package weed_server

import (
	"context"
	"fmt"
	"io"
	"math"
	"os"
	"strings"
	"time"

	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
	"github.com/seaweedfs/seaweedfs/weed/storage/backend"

	"github.com/seaweedfs/seaweedfs/weed/glog"
	"github.com/seaweedfs/seaweedfs/weed/operation"
	"github.com/seaweedfs/seaweedfs/weed/pb"
	"github.com/seaweedfs/seaweedfs/weed/pb/volume_server_pb"
	"github.com/seaweedfs/seaweedfs/weed/storage"
	"github.com/seaweedfs/seaweedfs/weed/storage/erasure_coding"
	"github.com/seaweedfs/seaweedfs/weed/storage/idx"
	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
	"github.com/seaweedfs/seaweedfs/weed/storage/types"
	"github.com/seaweedfs/seaweedfs/weed/util"
)

const BufferSizeLimit = 1024 * 1024 * 2

// VolumeCopy copy the .idx .dat .vif files, and mount the volume
func (vs *VolumeServer) VolumeCopy(req *volume_server_pb.VolumeCopyRequest, stream volume_server_pb.VolumeServer_VolumeCopyServer) error {
	if err := vs.checkGrpcAdminAuth(stream.Context()); err != nil {
		return err
	}
	if err := vs.CheckMaintenanceMode(); err != nil {
		return err
	}

	// A pre-existing local replica is NOT deleted up front. Deleting before the
	// source is confirmed reachable destroys a healthy copy on a transient
	// source outage (and, on retry, can lose the volume entirely). The delete is
	// deferred until ReadVolumeFileStatus below proves the source holds the
	// volume; readability alone is the gate (size/count comparisons invert after
	// divergent vacuum/compaction and would block valid re-replication).
	hasExistingVolume := vs.store.GetVolume(needle.VolumeId(req.VolumeId)) != nil

	// the master will not start compaction for read-only volumes, so it is safe to just copy files directly
	// copy .dat and .idx files
	//   read .idx .dat file size and timestamp
	//   send .idx file
	//   send .dat file
	//   confirm size and timestamp
	var volFileInfoResp *volume_server_pb.ReadVolumeFileStatusResponse
	var dataBaseFileName, indexBaseFileName, idxFileName, datFileName string
	var hasRemoteDatFile bool
	err := operation.WithVolumeServerClient(true, pb.ServerAddress(req.SourceDataNode), vs.grpcDialOption, func(client volume_server_pb.VolumeServerClient) error {
		var err error
		volFileInfoResp, err = client.ReadVolumeFileStatus(context.Background(),
			&volume_server_pb.ReadVolumeFileStatusRequest{
				VolumeId: req.VolumeId,
			})
		if nil != err {
			return fmt.Errorf("read volume file status failed, %w", err)
		}

		// Source is reachable and holds the volume: only now is it safe to drop
		// an existing local replica before overwriting its files.
		if hasExistingVolume {
			glog.V(0).Infof("volume %d already exists. deleting before copying from %s...", req.VolumeId, req.SourceDataNode)
			// keep remote data: the inbound copy carries a .vif that may point at
			// the same cloud-tier object the existing volume references.
			if delErr := vs.store.DeleteVolume(needle.VolumeId(req.VolumeId), false, true); delErr != nil {
				return fmt.Errorf("failed to delete existing volume %d: %v", req.VolumeId, delErr)
			}
			glog.V(0).Infof("deleted existing volume %d before copying.", req.VolumeId)
		}

		diskType := volFileInfoResp.DiskType
		if req.DiskType != "" {
			diskType = req.DiskType
		}
		hasRemoteDatFile = volFileInfoResp.VolumeInfo != nil && len(volFileInfoResp.VolumeInfo.Files) > 0
		// a remote-backed volume only lands its .idx/.vif locally; the .dat stays in the tier
		neededSpace := volFileInfoResp.DatFileSize
		if hasRemoteDatFile {
			neededSpace = volFileInfoResp.IdxFileSize
		}
		location := vs.store.FindFreeLocation(func(location *storage.DiskLocation) bool {
			return location.DiskType == types.ToDiskType(diskType) &&
				location.AvailableSpace.Load() > neededSpace
		})
		if location == nil {
			return fmt.Errorf("%s %s", util.ErrVolumeNoSpaceLeft, types.ToDiskType(diskType).ReadableString())
		}

		dataBaseFileName = storage.VolumeFileName(location.Directory, volFileInfoResp.Collection, int(req.VolumeId))
		indexBaseFileName = storage.VolumeFileName(location.IdxDirectory, volFileInfoResp.Collection, int(req.VolumeId))

