json_escape: add fast-path for when we don't need to escape.

[ccan] / ccan / json_escape / json_escape.c

diff --git a/ccan/json_escape/json_escape.c b/ccan/json_escape/json_escape.c
index d344940de0a5d934da693b959857326da194fb55..ed4bfab944504a48db7c9e1b4cdd2825d8863bf2 100644 (file)
--- a/ccan/json_escape/json_escape.c
+++ b/ccan/json_escape/json_escape.c
@@ -19,6 +19,18 @@ bool json_escape_eq(const struct json_escape *a, const struct json_escape *b)
        return streq(a->s, b->s);
 }
 
+bool json_escape_needed(const char *str, size_t len)
+{
+       for (size_t i = 0; i < len; i++) {
+               if ((unsigned)str[i] < ' '
+                   || str[i] == 127
+                   || str[i] == '"'
+                   || str[i] == '\\')
+                       return true;
+       }
+       return false;
+}
+
 static struct json_escape *escape(const tal_t *ctx,
                                  const char *str TAKES,
                                  size_t len,
@@ -27,6 +39,16 @@ static struct json_escape *escape(const tal_t *ctx,
        struct json_escape *esc;
        size_t i, n;
 
+       /* Fast path: can steal, and nothing to escape. */
+       if (is_taken(str)
+           && tal_count(str) > len
+           && !json_escape_needed(str, len)) {
+               taken(str);
+               esc = (struct json_escape *)tal_steal(ctx, str);
+               esc->s[len] = '\0';
+               return esc;
+       }
+
        /* Worst case: all \uXXXX */
        esc = (struct json_escape *)tal_arr(ctx, char, len * 6 + 1);