azureblob/b2/dropbox/gcs/koofr/qingstor/s3: fix 0 length files

In 0386d22cc9 we introduced a test for 0 length files read the
way mount does.

This test failed on these backends which we fix up here.

backend/azureblob/azureblob.go

@@ -13,6 +13,7 @@ import (
 	"encoding/hex"
 	"fmt"
 	"io"
+	"log"
 	"net/http"
 	"net/url"
 	"path"
@@ -1185,7 +1186,7 @@ func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (in io.Read
 	if o.AccessTier() == azblob.AccessTierArchive {
 		return nil, errors.Errorf("Blob in archive tier, you need to set tier to hot or cool first")
 	}
-
+	fs.FixRangeOption(options, o.size)
 	for _, option := range options {
 		switch x := option.(type) {
 		case *fs.RangeOption:
@@ -1205,6 +1206,7 @@ func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (in io.Read
 	ac := azblob.BlobAccessConditions{}
 	var dowloadResponse *azblob.DownloadResponse
 	err = o.fs.pacer.Call(func() (bool, error) {
+		log.Printf("offset=%d, count=%v", offset, count)
 		dowloadResponse, err = blob.Download(ctx, offset, count, ac, false)
 		return o.fs.shouldRetry(err)
 	})

backend/b2/b2.go

@@ -1531,6 +1531,7 @@ var _ io.ReadCloser = &openFile{}
 
 // Open an object for read
 func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (in io.ReadCloser, err error) {
+	fs.FixRangeOption(options, o.size)
 	opts := rest.Opts{
 		Method:  "GET",
 		Options: options,

backend/dropbox/dropbox.go

@@ -975,6 +975,7 @@ func (o *Object) Storable() bool {
 
 // Open an object for read
 func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (in io.ReadCloser, err error) {
+	fs.FixRangeOption(options, o.bytes)
 	headers := fs.OpenOptionHeaders(options)
 	arg := files.DownloadArg{Path: o.remotePath(), ExtraHeaders: headers}
 	err = o.fs.pacer.Call(func() (bool, error) {

backend/googlecloudstorage/googlecloudstorage.go

@@ -966,6 +966,7 @@ func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (in io.Read
 	if err != nil {
 		return nil, err
 	}
+	fs.FixRangeOption(options, o.bytes)
 	fs.OpenOptionAddHTTPHeaders(req.Header, options)
 	var res *http.Response
 	err = o.fs.pacer.Call(func() (bool, error) {

backend/koofr/koofr.go

@@ -154,6 +154,7 @@ func (o *Object) SetModTime(ctx context.Context, mtime time.Time) error {
 func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (io.ReadCloser, error) {
 	var sOff, eOff int64 = 0, -1
 
+	fs.FixRangeOption(options, o.Size())
 	for _, option := range options {
 		switch x := option.(type) {
 		case *fs.SeekOption:
@@ -170,13 +171,6 @@ func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (io.ReadClo
 	if sOff == 0 && eOff < 0 {
 		return o.fs.client.FilesGet(o.fs.mountID, o.fullPath())
 	}
-	if sOff < 0 {
-		sOff = o.Size() - eOff
-		eOff = o.Size()
-	}
-	if eOff > o.Size() {
-		eOff = o.Size()
-	}
 	span := &koofrclient.FileSpan{
 		Start: sOff,
 		End:   eOff,

backend/qingstor/qingstor.go

@@ -964,6 +964,7 @@ func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (io.ReadClo
 
 	key := o.fs.root + o.remote
 	req := qs.GetObjectInput{}
+	fs.FixRangeOption(options, o.size)
 	for _, option := range options {
 		switch option.(type) {
 		case *fs.RangeOption, *fs.SeekOption:

backend/s3/s3.go

@@ -1765,6 +1765,7 @@ func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (in io.Read
 		Bucket: &o.fs.bucket,
 		Key:    &key,
 	}
+	fs.FixRangeOption(options, o.bytes)
 	for _, option := range options {
 		switch option.(type) {
 		case *fs.RangeOption, *fs.SeekOption:

vfs/write_test.go

@@ -11,6 +11,7 @@ import (
 	"github.com/pkg/errors"
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fstest"
+	"github.com/rclone/rclone/lib/random"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -288,12 +289,19 @@ func TestWriteFileModTimeWithOpenWriters(t *testing.T) {
 	}
 }
 
-func TestFileZeroLength(t *testing.T) {
+func testFileReadAt(t *testing.T, n int) {
 	r := fstest.NewRun(t)
 	defer r.Finalise()
 	vfs, fh := writeHandleCreate(t, r)
 
-	// Close the file without writing to it
+	contents := []byte(random.String(n))
+	if n != 0 {
+		written, err := fh.Write(contents)
+		require.NoError(t, err)
+		assert.Equal(t, n, written)
+	}
+
+	// Close the file without writing to it if n==0
 	err := fh.Close()
 	if errors.Cause(err) == fs.ErrorCantUploadEmptyFiles {
 		t.Logf("skipping test: %v", err)
@@ -301,18 +309,27 @@ func TestFileZeroLength(t *testing.T) {
 	}
 	assert.NoError(t, err)
 
-	// read the 0 length file back in using ReadAt into a buffer
+	// read the file back in using ReadAt into a buffer
 	// this simulates what mount does
 	rd, err := vfs.OpenFile("file1", os.O_RDONLY, 0)
 	require.NoError(t, err)
 
 	buf := make([]byte, 1024)
-	n, err := rd.ReadAt(buf, 0)
+	read, err := rd.ReadAt(buf, 0)
 	if err != io.EOF {
 		assert.NoError(t, err)
 	}
-	assert.Equal(t, 0, n)
+	assert.Equal(t, read, n)
+	assert.Equal(t, contents, buf[:read])
 
 	err = rd.Close()
 	assert.NoError(t, err)
 }
+
+func TestFileReadAtZeroLength(t *testing.T) {
+	testFileReadAt(t, 0)
+}
+
+func TestFileReadAtNonZeroLength(t *testing.T) {
+	testFileReadAt(t, 100)
+}