package weed_server

import (
	"bytes"
	"context"
	"crypto/md5"
	"errors"
	"fmt"
	"io"
	"math"
	"net/http"
	"os"
	"path"
	"strconv"
	"strings"
	"time"

	"github.com/seaweedfs/seaweedfs/weed/filer"
	"github.com/seaweedfs/seaweedfs/weed/format"
	_ "github.com/seaweedfs/seaweedfs/weed/format/hlsts"
	_ "github.com/seaweedfs/seaweedfs/weed/format/parquet"
	"github.com/seaweedfs/seaweedfs/weed/glog"
	"github.com/seaweedfs/seaweedfs/weed/operation"
	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
	"github.com/seaweedfs/seaweedfs/weed/s3api/s3_constants"
	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
	"github.com/seaweedfs/seaweedfs/weed/util"
	"github.com/seaweedfs/seaweedfs/weed/util/chunk_cache"
)

const (
	// Query parameters follow the mv.from/cp.from dotted convention so the
	// general POST endpoint cannot collide with pass-through client params.
	formatIngestParam = "format.ingest"
	formatRepackParam = "format.repack"

	// formatLayoutChunksKey binds a layout to the chunk list it described, so
	// any other writer that changes the chunks invalidates the views.
	formatLayoutChunksKey = "x-seaweedfs-format-layout-chunks"

	maxFormatSidecarBytes = 16 << 20
	formatSniffBytes      = 512
	// defaultFormatChunkSizeMB caps extent chunks when no maxMB is configured.
	// Extent chunks are buffered in memory, so the limit must never be absent.
	defaultFormatChunkSizeMB = 4
)

// formatChunkIdentity digests the chunk list a layout was written against,
// covering every field that changes what a read returns: a FUSE truncate, for
// one, mutates Size while keeping the chunk's id.
func formatChunkIdentity(chunks []*filer_pb.FileChunk) []byte {
	digest := md5.New()
	for _, chunk := range chunks {
		fmt.Fprintf(digest, "%d:%s:%d:%d:%x:%t:%t:%d;",
			chunk.Offset, chunk.GetFileIdString(), chunk.Size, chunk.ModifiedTsNs,
			chunk.CipherKey, chunk.IsCompressed, chunk.IsChunkManifest, chunk.SseType)
	}
	return digest.Sum(nil)
}

// repackSourceIdentity digests every entry field that influenced a repack's
// output: the chunk list it read, the size the layout was validated against,
// the TTL and expiry anchors its new chunks were assigned with, and the
// hard-link and remote state its guards evaluated.
func repackSourceIdentity(entry *filer.Entry) []byte {
	digest := md5.New()
	digest.Write(formatChunkIdentity(entry.GetChunks()))
	digest.Write(entry.Content)
	fmt.Fprintf(digest, "%d:%d:%d:%d:%d:%t:%x:%t",
		len(entry.Content), entry.FileSize, entry.TtlSec, entry.Crtime.UnixNano(), entry.Mtime.UnixNano(),
		entry.IsExpireS3Enabled(), []byte(entry.HardLinkId), entry.Remote != nil)
	return digest.Sum(nil)
}

// roundUpToVolumeTTL returns the smallest volume-TTL-representable seconds
// value not below the argument. A volume TTL is at most 255 of one unit and
// SecondsToTTL truncates anything else downward, which would let chunks
// expire before their entry - or, under a minute, never.
func roundUpToVolumeTTL(seconds int64) int32 {
	for _, unit := range []int64{60, 3600, 24 * 3600, 7 * 24 * 3600, 30 * 24 * 3600, 365 * 24 * 3600} {
		count := (seconds + unit - 1) / unit
		if count <= 255 && count*unit <= math.MaxInt32 {
			return int32(count * unit)
		}
	}
	// Nothing above ~68 years rounds up within int32; no volume TTL keeps the
	// chunks past the entry, which is the safe direction.
	return 0
}

// formatChunkSizeLimit mirrors the autoChunk maxMB resolution.
func (fs *FilerServer) formatChunkSizeLimit(r *http.Request) int64 {
	parsedMaxMB, _ := strconv.ParseInt(r.URL.Query().Get("maxMB"), 10, 32)
	maxMB := int32(parsedMaxMB)
	if maxMB <= 0 && fs.option.MaxMB > 0 {
		maxMB = int32(fs.option.MaxMB)
	}
	if maxMB <= 0 {
		maxMB = defaultFormatChunkSizeMB
	}
	return int64(maxMB) * 1024 * 1024
}

