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Date:   Mon, 20 Sep 2021 21:41:27 -0400
From:   Jeff King <peff@peff.net>
To:     Hamza Mahfooz <someguy@effective-light.com>
Cc:     git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>
Subject: [PATCH 1/2] grep: stop modifying buffer in strip_timestamp
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When grepping for headers in commit objects, we receive individual
lines (e.g., "author Name <email> 1234 -0000"), and then strip off the
timestamp to do our match. We do so by writing a NUL byte over the
whitespace separator, and then remembering to restore it later.

We had to do it this way when this was added back in a4d7d2c6db (log
--author/--committer: really match only with name part, 2008-09-04),
because we fed the result directly to regexec(), which expects a
NUL-terminated string. But since b7d36ffca0 (regex: use regexec_buf(),
2016-09-21), we have a function which can match on part of a buffer.

So instead of modifying the string, we can instead just move the "eol"
pointer, and the rest of the code will do the right thing. This will let
the next patch make more use of "const" in grep functions.

Signed-off-by: Jeff King <peff@peff.net>
---
I think this is fairly safe. It would fail subtly if somebody _did_ rely
on the NUL, but we just call into patmatch(), which calls functions
which handle the length-delimited buffer.

 grep.c | 18 ++++--------------
 1 file changed, 4 insertions(+), 14 deletions(-)

diff --git a/grep.c b/grep.c
index 35708ce973..3b372ec29d 100644
--- a/grep.c
+++ b/grep.c
@@ -922,20 +922,16 @@ static int patmatch(struct grep_pat *p, char *line, char *eol,
 	return hit;
 }
 
-static int strip_timestamp(char *bol, char **eol_p)
+static void strip_timestamp(char *bol, char **eol_p)
 {
 	char *eol = *eol_p;
-	int ch;
 
 	while (bol < --eol) {
 		if (*eol != '>')
 			continue;
 		*eol_p = ++eol;
-		ch = *eol;
-		*eol = '\0';
-		return ch;
+		break;
 	}
-	return 0;
 }
 
 static struct {
@@ -952,7 +948,6 @@ static int match_one_pattern(struct grep_pat *p, char *bol, char *eol,
 			     regmatch_t *pmatch, int eflags)
 {
 	int hit = 0;
-	int saved_ch = 0;
 	const char *start = bol;
 
 	if ((p->token != GREP_PATTERN) &&
@@ -968,7 +963,7 @@ static int match_one_pattern(struct grep_pat *p, char *bol, char *eol,
 		switch (p->field) {
 		case GREP_HEADER_AUTHOR:
 		case GREP_HEADER_COMMITTER:
-			saved_ch = strip_timestamp(bol, &eol);
+			strip_timestamp(bol, &eol);
 			if (eol == end)
 				goto again;
 			break;
@@ -981,7 +976,7 @@ static int match_one_pattern(struct grep_pat *p, char *bol, char *eol,
 		len = header_field[p->field].len;
 
 		if (strncmp(bol, field, len))
-			goto restore;
+			return 0;
 
 		bol += len;
 	}
@@ -1035,11 +1030,6 @@ static int match_one_pattern(struct grep_pat *p, char *bol, char *eol,
 		pmatch[0].rm_eo += bol - start;
 	}
 
-restore:
-	if (p->token == GREP_PATTERN_HEAD && saved_ch)
-		*eol = saved_ch;
-
-
 	return hit;
 }
 
-- 
2.33.0.1023.gc687d0d3c8