		// The .note marks the copy as in-progress; a leftover note fails the
		// volume load on restart, so a write failure must abort the copy.
		if noteErr := util.WriteFile(dataBaseFileName+".note", []byte(fmt.Sprintf("copying from %s", req.SourceDataNode)), 0755); noteErr != nil {
			err = noteErr
			return fmt.Errorf("write .note for volume %d: %w", req.VolumeId, noteErr)
		}

		defer func() {
			if err != nil {
				os.Remove(dataBaseFileName + ".dat")
				os.Remove(indexBaseFileName + ".idx")
				os.Remove(dataBaseFileName + ".vif")
				os.Remove(dataBaseFileName + ".note")
			}
		}()

		var preallocateSize int64
		if grpcErr := pb.WithMasterClient(context.Background(), false, vs.GetMaster(context.Background()), vs.grpcDialOption, false, func(client master_pb.SeaweedClient) error {
			resp, err := client.GetMasterConfiguration(context.Background(), &master_pb.GetMasterConfigurationRequest{})
			if err != nil {
				return fmt.Errorf("get master %s configuration: %v", vs.GetMaster(context.Background()), err)
			}
			if resp.VolumePreallocate {
				preallocateSize = int64(resp.VolumeSizeLimitMB) * (1 << 20)
			}
			return nil
		}); grpcErr != nil {
			glog.V(0).Infof("connect to %s: %v", vs.GetMaster(context.Background()), grpcErr)
		}

		if preallocateSize > 0 && !hasRemoteDatFile {
			volumeFile := dataBaseFileName + ".dat"
			_, err := backend.CreateVolumeFile(volumeFile, preallocateSize, 0)
			if err != nil {
				return fmt.Errorf("create volume file %s: %v", volumeFile, err)
			}
		}

		// println("source:", volFileInfoResp.String())
		copyResponse := &volume_server_pb.VolumeCopyResponse{}
		reportInterval := int64(1024 * 1024 * 128)
		nextReportTarget := reportInterval
		var modifiedTsNs int64
		var sendErr error
		var ioBytePerSecond int64
		if req.IoBytePerSecond <= 0 {
			ioBytePerSecond = vs.maintenanceBytePerSecond
		} else {
			ioBytePerSecond = req.IoBytePerSecond
		}
		throttler := util.NewWriteThrottler(ioBytePerSecond)

		if !hasRemoteDatFile {
			if modifiedTsNs, err = vs.doCopyFileWithThrottler(client, false, req.Collection, req.VolumeId, volFileInfoResp.CompactionRevision, volFileInfoResp.DatFileSize, dataBaseFileName, ".dat", false, true, func(processed int64) bool {
				if processed > nextReportTarget {
					copyResponse.ProcessedBytes = processed
					if sendErr = stream.Send(copyResponse); sendErr != nil {
						return false
					}
					nextReportTarget = processed + reportInterval
				}
				return true
			}, throttler); err != nil {
				return err
			}
			if sendErr != nil {
				return sendErr
			}
			if modifiedTsNs > 0 {
				os.Chtimes(dataBaseFileName+".dat", time.Unix(0, modifiedTsNs), time.Unix(0, modifiedTsNs))
			}
		}

		if modifiedTsNs, err = vs.doCopyFileWithThrottler(client, false, req.Collection, req.VolumeId, volFileInfoResp.CompactionRevision, volFileInfoResp.IdxFileSize, indexBaseFileName, ".idx", false, false, nil, throttler); err != nil {
			return err
		}
		if modifiedTsNs > 0 {
			os.Chtimes(indexBaseFileName+".idx", time.Unix(0, modifiedTsNs), time.Unix(0, modifiedTsNs))
		}

		if modifiedTsNs, err = vs.doCopyFileWithThrottler(client, false, req.Collection, req.VolumeId, volFileInfoResp.CompactionRevision, 1024*1024, dataBaseFileName, ".vif", false, true, nil, throttler); err != nil {
			return err
		}
		if modifiedTsNs > 0 {
			os.Chtimes(dataBaseFileName+".vif", time.Unix(0, modifiedTsNs), time.Unix(0, modifiedTsNs))
		}

