[v2] receive-pack.c: consolidate find header logic

Commit Message

John Cai Dec. 29, 2021, 6:19 a.m. UTC

From: John Cai <[e-mail]>

There are two functions that have very similar logic of finding a header
value. find_commit_header, and find_header. We can conslidate the logic
by using find_commit_header and replacing the logic in find_header.

Introduce a new function find_header_max, which is equivalent to
find_commit_header except it takes a len parameter that determines how
many bytes to read. find_commit_header can then call find_header_max
with 0 as the len.

This cleans up duplicate logic, as the logic for finding header values
is now all in one place.

Signed-off-by: John Cai <[e-mail]>
---
    Consolidate find_header logic into one function
    
    This addresses the NEEDSWORK comment in builtin/receive-pack.c:
    
     /**
       * NEEDSWORK: reuse find_commit_header() from jk/commit-author-parsing
       * after dropping "_commit" from its name and possibly moving it out
       * of commit.c
       **/
    
    
    There is some duplicated logic between find_header and
    find_commit_header that can be consolidated instead of having two places
    in the code that do essentially the same thing. For the sake of simpler
    and more DRY code, use find_commit_header and rename it to find_header
    since it is not limited to finding headers for only commits.
    
    Changes since v1:
    
     * got rid of renaming from find_commit_header -> find_header since the
       renaming did not provide much value
     * simplified logic in find_header
     * introduce find_header_max function, which is what find_commit_header
       was before except it adds a "len" parameter to determine how much of
       the buffer to read.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1125%2Fjohn-cai%2Fjc%2Freplace-find-header-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1125/john-cai/jc/replace-find-header-v2
Pull-Request: https://github.com/git/git/pull/1125

Range-diff vs v1:

 1:  9465c20d4bd ! 1:  5e0d90d642b receive-pack.c: consolidate find header logic
     @@ Commit message
          There are two functions that have very similar logic of finding a header
          value. find_commit_header, and find_header. We can conslidate the logic
          by using find_commit_header and replacing the logic in find_header.
     -    This helps clean up the code, as the logic for finding header values can
     -    stay in one place.
     +
     +    Introduce a new function find_header_max, which is equivalent to
     +    find_commit_header except it takes a len parameter that determines how
     +    many bytes to read. find_commit_header can then call find_header_max
     +    with 0 as the len.
     +
     +    This cleans up duplicate logic, as the logic for finding header values
     +    is now all in one place.
      
          Signed-off-by: John Cai <[e-mail]>
      
     @@ builtin/receive-pack.c: static char *prepare_push_cert_nonce(const char *path, t
      - * after dropping "_commit" from its name and possibly moving it out
      - * of commit.c
      - */
     --static char *find_header(const char *msg, size_t len, const char *key,
     --			 const char **next_line)
     -+static char *find_header_value(const char *msg, const char *key, const char **next_line)
     + static char *find_header(const char *msg, size_t len, const char *key,
     + 			 const char **next_line)
       {
      -	int key_len = strlen(key);
      -	const char *line = msg;
     @@ builtin/receive-pack.c: static char *prepare_push_cert_nonce(const char *path, t
      -			return xmemdupz(line + offset, (eol - line) - offset);
      -		}
      -		line = *eol ? eol + 1 : NULL;
     +-	}
     +-	return NULL;
      +	size_t out_len;
     -+	const char *eol;
     -+	char *ret;
     ++	const char *val = find_header_max(msg, key, len, &out_len);
      +
     -+	const char *val = find_commit_header(msg, key, &out_len);
      +	if (val == NULL)
      +		return NULL;
      +
     -+	eol = strchrnul(val, '\n');
     -+	if (next_line) {
     -+		*next_line = *eol ? eol + 1: eol;
     - 	}
     --	return NULL;
     -+
     -+	ret = xmalloc(out_len+1);
     -+	memcpy(ret, val, out_len);
     -+	ret[out_len] = '\0';
     ++	if (next_line)
     ++		*next_line = val + out_len + 1;
      +
     -+	return ret;
     ++	return xmemdupz(val, out_len);
       }
       
       /*
     -@@ builtin/receive-pack.c: static int constant_memequal(const char *a, const char *b, size_t n)
     +
     + ## commit.c ##
     +@@ commit.c: struct commit_list **commit_list_append(struct commit *commit,
     + 	return &new_commit->next;
     + }
       
     - static const char *check_nonce(const char *buf, size_t len)
     +-const char *find_commit_header(const char *msg, const char *key, size_t *out_len)
     ++const char *find_header_max(const char *msg, const char *key,
     ++			size_t len,
     ++			size_t *out_len)
       {
     --	char *nonce = find_header(buf, len, "nonce", NULL);
     -+	char *nonce = find_header_value(buf, "nonce", NULL);
     -+
     - 	timestamp_t stamp, ostamp;
     - 	char *bohmac, *expect = NULL;
     - 	const char *retval = NONCE_BAD;
     -@@ builtin/receive-pack.c: static int check_cert_push_options(const struct string_list *push_options)
     - 	if (!len)
     - 		return 1;
     + 	int key_len = strlen(key);
     + 	const char *line = msg;
       
