The optimization in trancode() to return the concatenated STRING_LIST

when the encoding and decoding are the same is only allowed when the
decoding was legal. Also, use a VRT function to concatenate the
STRING_LIST into workspace (rather than rolling our own).

src/tests/xcode.vtc

@@ -56,6 +56,14 @@ varnish v1 -vcl+backend {
 						   "+/+/" + req.http.foo);
 	  set resp.http.badpad = convert.transcode(BASE64URLNOPAD, IDENTITY,
 						   "TWFu" + req.http.foo);
+	  set resp.http.badhex2hex = convert.transcode(HEX, HEX, "abcdefg");
+	  set resp.http.bad64264 = convert.transcode(BASE64, BASE64,
+						     "_-_-" + req.http.foo);
+	  set resp.http.badurl2url = convert.transcode(BASE64URL, BASE64URL,
+						       "/+/+" + req.http.foo);
+	  set resp.http.badpad2pad
+	    = convert.transcode(BASE64URLNOPAD, BASE64URLNOPAD,
+				"Zm9v" + req.http.foo);
 	}
 } -start
 
@@ -73,9 +81,13 @@ client c1 {
 	expect resp.http.b64url2b64url == "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
 	expect resp.http.b64urlnopad2b64urlnopad == "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
 	expect resp.http.badhex == ""
+	expect resp.http.badhex2hex == ""
 	expect resp.http.bad64 == ""
+	expect resp.http.bad64264 == ""
 	expect resp.http.badurl == ""
+	expect resp.http.badurl2url == ""
 	expect resp.http.badpad == ""
+	expect resp.http.badpad2pad == ""
 }
 
 client c1 -run
@@ -89,6 +101,14 @@ logexpect l1 -v v1 -d 1 -g vxid -q "VCL_Error" {
         expect * = VCL_Error "^vmod convert error: cannot decode, illegal encoding beginning with \"\+/\+/\"$"
 #"
         expect * = VCL_Error "^vmod convert error: cannot decode, illegal encoding beginning with \"TWFu\"$"
+#"
+        expect * = VCL_Error "^vmod convert error: cannot decode, illegal encoding beginning with \"abcdefg\"$"
+#"
+        expect * = VCL_Error "^vmod convert error: cannot decode, illegal encoding beginning with \"_-_-\"$"
+#"
+        expect * = VCL_Error "^vmod convert error: cannot decode, illegal encoding beginning with \"/\+/\+\"$"
+#"
+        expect * = VCL_Error "^vmod convert error: cannot decode, illegal encoding beginning with \"Zm9v\"$"
 #"
 	expect * = End
 } -start

src/vmod_convert.c

@@ -71,43 +71,6 @@ static const struct vmod_priv const null_blob[1] =
 	}
 };
 
-static inline VCL_STRING
-concat_va(struct ws *ws, const char *p, va_list ap)
-{
-	const char *next;
-	struct wb_s wb;
-
-	CHECK_OBJ_NOTNULL(ws, WS_MAGIC);
-	if (p == vrt_magic_string_end)
-		return "";
-
-	SKIP_EMPTY(next, ap);
-
-	if (next == vrt_magic_string_end) {
-		if ( p == NULL || *p == '\0')
-			return "";
-		else
-			return p;
-	}
-
-	if (!wb_create(ws, &wb) || !wb_append(&wb, p, -1))
-		return NULL;
-
-	do {
-		if (!wb_append(&wb, next, -1)) {
-			wb_reset(&wb);
-			return NULL;
-		}
-		SKIP_EMPTY(next, ap);
-	} while (next != vrt_magic_string_end);
-
-	if (wb_len(&wb) == 0) {
-		wb_reset(&wb);
-		return "";
-	}
-	return wb_finish(&wb, NULL);
-}
-
 static inline size_t
 decode_l_va(enum encoding dec, const char * const p, va_list ap)
 {
@@ -318,6 +281,7 @@ vmod_decode(VRT_CTX, VCL_ENUM decs, const char *p, ...) {
 		ILLEGAL(ctx, "decode()");
 		return NULL;
 	}
+	CHECK_OBJ_NOTNULL(ctx->ws, WS_MAGIC);
 
 	snap = WS_Snapshot(ctx->ws);
 	if ((b = WS_Alloc(ctx->ws, sizeof(struct vmod_priv))) == NULL) {
@@ -368,6 +332,7 @@ vmod_encode(VRT_CTX, VCL_ENUM encs, VCL_BLOB b) {
 	if (b == NULL)
 		return NULL;
 
+	CHECK_OBJ_NOTNULL(ctx->ws, WS_MAGIC);
 	if (wb_create(ctx->ws, &wb) == NULL) {
 		ERRNOMEM(ctx, "cannot encode");
 		return NULL;
@@ -401,18 +366,7 @@ vmod_transcode(VRT_CTX, VCL_ENUM decs, VCL_ENUM encs, const char *p, ...) {
 		ILLEGAL(ctx, "transcode()");
 		return NULL;
 	}
-
-	/*
-	 * If the encoding and decoding are the same, just return the
-	 * concatenated string.
-	 * XXX: Doesn't reject illegal decodings.
-	 */
-	if (enc == dec) {
-		va_start(ap, p);
-		VCL_STRING s = concat_va(ctx->ws, p, ap);
-		va_end(ap);
-		return s;
-	}
+	CHECK_OBJ_NOTNULL(ctx->ws, WS_MAGIC);
 
 	/* Allocate space for the decoded blob on the stack */
 	va_start(ap, p);
@@ -432,6 +386,17 @@ vmod_transcode(VRT_CTX, VCL_ENUM decs, VCL_ENUM encs, const char *p, ...) {
 		return NULL;
 	}
 
+	/*
+	 * If the encoding and decoding are the same, and the decoding was
+	 * legal, just return the concatenated string.
+	 */
+	if (enc == dec) {
+		va_start(ap, p);
+		VCL_STRING s = VRT_String(ctx->ws, NULL, p, ap);
+		va_end(ap);
+		return s;
+	}
+
 	if (wb_create(ctx->ws, &wb) == NULL) {
 		ERRNOMEM(ctx, "cannot encode after decode");
 		return NULL;