		// A leftover .note fails the load on the next restart, so a removal
		// failure must fail the copy rather than be silently swallowed.
		if noteErr := os.Remove(dataBaseFileName + ".note"); noteErr != nil && !os.IsNotExist(noteErr) {
			err = noteErr
			return fmt.Errorf("remove .note for volume %d: %w", req.VolumeId, noteErr)
		}

		return nil
	})

	if err != nil {
		return err
	}
	if dataBaseFileName == "" {
		return fmt.Errorf("not found volume %d file", req.VolumeId)
	}

	idxFileName = indexBaseFileName + ".idx"
	datFileName = dataBaseFileName + ".dat"

	defer func() {
		if err != nil && dataBaseFileName != "" {
			os.Remove(idxFileName)
			os.Remove(datFileName)
			os.Remove(dataBaseFileName + ".vif")
		}
	}()

	if err = checkCopyFiles(volFileInfoResp, hasRemoteDatFile, idxFileName, datFileName); err != nil { // added by panyc16
		return err
	}

	var lastAppendAtNs = volFileInfoResp.DatFileTimestampSeconds * uint64(time.Second)
	if !hasRemoteDatFile {
		if appendAtNs, appendErr := findLastAppendAtNsFromCopiedFiles(idxFileName, datFileName, needle.Version(volFileInfoResp.Version)); appendErr == nil && appendAtNs > 0 {
			lastAppendAtNs = appendAtNs
		} else if appendErr != nil {
			glog.V(1).Infof("failed to find last append timestamp for volume %d: %v", req.VolumeId, appendErr)
		}
	}

	// mount the volume
	err = vs.store.MountVolume(needle.VolumeId(req.VolumeId))
	if err != nil {
		return fmt.Errorf("failed to mount volume %d: %v", req.VolumeId, err)
	}

	if err = stream.Send(&volume_server_pb.VolumeCopyResponse{
		LastAppendAtNs: lastAppendAtNs,
	}); err != nil {
		glog.Errorf("send response: %v", err)
	}

	return err
}

func (vs *VolumeServer) doCopyFile(client volume_server_pb.VolumeServerClient, isEcVolume bool, collection string, vid, compactRevision uint32, stopOffset uint64, baseFileName, ext string, isAppend, ignoreSourceFileNotFound bool, progressFn storage.ProgressFunc) (modifiedTsNs int64, err error) {
	return vs.doCopyFileWithThrottler(client, isEcVolume, collection, vid, compactRevision, stopOffset, baseFileName, ext, isAppend, ignoreSourceFileNotFound, progressFn, util.NewWriteThrottler(vs.maintenanceBytePerSecond))
}

func (vs *VolumeServer) doCopyFileWithThrottler(client volume_server_pb.VolumeServerClient, isEcVolume bool, collection string, vid, compactRevision uint32, stopOffset uint64, baseFileName, ext string, isAppend, ignoreSourceFileNotFound bool, progressFn storage.ProgressFunc, throttler *util.WriteThrottler) (modifiedTsNs int64, err error) {

	copyFileClient, err := client.CopyFile(context.Background(), &volume_server_pb.CopyFileRequest{
		VolumeId:                 vid,
		Ext:                      ext,
		CompactionRevision:       compactRevision,
		StopOffset:               stopOffset,
		Collection:               collection,
		IsEcVolume:               isEcVolume,
		IgnoreSourceFileNotFound: ignoreSourceFileNotFound,
	})
	if err != nil {
		return modifiedTsNs, fmt.Errorf("failed to start copying volume %d %s file: %v", vid, ext, err)
	}

	modifiedTsNs, err = writeToFile(copyFileClient, baseFileName+ext, throttler, isAppend, ignoreSourceFileNotFound, progressFn)
	if err != nil {
		return modifiedTsNs, fmt.Errorf("failed to copy %s file: %v", baseFileName+ext, err)
	}

	return modifiedTsNs, nil

}

/*
*
only check the differ of the file size
todo: maybe should check the received count and deleted count of the volume
*/
func checkCopyFiles(originFileInf *volume_server_pb.ReadVolumeFileStatusResponse, hasRemoteDatFile bool, idxFileName, datFileName string) error {
	stat, err := os.Stat(idxFileName)
	if err != nil {
		// If the idx file doesn't exist but the expected size is 0, that's OK (empty volume)
		if os.IsNotExist(err) && originFileInf.IdxFileSize == 0 {
			// empty volume, idx file not needed
		} else {
			return fmt.Errorf("stat idx file %s failed: %v", idxFileName, err)
		}
	} else if originFileInf.IdxFileSize != uint64(stat.Size()) {
		return fmt.Errorf("idx file %s size [%v] is not same as origin file size [%v]",
			idxFileName, stat.Size(), originFileInf.IdxFileSize)
	}

