version: refactor strbuf_sanitize()

The git_user_agent_sanitized() function performs some sanitizing to
avoid special characters being sent over the line and possibly messing
up with the protocol or with the parsing on the other side.

Let's extract this sanitizing into a new strbuf_sanitize() function, as
we will want to reuse it in a following patch, and let's put it into
strbuf.{c,h}.

While at it, let's also make a few small improvements:
  - use 'size_t' for 'i' instead of 'int',
  - move the declaration of 'i' inside the 'for ( ... )',
  - use strbuf_detach() to explicitly detach the string contained by
    the 'sb' strbuf.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

strbuf.c

@@ -1082,3 +1082,12 @@ void strbuf_strip_file_from_path(struct strbuf *sb)
 	char *path_sep = find_last_dir_sep(sb->buf);
 	strbuf_setlen(sb, path_sep ? path_sep - sb->buf + 1 : 0);
 }
+
+void strbuf_sanitize(struct strbuf *sb)
+{
+	strbuf_trim(sb);
+	for (size_t i = 0; i < sb->len; i++) {
+		if (sb->buf[i] <= 32 || sb->buf[i] >= 127)
+			sb->buf[i] = '.';
+	}
+}

strbuf.h

@@ -664,6 +664,13 @@ typedef int (*char_predicate)(char ch);
 void strbuf_addstr_urlencode(struct strbuf *sb, const char *name,
 			     char_predicate allow_unencoded_fn);
 
+/*
+ * Trim and replace each character with ascii code below 32 or above
+ * 127 (included) using a dot '.' character. Useful for sending
+ * capabilities.
+ */
+void strbuf_sanitize(struct strbuf *sb);
+
 __attribute__((format (printf,1,2)))
 int printf_ln(const char *fmt, ...);
 __attribute__((format (printf,2,3)))

version.c

@@ -24,15 +24,10 @@ const char *git_user_agent_sanitized(void)
 
 	if (!agent) {
 		struct strbuf buf = STRBUF_INIT;
-		int i;
 
 		strbuf_addstr(&buf, git_user_agent());
-		strbuf_trim(&buf);
-		for (i = 0; i < buf.len; i++) {
-			if (buf.buf[i] <= 32 || buf.buf[i] >= 127)
-				buf.buf[i] = '.';
-		}
-		agent = buf.buf;
+		strbuf_sanitize(&buf);
+		agent = strbuf_detach(&buf, NULL);
 	}
 
 	return agent;