From 79d94d504f8f3e82e994a4f63d37f56cebc6e7cc Mon Sep 17 00:00:00 2001
From: Robert Griesemer <gri@golang.org>
Date: Tue, 18 Nov 2008 18:08:05 -0800
Subject: [PATCH] Copyn

R=rsc
DELTA=34  (34 added, 0 deleted, 0 changed)
OCL=19541
CL=19545
---
 src/lib/io.go | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/src/lib/io.go b/src/lib/io.go
index 80f753a4bf..699f9196c3 100644
--- a/src/lib/io.go
+++ b/src/lib/io.go
@@ -76,3 +76,37 @@ export func MakeFullReader(fd Read) Read {
 	}
 	return &FullRead{fd}
 }
+
+// Copies n bytes (or until EOF is reached) from src to dst.
+// Returns the number of bytes copied and the error, if any.
+export func Copyn(src Read, dst Write, n int) (c int, err *os.Error) {
+	buf := new([]byte, 32*1024);  // BUG 6g crashes on non-pointer array slices
+	c = 0;
+	for c < n {
+		l := n - c;
+		if l > len(buf) {
+			l = len(buf)
+		}
+		nr, er := src.Read(buf[0 : l]);
+		if nr > 0 {
+			nw, ew := dst.Write(buf[0 : nr]);
+			if nw != nr || ew != nil {
+				c += nw;
+				if ew == nil {
+					ew = os.EIO
+				}
+				err = ew;
+				break;
+			}
+			c += nr;
+		}
+		if er != nil {
+			err = er;
+			break;
+		}
+		if nr == 0 {
+			break;
+		}
+	}
+	return c, err
+}