	if hasRemoteDatFile {
		return nil
	}

	stat, err = os.Stat(datFileName)
	if err != nil {
		return fmt.Errorf("get dat file info failed, %w", err)
	}
	if originFileInf.DatFileSize != uint64(stat.Size()) {
		return fmt.Errorf("the dat file size [%v] is not same as origin file size [%v]",
			stat.Size(), originFileInf.DatFileSize)
	}
	return nil
}

func findLastAppendAtNsFromCopiedFiles(idxFileName, datFileName string, version needle.Version) (uint64, error) {
	if version < needle.Version3 {
		return 0, nil
	}

	idxFile, err := os.Open(idxFileName)
	if err != nil {
		return 0, fmt.Errorf("open idx file %s: %w", idxFileName, err)
	}
	defer idxFile.Close()

	fi, err := idxFile.Stat()
	if err != nil {
		return 0, fmt.Errorf("stat idx file %s: %w", idxFileName, err)
	}
	if fi.Size() == 0 {
		return 0, nil
	}
	if fi.Size()%int64(types.NeedleMapEntrySize) != 0 {
		return 0, fmt.Errorf("unexpected idx file %s size: %d", idxFileName, fi.Size())
	}

	buf := make([]byte, types.NeedleMapEntrySize)
	if _, err := idxFile.ReadAt(buf, fi.Size()-int64(types.NeedleMapEntrySize)); err != nil {
		return 0, fmt.Errorf("read idx file %s: %w", idxFileName, err)
	}
	_, offset, _ := idx.IdxFileEntry(buf)
	if offset.IsZero() {
		return 0, nil
	}

	datFile, err := os.Open(datFileName)
	if err != nil {
		return 0, fmt.Errorf("open dat file %s: %w", datFileName, err)
	}
	defer datFile.Close()

	datBackend := backend.NewDiskFile(datFile)
	n, _, _, err := needle.ReadNeedleHeader(datBackend, version, offset.ToActualOffset())
	if err != nil {
		return 0, fmt.Errorf("read needle header %s offset %d: %w", datFileName, offset.ToActualOffset(), err)
	}

	tailOffset := offset.ToActualOffset() + int64(types.NeedleHeaderSize) + int64(n.Size)
	tail := make([]byte, needle.NeedleChecksumSize+types.TimestampSize)
	readCount, readErr := datBackend.ReadAt(tail, tailOffset)
	if readErr == io.EOF && readCount == len(tail) {
		readErr = nil
	}
	if readErr != nil {
		return 0, fmt.Errorf("read needle tail %s offset %d: %w", datFileName, tailOffset, readErr)
	}

	return util.BytesToUint64(tail[needle.NeedleChecksumSize : needle.NeedleChecksumSize+types.TimestampSize]), nil
}

func writeToFile(client volume_server_pb.VolumeServer_CopyFileClient, fileName string, wt *util.WriteThrottler, isAppend, ignoreSourceFileNotFound bool, progressFn storage.ProgressFunc) (modifiedTsNs int64, err error) {
	glog.V(4).Infof("writing to %s", fileName)

	// For an optional copy (ignoreSourceFileNotFound), stage into a temp sibling
	// and atomically rename on success, so a source that lacks the file cannot
	// truncate a valid pre-existing destination. Mandatory copies write in place.
	writePath := fileName
	stageThenCommit := ignoreSourceFileNotFound && !isAppend
	if stageThenCommit {
		writePath = fileName + ".copying"
	}

	flags := os.O_WRONLY | os.O_CREATE | os.O_TRUNC
	if isAppend {
		flags = os.O_WRONLY | os.O_CREATE
	}
	dst, err := os.OpenFile(writePath, flags, 0644)
	if err != nil {
		return modifiedTsNs, fmt.Errorf("open file %s: %w", writePath, err)
	}
	// Track the destination handle through a closer that runs at most once.
	// On Windows os.Remove fails while the file is still open, so any path
	// that wants to delete the file we just created must close the handle
	// first. The deferred call here is the safety net for normal returns.
	dstClosed := false
	closeDst := func() {
		if dstClosed {
			return
		}
		dstClosed = true
		_ = dst.Close()
	}
	defer closeDst()

