Fix behavior for empty file with .done(url)

If we set a done url (which is sent in Content-Location or Location for
a 301) with an empty file (POST with Upload-Length: 0), we would trigger
the two removed assertions. They are bad because a zero sized upload
is legit and can have a Content-Location.

src/tus_response.c

@@ -123,8 +123,6 @@ tus_response(VRT_CTX, const struct VPFX(tus_server) *tussrv,
 	http_Unset(r, hdr_cloc);
 
 	if (fdisk != NULL && fdisk->location_length > 0) {
-		/* cannot happen for creation */
-		assert(resp->status != 201);
 		if (fdisk->location[0] == '/' && fdisk->location[1] != '/') {
 			bprintf(buf, "%s%s", resp->schemeauth, fdisk->location);
 			loc = buf;
@@ -181,7 +179,6 @@ tus_response(VRT_CTX, const struct VPFX(tus_server) *tussrv,
 		VTIM_format(fdisk->upload_expires, t);
 		http_ForceHeader(r, hdr_exp, t);
 		if (resp->status == 201) {
-			AZ(fdisk->location_length);
 			AN(resp->schemeauth);
 			http_PrintfHeader(r, "Location: %s%s", resp->schemeauth,
 			    fdisk->url_path);

src/vtc/done.vtc

 varnishtest "test vmod-tus set done redirect"
 
 server s1 {
+	rxreq
+	txresp
+	expect req.method == PUT
+	expect req.bodylen == 0
+} -start
+
+server s2 {
 	rxreq
 	txresp
 	expect req.method == PUT
@@ -15,8 +22,11 @@ varnish v1 -vcl+backend {
 		basedir="/tmp/tus", max = 4MB);
 	}
 	sub vcl_backend_fetch {
-		if (bereq.url ~ "^/id") {
+		if (bereq.url ~ "^/id-empty") {
 			set bereq.backend = s1;
+		} else
+		if (bereq.url ~ "^/id") {
+			set bereq.backend = s2;
 		} else {
 			return (abandon);
 		}
@@ -35,8 +45,8 @@ varnish v1 -vcl+backend {
 	    }
 	}
 	sub vcl_deliver {
-	    tmp.deliver();
 	    tmp.done(req.url);
+	    tmp.deliver();
 	}
 } -start
 
@@ -94,4 +104,54 @@ client c1 {
 	expect resp.status == 301
 	expect resp.http.Location == "http://localhost/id"
 
-} -run
+} -start
+
+# empty file
+client c2 {
+	txreq -method "DELETE" -url "/id-empty" \
+		-hdr "Tus-Resumable: 1.0.0"
+	rxresp
+
+	txreq	-method POST \
+		-hdr "Upload-Length: 0" \
+		-hdr "Tus-Resumable: 1.0.0" \
+		-hdr "Content-Type: application/offset+octet-stream" \
+		-hdr "Id: id-empty"
+
+	rxresp
+	expect resp.status == 201
+	expect resp.http.Tus-Resumable == "1.0.0"
+	expect resp.http.Tus-Version == "1.0.0"
+	expect resp.http.Tus-Extension == "creation,creation-with-upload,expiration,termination,concatenation"
+	expect resp.http.Tus-Checksum-Algorithm == <undef>
+	expect resp.http.Tus-Max-Size == 4194304
+	expect resp.http.Upload-Offset == 0
+	expect resp.http.Upload-Length == 0
+	expect resp.http.Upload-Expires ~ "GMT$"
+	expect resp.http.Location == "http://localhost/id-empty"
+
+	# even for a done file, HEAD will return the correct metadata
+	txreq	-method HEAD -url "/id-empty" \
+		-hdr "Tus-Resumable: 1.0.0"
+	rxresp
+	expect resp.status == 200
+	expect resp.http.Tus-Resumable == "1.0.0"
+	expect resp.http.Tus-Version == "1.0.0"
+	expect resp.http.Tus-Extension == "creation,creation-with-upload,expiration,termination,concatenation"
+	expect resp.http.Tus-Checksum-Algorithm == <undef>
+	expect resp.http.Tus-Max-Size == 4194304
+	expect resp.http.Upload-Offset == 0
+	expect resp.http.Upload-Length == 0
+	expect resp.http.Upload-Expires ~ "GMT$"
+	expect resp.http.Content-Location == "http://localhost/id-empty"
+
+	txreq   -url "/id-empty" \
+		-hdr "Tus-Resumable: 1.0.0"
+	rxresp
+	expect resp.status == 301
+	expect resp.http.Location == "http://localhost/id-empty"
+
+} -start
+
+client c1 -wait
+client c2 -wait