reverse the arguments to io.Copy so the destination is on the

left, like an assignment, like strcpy, etc.

R=rsc
CC=go-dev
http://go/go-review/1016011

src/cmd/godoc/main.go

@@ -71,7 +71,7 @@ func exec(c *http.Conn, args []string) (status int) {
 	}
 
 	var buf bytes.Buffer;
-	io.Copy(r, &buf);
+	io.Copy(&buf, r);
 	wait, err := os.Wait(pid, 0);
 	if err != nil {
 		os.Stderr.Write(buf.Bytes());

src/pkg/archive/tar/reader.go

@@ -34,7 +34,7 @@ var (
 //			// end of tar archive
 //			break
 //		}
-//		io.Copy(tr, data);
+//		io.Copy(data, tr);
 //	}
 type Reader struct {
 	r	io.Reader;
@@ -99,7 +99,7 @@ func (tr *Reader) skipUnread() {
 	if sr, ok := tr.r.(io.Seeker); ok {
 		_, tr.err = sr.Seek(nr, 1);
 	} else {
-		_, tr.err = io.Copyn(tr.r, ignoreWriter{}, nr);
+		_, tr.err = io.Copyn(ignoreWriter{}, tr.r, nr);
 	}
 	tr.nb, tr.pad = 0, 0;
 }

src/pkg/archive/tar/writer.go

@@ -33,7 +33,7 @@ var (
 //	if err := tw.WriteHeader(hdr); err != nil {
 //		// handle error
 //	}
-//	io.Copy(data, tw);
+//	io.Copy(tw, data);
 //	tw.Close();
 type Writer struct {
 	w		io.Writer;

src/pkg/compress/gzip/gunzip_test.go

@@ -293,7 +293,7 @@ func TestInflater(t *testing.T) {
 			t.Errorf("%s: got name %s", tt.name, gzip.Name);
 		}
 		b.Reset();
-		n, err := io.Copy(gzip, b);
+		n, err := io.Copy(b, gzip);
 		if err != tt.err {
 			t.Errorf("%s: io.Copy: %v want %v", tt.name, err, tt.err);
 		}

src/pkg/compress/zlib/reader_test.go

@@ -80,7 +80,7 @@ func TestInflater(t *testing.T) {
 		}
 		defer zlib.Close();
 		b.Reset();
-		n, err := io.Copy(zlib, b);
+		n, err := io.Copy(b, zlib);
 		if err != nil {
 			if err != tt.err {
 				t.Errorf("%s: io.Copy: %v want %v", tt.desc, err, tt.err);

src/pkg/crypto/block/cbc_aes_test.go

@@ -78,7 +78,7 @@ func TestCBC_AES(t *testing.T) {
 		var crypt bytes.Buffer;
 		w := NewCBCEncrypter(c, tt.iv, &crypt);
 		var r io.Reader = bytes.NewBuffer(tt.in);
-		n, err := io.Copy(r, w);
+		n, err := io.Copy(w, r);
 		if n != int64(len(tt.in)) || err != nil {
 			t.Errorf("%s: CBCEncrypter io.Copy = %d, %v want %d, nil", test, n, err, len(tt.in));
 		} else if d := crypt.Bytes(); !same(tt.out, d) {
@@ -88,7 +88,7 @@ func TestCBC_AES(t *testing.T) {
 		var plain bytes.Buffer;
 		r = NewCBCDecrypter(c, tt.iv, bytes.NewBuffer(tt.out));
 		w = &plain;
-		n, err = io.Copy(r, w);
+		n, err = io.Copy(w, r);
 		if n != int64(len(tt.out)) || err != nil {
 			t.Errorf("%s: CBCDecrypter io.Copy = %d, %v want %d, nil", test, n, err, len(tt.out));
 		} else if d := plain.Bytes(); !same(tt.in, d) {

src/pkg/crypto/block/cfb_aes_test.go

@@ -287,7 +287,7 @@ func TestCFB_AES(t *testing.T) {
 		var crypt bytes.Buffer;
 		w := NewCFBEncrypter(c, tt.s, tt.iv, &crypt);
 		var r io.Reader = bytes.NewBuffer(tt.in);
-		n, err := io.Copy(r, w);
+		n, err := io.Copy(w, r);
 		if n != int64(len(tt.in)) || err != nil {
 			t.Errorf("%s: CFBEncrypter io.Copy = %d, %v want %d, nil", test, n, err, len(tt.in));
 		} else if d := crypt.Bytes(); !same(tt.out, d) {
@@ -297,7 +297,7 @@ func TestCFB_AES(t *testing.T) {
 		var plain bytes.Buffer;
 		r = NewCFBDecrypter(c, tt.s, tt.iv, bytes.NewBuffer(tt.out));
 		w = &plain;
-		n, err = io.Copy(r, w);
+		n, err = io.Copy(w, r);
 		if n != int64(len(tt.out)) || err != nil {
 			t.Errorf("%s: CFBDecrypter io.Copy = %d, %v want %d, nil", test, n, err, len(tt.out));
 		} else if d := plain.Bytes(); !same(tt.in, d) {

