code review 7312055: io: Simplify CopyN implementation by delegating to Copy.

src/pkg/io/io.go

Index: src/pkg/io/io.go 
=================================================================== 
--- a/src/pkg/io/io.go 
+++ b/src/pkg/io/io.go 
@@ -299,43 +299,12 @@ 
 // If dst implements the ReaderFrom interface, 
 // the copy is implemented using it. 
 func CopyN(dst Writer, src Reader, n int64) (written int64, err error) { 
-	// If the writer has a ReadFrom method, use it to do the copy. 
-	// Avoids a buffer allocation and a copy. 
-	if rt, ok := dst.(ReaderFrom); ok { 
-	written, err = rt.ReadFrom(LimitReader(src, n)) 
-	if written < n && err == nil { 
-	// rt stopped early; must have been EOF. 
-	err = EOF 
-	} 
-	return 
+	written, err = Copy(dst, LimitReader(src, n)) 
+	if written < n && err == nil { 
+	// src stopped early; must have been EOF. 
+	err = EOF 
	} 
-	buf := make([]byte, 32*1024) 
-	for written < n { 
-	l := len(buf) 
-	if d := n - written; d < int64(l) { 
-	l = int(d) 
-	} 
-	nr, er := src.Read(buf[0:l]) 
-	if nr > 0 { 
-	nw, ew := dst.Write(buf[0:nr]) 
-	if nw > 0 { 
-	written += int64(nw) 
-	} 
-	if ew != nil { 
-	err = ew 
-	break 
-	} 
-	if nr != nw { 
-	err = ErrShortWrite 
-	break 
-	} 
-	} 
-	if er != nil { 
-	err = er 
-	break 
-	} 
-	} 
-	return written, err 
+	return 
 } 
 
 // Copy copies from src to dst until either EOF is reached