     --	while ((option = find_header(buf, len, "push-option", &next_line))) {
     --		len -= (next_line - buf);
     -+	while ((option = find_header_value(buf, "push-option", &next_line))) {
     - 		buf = next_line;
     - 		options_seen++;
     - 		if (options_seen > push_options->nr
     -
     - ## commit.c ##
     +-	while (line) {
     ++	while (line && (len == 0 || line < msg + len)) {
     + 		const char *eol = strchrnul(line, '\n');
     + 
     + 		if (line == eol)
      @@ commit.c: const char *find_commit_header(const char *msg, const char *key, size_t *out_len
     - 		if (eol - line > key_len &&
     - 		    !strncmp(line, key, key_len) &&
     - 		    line[key_len] == ' ') {
     --			*out_len = eol - line - key_len - 1;
     -+			if (out_len != NULL)
     -+				*out_len = eol - line - key_len - 1;
     - 			return line + key_len + 1;
     - 		}
     - 		line = *eol ? eol + 1 : NULL;
     + 	return NULL;
     + }
     + 
     ++const char *find_commit_header(const char *msg, const char *key, size_t *out_len)
     ++{
     ++	return find_header_max(msg, key, 0, out_len);
     ++}
     + /*
     +  * Inspect the given string and determine the true "end" of the log message, in
     +  * order to find where to put a new Signed-off-by trailer.  Ignored are
     +
     + ## commit.h ##
     +@@ commit.h: void free_commit_extra_headers(struct commit_extra_header *extra);
     + 
     + /*
     +  * Search the commit object contents given by "msg" for the header "key".
     ++ * Reads up to "len" bytes of "msg".
     +  * Returns a pointer to the start of the header contents, or NULL. The length
     +  * of the header, up to the first newline, is returned via out_len.
     +  *
     +  * Note that some headers (like mergetag) may be multi-line. It is the caller's
     +  * responsibility to parse further in this case!
     +  */
     ++const char *find_header_max(const char *msg, const char *key,
     ++			size_t len,
     ++			size_t *out_len);
     ++
     + const char *find_commit_header(const char *msg, const char *key,
     + 			       size_t *out_len);
     + 
 2:  384a635daa2 < -:  ----------- commit.c: rename find_commit_header to find_header


 builtin/receive-pack.c | 33 ++++++++++-----------------------
 commit.c               | 10 ++++++++--
 commit.h               |  5 +++++
 3 files changed, 23 insertions(+), 25 deletions(-)


base-commit: 55b058a8bbcc54bd93c733035c995abc7967e539

Comments

Junio C Hamano Dec. 30, 2021, 11:01 p.m. UTC | #1

"John Cai via GitGitGadget" <[e-mail]> writes:

> From: John Cai <[e-mail]>
>
> There are two functions that have very similar logic of finding a header
> value. find_commit_header, and find_header. We can conslidate the logic
> by using find_commit_header and replacing the logic in find_header.
>
> Introduce a new function find_header_max, which is equivalent to
> find_commit_header except it takes a len parameter that determines how
> many bytes to read. find_commit_header can then call find_header_max
> with 0 as the len.

find_header_max() is not the name of the function that finds the
largest header?  That is misleading.

<git-compat-util.h> defines a few helper functions that take a
counted string, and they are named with _mem() suffix after the name
of their NUL-terminated counterparts (if exists).  skip_prefix() has
skip_prefix_mem(), strip_suffix() has strip_suffix_mem().

find_header_mem() or something along that line, perhaps?

> diff --git a/commit.c b/commit.c
> index a348f085b2b..2ed115e04a0 100644
> --- a/commit.c
> +++ b/commit.c
> @@ -1631,12 +1631,14 @@ struct commit_list **commit_list_append(struct commit *commit,
>  	return &new_commit->next;
>  }
>  
> -const char *find_commit_header(const char *msg, const char *key, size_t *out_len)
> +const char *find_header_max(const char *msg, const char *key,
> +			size_t len,
> +			size_t *out_len)

If <len> is meant to be the length part of <ptr,len> pair, we should
have it immediately after the <ptr> parameter.

	find_header_mem(const char *msg, size_t len,
        		const char *key, size_t *out_len)

That makes it clear to the readers that <msg, len> are close friends.

Also, I have a feeling that ...

>  {
>  	int key_len = strlen(key);
>  	const char *line = msg;
>  
> -	while (line) {
> +	while (line && (len == 0 || line < msg + len)) {

... we do not want this special casing of "if !len".  By making the
caller responsible to _always_ supply the length of msg, we can lose
the conditional.