src/pkg/crypto/block/ctr_aes_test.go

@@ -82,7 +82,7 @@ func TestCTR_AES(t *testing.T) {
 			in := tt.in[0 : len(tt.in)-j];
 			w := NewCTRWriter(c, tt.iv, &crypt);
 			var r io.Reader = bytes.NewBuffer(in);
-			n, err := io.Copy(r, w);
+			n, err := io.Copy(w, r);
 			if n != int64(len(in)) || err != nil {
 				t.Errorf("%s/%d: CTRWriter io.Copy = %d, %v want %d, nil", test, len(in), n, err, len(in));
 			} else if d, out := crypt.Bytes(), tt.out[0:len(in)]; !same(out, d) {
@@ -95,7 +95,7 @@ func TestCTR_AES(t *testing.T) {
 			out := tt.out[0 : len(tt.out)-j];
 			r := NewCTRReader(c, tt.iv, bytes.NewBuffer(out));
 			w := &plain;
-			n, err := io.Copy(r, w);
+			n, err := io.Copy(w, r);
 			if n != int64(len(out)) || err != nil {
 				t.Errorf("%s/%d: CTRReader io.Copy = %d, %v want %d, nil", test, len(out), n, err, len(out));
 			} else if d, in := plain.Bytes(), tt.in[0:len(out)]; !same(in, d) {

src/pkg/crypto/block/eax_aes_test.go

@@ -105,7 +105,7 @@ func TestEAXEncrypt_AES(t *testing.T) {
 		}
 		b.Reset();
 		enc := NewEAXEncrypter(c, tt.nonce, tt.header, 16, b);
-		n, err := io.Copy(bytes.NewBuffer(tt.msg), enc);
+		n, err := io.Copy(enc, bytes.NewBuffer(tt.msg));
 		if n != int64(len(tt.msg)) || err != nil {
 			t.Fatalf("%s: io.Copy into encrypter: %d, %s", test, n, err);
 		}
@@ -129,7 +129,7 @@ func TestEAXDecrypt_AES(t *testing.T) {
 		}
 		b.Reset();
 		dec := NewEAXDecrypter(c, tt.nonce, tt.header, 16, bytes.NewBuffer(tt.cipher));
-		n, err := io.Copy(dec, b);
+		n, err := io.Copy(b, dec);
 		if n != int64(len(tt.msg)) || err != nil {
 			t.Fatalf("%s: io.Copy into decrypter: %d, %s", test, n, err);
 		}

src/pkg/crypto/block/ecb_aes_test.go

@@ -103,7 +103,7 @@ func TestECB_AES(t *testing.T) {
 		var crypt bytes.Buffer;
 		w := NewECBEncrypter(c, &crypt);
 		var r io.Reader = bytes.NewBuffer(tt.in);
-		n, err := io.Copy(r, w);
+		n, err := io.Copy(w, r);
 		if n != int64(len(tt.in)) || err != nil {
 			t.Errorf("%s: ECBReader io.Copy = %d, %v want %d, nil", test, n, err, len(tt.in));
 		} else if d := crypt.Bytes(); !same(tt.out, d) {
@@ -113,7 +113,7 @@ func TestECB_AES(t *testing.T) {
 		var plain bytes.Buffer;
 		r = NewECBDecrypter(c, bytes.NewBuffer(tt.out));
 		w = &plain;
-		n, err = io.Copy(r, w);
+		n, err = io.Copy(w, r);
 		if n != int64(len(tt.out)) || err != nil {
 			t.Errorf("%s: ECBWriter io.Copy = %d, %v want %d, nil", test, n, err, len(tt.out));
 		} else if d := plain.Bytes(); !same(tt.in, d) {

