strbuf: add strbuf_add*_urlencode

This just follows the rfc3986 rules for percent-encoding
url data into a strbuf.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

strbuf.c

@@ -397,3 +397,40 @@ int strbuf_read_file(struct strbuf *sb, const char *path, size_t hint)
 
 	return len;
 }
+
+static int is_rfc3986_reserved(char ch)
+{
+	switch (ch) {
+		case '!': case '*': case '\'': case '(': case ')': case ';':
+		case ':': case '@': case '&': case '=': case '+': case '$':
+		case ',': case '/': case '?': case '#': case '[': case ']':
+			return 1;
+	}
+	return 0;
+}
+
+static int is_rfc3986_unreserved(char ch)
+{
+	return isalnum(ch) ||
+		ch == '-' || ch == '_' || ch == '.' || ch == '~';
+}
+
+void strbuf_add_urlencode(struct strbuf *sb, const char *s, size_t len,
+			  int reserved)
+{
+	strbuf_grow(sb, len);
+	while (len--) {
+		char ch = *s++;
+		if (is_rfc3986_unreserved(ch) ||
+		    (!reserved && is_rfc3986_reserved(ch)))
+			strbuf_addch(sb, ch);
+		else
+			strbuf_addf(sb, "%%%02x", ch);
+	}
+}
+
+void strbuf_addstr_urlencode(struct strbuf *sb, const char *s,
+			     int reserved)
+{
+	strbuf_add_urlencode(sb, s, strlen(s), reserved);
+}

strbuf.h

@@ -115,4 +115,9 @@ extern int launch_editor(const char *path, struct strbuf *buffer, const char *co
 extern int strbuf_branchname(struct strbuf *sb, const char *name);
 extern int strbuf_check_branch_ref(struct strbuf *sb, const char *name);
 
+extern void strbuf_add_urlencode(struct strbuf *, const char *, size_t,
+				 int reserved);
+extern void strbuf_addstr_urlencode(struct strbuf *, const char *,
+				    int reserved);
+
 #endif /* STRBUF_H */