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/import.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"os/signal"
+
+	storev1pb "code.tvl.fyi/tvix/store/protos"
+
+	"code.tvl.fyi/tvix/nar-bridge/pkg/reader"
+	log "github.com/sirupsen/logrus"
+)
+
+type ImportCmd struct {
+	NarPath string `name:"nar-path" help:"A path to a NAR file"`
+}
+
+// `help:"Read a NAR file and display some information"`
+
+func (cmd *ImportCmd) 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…")
+			os.Exit(1)
+		}
+	}()
+
+	log.Infof("Reading %v...", cmd.NarPath)
+
+	f, _ := os.Open(cmd.NarPath)
+
+	r := reader.New(f)
+
+	actualPathInfo, _ := r.Import(
+		context.Background(),
+		func(fileReader io.Reader) error {
+			return nil
+		},
+		func(directory *storev1pb.Directory) error {
+			return nil
+		},
+	)
+
+	fmt.Printf("Node: %+v\n", actualPathInfo.Node)
+	fmt.Printf("References: %+v\n", actualPathInfo.References)
+	fmt.Printf("Narinfo: %+v\n", actualPathInfo.Narinfo)
+	return nil
+}