>  		const char *eol = strchrnul(line, '\n');
>  
>  		if (line == eol)
> @@ -1653,6 +1655,10 @@ const char *find_commit_header(const char *msg, const char *key, size_t *out_len
>  	return NULL;
>  }
>  
> +const char *find_commit_header(const char *msg, const char *key, size_t *out_len)
> +{
> +	return find_header_max(msg, key, 0, out_len);

I.e. find_header_mem(msg, strlen(msg), key, out_len);

> diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
> index 9f4a0b816cf..b69ead8dcda 100644
> --- a/builtin/receive-pack.c
> +++ b/builtin/receive-pack.c
> @@ -581,32 +581,19 @@ static char *prepare_push_cert_nonce(const char *path, timestamp_t stamp)
>  	return strbuf_detach(&buf, NULL);
>  }
>  
> -/*
> - * NEEDSWORK: reuse find_commit_header() from jk/commit-author-parsing
> - * after dropping "_commit" from its name and possibly moving it out
> - * of commit.c
> - */
>  static char *find_header(const char *msg, size_t len, const char *key,
>  			 const char **next_line)
>  {
> +	size_t out_len;
> +	const char *val = find_header_max(msg, key, len, &out_len);
> +
> +	if (val == NULL)
> +		return NULL;
> +
> +	if (next_line)
> +		*next_line = val + out_len + 1;
> +
> +	return xmemdupz(val, out_len);
>  }

Yup, something along that line.  Note that find_header() does make
it clear that the <msg, len> parameters form a pair.  We want to do
the same for the new helper.

Patch

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 9f4a0b816cf..b69ead8dcda 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -581,32 +581,19 @@  static char *prepare_push_cert_nonce(const char *path, timestamp_t stamp)
 	return strbuf_detach(&buf, NULL);
 }
 
-/*
- * NEEDSWORK: reuse find_commit_header() from jk/commit-author-parsing
- * after dropping "_commit" from its name and possibly moving it out
- * of commit.c
- */
 static char *find_header(const char *msg, size_t len, const char *key,
 			 const char **next_line)
 {
-	int key_len = strlen(key);
-	const char *line = msg;
-
-	while (line && line < msg + len) {
-		const char *eol = strchrnul(line, '\n');
-
-		if ((msg + len <= eol) || line == eol)
-			return NULL;
-		if (line + key_len < eol &&
-		    !memcmp(line, key, key_len) && line[key_len] == ' ') {
-			int offset = key_len + 1;
-			if (next_line)
-				*next_line = *eol ? eol + 1 : eol;
-			return xmemdupz(line + offset, (eol - line) - offset);
-		}
-		line = *eol ? eol + 1 : NULL;
-	}
-	return NULL;
+	size_t out_len;
+	const char *val = find_header_max(msg, key, len, &out_len);
+
+	if (val == NULL)
+		return NULL;
+
+	if (next_line)
+		*next_line = val + out_len + 1;
+
+	return xmemdupz(val, out_len);
 }
 
 /*
diff --git a/commit.c b/commit.c
index a348f085b2b..2ed115e04a0 100644
--- a/commit.c
+++ b/commit.c
@@ -1631,12 +1631,14 @@  struct commit_list **commit_list_append(struct commit *commit,
 	return &new_commit->next;
 }
 
-const char *find_commit_header(const char *msg, const char *key, size_t *out_len)
+const char *find_header_max(const char *msg, const char *key,
+			size_t len,
+			size_t *out_len)
 {
 	int key_len = strlen(key);
 	const char *line = msg;
 
-	while (line) {
+	while (line && (len == 0 || line < msg + len)) {
 		const char *eol = strchrnul(line, '\n');
 
 		if (line == eol)
@@ -1653,6 +1655,10 @@  const char *find_commit_header(const char *msg, const char *key, size_t *out_len
 	return NULL;
 }
 
+const char *find_commit_header(const char *msg, const char *key, size_t *out_len)
+{
+	return find_header_max(msg, key, 0, out_len);
+}
 /*
  * Inspect the given string and determine the true "end" of the log message, in
  * order to find where to put a new Signed-off-by trailer.  Ignored are
diff --git a/commit.h b/commit.h
index 3ea32766bcb..41ec89af5b5 100644
--- a/commit.h
+++ b/commit.h
@@ -290,12 +290,17 @@  void free_commit_extra_headers(struct commit_extra_header *extra);
 
 /*
  * Search the commit object contents given by "msg" for the header "key".
+ * Reads up to "len" bytes of "msg".
  * Returns a pointer to the start of the header contents, or NULL. The length
  * of the header, up to the first newline, is returned via out_len.
  *
  * Note that some headers (like mergetag) may be multi-line. It is the caller's
  * responsibility to parse further in this case!
  */
+const char *find_header_max(const char *msg, const char *key,
+			size_t len,
+			size_t *out_len);
+
 const char *find_commit_header(const char *msg, const char *key,
 			       size_t *out_len);