Build fails when shared context directory contains non-ASCII characters

[maxproske]

Initially caught by docker/compose#13965 2 Compose services sharing a build context containing Chinese characters, but after some digging, every build dialed over gRPC fails. Same as #2793 which was closed as not reproducible.

Sanitize the shared key before it reaches gRPC.

Steps to reproduce:

mkdir -p 早

docker buildx create --name repro --driver docker-container
docker buildx build --builder repro 早

docker buildx bake -f - a b <<'EOF'
target "a" { context = "早" }
target "b" { context = "早" }
EOF

docker compose -f - build <<'EOF'
services:
  a: {build: 早}
  b: {build: 早}
EOF

All 3 fail with:

failed to dial gRPC: rpc error: code = Internal desc = rpc error: code = Internal desc = header key "x-docker-expose-session-sharedkey" contains value with non-printable ASCII characters

[maxproske]

Newbie question: if approved, worth me guarding downstream in buildkit too?

[crazy-max]

Thanks but I think this should probably be fixed in BuildKit by encoding the shared key when it's put into session metadata and decoding it in the session manager, rather than hashing it in Buildx.

[crazy-max]

opened moby/buildkit#6989