1 files changed, 197 insertions, 0 deletions
diff --git a/tvix/nar-bridge-go/pkg/http/nar_get.go b/tvix/nar-bridge-go/pkg/http/nar_get.go
new file mode 100644
index 000000000000..75797f8da90e
--- /dev/null
+++ b/tvix/nar-bridge-go/pkg/http/nar_get.go
@@ -0,0 +1,197 @@
+package http
+
+import (
+	"bytes"
+	"context"
+	"encoding/base64"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"net/http"
+	"sync"
+
+	castorev1pb "code.tvl.fyi/tvix/castore-go"
+	storev1pb "code.tvl.fyi/tvix/store-go"
+	"github.com/go-chi/chi/v5"
+	nixhash "github.com/nix-community/go-nix/pkg/hash"
+	"github.com/nix-community/go-nix/pkg/nixbase32"
+	log "github.com/sirupsen/logrus"
+)
+
+const (
+	narUrl = "/nar/{narhash:^([" + nixbase32.Alphabet + "]{52})$}.nar"
+)
+
+func renderNar(
+	ctx context.Context,
+	log *log.Entry,
+	directoryServiceClient castorev1pb.DirectoryServiceClient,
+	blobServiceClient castorev1pb.BlobServiceClient,
+	narHashDbMu *sync.Mutex,
+	narHashDb map[string]*narData,
+	w io.Writer,
+	narHash *nixhash.Hash,
+	headOnly bool,
+) error {
+	// look in the lookup table
+	narHashDbMu.Lock()
+	narData, found := narHashDb[narHash.SRIString()]
+	narHashDbMu.Unlock()
+
+	rootNode := narData.rootNode
+
+	// if we didn't find anything, return 404.
+	if !found {
+		return fmt.Errorf("narHash not found: %w", fs.ErrNotExist)
+	}
+
+	// if this was only a head request, we're done.
+	if headOnly {
+		return nil
+	}
+
+	directories := make(map[string]*castorev1pb.Directory)
+
+	// If the root node is a directory, ask the directory service for all directories
+	if pathInfoDirectory := rootNode.GetDirectory(); pathInfoDirectory != nil {
+		rootDirectoryDigest := pathInfoDirectory.GetDigest()
+		log = log.WithField("root_directory", base64.StdEncoding.EncodeToString(rootDirectoryDigest))
+
+		directoryStream, err := directoryServiceClient.Get(ctx, &castorev1pb.GetDirectoryRequest{
+			ByWhat: &castorev1pb.GetDirectoryRequest_Digest{
+				Digest: rootDirectoryDigest,
+			},
+			Recursive: true,
+		})
+		if err != nil {
+			return fmt.Errorf("unable to query directory stream: %w", err)
+		}
+
+		// For now, we just stream all of these locally and put them into a hashmap,
+		// which is used in the lookup function below.
+		for {
+			directory, err := directoryStream.Recv()
+			if err != nil {
+				if err == io.EOF {
+					break
+				}
+				return fmt.Errorf("unable to receive from directory stream: %w", err)
+			}
+
+			// calculate directory digest
+			// TODO: do we need to do any more validation?
+			directoryDgst, err := directory.Digest()
+			if err != nil {
+				return fmt.Errorf("unable to calculate directory digest: %w", err)
+			}
+
+			log.WithField("directory", base64.StdEncoding.EncodeToString(directoryDgst)).Debug("received directory node")
+
+			directories[hex.EncodeToString(directoryDgst)] = directory
+		}
+
+	}
+
+	// render the NAR file
+	err := storev1pb.Export(
+		w,
+		rootNode,
+		func(directoryDigest []byte) (*castorev1pb.Directory, error) {
+			log.WithField("directory", base64.StdEncoding.EncodeToString(directoryDigest)).Debug("Get directory")
+			directoryRefStr := hex.EncodeToString(directoryDigest)
+			directory, found := directories[directoryRefStr]
+			if !found {
+				return nil, fmt.Errorf(
+					"directory with hash %v does not exist: %w",
+					directoryDigest,
+					fs.ErrNotExist,
+				)
+			}
+
+			return directory, nil
+		},
+		func(blobDigest []byte) (io.ReadCloser, error) {
+			log.WithField("blob", base64.StdEncoding.EncodeToString(blobDigest)).Debug("Get blob")
+			resp, err := blobServiceClient.Read(ctx, &castorev1pb.ReadBlobRequest{
+				Digest: blobDigest,
+			})
+			if err != nil {
+				return nil, fmt.Errorf("unable to get blob: %w", err)
+			}
+
+			// set up a pipe, let a goroutine write, return the reader.
+			pR, pW := io.Pipe()
+
+			go func() {
+				for {
+					chunk, err := resp.Recv()
+					if errors.Is(err, io.EOF) {
+						break
+					}
+					if err != nil {
+						pW.CloseWithError(fmt.Errorf("receiving chunk: %w", err))
+						return
+					}
+
+					// write the received chunk to the writer part of the pipe
+					if _, err := io.Copy(pW, bytes.NewReader(chunk.GetData())); err != nil {
+						log.WithError(err).Error("writing chunk to pipe")
+						pW.CloseWithError(fmt.Errorf("writing chunk to pipe: %w", err))
+						return
+					}
+				}
+				pW.Close()
+
+			}()
+
+			return io.NopCloser(pR), nil
+		},
+	)
+	if err != nil {
+		return fmt.Errorf("unable to export nar: %w", err)
+	}
+	return nil
+}
+
+func registerNarGet(s *Server) {
+	// produce a handler for rendering NAR files.
+	genNarHandler := func(isHead bool) func(w http.ResponseWriter, r *http.Request) {
+		return func(w http.ResponseWriter, r *http.Request) {
+			defer r.Body.Close()
+
+			ctx := r.Context()
+
+			// parse the narhash sent in the request URL
+			narHash, err := parseNarHashFromUrl(chi.URLParamFromCtx(ctx, "narhash"))
+			if err != nil {
+				log.WithError(err).WithField("url", r.URL).Error("unable to decode nar hash from url")
+				w.WriteHeader(http.StatusBadRequest)
+				_, err := w.Write([]byte("unable to decode nar hash from url"))
+				if err != nil {
+					log.WithError(err).Errorf("unable to write error message to client")
+				}
+
+				return
+			}
+
+			log := log.WithField("narhash_url", narHash.SRIString())
+
+			// TODO: inline more of that function here?
+			err = renderNar(ctx, log, s.directoryServiceClient, s.blobServiceClient, &s.narDbMu, s.narDb, w, narHash, isHead)
+			if err != nil {
+				if errors.Is(err, fs.ErrNotExist) {
+					w.WriteHeader(http.StatusNotFound)
+				} else {
+					log.WithError(err).Warn("unable to render nar")
+					w.WriteHeader(http.StatusInternalServerError)
+				}
+			}
+
+		}
+	}
+
+	s.handler.Head(narUrl, genNarHandler(true))
+	s.handler.Get(narUrl, genNarHandler(false))
+}