Fix handling of zero-size PATCH on an already completed upload

If .done() is _not_ used, we trigger another upload to the server - not
clear if this is the best behavior.

With .done(), we simply return the same metadata with a 204 which we
returned with the last PATCH.

src/tus_request.c

@@ -470,6 +470,10 @@ tus_request(VRT_CTX, struct VPFX(tus_server) *tussrv,
 			r->s.status = 409;
 			return (0);
 		}
+		if (fdisk->location_length > 0) {
+			r->s.status = 204;	/* done file */
+			return (0);
+		}
 		r->s.status = tus_body_to_file(ctx, r->fcore);
 		break;
 	}

src/vtc/done.vtc

@@ -83,6 +83,26 @@ client c1 {
 	expect resp.http.Upload-Expires ~ "GMT$"
 	expect resp.http.Location == "http://localhost/id"
 
+	# zero PATCH after completed
+	txreq	-method PATCH -url "/id" \
+		-hdr "Tus-Resumable: 1.0.0" \
+		-hdr "Content-Type: application/offset+octet-stream" \
+		-hdr "Id: id" \
+		-hdr "Upload-Length: 386550" \
+		-hdr "Upload-Offset: 386550"
+	rxresp
+	# XXX or 409 ?
+	expect resp.status == 204
+	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 == 386550
+	expect resp.http.Upload-Length == 386550
+	expect resp.http.Upload-Expires ~ "GMT$"
+	expect resp.http.Content-Location == "http://localhost/id"
+
 	# even for a done file, HEAD will return the correct metadata
 	txreq	-method HEAD -url "/id" \
 		-hdr "Tus-Resumable: 1.0.0"

src/vtc/multipart.vtc

@@ -12,10 +12,16 @@ server s1 {
 
 server s2 {
 	rxreq
+	expect req.method == PUT
+	expect req.url == /vtc
+	expect req.bodylen == 10240
 	txresp
+
+	rxreq
 	expect req.method == PUT
 	expect req.url == /vtc
 	expect req.bodylen == 10240
+	txresp
 } -start
 
 server s3 {
@@ -41,7 +47,7 @@ varnish v1 -vcl+backend {
 	    new test = tus.server("https://my.origin");
 	    new tmp = tus.server("http://localhost",
 		basedir="/tmp/tus", max = 314500B,
-		multipart = 8192B);
+		multipart = 10240B);
 	}
 	sub vcl_backend_fetch {
 		if (bereq.url ~ "^/tus") {
@@ -56,6 +62,9 @@ varnish v1 -vcl+backend {
 			return (abandon);
 		}
 	}
+	sub vcl_backend_error {
+		return (retry);
+	}
 	sub vcl_recv {
 	    if (tmp.recv(id=req.http.id)) {
 		return(pass);
@@ -80,6 +89,7 @@ varnish v1 -vcl+backend {
 	}
 	sub vcl_deliver {
 	    call meta;
+	    tmp.done(req.url);
 	    tmp.deliver();
 	}
 } -start
@@ -220,12 +230,31 @@ client c2 {
 	txreq	-method PATCH -url "/vtc" \
 		-hdr "Tus-Resumable: 1.0.0" \
 		-hdr "Content-Type: application/offset+octet-stream" \
-		-hdr "Upload-Length: 2048" \
+		-hdr "Upload-Length: 10240" \
 		-hdr "Upload-Offset: 8192" \
 		-bodylen 2048
 	rxresp
 	expect resp.status == 409
 
+	# zero PATCH after completed
+	txreq	-method PATCH -url "/vtc" \
+		-hdr "Tus-Resumable: 1.0.0" \
+		-hdr "Content-Type: application/offset+octet-stream" \
+		-hdr "Upload-Length: 10240" \
+		-hdr "Upload-Offset: 10240"
+	rxresp
+	# XXX or 409 ?
+	expect resp.status == 204
+	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 == 314500
+	expect resp.http.Upload-Offset == 10240
+	expect resp.http.Upload-Length == 10240
+	expect resp.http.Upload-Expires ~ "GMT$"
+	## XXX only for HEAD?
+	expect resp.http.Upload-Metadata == "filename d29ybGRfZG9taW5hdGlvbl9wbGFuLnBkZg==,is_confidential"
 } -start
 
 # part1

src/vtc/plain.vtc

@@ -534,7 +534,19 @@ varnish v1 -start
 
 # check that objects are still present
 
+server s2 -start
+
 client c2 {
+	# triggers another upload, because .done() is not used
+	# XXX correct?
+	txreq	-method PATCH -url "/vtc" \
+		-hdr "Tus-Resumable: 1.0.0" \
+		-hdr "Content-Type: application/offset+octet-stream" \
+		-hdr "Upload-Length: 100" \
+		-hdr "Upload-Offset: 100"
+	rxresp
+	expect resp.status == 204
+
 	txreq	-method HEAD -url "/vtc" \
 		-hdr "Tus-Resumable: 1.0.0"
 	rxresp