	// removeIncomplete deletes the partially-written file we just opened
	// with O_TRUNC. Used on stream / write / cancellation errors so a
	// caller (notably VolumeEcShardsCopy distributing .ecx) doesn't end
	// up with a 0-byte stub that downstream code mistakes for a valid
	// empty file. Skip in isAppend mode — the existing content is not
	// ours to remove, and resumable appends rely on partial state.
	removeIncomplete := func(reason string) {
		if isAppend {
			return
		}
		closeDst()
		if removeErr := os.Remove(writePath); removeErr != nil && !os.IsNotExist(removeErr) {
			glog.Warningf("failed to remove incomplete file %s after %s: %v", writePath, reason, removeErr)
		} else if removeErr == nil {
			glog.V(1).Infof("removed incomplete file %s after %s", writePath, reason)
		}
	}

	var progressedBytes int64
	for {
		resp, receiveErr := client.Recv()
		if receiveErr == io.EOF {
			break
		}
		if resp != nil && resp.ModifiedTsNs != 0 {
			modifiedTsNs = resp.ModifiedTsNs
		}
		if receiveErr != nil {
			removeIncomplete("receive error")
			return modifiedTsNs, fmt.Errorf("receiving %s: %w", fileName, receiveErr)
		}
		if _, writeErr := dst.Write(resp.FileContent); writeErr != nil {
			removeIncomplete("write error")
			return modifiedTsNs, fmt.Errorf("write file %s: %w", fileName, writeErr)
		}
		progressedBytes += int64(len(resp.FileContent))
		if progressFn != nil {
			if !progressFn(progressedBytes) {
				removeIncomplete("progress cancelled")
				return modifiedTsNs, fmt.Errorf("interrupted copy operation")
			}
		}
		wt.MaybeSlowdown(int64(len(resp.FileContent)))
	}
	// If we never received a modifiedTsNs, it means the source file did not exist.
	// Remove the empty file we created to avoid leaving corrupted empty files.
	// Note: We check modifiedTsNs (not progressedBytes) because an empty source file
	// is valid and should result in an empty destination file.
	if modifiedTsNs == 0 && !isAppend {
		closeDst()
		if removeErr := os.Remove(writePath); removeErr != nil && !os.IsNotExist(removeErr) {
			glog.V(1).Infof("failed to remove empty file %s: %v", writePath, removeErr)
		} else if removeErr == nil {
			glog.V(1).Infof("removed empty file %s (source file not found)", writePath)
		}
		return modifiedTsNs, nil
	}

	// Commit the staged temp into place.
	if stageThenCommit {
		closeDst()
		if renameErr := os.Rename(writePath, fileName); renameErr != nil {
			os.Remove(writePath)
			return modifiedTsNs, fmt.Errorf("commit copied file %s: %w", fileName, renameErr)
		}
	}
	return modifiedTsNs, nil
}

func (vs *VolumeServer) ReadVolumeFileStatus(ctx context.Context, req *volume_server_pb.ReadVolumeFileStatusRequest) (*volume_server_pb.ReadVolumeFileStatusResponse, error) {
	resp := &volume_server_pb.ReadVolumeFileStatusResponse{}
	v := vs.store.GetVolume(needle.VolumeId(req.VolumeId))
	if v == nil {
		return nil, fmt.Errorf("not found volume id %d", req.VolumeId)
	}

	resp.VolumeId = req.VolumeId
	datSize, idxSize, modTime := v.FileStat()
	resp.DatFileSize = datSize
	resp.IdxFileSize = idxSize
	resp.DatFileTimestampSeconds = uint64(modTime.Unix())
	resp.IdxFileTimestampSeconds = uint64(modTime.Unix())
	resp.FileCount = v.FileCount()
	resp.CompactionRevision = uint32(v.CompactionRevision)
	resp.Collection = v.Collection
	resp.DiskType = string(v.DiskType())
	resp.VolumeInfo = v.GetVolumeInfo()
	resp.Version = uint32(v.Version())
	return resp, nil
}

// checkVolumeFileExtension guards the client-supplied Ext that CopyFile and
// ReceiveFile turn into an on-disk path. Both RPCs are intentionally ungated
// for cluster-internal peers (see volume_grpc_admin_auth_coverage_test.go), so
// this is the only check standing between a peer request and the os.Open /
// os.Create target: without it an Ext like "/../../x" is joined onto the volume
// directory and, once path-cleaned, resolves outside it. A genuine extension is
// a leading dot followed by alphanumerics -- ".dat", ".idx", ".vif", ".ecx",
// ".ecj", ".ecsum", ".ec00".. -- and never contains a separator or "..".
func checkVolumeFileExtension(ext string) error {
	if len(ext) < 2 || ext[0] != '.' {
		return fmt.Errorf("invalid file extension %q", ext)
	}
	for _, r := range ext[1:] {
		if r < '0' || (r > '9' && r < 'A') || (r > 'Z' && r < 'a') || r > 'z' {
			return fmt.Errorf("invalid file extension %q", ext)
		}
	}
	return nil
}

