Re: [PATCH v2] strbuf: add and use strbuf_insertstr()

[Jeff King <peff@peff.net>]

On Sun, Feb 09, 2020 at 12:36:22PM -0500, Eric Sunshine wrote:

> On Sun, Feb 9, 2020 at 8:45 AM René Scharfe <l.s.r@web.de> wrote:
> > Add a function for inserting a C string into a strbuf.  Use it
> > throughout the source to get rid of magic string length constants and
> > explicit strlen() calls.
> >
> > Like strbuf_addstr(), implement it as an inline function to avoid the
> > implicit strlen() calls to cause runtime overhead.
> >
> > Signed-off-by: René Scharfe <l.s.r@web.de>
> > ---
> > diff --git a/mailinfo.c b/mailinfo.c
> > @@ -570,7 +570,7 @@ static int check_header(struct mailinfo *mi,
> >                 len = strlen("Content-Type: ");
> >                 strbuf_add(&sb, line->buf + len, line->len - len);
> >                 decode_header(mi, &sb);
> > -               strbuf_insert(&sb, 0, "Content-Type: ", len);
> > +               strbuf_insertstr(&sb, 0, "Content-Type: ");
> >                 handle_content_type(mi, &sb);
> 
> Meh. We've already computed the length of "Content-Type: " a few lines
> earlier, so taking advantage of that value when inserting the string
> literal is perfectly sensible. Thus, I'm not convinced that this
> change is an improvement.

I had a similar thought. I kind of wonder if all of these "len" bits
(and their repeated strings) could go away if cmp_header() just used
skip_iprefix() under the hood and had a pointer out-parameter.

Something like the (largely untested) patch below. That would also make
it easy to support arbitrary amounts of whitespace after the header,
which I think are allowed by the standard (whereas now we'd parse
"Content-type:    text/plain" as "    text/plain", which is silly).

Worth doing?

---
diff --git a/mailinfo.c b/mailinfo.c
index b395adbdf2..bbb5b429f8 100644
--- a/mailinfo.c
+++ b/mailinfo.c
@@ -346,11 +346,16 @@ static const char *header[MAX_HDR_PARSED] = {
 	"From","Subject","Date",
 };
 
-static inline int cmp_header(const struct strbuf *line, const char *hdr)
+static inline int cmp_header(const struct strbuf *line, const char *hdr,
+			     const char **outval)
 {
-	int len = strlen(hdr);
-	return !strncasecmp(line->buf, hdr, len) && line->len > len &&
-			line->buf[len] == ':' && isspace(line->buf[len + 1]);
+	const char *val;
+	if (!skip_iprefix(line->buf, hdr, &val) ||
+	    *val++ != ':' ||
+	    !isspace(*val++))
+		return 0;
+	*outval = val;
+	return 1;
 }
 
 static int is_format_patch_separator(const char *line, int len)
@@ -547,17 +552,17 @@ static int check_header(struct mailinfo *mi,
 			const struct strbuf *line,
 			struct strbuf *hdr_data[], int overwrite)
 {
-	int i, ret = 0, len;
+	int i, ret = 0;
 	struct strbuf sb = STRBUF_INIT;
+	const char *val;
 
 	/* search for the interesting parts */
 	for (i = 0; header[i]; i++) {
-		int len = strlen(header[i]);
-		if ((!hdr_data[i] || overwrite) && cmp_header(line, header[i])) {
+		if ((!hdr_data[i] || overwrite) && cmp_header(line, header[i], &val)) {
 			/* Unwrap inline B and Q encoding, and optionally
 			 * normalize the meta information to utf8.
 			 */
-			strbuf_add(&sb, line->buf + len + 2, line->len - len - 2);
+			strbuf_addstr(&sb, val);
 			decode_header(mi, &sb);
 			handle_header(&hdr_data[i], &sb);
 			ret = 1;
@@ -566,26 +571,22 @@ static int check_header(struct mailinfo *mi,
 	}
 
 	/* Content stuff */
-	if (cmp_header(line, "Content-Type")) {
-		len = strlen("Content-Type: ");
-		strbuf_add(&sb, line->buf + len, line->len - len);
+	if (cmp_header(line, "Content-Type", &val)) {
+		strbuf_addstr(&sb, val);
 		decode_header(mi, &sb);
-		strbuf_insert(&sb, 0, "Content-Type: ", len);
 		handle_content_type(mi, &sb);
 		ret = 1;
 		goto check_header_out;
 	}
-	if (cmp_header(line, "Content-Transfer-Encoding")) {
-		len = strlen("Content-Transfer-Encoding: ");
-		strbuf_add(&sb, line->buf + len, line->len - len);
+	if (cmp_header(line, "Content-Transfer-Encoding", &val)) {
+		strbuf_addstr(&sb, val);
 		decode_header(mi, &sb);
 		handle_content_transfer_encoding(mi, &sb);
 		ret = 1;
 		goto check_header_out;
 	}
-	if (cmp_header(line, "Message-Id")) {
-		len = strlen("Message-Id: ");
-		strbuf_add(&sb, line->buf + len, line->len - len);
+	if (cmp_header(line, "Message-Id", &val)) {
+		strbuf_addstr(&sb, val);
 		decode_header(mi, &sb);
 		if (mi->add_message_id)
 			mi->message_id = strbuf_detach(&sb, NULL);
@@ -607,8 +608,9 @@ static int is_inbody_header(const struct mailinfo *mi,
 			    const struct strbuf *line)
 {
 	int i;
+	const char *val;
 	for (i = 0; header[i]; i++)
-		if (!mi->s_hdr_data[i] && cmp_header(line, header[i]))
+		if (!mi->s_hdr_data[i] && cmp_header(line, header[i], &val))
 			return 1;
 	return 0;
 }