code review 4538088: http,io,net: sendfile support

src/pkg/io/io.go

Index: src/pkg/io/io.go
===================================================================
--- a/src/pkg/io/io.go
+++ b/src/pkg/io/io.go
@@ -117,6 +117,12 @@
 	ReadFrom(r Reader) (n int64, err os.Error)
 }
 
+// ReaderNFrom is the interface that wraps the ReadNFrom method.
+type ReaderNFrom interface {
+	// ReadNFrom reads no more than n bytes from r.
+	ReadNFrom(r Reader, n int64) (int64, os.Error)
+}
+
 // WriterTo is the interface that wraps the WriteTo method.
 type WriterTo interface {
 	WriteTo(w Writer) (n int64, err os.Error)
@@ -216,16 +222,25 @@
 // If dst implements the ReaderFrom interface,
 // the copy is implemented by calling dst.ReadFrom(src).

[r, 2011/05/24 03:00:29]

or ReadNFrom

 func Copyn(dst Writer, src Reader, n int64) (written int64, err os.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 {
+	// If the writer has a ReadNFrom or ReadFrom method, use it to
+	// do the copy.  Avoids a buffer allocation and a copy.
+	hasReader := false
+	if rt, hasReader := dst.(ReaderNFrom); hasReader {

[r, 2011/05/24 03:00:29]

this hasReader shadows the other one.

+		written, err = rt.ReadNFrom(src, n)
+	} else if rt, hasReader := dst.(ReaderFrom); hasReader {
 		written, err = rt.ReadFrom(LimitReader(src, n))
+	}
+	if hasReader {
 		if written < n && err == nil {
 			// rt stopped early; must have been EOF.
 			err = os.EOF
 		}
 		return
 	}
+	return BufferedCopyn(dst, src, n)
+}
+
+func BufferedCopyn(dst Writer, src Reader, n int64) (written int64, err os.Error) {

[r, 2011/05/24 03:00:29]

doc comment.

i'm not happy to see BufferedCopy arrive.  function names shouldn't have to
advertise their implementation.

 	buf := make([]byte, 32*1024)
 	for written < n {
 		l := len(buf)
@@ -273,6 +288,10 @@
 	if wt, ok := src.(WriterTo); ok {
 		return wt.WriteTo(dst)
 	}
+	return BufferedCopy(dst, src)
+}
+
+func BufferedCopy(dst Writer, src Reader) (written int64, err os.Error) {
 	buf := make([]byte, 32*1024)
 	for {
 		nr, er := src.Read(buf)