b2: fix chunked streaming uploads

Streaming uploads are used by rclone rcat and rclone mount
--vfs-cache-mode off.

After the multipart chunker refactor the multipart chunked streaming
upload was accidentally mixing the first and the second parts up which
was causing corrupted uploads.

This was caused by a simple off by one error in the refactoring where
we went from 1 based part number counting to 0 based part number
counting.

Fixing this revealed that the metadata wasn't being re-read for the
copied object either.

This fixes both of those issues and adds an integration tests so it
won't happen again.

Fixes #7367

backend/b2/b2_internal_test.go

@@ -1,10 +1,14 @@
 package b2
 
 import (
+	"bytes"
 	"context"
+	"fmt"
 	"testing"
 	"time"
 
+	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/object"
 	"github.com/rclone/rclone/fstest"
 	"github.com/rclone/rclone/fstest/fstests"
 	"github.com/rclone/rclone/lib/random"
@@ -191,7 +195,7 @@ func (f *Fs) InternalTestChunkedCopy(t *testing.T) {
 
 	// Set copy cutoff to mininum value so we make chunks
 	origCutoff := f.opt.CopyCutoff
-	f.opt.CopyCutoff = 5 * 1024 * 1024
+	f.opt.CopyCutoff = minChunkSize
 	defer func() {
 		f.opt.CopyCutoff = origCutoff
 	}()
@@ -216,9 +220,57 @@ func (f *Fs) InternalTestChunkedCopy(t *testing.T) {
 	assert.Equal(t, contents, gotContents)
 }
 
+// The integration tests do a reasonable job of testing the normal
+// streaming upload but don't test the chunked streaming upload.
+func (f *Fs) InternalTestChunkedStreamingUpload(t *testing.T, size int) {
+	ctx := context.Background()
+	contents := random.String(size)
+	item := fstest.NewItem(fmt.Sprintf("chunked-streaming-upload-%d", size), contents, fstest.Time("2001-05-06T04:05:06.499Z"))
+
+	// Set chunk size to mininum value so we make chunks
+	origOpt := f.opt
+	f.opt.ChunkSize = minChunkSize
+	f.opt.UploadCutoff = 0
+	defer func() {
+		f.opt = origOpt
+	}()
+
+	// Do the streaming upload
+	src := object.NewStaticObjectInfo(item.Path, item.ModTime, -1, true, item.Hashes, f)
+	in := bytes.NewBufferString(contents)
+	dst, err := f.PutStream(ctx, in, src)
+	require.NoError(t, err)
+	defer func() {
+		assert.NoError(t, dst.Remove(ctx))
+	}()
+
+	// Check size
+	assert.Equal(t, int64(size), dst.Size())
+
+	// Check modtime
+	srcModTime := src.ModTime(ctx)
+	dstModTime := dst.ModTime(ctx)
+	assert.Equal(t, srcModTime, dstModTime)
+
+	// Make sure contents are correct
+	gotContents := fstests.ReadObject(ctx, t, dst, -1)
+	assert.Equal(t, contents, gotContents, "Contents incorrect")
+}
+
 // -run TestIntegration/FsMkdir/FsPutFiles/Internal
 func (f *Fs) InternalTest(t *testing.T) {
 	t.Run("ChunkedCopy", f.InternalTestChunkedCopy)
+	for _, size := range []fs.SizeSuffix{
+		minChunkSize - 1,
+		minChunkSize,
+		minChunkSize + 1,
+		(3 * minChunkSize) / 2,
+		(5 * minChunkSize) / 2,
+	} {
+		t.Run(fmt.Sprintf("ChunkedStreamingUpload/%d", size), func(t *testing.T) {
+			f.InternalTestChunkedStreamingUpload(t, int(size))
+		})
+	}
 }
 
 var _ fstests.InternalTester = (*Fs)(nil)