feat(tvix/nar-bridge): init

This provides a Nix HTTP Binary Cache interface in front of a tvix-store
that's reachable via gRPC.

TODOs:

 - remove import command, move serve up to toplevel. We have nix-copy-
   closure and tvix-store commands.
 - loop into CI. We should be able to fetch the protos as a third-party
   dependency.
 - Check if we can test nar-bridge slightly easier in an integration
   test.
 - Ensure we support connecting to unix sockets and grpc+http at least,
   using the same syntax as tvix-store.
 - Don't buffer the entire blob when rendering NAR

Co-Authored-By: Connor Brewster <cbrewster@hey.com>
Co-Authored-By: Márton Boros <martonboros@gmail.com>
Co-Authored-By: Vo Minh Thu <noteed@gmail.com>

Change-Id: I6064474e49dfe78cea67676957462d9f28658d4a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9339
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/nar-bridge/pkg/server/directory_upload.go

@@ -0,0 +1,66 @@
+package server
+
+import (
+	"context"
+	"encoding/base64"
+	"fmt"
+
+	storev1pb "code.tvl.fyi/tvix/store/protos"
+	log "github.com/sirupsen/logrus"
+)
+
+type DirectoriesUploader struct {
+	ctx                       context.Context
+	directoryServiceClient    storev1pb.DirectoryServiceClient
+	directoryServicePutStream storev1pb.DirectoryService_PutClient
+}
+
+func NewDirectoriesUploader(ctx context.Context, directoryServiceClient storev1pb.DirectoryServiceClient) *DirectoriesUploader {
+	return &DirectoriesUploader{
+		ctx:                       ctx,
+		directoryServiceClient:    directoryServiceClient,
+		directoryServicePutStream: nil,
+	}
+}
+
+func (du *DirectoriesUploader) Put(directory *storev1pb.Directory) error {
+	directoryDgst, err := directory.Digest()
+	if err != nil {
+		return fmt.Errorf("failed calculating directory digest: %w", err)
+	}
+
+	// Send the directory to the directory service
+	// If the stream hasn't been initialized yet, do it first
+	if du.directoryServicePutStream == nil {
+		directoryServicePutStream, err := du.directoryServiceClient.Put(du.ctx)
+		if err != nil {
+			return fmt.Errorf("unable to initialize directory service put stream: %v", err)
+		}
+		du.directoryServicePutStream = directoryServicePutStream
+	}
+
+	// send the directory out
+	err = du.directoryServicePutStream.Send(directory)
+	if err != nil {
+		return fmt.Errorf("error sending directory: %w", err)
+	}
+	log.WithField("digest", base64.StdEncoding.EncodeToString(directoryDgst)).Info("uploaded directory")
+
+	return nil
+}
+
+// Done is called whenever we're
+func (du *DirectoriesUploader) Done() (*storev1pb.PutDirectoryResponse, error) {
+	// only close once, and only if we opened.
+	if du.directoryServicePutStream == nil {
+		return nil, nil
+	}
+	putDirectoryResponse, err := du.directoryServicePutStream.CloseAndRecv()
+	if err != nil {
+		return nil, fmt.Errorf("unable to close directory service put stream: %v", err)
+	}
+
+	du.directoryServicePutStream = nil
+
+	return putDirectoryResponse, nil
+}