bufio: make Writer.ReadFrom not flush prematurely. For example,
many small writes to a network may be less efficient that a few
large writes.
This fixes net/http's TestClientWrites, broken by 6565056 that
introduced Writer.ReadFrom. That test implicitly assumed that
calling io.Copy on a *bufio.Writer wouldn't write to the
underlying network until the buffer was full.
R=dsymonds
CC=bradfitz, golang-dev, mchaten, mikioh.mikioh
https://golang.org/cl/6743044
diff --git a/src/pkg/bufio/bufio_test.go b/src/pkg/bufio/bufio_test.go
index 3d07639..763b123 100644
--- a/src/pkg/bufio/bufio_test.go
+++ b/src/pkg/bufio/bufio_test.go
@@ -881,6 +881,64 @@
}
}
+// TestWriterReadFromCounts tests that using io.Copy to copy into a
+// bufio.Writer does not prematurely flush the buffer. For example, when
+// buffering writes to a network socket, excessive network writes should be
+// avoided.
+func TestWriterReadFromCounts(t *testing.T) {
+ var w0 writeCountingDiscard
+ b0 := NewWriterSize(&w0, 1234)
+ b0.WriteString(strings.Repeat("x", 1000))
+ if w0 != 0 {
+ t.Fatalf("write 1000 'x's: got %d writes, want 0", w0)
+ }
+ b0.WriteString(strings.Repeat("x", 200))
+ if w0 != 0 {
+ t.Fatalf("write 1200 'x's: got %d writes, want 0", w0)
+ }
+ io.Copy(b0, &onlyReader{strings.NewReader(strings.Repeat("x", 30))})
+ if w0 != 0 {
+ t.Fatalf("write 1230 'x's: got %d writes, want 0", w0)
+ }
+ io.Copy(b0, &onlyReader{strings.NewReader(strings.Repeat("x", 9))})
+ if w0 != 1 {
+ t.Fatalf("write 1239 'x's: got %d writes, want 1", w0)
+ }
+
+ var w1 writeCountingDiscard
+ b1 := NewWriterSize(&w1, 1234)
+ b1.WriteString(strings.Repeat("x", 1200))
+ b1.Flush()
+ if w1 != 1 {
+ t.Fatalf("flush 1200 'x's: got %d writes, want 1", w1)
+ }
+ b1.WriteString(strings.Repeat("x", 89))
+ if w1 != 1 {
+ t.Fatalf("write 1200 + 89 'x's: got %d writes, want 1", w1)
+ }
+ io.Copy(b1, &onlyReader{strings.NewReader(strings.Repeat("x", 700))})
+ if w1 != 1 {
+ t.Fatalf("write 1200 + 789 'x's: got %d writes, want 1", w1)
+ }
+ io.Copy(b1, &onlyReader{strings.NewReader(strings.Repeat("x", 600))})
+ if w1 != 2 {
+ t.Fatalf("write 1200 + 1389 'x's: got %d writes, want 2", w1)
+ }
+ b1.Flush()
+ if w1 != 3 {
+ t.Fatalf("flush 1200 + 1389 'x's: got %d writes, want 3", w1)
+ }
+}
+
+// A writeCountingDiscard is like ioutil.Discard and counts the number of times
+// Write is called on it.
+type writeCountingDiscard int
+
+func (w *writeCountingDiscard) Write(p []byte) (int, error) {
+ *w++
+ return len(p), nil
+}
+
// An onlyReader only implements io.Reader, no matter what other methods the underlying implementation may have.
type onlyReader struct {
r io.Reader
