clarified error conditions in digest.update(): error if the vmod_priv

object is NULL. If the blob's length is 0 or its priv pointer is NULL,
pass over it silently -- not an error, but no need to call the hash
update.

src/tests/md5.vtc

@@ -575,7 +575,7 @@ varnish v1 -vcl {
 	backend b { .host = "${bad_ip}"; }
 
 	sub vcl_init {
-		new a = blobcode.blob(IDENTITY, "a");
+		new empty = blobcode.blob(IDENTITY, "");
 		new d1 = blobdigest.digest(MD5);
 	}
 
@@ -584,12 +584,12 @@ varnish v1 -vcl {
 	}
 
 	sub vcl_synth {
-		if (!d1.update(a.get())) {
+		if (!d1.update(empty.get())) {
 			set resp.status = 500;
 			return(deliver);
 		}
-		set resp.http.a = blobcode.encode(HEXUC, d1.final());
-		if (!d1.update(a.get())) {
+		set resp.http.empty = blobcode.encode(HEXUC, d1.final());
+		if (!d1.update(empty.get())) {
 			set resp.status = 500;
 			return(deliver);
 		}
@@ -600,7 +600,7 @@ client c1 {
 	txreq
 	rxresp
 	expect resp.status == 500
-	expect resp.http.a == "0CC175B9C0F1B6A831C399E269772661"
+	expect resp.http.empty == "D41D8CD98F00B204E9800998ECF8427E"
 } -run
 
 logexpect l1 -v v1 -d 1 -g vxid -q "VCL_Error" {

src/vmod_blobdigest.c

@@ -327,13 +327,14 @@ vmod_digest_update(VRT_CTX, struct vmod_blobdigest_digest *h, VCL_BLOB b)
 		return 0;
 	}
 
-	/* XXX: is b == NULL an error? */
-	/* XXX: no error calling .update() after .final() in these cases */
-	if (b == NULL || b->len == 0 || b->priv == NULL)
-		return 1;
+	if (b == NULL) {
+		VERR(ctx, "null BLOB passed to %s.update()", h->vcl_name);
+		return 0;
+	}
 
 	if (INIT_FINI(ctx)) {
-		update(h->hash, &h->ctx, b->priv, b->len);
+		if (b->len > 0 && b->priv != NULL)
+			update(h->hash, &h->ctx, b->priv, b->len);
 		return 1;
 	}
 
@@ -343,7 +344,8 @@ vmod_digest_update(VRT_CTX, struct vmod_blobdigest_digest *h, VCL_BLOB b)
 		VERR(ctx, "already finalized in %s.update()", h->vcl_name);
 		return 0;
 	}
-	update(h->hash, &task->ctx, b->priv, b->len);
+	if (b->len > 0 && b->priv != NULL)
+		update(h->hash, &task->ctx, b->priv, b->len);
 	return 1;
 }