// checkVolumeCollection guards the client-supplied Collection, which CopyFile
// and ReceiveFile fold into a path component ("<collection>_<vid>"). An empty
// collection is the default; any other value must be a single path element so a
// collection like "../../x" cannot climb out of the volume directory once
// path-cleaned. Collection names are user-facing and may hold '.' or '-', so
// this rejects only separators and bare parent references rather than the
// stricter alphanumeric rule used for extensions.
func checkVolumeCollection(collection string) error {
	if collection == "." || collection == ".." || strings.ContainsAny(collection, `/\`) {
		return fmt.Errorf("invalid collection %q", collection)
	}
	return nil
}

// CopyFile client pulls the volume related file from the source server.
// if req.CompactionRevision != math.MaxUint32, it ensures the compact revision is as expected
// The copying still stop at req.StopOffset, but you can set it to math.MaxUint64 in order to read all data.
func (vs *VolumeServer) CopyFile(req *volume_server_pb.CopyFileRequest, stream volume_server_pb.VolumeServer_CopyFileServer) error {

	if err := checkVolumeFileExtension(req.Ext); err != nil {
		return err
	}
	if err := checkVolumeCollection(req.Collection); err != nil {
		return err
	}

	var fileName string
	if !req.IsEcVolume {
		v := vs.store.GetVolume(needle.VolumeId(req.VolumeId))
		if v == nil {
			return fmt.Errorf("not found volume id %d", req.VolumeId)
		}

		if uint32(v.CompactionRevision) != req.CompactionRevision && req.CompactionRevision != math.MaxUint32 {
			return fmt.Errorf("volume %d is compacted", req.VolumeId)
		}
		v.SyncToDisk()
		fileName = v.FileName(req.Ext)
	} else {
		// Sync EC volume files to disk before copying to ensure deletions are visible
		// This fixes issue #7751 where deleted files in encoded volumes were not
		// properly marked as deleted when decoded.
		if ecVolume, found := vs.store.FindEcVolume(needle.VolumeId(req.VolumeId)); found {
			ecVolume.Sync()
		}

		baseFileName := erasure_coding.EcShardBaseFileName(req.Collection, int(req.VolumeId)) + req.Ext
		for _, location := range vs.store.Locations {
			tName := util.Join(location.Directory, baseFileName)
			if util.FileExists(tName) {
				fileName = tName
			}
			tName = util.Join(location.IdxDirectory, baseFileName)
			if util.FileExists(tName) {
				fileName = tName
			}
		}
		if fileName == "" {
			if req.IgnoreSourceFileNotFound {
				return nil
			}
			return fmt.Errorf("CopyFile not found ec volume id %d", req.VolumeId)
		}
	}

	bytesToRead := int64(req.StopOffset)

	file, err := os.Open(fileName)
	if err != nil {
		if os.IsNotExist(err) {
			// If file doesn't exist and we're asked to copy 0 bytes (empty file),
			// or if IgnoreSourceFileNotFound is set, treat as success
			if req.IgnoreSourceFileNotFound || req.StopOffset == 0 {
				return nil
			}
		}
		return err
	}
	defer file.Close()

	fileInfo, err := file.Stat()
	if err != nil {
		return err
	}
	fileModTsNs := fileInfo.ModTime().UnixNano()

	buffer := make([]byte, BufferSizeLimit)

	for bytesToRead > 0 {
		bytesread, err := file.Read(buffer)

		// println(fileName, "read", bytesread, "bytes, with target", bytesToRead)

		if err != nil {
			if err != io.EOF {
				return err
			}
			// println(fileName, "read", bytesread, "bytes, with target", bytesToRead, "err", err.Error())
			break
		}

		if int64(bytesread) > bytesToRead {
			bytesread = int(bytesToRead)
		}
		err = stream.Send(&volume_server_pb.CopyFileResponse{
			FileContent:  buffer[:bytesread],
			ModifiedTsNs: fileModTsNs,
		})
		if err != nil {
			// println("sending", bytesread, "bytes err", err.Error())
			return err
		}
		fileModTsNs = 0 // only send once

		bytesToRead -= int64(bytesread)

