undo CL 86220044 / 41388e58be65

bufio: undo incorrect bug fix

««« original CL description
bufio: fix potential endless loop in ReadByte

Fixes #7745.

LGTM=bradfitz, r
R=r, bradfitz
CC=golang-codereviews
https://golang.org/cl/86220044
»»»

LGTM=adg
R=r, adg
CC=golang-codereviews
https://golang.org/cl/85550045

src/pkg/bufio/bufio.go

@@ -88,22 +88,15 @@ func (b *Reader) fill() {
 		b.r = 0
 	}
 
-	// Read new data: try a limited number of times.
-	for i := maxConsecutiveEmptyReads; i > 0; i-- {
-		n, err := b.rd.Read(b.buf[b.w:])
-		if n < 0 {
-			panic(errNegativeRead)
-		}
-		b.w += n
-		if err != nil {
-			b.err = err
-			return
-		}
-		if n > 0 {
-			return
-		}
+	// Read new data.
+	n, err := b.rd.Read(b.buf[b.w:])
+	if n < 0 {
+		panic(errNegativeRead)
+	}
+	b.w += n
+	if err != nil {
+		b.err = err
 	}
-	b.err = io.ErrNoProgress
 }
 
 func (b *Reader) readErr() error {
@@ -158,9 +151,6 @@ func (b *Reader) Read(p []byte) (n int, err error) {
 			// Large read, empty buffer.
 			// Read directly into p to avoid copy.
 			n, b.err = b.rd.Read(p)
-			if n < 0 {
-				panic(errNegativeRead)
-			}
 			if n > 0 {
 				b.lastByte = int(p[n-1])
 				b.lastRuneSize = -1

src/pkg/bufio/bufio_test.go

@@ -14,7 +14,6 @@ import (
 	"strings"
 	"testing"
 	"testing/iotest"
-	"time"
 	"unicode/utf8"
 )
 
@@ -175,34 +174,6 @@ func TestReader(t *testing.T) {
 	}
 }
 
-type zeroReader struct{}
-
-func (zeroReader) Read(p []byte) (int, error) {
-	return 0, nil
-}
-
-func TestZeroReader(t *testing.T) {
-	var z zeroReader
-	r := NewReader(z)
-
-	c := make(chan error)
-	go func() {
-		_, err := r.ReadByte()
-		c <- err
-	}()
-
-	select {
-	case err := <-c:
-		if err == nil {
-			t.Error("error expected")
-		} else if err != io.ErrNoProgress {
-			t.Error("unexpected error:", err)
-		}
-	case <-time.After(time.Second):
-		t.Error("test timed out (endless loop in ReadByte?)")
-	}
-}
-
 // A StringReader delivers its data one string segment at a time via Read.
 type StringReader struct {
 	data []string