src/pkg/crypto/block/ecb_test.go

@@ -75,20 +75,20 @@ func TestECBEncrypter(t *testing.T) {
 			// copy plain into w in increasingly large chunks: 1, 1, 2, 4, 8, ...
 			// if frag != 0, move the 1 to the end to cause fragmentation.
 			if frag == 0 {
-				_, err := io.Copyn(r, w, 1);
+				_, err := io.Copyn(w, r, 1);
 				if err != nil {
 					t.Errorf("block=%d frag=0: first Copyn: %s", block, err);
 					continue;
 				}
 			}
 			for n := 1; n <= len(plain)/2; n *= 2 {
-				_, err := io.Copyn(r, w, int64(n));
+				_, err := io.Copyn(w, r, int64(n));
 				if err != nil {
 					t.Errorf("block=%d frag=%d: Copyn %d: %s", block, frag, n, err);
 				}
 			}
 			if frag != 0 {
-				_, err := io.Copyn(r, w, 1);
+				_, err := io.Copyn(w, r, 1);
 				if err != nil {
 					t.Errorf("block=%d frag=1: last Copyn: %s", block, err);
 					continue;
@@ -140,20 +140,20 @@ func testECBDecrypter(t *testing.T, maxio int) {
 				// read from crypt in increasingly large chunks: 1, 1, 2, 4, 8, ...
 				// if frag == 1, move the 1 to the end to cause fragmentation.
 				if frag == 0 {
-					_, err := io.Copyn(r, b, 1);
+					_, err := io.Copyn(b, r, 1);
 					if err != nil {
 						t.Errorf("%s: first Copyn: %s", test, err);
 						continue;
 					}
 				}
 				for n := 1; n <= maxio/2; n *= 2 {
-					_, err := io.Copyn(r, b, int64(n));
+					_, err := io.Copyn(b, r, int64(n));
 					if err != nil {
 						t.Errorf("%s: Copyn %d: %s", test, n, err);
 					}
 				}
 				if frag != 0 {
-					_, err := io.Copyn(r, b, 1);
+					_, err := io.Copyn(b, r, 1);
 					if err != nil {
 						t.Errorf("%s: last Copyn: %s", test, err);
 						continue;

src/pkg/crypto/block/ofb_aes_test.go

@@ -80,7 +80,7 @@ func TestOFB_AES(t *testing.T) {
 			in := tt.in[0 : len(tt.in)-j];
 			w := NewOFBWriter(c, tt.iv, &crypt);
 			var r io.Reader = bytes.NewBuffer(in);
-			n, err := io.Copy(r, w);
+			n, err := io.Copy(w, r);
 			if n != int64(len(in)) || err != nil {
 				t.Errorf("%s/%d: OFBWriter io.Copy = %d, %v want %d, nil", test, len(in), n, err, len(in));
 			} else if d, out := crypt.Bytes(), tt.out[0:len(in)]; !same(out, d) {
@@ -93,7 +93,7 @@ func TestOFB_AES(t *testing.T) {
 			out := tt.out[0 : len(tt.out)-j];
 			r := NewOFBReader(c, tt.iv, bytes.NewBuffer(out));
 			w := &plain;
-			n, err := io.Copy(r, w);
+			n, err := io.Copy(w, r);
 			if n != int64(len(out)) || err != nil {
 				t.Errorf("%s/%d: OFBReader io.Copy = %d, %v want %d, nil", test, len(out), n, err, len(out));
 			} else if d, in := plain.Bytes(), tt.in[0:len(out)]; !same(in, d) {

src/pkg/crypto/block/xor_test.go

@@ -60,14 +60,14 @@ func testXorWriter(t *testing.T, maxio int) {
 			// copy plain into w in increasingly large chunks: 1, 1, 2, 4, 8, ...
 			// if frag != 0, move the 1 to the end to cause fragmentation.
 			if frag == 0 {
-				_, err := io.Copyn(r, w, 1);
+				_, err := io.Copyn(w, r, 1);
 				if err != nil {
 					t.Errorf("%s: first Copyn: %s", test, err);
 					continue;
 				}
 			}
 			for n := 1; n <= len(plain)/2; n *= 2 {
-				_, err := io.Copyn(r, w, int64(n));
+				_, err := io.Copyn(w, r, int64(n));
 				if err != nil {
 					t.Errorf("%s: Copyn %d: %s", test, n, err);
 				}
@@ -130,14 +130,14 @@ func testXorReader(t *testing.T, maxio int) {
 				// read from crypt in increasingly large chunks: 1, 1, 2, 4, 8, ...
 				// if frag == 1, move the 1 to the end to cause fragmentation.
 				if frag == 0 {
-					_, err := io.Copyn(r, b, 1);
+					_, err := io.Copyn(b, r, 1);
 					if err != nil {
 						t.Errorf("%s: first Copyn: %s", test, err);
 						continue;
 					}
 				}
 				for n := 1; n <= maxio/2; n *= 2 {
-					_, err := io.Copyn(r, b, int64(n));
+					_, err := io.Copyn(b, r, int64(n));
 					if err != nil {
 						t.Errorf("%s: Copyn %d: %s", test, n, err);
 					}

