json: make json_add_string do partial escapes.

This is useful when we log a JSON-escaped string, so we don't double-escape.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

cli/Makefile

@@ -4,6 +4,7 @@ LIGHTNING_CLI_OBJS := $(LIGHTNING_CLI_SRC:.c=.o)
 LIGHTNING_CLI_COMMON_OBJS :=			\
 	common/configdir.o			\
 	common/json.o				\
+	common/json_escaped.o			\
 	common/version.o
 
 lightning-cli-all: cli/lightning-cli

cli/test/Makefile

@@ -12,6 +12,7 @@ CLI_TEST_COMMON_OBJS :=				\
 	common/daemon_conn.o			\
 	common/htlc_state.o			\
 	common/json.o				\
+	common/json_escaped.o			\
 	common/pseudorand.o			\
 	common/memleak.o			\
 	common/msg_queue.o			\

common/json.c

@@ -409,18 +409,11 @@ void json_add_literal(struct json_result *result, const char *fieldname,
 
 void json_add_string(struct json_result *result, const char *fieldname, const char *value)
 {
-	char *escaped = tal_strdup(result, value);
-	size_t i;
+	struct json_escaped *esc = json_partial_escape(NULL, value);
 
 	json_start_member(result, fieldname);
-	for (i = 0; escaped[i]; i++) {
-		/* Replace any funny business.  Better safe than accurate! */
-		if (escaped[i] == '\\'
-		    || escaped[i] == '"'
-		    || !cisprint(escaped[i]))
-			escaped[i] = '?';
-	}
-	result_append_fmt(result, "\"%s\"", escaped);
+	result_append_fmt(result, "\"%s\"", esc->s);
+	tal_free(esc);
 }
 
 void json_add_bool(struct json_result *result, const char *fieldname, bool value)

common/json.h

@@ -76,7 +76,7 @@ void json_object_end(struct json_result *ptr);
 struct json_result *new_json_result(const tal_t *ctx);
 
 /* '"fieldname" : "value"' or '"value"' if fieldname is NULL.  Turns
- * any unusual chars into ?.
+ * any non-printable chars into JSON escapes, but leaves existing escapes alone.
  */
 void json_add_string(struct json_result *result, const char *fieldname, const char *value);
 

common/json_escaped.c

@@ -35,7 +35,9 @@ bool json_escaped_eq(const struct json_escaped *a,
 	return streq(a->s, b->s);
 }
 
-struct json_escaped *json_escape(const tal_t *ctx, const char *str TAKES)
+static struct json_escaped *escape(const tal_t *ctx,
+				   const char *str TAKES,
+				   bool partial)
 {
 	struct json_escaped *esc;
 	size_t i, n;
@@ -62,6 +64,31 @@ struct json_escaped *json_escape(const tal_t *ctx, const char *str TAKES)
 			escape = 'r';
 			break;
 		case '\\':
+			if (partial) {
+				/* Don't double-escape standard escapes. */
+				if (str[i+1] == 'n'
+				    || str[i+1] == 'b'
+				    || str[i+1] == 'f'
+				    || str[i+1] == 't'
+				    || str[i+1] == 'r'
+				    || str[i+1] == '/'
+				    || str[i+1] == '\\'
+				    || str[i+1] == '"') {
+					escape = str[i+1];
+					i++;
+					break;
+				}
+				if (str[i+1] == 'u'
+				    && cisxdigit(str[i+2])
+				    && cisxdigit(str[i+3])
+				    && cisxdigit(str[i+4])
+				    && cisxdigit(str[i+5])) {
+					    memcpy(esc->s + n, str + i, 6);
+					    n += 5;
+					    i += 5;
+					    continue;
+				}
+			} /* fall thru */
 		case '"':
 			escape = str[i];
 			break;
@@ -85,6 +112,16 @@ struct json_escaped *json_escape(const tal_t *ctx, const char *str TAKES)
 	return esc;
 }
 
