version: refactor redact_non_printables()

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 redact_non_printables() function,
as we will want to reuse it in a following patch.

For now the new redact_non_printables() function is still static as
it's only needed locally.

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 'buf' strbuf.

Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Usman Akinyemi <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: Unique-Usman

version.c

@@ -6,6 +6,20 @@
 const char git_version_string[] = GIT_VERSION;
 const char git_built_from_commit_string[] = GIT_BUILT_FROM_COMMIT;
 
+/*
+ * Trim and replace each character with ascii code below 32 or above
+ * 127 (included) using a dot '.' character.
+ * TODO: ensure consecutive non-printable characters are only replaced once
+*/
+static void redact_non_printables(struct strbuf *buf)
+{
+	strbuf_trim(buf);
+	for (size_t i = 0; i < buf->len; i++) {
+		if (buf->buf[i] <= 32 || buf->buf[i] >= 127)
+			buf->buf[i] = '.';
+	}
+}
+
 const char *git_user_agent(void)
 {
 	static const char *agent = NULL;
@@ -27,12 +41,8 @@ const char *git_user_agent_sanitized(void)
 		struct strbuf buf = STRBUF_INIT;
 
 		strbuf_addstr(&buf, git_user_agent());
-		strbuf_trim(&buf);
-		for (size_t i = 0; i < buf.len; i++) {
-			if (buf.buf[i] <= 32 || buf.buf[i] >= 127)
-				buf.buf[i] = '.';
-		}
-		agent = buf.buf;
+		redact_non_printables(&buf);
+		agent = strbuf_detach(&buf, NULL);
 	}
 
 	return agent;