// copyStandardHeadersToExtended matches what saveMetaData keeps on an entry.
func copyStandardHeadersToExtended(r *http.Request, extended map[string][]byte) {
	for k, v := range r.Header {
		if len(v) > 0 && len(v[0]) > 0 {
			if strings.HasPrefix(k, needle.PairNamePrefix) || k == "Cache-Control" || k == "Expires" || k == "Content-Disposition" {
				extended[k] = []byte(v[0])
			}
			if k == "Response-Content-Disposition" {
				extended["Content-Disposition"] = []byte(v[0])
			}
		}
	}
}

// formatIngest handles POST /path?format.ingest=<adapter>: a multipart body
// with an "index" sidecar part describing the media's extents, then the
// "media" bytes. Storage chunks are cut on the boundaries the sidecar declares.
func (fs *FilerServer) formatIngest(ctx context.Context, w http.ResponseWriter, r *http.Request, so *operation.StorageOption) {
	adapterName := r.URL.Query().Get(formatIngestParam)
	adapter := format.ByName(adapterName)
	if adapter == nil {
		writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("unknown format %q", adapterName))
		return
	}
	sidecarIndexer, ok := adapter.(format.SidecarIndexer)
	if !ok {
		writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("format %q does not support sidecar ingest", adapterName))
		return
	}
	if strings.HasSuffix(r.URL.Path, "/") {
		writeJsonError(w, r, http.StatusBadRequest, errors.New("format ingest target must be a file path"))
		return
	}
	if enforced, err := fs.wormEnforcedForEntry(ctx, r.URL.Path); err != nil {
		writeJsonError(w, r, http.StatusInternalServerError, err)
		return
	} else if enforced {
		writeJsonError(w, r, http.StatusForbidden, errors.New("cannot replace WORM-enforced entry"))
		return
	}

	multipartReader, err := r.MultipartReader()
	if err != nil {
		writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("format ingest requires multipart/form-data: %w", err))
		return
	}
	sidecarPart, err := multipartReader.NextPart()
	if err != nil {
		writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("read index part: %w", err))
		return
	}
	if sidecarPart.FormName() != "index" {
		writeJsonError(w, r, http.StatusBadRequest, errors.New("first multipart part must be named index"))
		return
	}
	sidecar, err := io.ReadAll(io.LimitReader(sidecarPart, maxFormatSidecarBytes+1))
	sidecarPart.Close()
	if err != nil {
		writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("read index part: %w", err))
		return
	}
	if len(sidecar) > maxFormatSidecarBytes {
		writeJsonError(w, r, http.StatusRequestEntityTooLarge, fmt.Errorf("index part exceeds %d bytes", maxFormatSidecarBytes))
		return
	}
	layout, err := sidecarIndexer.IndexSidecar(sidecar)
	if err != nil {
		writeJsonError(w, r, http.StatusBadRequest, err)
		return
	}
	if err := layout.Validate(-1); err != nil {
		writeJsonError(w, r, http.StatusBadRequest, err)
		return
	}

	mediaPart, err := multipartReader.NextPart()
	if err != nil {
		writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("read media part: %w", err))
		return
	}
	if mediaPart.FormName() != "media" {
		writeJsonError(w, r, http.StatusBadRequest, errors.New("second multipart part must be named media"))
		return
	}
	defer mediaPart.Close()
	contentType := mediaPart.Header.Get("Content-Type")
	if contentType == "" {
		contentType = "application/octet-stream"
	}

	cutter := layout.Cutter(fs.formatChunkSizeLimit(r))
	fileChunks, md5Hash, written, uploadErr, _ := fs.uploadReaderToBoundedChunks(ctx, r, mediaPart, 0, cutter, path.Base(r.URL.Path), contentType, false, so)
	cleanup := func() { fs.filer.DeleteUncommittedChunks(context.WithoutCancel(ctx), fileChunks) }
	if uploadErr != nil {
		cleanup()
		writeJsonError(w, r, http.StatusInternalServerError, uploadErr)
		return
	}
	if total := layout.TotalSize(); written != total {
		cleanup()
		writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("media is %d bytes but the index describes %d", written, total))
		return
	}
	var extra [1]byte
	if n, _ := io.ReadFull(mediaPart, extra[:]); n != 0 {
		cleanup()
		writeJsonError(w, r, http.StatusBadRequest, errors.New("media has trailing bytes beyond the index"))
		return
	}
	if extraPart, nextErr := multipartReader.NextPart(); nextErr == nil {
		extraPart.Close()
		cleanup()
		writeJsonError(w, r, http.StatusBadRequest, errors.New("unexpected multipart part after media"))
		return
	}

