Add File.ReadFrom test with a Sized Reader

This tests ReadFrom's determining concurrency from the estimated input
size. go test -cover -integration, before:

coverage: 77.3% of statements

After:

coverage: 79.2% of statements

client_integration_test.go

@@ -7,6 +7,7 @@ import (
 	"bytes"
 	"crypto/sha1"
 	"errors"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"math/rand"
@@ -164,7 +165,7 @@ func netPipe(t testing.TB) (io.ReadWriteCloser, io.ReadWriteCloser) {
 	return c1, r.Conn
 }
 
-func testClientGoSvr(t testing.TB, readonly bool, delay time.Duration) (*Client, *exec.Cmd) {
+func testClientGoSvr(t testing.TB, readonly bool, delay time.Duration, opts ...ClientOption) (*Client, *exec.Cmd) {
 	c1, c2 := netPipe(t)
 
 	options := []ServerOption{WithDebug(os.Stderr)}
@@ -183,7 +184,7 @@ func testClientGoSvr(t testing.TB, readonly bool, delay time.Duration) (*Client,
 		wr = newDelayedWriter(wr, delay)
 	}
 
-	client, err := NewClientPipe(c2, wr)
+	client, err := NewClientPipe(c2, wr, opts...)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -194,13 +195,13 @@ func testClientGoSvr(t testing.TB, readonly bool, delay time.Duration) (*Client,
 
 // testClient returns a *Client connected to a locally running sftp-server
 // the *exec.Cmd returned must be defer Wait'd.
-func testClient(t testing.TB, readonly bool, delay time.Duration) (*Client, *exec.Cmd) {
+func testClient(t testing.TB, readonly bool, delay time.Duration, opts ...ClientOption) (*Client, *exec.Cmd) {
 	if !*testIntegration {
 		t.Skip("skipping integration test")
 	}
 
 	if *testServerImpl {
-		return testClientGoSvr(t, readonly, delay)
+		return testClientGoSvr(t, readonly, delay, opts...)
 	}
 
 	cmd := exec.Command(*testSftp, "-e", "-R", "-l", debuglevel) // log to stderr, read only
@@ -228,7 +229,7 @@ func testClient(t testing.TB, readonly bool, delay time.Duration) (*Client, *exe
 		t.Skipf("could not start sftp-server process: %v", err)
 	}
 
-	sftp, err := NewClientPipe(pr, pw)
+	sftp, err := NewClientPipe(pr, pw, opts...)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -1489,6 +1490,59 @@ func TestClientReadFrom(t *testing.T) {
 	}
 }
 
+// A sizedReader is a Reader with a completely arbitrary Size.
+type sizedReader struct {
+	io.Reader
+	size int
+}
+
+func (r *sizedReader) Size() int { return r.size }
+
+// Test File.ReadFrom's handling of a Reader's Size:
+// it should be used as a heuristic for determining concurrency only.
+func TestClientReadFromSizeMismatch(t *testing.T) {
+	const (
+		packetSize = 1024
+		filesize   = 4 * packetSize
+	)
+
+	sftp, cmd := testClient(t, READWRITE, NODELAY, MaxPacketChecked(packetSize), UseConcurrentWrites(true))
+	defer cmd.Wait()
+	defer sftp.Close()
+
+	d, err := ioutil.TempDir("", "sftptest-readfrom-size-mismatch")
+	if err != nil {
+		t.Fatal("cannot create temp dir:", err)
+	}
+	defer os.RemoveAll(d)
+
+	buf := make([]byte, filesize)
+
+	for i, reportedSize := range []int{
+		-1, filesize - 100, filesize, filesize + 100,
+	} {
+		t.Run(fmt.Sprint(i), func(t *testing.T) {
+			r := &sizedReader{Reader: bytes.NewReader(buf), size: reportedSize}
+
+			f := path.Join(d, fmt.Sprint(i))
+			w, err := sftp.Create(f)
+			if err != nil {
+				t.Fatal("unexpected error:", err)
+			}
+			defer w.Close()
+
+			n, err := w.ReadFrom(r)
+			assert.EqualValues(t, filesize, n)
+
+			fi, err := os.Stat(f)
+			if err != nil {
+				t.Fatal("unexpected error:", err)
+			}
+			assert.EqualValues(t, filesize, fi.Size())
+		})
+	}
+}
+
 // Issue #145 in github
 // Deadlock in ReadFrom when network drops after 1 good packet.
 // Deadlock would occur anytime desiredInFlight-inFlight==2 and 2 errors