src/pkg/go/parser/interface.go

@@ -36,7 +36,7 @@ func readSource(filename string, src interface{}) ([]byte, os.Error) {
 			}
 		case io.Reader:
 			var buf bytes.Buffer;
-			_, err := io.Copy(s, &buf);
+			_, err := io.Copy(&buf, s);
 			if err != nil {
 				return nil, err;
 			}

src/pkg/http/fs.go

@@ -151,7 +151,7 @@ func serveFileInternal(c *Conn, r *Request, name string, redirect bool) {
 		}
 		c.Write(b);
 	}
-	io.Copy(f, c);
+	io.Copy(c, f);
 }
 
 // ServeFile replies to the request with the contents of the named file or directory.

src/pkg/http/triv.go

@@ -43,7 +43,7 @@ func (ctr *Counter) ServeHTTP(c *http.Conn, req *http.Request) {
 		ctr.n++;
 	case "POST":
 		buf := new(bytes.Buffer);
-		io.Copy(req.Body, buf);
+		io.Copy(buf, req.Body);
 		body := buf.String();
 		if n, err := strconv.Atoi(body); err != nil {
 			fmt.Fprintf(c, "bad POST: %v\nbody: [%v]\n", err, body);
@@ -69,7 +69,7 @@ func FileServer(c *http.Conn, req *http.Request) {
 		fmt.Fprintf(c, "open %s: %v\n", path, err);
 		return;
 	}
-	n, err1 := io.Copy(f, c);
+	n, err1 := io.Copy(c, f);
 	fmt.Fprintf(c, "[%d bytes]\n", n);
 	f.Close();
 }
@@ -128,7 +128,7 @@ func DateServer(c *http.Conn, req *http.Request) {
 		fmt.Fprintf(c, "fork/exec: %s\n", err);
 		return;
 	}
-	io.Copy(r, c);
+	io.Copy(c, r);
 	wait, err := os.Wait(pid, 0);
 	if err != nil {
 		fmt.Fprintf(c, "wait: %s\n", err);

src/pkg/io/io.go

@@ -179,7 +179,7 @@ func ReadFull(r Reader, buf []byte) (n int, err os.Error) {
 
 // Copyn copies n bytes (or until an error) from src to dst.
 // It returns the number of bytes copied and the error, if any.
-func Copyn(src Reader, dst Writer, n int64) (written int64, err os.Error) {
+func Copyn(dst Writer, src Reader, n int64) (written int64, err os.Error) {
 	buf := make([]byte, 32*1024);
 	for written < n {
 		l := len(buf);
@@ -212,7 +212,7 @@ func Copyn(src Reader, dst Writer, n int64) (written int64, err os.Error) {
 // Copy copies from src to dst until either EOF is reached
 // on src or an error occurs.  It returns the number of bytes
 // copied and the error, if any.
-func Copy(src Reader, dst Writer) (written int64, err os.Error) {
+func Copy(dst Writer, src Reader) (written int64, err os.Error) {
 	buf := make([]byte, 32*1024);
 	for {
 		nr, er := src.Read(buf);

src/pkg/io/utils.go

@@ -15,7 +15,7 @@ import (
 // ReadAll reads from r until an error or EOF and returns the data it read.
 func ReadAll(r Reader) ([]byte, os.Error) {
 	var buf bytes.Buffer;
-	_, err := Copy(r, &buf);
+	_, err := Copy(&buf, r);
 	return buf.Bytes(), err;
 }
 

src/pkg/os/os_test.go

@@ -325,7 +325,7 @@ func TestForkExec(t *testing.T) {
 	w.Close();
 
 	var b bytes.Buffer;
-	io.Copy(r, &b);
+	io.Copy(&b, r);
 	output := b.String();
 	expect := "/\n";
 	if output != expect {
@@ -603,7 +603,7 @@ func run(t *testing.T, cmd []string) string {
 	w.Close();
 
 	var b bytes.Buffer;
-	io.Copy(r, &b);
+	io.Copy(&b, r);
 	Wait(pid, 0);
 	output := b.String();
 	if n := len(output); n > 0 && output[n-1] == '\n' {