	fileChunks, err = filer.MaybeManifestize(fs.saveAsChunk(ctx, so), fileChunks)
	if err != nil {
		cleanup()
		writeJsonError(w, r, http.StatusInternalServerError, err)
		return
	}
	encoded, err := layout.Encode()
	if err != nil {
		cleanup()
		writeJsonError(w, r, http.StatusInternalServerError, err)
		return
	}

	mode := uint64(0660)
	if text := r.URL.Query().Get("mode"); text != "" {
		if mode, err = strconv.ParseUint(text, 8, 32); err != nil {
			cleanup()
			writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("invalid mode %q", text))
			return
		}
	}
	now := time.Now()
	entry := &filer.Entry{
		FullPath: util.FullPath(r.URL.Path),
		Attr: filer.Attr{
			Mtime: now, Crtime: now,
			Mode: os.FileMode(mode), Uid: OS_UID, Gid: OS_GID,
			TtlSec: so.TtlSeconds, Mime: contentType,
			Md5: md5Hash.Sum(nil), FileSize: uint64(written),
		},
		Chunks: fileChunks,
		Extended: map[string][]byte{
			format.LayoutKey:      encoded,
			formatLayoutChunksKey: formatChunkIdentity(fileChunks),
		},
	}
	copyStandardHeadersToExtended(r, entry.Extended)
	// commit under the entry lock like saveMetaData, so ingest overwrites
	// serialize with gRPC writers, renames, and repack
	pathLock := fs.entryLockTable.AcquireLock("formatIngest", entry.FullPath, util.ExclusiveLock)
	defer fs.entryLockTable.ReleaseLock(entry.FullPath, pathLock)
	// recheck under the lock: WORM may have been enabled during the upload
	if enforced, wormErr := fs.wormEnforcedForEntry(ctx, r.URL.Path); wormErr != nil {
		cleanup()
		writeJsonError(w, r, http.StatusInternalServerError, wormErr)
		return
	} else if enforced {
		cleanup()
		writeJsonError(w, r, http.StatusForbidden, errors.New("cannot replace WORM-enforced entry"))
		return
	}
	if err := fs.filer.CreateEntry(context.WithoutCancel(ctx), entry, nil, false, false, nil, skipCheckParentDirEntry(r), so.MaxFileNameLength); err != nil {
		cleanup()
		writeJsonError(w, r, http.StatusInternalServerError, err)
		return
	}
	writeJsonQuiet(w, r, http.StatusCreated, FilerPostResult{Name: entry.Name(), Size: written})
}

// formatRepack handles POST /path?format.repack=<adapter>: it derives the
// layout from the stored bytes and rewrites the entry's chunks cut on extent
// boundaries. The bytes do not change, only where they are cut.
func (fs *FilerServer) formatRepack(ctx context.Context, w http.ResponseWriter, r *http.Request, so *operation.StorageOption) {
	adapterName := r.URL.Query().Get(formatRepackParam)
	adapter := format.ByName(adapterName)
	if adapter == nil {
		writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("unknown format %q", adapterName))
		return
	}
	indexer, ok := adapter.(format.Indexer)
	if !ok {
		writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("format %q does not support repack", adapterName))
		return
	}
	fullPath := util.FullPath(r.URL.Path)
	// Serializes gRPC writers, renames, and this filer's HTTP overwrites;
	// cross-filer serialization needs owner routing.
	pathLock := fs.entryLockTable.AcquireLock("formatRepack", fullPath, util.ExclusiveLock)
	defer fs.entryLockTable.ReleaseLock(fullPath, pathLock)