+struct json_escaped *json_partial_escape(const tal_t *ctx, const char *str TAKES)
+{
+	return escape(ctx, str, true);
+}
+
+struct json_escaped *json_escape(const tal_t *ctx, const char *str TAKES)
+{
+	return escape(ctx, str, false);
+}
+
 /* By policy, we don't handle \u.  Use UTF-8. */
 const char *json_escaped_unescape(const tal_t *ctx,
 				  const struct json_escaped *esc)

common/json_escaped.h

@@ -12,6 +12,10 @@ struct json_escaped {
 /* @str be a valid UTF-8 string */
 struct json_escaped *json_escape(const tal_t *ctx, const char *str TAKES);
 
+/* @str is a valid UTF-8 string which may already contain escapes. */
+struct json_escaped *json_partial_escape(const tal_t *ctx,
+					 const char *str TAKES);
+
 /* Extract a JSON-escaped string. */
 struct json_escaped *json_tok_escaped_string(const tal_t *ctx,
 					     const char *buffer,

common/test/run-json.c

@@ -67,12 +67,13 @@ static int test_json_filter(void)
 	x = json_get_member(str, toks, "x");
 	assert(x);
 	assert(x->type == JSMN_STRING);
-	assert((x->end - x->start) == 255);
+
+	/* There are 7 one-letter escapes, and (32-5) \uXXXX escapes. */
+	assert((x->end - x->start) == 255 + 7*1 + (32-5)*5);
+	/* No control characters. */
 	for (i = x->start; i < x->end; i++) {
-		assert(cisprint(str[i]));
-		assert(str[i] != '\\');
-		assert(str[i] != '"');
-		assert(str[i] == '?' || str[i] == badstr[i - x->start]);
+		assert((unsigned)str[i] >= ' ');
+		assert((unsigned)str[i] != 127);
 	}
 	tal_free(result);
 	return 0;
@@ -112,11 +113,44 @@ static void test_json_escape(void)
 	}
 }
 
+static void test_json_partial(void)
+{
+	const tal_t *ctx = tal(NULL, char);
+
+	assert(streq(json_partial_escape(ctx, "\\")->s, "\\\\"));
+	assert(streq(json_partial_escape(ctx, "\\\\")->s, "\\\\"));
+	assert(streq(json_partial_escape(ctx, "\\\\\\")->s, "\\\\\\\\"));
+	assert(streq(json_partial_escape(ctx, "\\\\\\\\")->s, "\\\\\\\\"));
+	assert(streq(json_partial_escape(ctx, "\\n")->s, "\\n"));
+	assert(streq(json_partial_escape(ctx, "\n")->s, "\\n"));
+	assert(streq(json_partial_escape(ctx, "\\\"")->s, "\\\""));
+	assert(streq(json_partial_escape(ctx, "\"")->s, "\\\""));
+	assert(streq(json_partial_escape(ctx, "\\t")->s, "\\t"));
+	assert(streq(json_partial_escape(ctx, "\t")->s, "\\t"));
+	assert(streq(json_partial_escape(ctx, "\\b")->s, "\\b"));
+	assert(streq(json_partial_escape(ctx, "\b")->s, "\\b"));
+	assert(streq(json_partial_escape(ctx, "\\r")->s, "\\r"));
+	assert(streq(json_partial_escape(ctx, "\r")->s, "\\r"));
+	assert(streq(json_partial_escape(ctx, "\\f")->s, "\\f"));
+	assert(streq(json_partial_escape(ctx, "\f")->s, "\\f"));
+	/* You're allowed to escape / according to json.org. */
+	assert(streq(json_partial_escape(ctx, "\\/")->s, "\\/"));
+	assert(streq(json_partial_escape(ctx, "/")->s, "/"));
+
+	assert(streq(json_partial_escape(ctx, "\\u0FFF")->s, "\\u0FFF"));
+	assert(streq(json_partial_escape(ctx, "\\u0FFFx")->s, "\\u0FFFx"));
+
+	/* Unknown escapes should be escaped. */
+	assert(streq(json_partial_escape(ctx, "\\x")->s, "\\\\x"));
+	tal_free(ctx);
+}
+
 int main(void)
 {
 	test_json_tok_bitcoin_amount();
 	test_json_filter();
 	test_json_escape();
+	test_json_partial();
 	assert(!taken_any());
 	take_cleanup();
 }