + strlen("author "))) ||
> + buf_skipprefix,
> + line_end - buf_skipprefix) ||

Looks reasonable (sans whitespace damage).

>      !ident.date_begin || !ident.date_end)
>   goto fail_exit; /* malformed "author" line */
>   break;
> @@ -1113,7 +1116,7 @@ int parse_signed_commit(const unsigned char *sha1,
>   next = next ? next + 1 : tail;
>   if (in_signature && line[0] == ' ')
>   sig = line + 1;
> - else if (starts_with(line, gpg_sig_header) &&
> + else if (skip_prefix(line, gpg_sig_header) &&
>   line[gpg_sig_header_len] == ' ')
>   sig = line + gpg_sig_header_len + 1;
>   if (sig) {
> @@ -1193,7 +1196,7 @@ static void parse_gpg_output(struct signature_check *sigc)
>   for (i = 0; i < ARRAY_SIZE(sigcheck_gpg_status); i++) {
>   const char *found, *next;
>
> - if (starts_with(buf, sigcheck_gpg_status[i].check + 1)) {
> + if (skip_prefix(buf, sigcheck_gpg_status[i].check + 1)) {
>   /* At the very beginning of the buffer */
>   found = buf + strlen(sigcheck_gpg_status[i].check + 1);
>   } else {

For these two sets of changes, unless you are actually taking
advantage of the return value of skip_prefix(), the mere mechanical
replacement of starts_with() with skip_prefix() actually hurts
readability. Examine each of these cases more carefully to determine
whether skip_prefix() is in fact useful. If so, take advantage of it.
If not, explain in the patch commentary why skip_prefix() doesn't
help.

> --
> 1.9.0.138.g2de3478