fix(remote): dial remote plugins through passthrough

internal/adapters/plugin/remote.go

@@ -5,6 +5,7 @@ import (
 	"crypto/x509"
 	"fmt"
 	"log/slog"
+	"net"
 	"net/url"
 	"strings"
 	"time"
@@ -66,7 +67,7 @@ func (e *RemotePluginExecutor) Execute(ctx context.Context, plugin Info, request
 		transportCreds = insecure.NewCredentials()
 	}
 
-	conn, err := grpc.NewClient(host, grpc.WithTransportCredentials(transportCreds))
+	conn, err := grpc.NewClient(dialTarget(host), grpc.WithTransportCredentials(transportCreds))
 	if err != nil {
 		return nil, fmt.Errorf("failed to connect to gRPC server %s: %w", host, err)
 	}
@@ -103,6 +104,20 @@ func (e *RemotePluginExecutor) Execute(ctx context.Context, plugin Info, request
 	return resp.CodeGeneratorResponse, nil
 }
 
+// dialTarget is the gRPC target for a plugin host: passthrough, so the system
+// resolver answers the name when the connection is made. grpc-go's default dns
+// resolver queries the nameservers itself, and on a machine whose first one
+// does not answer (a VPN's, typically) it waited about twenty seconds on every
+// connection, localhost included. A host without a port gets 443, which is
+// what that resolver assumed.
+func dialTarget(host string) string {
+	if _, _, err := net.SplitHostPort(host); err != nil {
+		host = net.JoinHostPort(strings.Trim(host, "[]"), "443")
+	}
+
+	return "passthrough:///" + host
+}
+
 // - localhost:8080/python:v1.35
 // - http://localhost:8080/python:v1.35
 // - https://example.com/python:v1.35

internal/adapters/plugin/remote_test.go

@@ -0,0 +1,35 @@
+package plugin
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestRemotePluginTarget(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		source  string
+		target  string
+		name    string
+		version string
+	}{
+		{"localhost:8080/grpc/go:v1.6.2", "passthrough:///localhost:8080", "grpc/go", "v1.6.2"},
+		{"http://127.0.0.1:8080/protocolbuffers/go", "passthrough:///127.0.0.1:8080", "protocolbuffers/go", "latest"},
+		{"https://plugins.example.com/grpc/go:v1.6.2", "passthrough:///plugins.example.com:443", "grpc/go", "v1.6.2"},
+		{"enterprise.plugins.beta.easyp.tech:443/bufbuild/es:v2.12.0", "passthrough:///enterprise.plugins.beta.easyp.tech:443", "bufbuild/es", "v2.12.0"},
+	}
+
+	e := &RemotePluginExecutor{}
+
+	for _, tt := range tests {
+		host, name, version, err := e.parsePluginURL(tt.source)
+		require.NoError(t, err, tt.source)
+
+		assert.Equal(t, tt.target, dialTarget(host), tt.source)
+		assert.Equal(t, tt.name, name, tt.source)
+		assert.Equal(t, tt.version, version, tt.source)
+	}
+}