Fix unescape error detection and make it tolerate quotes

src/vmod_j.c

@@ -519,14 +519,12 @@ vmod_unescape(VRT_CTX, VCL_STRING p, VCL_STRING fallback)
 
 	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
 
-	if (*p != '"' || p[strlen(p) - 1] != '"') {
-		fail(ctx, fallback, "j.unescape() argument missing quotes");
-		return (fallback);
-	}
-	p++;
+	if (*p == '"')
+		p++;
 
 	WS_VSB_new(vsb, ctx->ws);
-	if (vsbjunquot(vsb, p, &err) && err != NULL) {
+	if (! vsbjunquot(vsb, p, &err) && err != NULL) {
+		WS_Release(ctx->ws, 0);
 		fail(ctx, fallback, "j.unescape() error at: ...%.10s", err);
 		return (fallback);
 	}
@@ -540,7 +538,7 @@ vmod_unescape(VRT_CTX, VCL_STRING p, VCL_STRING fallback)
 		return (r);
 
 	l--;
-	assert(r[l] == '"');
-	r[l] = '\0';
+	if (r[l] == '"')
+		r[l] = '\0';
 	return (r);
 }

src/vmod_j.man.rst

@@ -451,6 +451,9 @@ STRING unescape(STRING, STRING fallback=0)
 
 Utility function to decode JSON strings into UTF-8.
 
+The string may contain surrounding quotes, which are silently removed,
+even if only left *or* right quotes are present.
+
 If decoding fails and *fallback* is provided, the error is logged with
 tag ``Error`` and *fallback* is returned. Otherwise, the VCL is failed.
 

src/vmod_j.vcc

@@ -385,6 +385,9 @@ $Function STRING unescape(STRING, STRING fallback=0)
 
 Utility function to decode JSON strings into UTF-8.
 
+The string may contain surrounding quotes, which are silently removed,
+even if only left *or* right quotes are present.
+
 If decoding fails and *fallback* is provided, the error is logged with
 tag ``Error`` and *fallback* is returned. Otherwise, the VCL is failed.
 

src/vtc/vmod_j.vtc

@@ -110,7 +110,7 @@ varnish v1 -vcl {
 		set resp.http.o4 = j.object(j.string("A") + j.object(j.nil()));
 
 		set resp.http.unok = j.unescape({""abc""});
-		set resp.http.unno = j.unescape("", j.null());
+		set resp.http.unno = j.unescape("\udc00", j.null());
 
 		set resp.body = "";
 		return (deliver);