	}

	// If no data has been sent in the loop (e.g. for an empty file, or when stopOffset is 0),
	// we still need to send the ModifiedTsNs so the client knows the source file exists.
	// fileModTsNs is set to 0 after the first send, so if it's still non-zero,
	// we haven't sent anything yet.
	if fileModTsNs != 0 {
		err = stream.Send(&volume_server_pb.CopyFileResponse{
			ModifiedTsNs: fileModTsNs,
		})
		if err != nil {
			return err
		}
	}

	return nil
}

// diskHoldsEcShardFile reports whether dir contains any <vid>.ecNN shard file,
// so a decoded <vid>.dat is never staged beside a shard. Unlike FindEcVolume,
// it also catches shards present on disk but not mounted.
func diskHoldsEcShardFile(dir, collection string, vid needle.VolumeId) bool {
	base := erasure_coding.EcShardFileName(collection, dir, int(vid))
	for i := 0; i < erasure_coding.MaxShardCount; i++ {
		if fi, err := os.Stat(base + erasure_coding.ToExt(i)); err == nil && !fi.IsDir() && fi.Size() > 0 {
			return true
		}
	}
	return false
}

// ReceiveFile receives a file stream from client and writes it to storage
func (vs *VolumeServer) ReceiveFile(stream volume_server_pb.VolumeServer_ReceiveFileServer) error {
	if err := vs.CheckMaintenanceMode(); err != nil {
		return err
	}

	var fileInfo *volume_server_pb.ReceiveFileInfo
	var targetFile *os.File
	var filePath string
	var bytesWritten uint64

	defer func() {
		if targetFile != nil {
			targetFile.Close()
		}
	}()

	for {
		req, err := stream.Recv()
		if err == io.EOF {
			// Stream completed successfully
			if targetFile != nil {
				targetFile.Sync()
				glog.V(1).Infof("Successfully received file %s (%d bytes)", filePath, bytesWritten)
			}
			return stream.SendAndClose(&volume_server_pb.ReceiveFileResponse{
				BytesWritten: bytesWritten,
			})
		}
		if err != nil {
			// Clean up on error
			if targetFile != nil {
				targetFile.Close()
				os.Remove(filePath)
			}
			glog.Errorf("Failed to receive stream: %v", err)
			return fmt.Errorf("failed to receive stream: %v", err)
		}

		switch data := req.Data.(type) {
		case *volume_server_pb.ReceiveFileRequest_Info:
			// First message contains file info
			fileInfo = data.Info
			glog.V(1).Infof("ReceiveFile: volume %d, ext %s, collection %s, shard %d, size %d",
				fileInfo.VolumeId, fileInfo.Ext, fileInfo.Collection, fileInfo.ShardId, fileInfo.FileSize)

			if err := checkVolumeFileExtension(fileInfo.Ext); err != nil {
				glog.Errorf("ReceiveFile: %v", err)
				return stream.SendAndClose(&volume_server_pb.ReceiveFileResponse{
					Error: err.Error(),
				})
			}
			if err := checkVolumeCollection(fileInfo.Collection); err != nil {
				glog.Errorf("ReceiveFile: %v", err)
				return stream.SendAndClose(&volume_server_pb.ReceiveFileResponse{
					Error: err.Error(),
				})
			}

			if fileInfo.IsEcVolume {
				// os.Create below truncates in place; a mounted EcVolume
				// holds fds on the same inodes, so overwriting corrupts
				// live readers.
				if _, mounted := vs.store.FindEcVolume(needle.VolumeId(fileInfo.VolumeId)); mounted {
					mountedDisks := vs.store.FindEcVolumeDiskIds(needle.VolumeId(fileInfo.VolumeId))
					glog.Errorf("ReceiveFile: ec volume %d is mounted on disk_ids:%v; refusing overwrite for %s", fileInfo.VolumeId, mountedDisks, fileInfo.Ext)
					return stream.SendAndClose(&volume_server_pb.ReceiveFileResponse{
						Error: fmt.Sprintf("ec volume %d is mounted on disk_ids:%v; unmount before ReceiveFile", fileInfo.VolumeId, mountedDisks),
					})
				}

				// disk_id=0 means "unset" (protobuf default), so auto-select
				// using the same primitive as VolumeEcShardsCopy: prefer a
				// disk that has the EC volume mounted, then a disk that owns
				// the .ecx on disk (the volume hasn't been mounted yet —
				// relevant when shards stream in mid-rebuild before any
				// mount has happened; see #9212), then any HDD, then any
				// disk.
				var targetLocation *storage.DiskLocation
				if fileInfo.DiskId > 0 {
					if fileInfo.DiskId >= uint32(len(vs.store.Locations)) {
						glog.Errorf("ReceiveFile: invalid disk_id %d: only have %d disks", fileInfo.DiskId, len(vs.store.Locations))
						return stream.SendAndClose(&volume_server_pb.ReceiveFileResponse{
							Error: fmt.Sprintf("invalid disk_id %d: only have %d disks", fileInfo.DiskId, len(vs.store.Locations)),
						})
					}
					targetLocation = vs.store.Locations[fileInfo.DiskId]
				} else {
					// Pass the build's default data-shard count for the helper's
					// free-slot maths; it's a parameter so custom-ratio builds
					// (e.g. enterprise) can swap it without touching this file.
					targetLocation = vs.store.FindEcShardTargetLocation(fileInfo.Collection, needle.VolumeId(fileInfo.VolumeId), erasure_coding.DataShardsCount)
				}
				if targetLocation == nil {
					glog.Errorf("ReceiveFile: no storage location available")
					return stream.SendAndClose(&volume_server_pb.ReceiveFileResponse{
						Error: "no storage location available",
					})
				}