	// checked under the lock so a concurrent WORM enable cannot land between
	// validation and the entry swap
	if enforced, err := fs.wormEnforcedForEntry(ctx, r.URL.Path); err != nil {
		writeJsonError(w, r, http.StatusInternalServerError, err)
		return
	} else if enforced {
		writeJsonError(w, r, http.StatusForbidden, errors.New("cannot repack WORM-enforced entry"))
		return
	}

	entry, err := fs.filer.FindEntry(ctx, fullPath)
	if err != nil {
		if errors.Is(err, filer_pb.ErrNotFound) {
			writeJsonError(w, r, http.StatusNotFound, err)
		} else {
			writeJsonError(w, r, http.StatusInternalServerError, err)
		}
		return
	}
	if entry.IsDirectory() {
		writeJsonError(w, r, http.StatusBadRequest, errors.New("cannot repack a directory"))
		return
	}
	oldChunks := entry.GetChunks()
	sourceIdentity := repackSourceIdentity(entry)
	if len(oldChunks) == 0 {
		writeJsonError(w, r, http.StatusBadRequest, errors.New("entry has no chunks to repack"))
		return
	}
	if len(entry.HardLinkId) != 0 || entry.Remote != nil {
		writeJsonError(w, r, http.StatusBadRequest, errors.New("cannot repack hard-linked or remote entries"))
		return
	}
	// the repack reader sees only chunks; inline content would be dropped
	if len(entry.Content) != 0 {
		writeJsonError(w, r, http.StatusBadRequest, errors.New("cannot repack entries with inline content"))
		return
	}
	for _, chunk := range oldChunks {
		if chunk.SseType != filer_pb.SSEType_NONE {
			writeJsonError(w, r, http.StatusBadRequest, errors.New("cannot repack server-side encrypted entries"))
			return
		}
	}

	// Repack rewrites where bytes are cut, never their lifetime: new chunks
	// carry the entry's remaining TTL, not the request query's nor a restart
	// of the original span.
	so.TtlSeconds = entry.TtlSec
	if entry.TtlSec > 0 {
		// mirror FindEntry's expiry anchors: S3-expiring entries age from
		// Mtime, everything else from Crtime
		expiresAt := entry.Crtime.Add(time.Duration(entry.TtlSec) * time.Second)
		if entry.IsExpireS3Enabled() {
			expiresAt = entry.GetS3ExpireTime()
		}
		remaining := (int64(time.Until(expiresAt)) + int64(time.Second) - 1) / int64(time.Second)
		if remaining <= 0 {
			writeJsonError(w, r, http.StatusBadRequest, errors.New("entry TTL has already expired"))
			return
		}
		so.TtlSeconds = roundUpToVolumeTTL(remaining)
	}

	if entry.FileSize > math.MaxInt64 {
		writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("file size %d overflows int64", entry.FileSize))
		return
	}
	size := int64(entry.FileSize)
	lookup := fs.filer.MasterClient.GetLookupFileIdFunction()
	chunkViews := filer.ViewFromChunks(ctx, lookup, oldChunks, 0, size)
	readerCache := filer.NewReaderCache(8, chunk_cache.NewChunkCacheInMemory(16), lookup, nil)
	readerAt := filer.NewChunkReaderAtFromClient(ctx, readerCache, chunkViews, size, filer.DefaultPrefetchCount)
	// Close releases the private reader cache and its in-flight prefetches.
	defer readerAt.Close()

	// cheap magic-byte gate before handing the bytes to the parser
	if sniffer, ok := adapter.(format.Sniffer); ok {
		hint := format.Hint{Name: entry.Name(), ContentType: entry.Attr.Mime, Size: size}
		sniffSize := int64(formatSniffBytes)
		if sniffSize > size {
			sniffSize = size
		}
		head := make([]byte, sniffSize)
		if _, err := readerAt.ReadAt(head, 0); err != nil && err != io.EOF {
			writeJsonError(w, r, http.StatusInternalServerError, fmt.Errorf("read head: %w", err))
			return
		}
		tail := make([]byte, sniffSize)
		if _, err := readerAt.ReadAt(tail, size-sniffSize); err != nil && err != io.EOF {
			writeJsonError(w, r, http.StatusInternalServerError, fmt.Errorf("read tail: %w", err))
			return
		}
		hint.Head, hint.Tail = head, tail
		if !sniffer.Sniff(hint) {
			writeJsonError(w, r, http.StatusBadRequest, fmt.Errorf("%s does not look like %s", entry.Name(), adapterName))
			return
		}
	}

	layout, err := indexer.Index(ctx, readerAt, size)
	if err != nil {
		writeJsonError(w, r, http.StatusBadRequest, err)
		return
	}
	if err := layout.Validate(size); err != nil {
		writeJsonError(w, r, http.StatusBadRequest, err)
		return
	}

