snapshotter example fails with a protocol error

[mythi]

With ctr i pull --snapshotter custom docker.io/library/hello-world:latest given by the README, the snapshotter server returns a protocol error:

...
unpacking linux/amd64 sha256:97a379f4f88575512824f3b352bc03cd75e239179eea0fecc38e597b2209f49a...
ctr: failed to prepare extraction snapshot "extract-947546364-RurZ sha256:e07ee1baac5fae6a26f30cabfe54a36d3402f96afda318fe0a96cec4ca393359": stream terminated by RST_STREAM with error code: PROTOCOL_ERROR: unknown

A snippet from the snapshotter logs:

...
DEBUG [h2::codec::framed_read] received frame=Headers { stream_id: StreamId(1), flags: (0x4: END_HEADERS) }
TRACE [tracing::span::active] <- FramedRead::poll_next
TRACE [tracing::span] -- FramedRead::poll_next
TRACE [h2::proto::connection] recv HEADERS frame=Headers { stream_id: StreamId(1), flags: (0x4: END_HEADERS) }
TRACE [h2::proto::streams::flow_control] inc_window; sz=1048576; old=0; new=1048576
TRACE [h2::proto::streams::flow_control] inc_window; sz=65535; old=0; new=65535
TRACE [h2::proto::streams::streams] recv_headers; stream=StreamId(1); state=State { inner: Idle }
TRACE [h2::proto::streams::recv] opening stream; init_window=1048576
DEBUG [h2::server] malformed headers: malformed authority (b"unix:///tmp/snap2.sock"): invalid uri character
TRACE [h2::proto::streams::send] send_reset(..., reason=PROTOCOL_ERROR, initiator=Library, stream=StreamId(1), ..., is_reset=false; is_closed=false; pending_send.is_empty=true; state=State { inner: Open { local: 
AwaitingHeaders, remote: Streaming } } 
TRACE [h2::proto::streams::prioritize] clear_queue; stream.id=StreamId(1)
TRACE [tracing::span::active] -> clear_queue
TRACE [tracing::span::active] <- clear_queue
TRACE [tracing::span] -- clear_queue
...

[mxpv]

The example from the snapshotter crate is not an actual snapshotter implementation. It's rather an example how to implement Snapshots trait and how to bootstrap snapshotter server.

[mythi]

I was aware of it but wasn't expecting an error like this. Perhaps the readme could add a line about the expected output.

[mythi]

I briefly looked into this yesterday again and I believe this depends on hyperium/h2#612. Some work was done in grpc-go (grpc/grpc-go#3730) but that does not seem to help.

[mythi]

@mxpv there seems to a small problem with containerd itself too. grpc-go handles the authority information

https://github.com/grpc/grpc-go/blob/5682cc6a321507ce2a865beb8dd4bed9a5db0e06/clientconn.go#L1654-L1665

but containerd does not pass the address in the expected format:

diff --git a/client.go b/client.go
index 1c2202e..dbe1252 100644
--- a/client.go
+++ b/client.go
@@ -142,7 +142,7 @@ func New(address string, opts ...ClientOpt) (*Client, error) {
                connector := func() (*grpc.ClientConn, error) {
                        ctx, cancel := context.WithTimeout(context.Background(), copts.timeout)
                        defer cancel()
-                       conn, err := grpc.DialContext(ctx, dialer.DialAddress(address), gopts...)
+                       conn, err := grpc.DialContext(ctx, address, gopts...)
                        if err != nil {
                                return nil, fmt.Errorf("failed to dial %q: %w", address, err)
                        }

(just tested with the example here and that worked. I could prepare a better patch to containerd after checking all cases are covered).

[mythi]

but containerd does not pass the address in the expected format:

quoting myself. this makes no sense. I've been using Debian Unstable's containerd 1.6.2 but it seems they build using an ancient grpc-go which does not have the authority improvements. A locally built containerd works just fine.