				// Create EC shard file path
				baseFileName := erasure_coding.EcShardBaseFileName(fileInfo.Collection, int(fileInfo.VolumeId))
				filePath = util.Join(targetLocation.Directory, baseFileName+fileInfo.Ext)
			} else {
				// Regular volume file
				v := vs.store.GetVolume(needle.VolumeId(fileInfo.VolumeId))
				if v == nil {
					if fileInfo.DiskType == "" {
						glog.Errorf("ReceiveFile: volume %d not found", fileInfo.VolumeId)
						return stream.SendAndClose(&volume_server_pb.ReceiveFileResponse{
							Error: fmt.Sprintf("volume %d not found", fileInfo.VolumeId),
						})
					}
					// Staged-new-volume mode (EC decode onto a clean peer): the
					// volume does not exist here yet. Pick a free-slot disk location
					// of the requested medium and stage the file as
					// <base><ext>.copying, to be renamed into place and mounted by
					// VolumeEcShardsToVolume(from_staged). .idx.copying/.vif.copying
					// are not valid volume names, so the scanner never half-loads.
					want := types.ToDiskType(fileInfo.DiskType)
					stagedVid := needle.VolumeId(fileInfo.VolumeId)
					loc := vs.store.FindFreeLocation(func(l *storage.DiskLocation) bool {
						if l.DiskType != want {
							return false
						}
						// Don't stage the decoded .dat onto a disk that holds a shard
						// of this vid. Check the mounted map and the on-disk files, so
						// an unmounted or orphan shard (on disk, absent from the map)
						// is caught too.
						if _, holds := l.FindEcVolume(stagedVid); holds {
							return false
						}
						return !diskHoldsEcShardFile(l.Directory, fileInfo.Collection, stagedVid)
					})
					if loc == nil {
						return stream.SendAndClose(&volume_server_pb.ReceiveFileResponse{
							Error: fmt.Sprintf("no %s disk location with a free slot for volume %d", fileInfo.DiskType, fileInfo.VolumeId),
						})
					}
					filePath = storage.VolumeFileName(loc.Directory, fileInfo.Collection, int(fileInfo.VolumeId)) + fileInfo.Ext + ".copying"
				} else {
					filePath = v.FileName(fileInfo.Ext)
				}
			}

			// Create target file
			targetFile, err = os.Create(filePath)
			if err != nil {
				glog.Errorf("ReceiveFile: failed to create file %s: %v", filePath, err)
				return stream.SendAndClose(&volume_server_pb.ReceiveFileResponse{
					Error: fmt.Sprintf("failed to create file: %v", err),
				})
			}
			glog.V(1).Infof("ReceiveFile: created target file %s", filePath)

		case *volume_server_pb.ReceiveFileRequest_FileContent:
			// Subsequent messages contain file content
			if targetFile == nil {
				glog.Errorf("ReceiveFile: file info must be sent first")
				return stream.SendAndClose(&volume_server_pb.ReceiveFileResponse{
					Error: "file info must be sent first",
				})
			}

			n, err := targetFile.Write(data.FileContent)
			if err != nil {
				targetFile.Close()
				os.Remove(filePath)
				glog.Errorf("ReceiveFile: failed to write to file %s: %v", filePath, err)
				return stream.SendAndClose(&volume_server_pb.ReceiveFileResponse{
					Error: fmt.Sprintf("failed to write file: %v", err),
				})
			}
			bytesWritten += uint64(n)
			glog.V(2).Infof("ReceiveFile: wrote %d bytes to %s (total: %d)", n, filePath, bytesWritten)

		default:
			glog.Errorf("ReceiveFile: unknown message type")
			return stream.SendAndClose(&volume_server_pb.ReceiveFileResponse{
				Error: "unknown message type",
			})
		}
	}
}