	cutter := layout.Cutter(fs.formatChunkSizeLimit(r))
	newChunks, md5Hash, written, uploadErr, _ := fs.uploadReaderToBoundedChunks(ctx, r, io.NewSectionReader(readerAt, 0, size), 0, cutter, entry.Name(), entry.Attr.Mime, false, so)
	cleanup := func() { fs.filer.DeleteUncommittedChunks(context.WithoutCancel(ctx), newChunks) }
	if uploadErr != nil {
		cleanup()
		writeJsonError(w, r, http.StatusInternalServerError, uploadErr)
		return
	}
	if written != size {
		cleanup()
		writeJsonError(w, r, http.StatusInternalServerError, fmt.Errorf("read %d of %d bytes", written, size))
		return
	}
	newChunks, err = filer.MaybeManifestize(fs.saveAsChunk(ctx, so), newChunks)
	if err != nil {
		cleanup()
		writeJsonError(w, r, http.StatusInternalServerError, err)
		return
	}
	encoded, err := layout.Encode()
	if err != nil {
		cleanup()
		writeJsonError(w, r, http.StatusInternalServerError, err)
		return
	}

	// The entry lock is filer-local, so a writer on another filer is not
	// blocked by it. Re-read from the store and conflict on any change to
	// state that influenced this repack - chunks, size, TTL and expiry
	// anchors, hard-link and remote state - so the swap can never pair fresh
	// metadata with chunks built from stale inputs. The unguarded window
	// shrinks from the whole repack to this commit; within it repack races
	// like any ordinary writer. Closing it needs owner routing.
	current, err := fs.filer.FindEntry(ctx, fullPath)
	if err != nil {
		cleanup()
		if errors.Is(err, filer_pb.ErrNotFound) {
			writeJsonError(w, r, http.StatusConflict, errors.New("entry was deleted during repack"))
		} else {
			writeJsonError(w, r, http.StatusInternalServerError, err)
		}
		return
	}
	if !bytes.Equal(repackSourceIdentity(current), sourceIdentity) {
		cleanup()
		writeJsonError(w, r, http.StatusConflict, errors.New("entry changed during repack"))
		return
	}
	if enforced, wormErr := fs.wormEnforcedForEntry(ctx, r.URL.Path); wormErr != nil {
		cleanup()
		writeJsonError(w, r, http.StatusInternalServerError, wormErr)
		return
	} else if enforced {
		cleanup()
		writeJsonError(w, r, http.StatusForbidden, errors.New("cannot repack WORM-enforced entry"))
		return
	}

	// build from the fresh read so a concurrent metadata-only update on
	// another filer is carried forward, not clobbered
	newEntry := *current
	newEntry.Chunks = newChunks
	newEntry.Extended = make(map[string][]byte)
	for k, v := range current.Extended {
		newEntry.Extended[k] = v
	}
	newEntry.Extended[format.LayoutKey] = encoded
	newEntry.Extended[formatLayoutChunksKey] = formatChunkIdentity(newChunks)
	if len(newEntry.Md5) == 0 {
		newEntry.Md5 = md5Hash.Sum(nil)
	}
	if err := fs.filer.UpdateEntry(context.WithoutCancel(ctx), current, &newEntry); err != nil {
		cleanup()
		writeJsonError(w, r, http.StatusInternalServerError, err)
		return
	}
	fs.filer.DeleteChunks(context.WithoutCancel(ctx), fullPath, current.GetChunks())
	// Filer.UpdateEntry only writes the store; notify subscribers (sync,
	// backup, replication) of the new chunk ids like the gRPC path does.
	fs.filer.NotifyUpdateEvent(ctx, current, &newEntry, true, false, nil)
	writeJsonQuiet(w, r, http.StatusOK, map[string]interface{}{
		"name": entry.Name(), "size": size, "extents": len(layout.ExtentSizes),
	})
}

