patch-id.c: use strbuf instead of a fixed buffer

get_one_patchid() uses a rather dumb heuristic to determine if the
passed buffer is part of the next commit. Whenever the first 40 bytes
are a valid hexadecimal sha1 representation, get_one_patchid() returns
next_sha1.

Once the current line is longer than the fixed buffer, this will break
(provided the additional bytes make a valid hexadecimal sha1). As a result
patch-id returns incorrect results. Instead, use strbuf and read one line
at a time.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Michael Schubert <mschub@elegosoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/patch-id.c

@@ -56,13 +56,13 @@ static int scan_hunk_header(const char *p, int *p_before, int *p_after)
 	return 1;
 }
 
-static int get_one_patchid(unsigned char *next_sha1, git_SHA_CTX *ctx)
+static int get_one_patchid(unsigned char *next_sha1, git_SHA_CTX *ctx, struct strbuf *line_buf)
 {
-	static char line[1000];
 	int patchlen = 0, found_next = 0;
 	int before = -1, after = -1;
 
-	while (fgets(line, sizeof(line), stdin) != NULL) {
+	while (strbuf_getwholeline(line_buf, stdin, '\n') != EOF) {
+		char *line = line_buf->buf;
 		char *p = line;
 		int len;
 
@@ -133,14 +133,16 @@ static void generate_id_list(void)
 	unsigned char sha1[20], n[20];
 	git_SHA_CTX ctx;
 	int patchlen;
+	struct strbuf line_buf = STRBUF_INIT;
 
 	git_SHA1_Init(&ctx);
 	hashclr(sha1);
 	while (!feof(stdin)) {
-		patchlen = get_one_patchid(n, &ctx);
+		patchlen = get_one_patchid(n, &ctx, &line_buf);
 		flush_current_id(patchlen, sha1, &ctx);
 		hashcpy(sha1, n);
 	}
+	strbuf_release(&line_buf);
 }
 
 static const char patch_id_usage[] = "git patch-id < patch";