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/cmd/nar_bridge/serve.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+	"os"
+	"os/signal"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+
+	"code.tvl.fyi/tvix/nar-bridge/pkg/server"
+	storev1pb "code.tvl.fyi/tvix/store/protos"
+	log "github.com/sirupsen/logrus"
+)
+
+type ServeCmd struct {
+	ListenAddr      string `name:"listen-addr" help:"The address this service listens on" type:"string" default:"[::]:9000"` //nolint:lll
+	EnableAccessLog bool   `name:"access-log" help:"Enable access logging" type:"bool" default:"true" negatable:""`          //nolint:lll
+	StoreAddr       string `name:"store-addr" help:"The address to the tvix-store RPC interface this will connect to"`
+}
+
+// `help:"Expose a tvix-store RPC interface as NAR/NARInfo"`
+func (cmd *ServeCmd) Run() error {
+	retcode := 0
+
+	defer func() { os.Exit(retcode) }()
+
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, os.Interrupt)
+
+	go func() {
+		for range c {
+			log.Info("Received Signal, shutting down…")
+			//s.Close()
+			os.Exit(1)
+		}
+	}()
+
+	// connect to tvix-store
+	log.Debugf("Dialing to %v", cmd.StoreAddr)
+	conn, err := grpc.Dial(cmd.StoreAddr, grpc.WithTransportCredentials(insecure.NewCredentials()))
+	if err != nil {
+		log.Fatalf("did not connect: %v", err)
+	}
+	defer conn.Close()
+
+	log.Printf("Starting nar-bridge at %v", cmd.ListenAddr)
+	s := server.New(
+		storev1pb.NewDirectoryServiceClient(conn),
+		storev1pb.NewBlobServiceClient(conn),
+		storev1pb.NewPathInfoServiceClient(conn),
+		cmd.EnableAccessLog,
+		30,
+	)
+
+	err = s.ListenAndServe(cmd.ListenAddr)
+	if err != nil {
+		log.Error("Server failed: %w", err)
+	}
+	return nil
+}