// serveFormatView answers GET/HEAD /path?view=<adapter> for entries carrying a
// layout. The layout is advisory: any inconsistency yields 404 here while the
// plain read path stays untouched.
func (fs *FilerServer) serveFormatView(ctx context.Context, w http.ResponseWriter, r *http.Request, entry *filer.Entry, viewName string) {
	adapter := format.ByName(viewName)
	viewer, viewerOk := adapter.(format.Viewer)
	if adapter == nil || !viewerOk {
		http.Error(w, "no such view", http.StatusNotFound)
		return
	}
	encoded := entry.Extended[format.LayoutKey]
	if len(encoded) == 0 {
		http.Error(w, "entry has no format layout", http.StatusNotFound)
		return
	}
	layout, err := format.DecodeLayout(encoded)
	if err != nil || layout.Format != viewName {
		http.Error(w, "entry has no such format layout", http.StatusNotFound)
		return
	}
	// a size beyond int64 would read as negative, which Validate treats as
	// "skip the size check"
	if entry.FileSize > math.MaxInt64 {
		http.Error(w, "format layout is stale", http.StatusNotFound)
		return
	}
	if err := layout.Validate(int64(entry.FileSize)); err != nil {
		glog.WarningfCtx(ctx, "stale format layout on %s: %v", entry.FullPath, err)
		http.Error(w, "format layout is stale", http.StatusNotFound)
		return
	}
	// A write outside the format endpoints (offset writes, appends, mounts)
	// changes the chunks but keeps Extended, so the layout no longer
	// describes the bytes even when the total size still matches. Inline
	// content is disqualifying outright: format entries are never written
	// with it, and reads would prefer it over the chunks the layout maps.
	if len(entry.Content) != 0 || !bytes.Equal(entry.Extended[formatLayoutChunksKey], formatChunkIdentity(entry.GetChunks())) {
		glog.WarningfCtx(ctx, "format layout on %s no longer matches its bytes", entry.FullPath)
		http.Error(w, "format layout is stale", http.StatusNotFound)
		return
	}

	// The view's validator must change when the layout or the requested
	// representation changes, even when the media bytes and their MD5 do not:
	// re-ingesting with a different sidecar must invalidate cached views.
	viewIdentity := md5.New()
	viewIdentity.Write([]byte(filer.ETagEntry(entry)))
	viewIdentity.Write(encoded)
	viewIdentity.Write([]byte(r.URL.RawQuery))
	viewEntry := *entry
	viewEntry.Md5 = viewIdentity.Sum(nil)
	if checkPreconditions(w, r, &viewEntry) {
		return
	}

	plan, err := viewer.View(format.ViewRequest{Query: r.URL.Query()}, format.Object{
		Name: entry.Name(), Size: int64(entry.FileSize), Layout: layout,
	})
	if err != nil {
		if errors.Is(err, format.ErrNoSuchView) {
			http.NotFound(w, r)
		} else {
			http.Error(w, err.Error(), http.StatusInternalServerError)
		}
		return
	}

	// pass through stored headers the way plain reads do
	for k, v := range entry.Extended {
		if !strings.HasPrefix(k, "xattr-") && !s3_constants.IsSeaweedFSInternalHeader(k) {
			w.Header().Set(k, string(v))
		}
	}
	// view responses are whole documents or whole extents
	w.Header().Set("Accept-Ranges", "none")
	w.Header().Set("Content-Type", plan.ContentType)
	SetEtag(w, filer.ETagEntry(&viewEntry))

	if plan.Body != nil {
		w.Header().Set("Content-Length", strconv.Itoa(len(plan.Body)))
		if r.Method == http.MethodHead {
			return
		}
		if _, err := w.Write(plan.Body); err != nil {
			glog.V(2).InfofCtx(ctx, "write %s view of %s: %v", viewName, entry.FullPath, err)
		}
		return
	}

	offset, extentSize, ok := layout.ExtentRange(plan.Extent)
	if !ok {
		http.NotFound(w, r)
		return
	}
	w.Header().Set("Content-Length", strconv.FormatInt(extentSize, 10))
	if r.Method == http.MethodHead {
		return
	}
	streamCtx, cancel := context.WithCancel(ctx)
	defer cancel()
	streamFn, err := filer.PrepareStreamContentWithPrefetch(streamCtx, fs.filer.MasterClient, fs.maybeGetVolumeReadJwtAuthorizationToken, entry.GetChunks(), offset, extentSize, fs.option.DownloadMaxBytesPs, filer.DefaultPrefetchCount)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	if err := streamFn(w); err != nil {
		glog.ErrorfCtx(ctx, "stream %s view extent %d of %s: %v", viewName, plan.Extent, entry.FullPath, err)
	}
}