Use $Restrict

src/tests/test01.vtc

@@ -15,9 +15,7 @@ varnish v1 -vcl+backend {
 	}
 
 	sub vcl_recv {
-		# wrong, triggers error
-		blobsynth.synthetic(gif.get());
-		return(synth(200));
+		return (synth(200));
 	}
 
 	sub vcl_synth {
@@ -27,11 +25,6 @@ varnish v1 -vcl+backend {
 	}
 } -start
 
-logexpect l1 -v v1 -g raw -d 1 {
-	expect    0 0	CLI		{^Rd vcl.load}
-	expect 1001 *	VCL_Error	{^blobsynth.synthetic.. only valid in}
-} -start
-
 client c1 {
 	txreq -url "/"
 	rxresp
@@ -40,4 +33,18 @@ client c1 {
 
 client c1 -run
 
-logexpect l1 -wait
+varnish v1 -errvcl {Not available in subroutine 'vcl_recv'} {
+	import blob;
+	import ${vmod_blobsynth};
+
+	sub vcl_init {
+		new gif = blob.blob(BASE64,
+			"R0lGODlhAQABAPAAAAAAAAAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==");
+	}
+
+	sub vcl_recv {
+		# wrong, triggers error
+		blobsynth.synthetic(gif.get());
+		return(synth(200));
+	}
+}
\ No newline at end of file

src/vmod_blobsynth.c

@@ -16,12 +16,7 @@ vmod_synthetic(VRT_CTX, VCL_BLOB body)
 {
 	struct vsb *vsb;
 
-	if ((ctx->method & (VCL_MET_SYNTH | VCL_MET_BACKEND_ERROR)) == 0) {
-		VSLb(ctx->vsl, SLT_VCL_Error,
-		    "blobsynth.synthetic() only valid in vcl_synth{}"
-		    " and vcl_backend_error{}");
-		return;
-	}
+	AN(ctx->method & (VCL_MET_SYNTH | VCL_MET_BACKEND_ERROR));
 
 	CAST_OBJ_NOTNULL(vsb, ctx->specific, VSB_MAGIC);
 

src/vmod_blobsynth.vcc

@@ -14,6 +14,4 @@ $Function VOID synthetic(BLOB blob)
 Create a synthetic response from *blob*, equivalent to the
 ``synthetic()`` built-in function except for the argument type.
 
-Needs to be called from ``vcl_synth`` or
-``vcl_backend_error``. Otherwise, the function has no effect other
-than logging a ``VCL_Error`` message to VSL.
+$Restrict vcl_synth vcl_backend_error