net/http: add NoBody, don't return nil from NewRequest on zero bodies

This is an alternate solution to https://golang.org/cl/31445

Instead of making NewRequest return a request with Request.Body == nil
to signal a zero byte body, add a well-known variable that means
explicitly zero.

Too many tests inside Google (and presumably the outside world)
broke.

Change-Id: I78f6ecca8e8aa1e12179c234ccfb6bcf0ee29ba8
Reviewed-on: https://go-review.googlesource.com/31726
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>

src/net/http/http.go

@@ -5,6 +5,7 @@
 package http
 
 import (
+	"io"
 	"strconv"
 	"strings"
 	"time"
@@ -81,3 +82,21 @@ func hexEscapeNonASCII(s string) string {
 	}
 	return string(b)
 }
+
+// NoBody is an io.ReadCloser with no bytes. Read always returns EOF
+// and Close always returns nil. It can be used in an outgoing client
+// request to explicitly signal that a request has zero bytes.
+// An alternative, however, is to simply set Request.Body to nil.
+var NoBody = noBody{}
+
+type noBody struct{}
+
+func (noBody) Read([]byte) (int, error)         { return 0, io.EOF }
+func (noBody) Close() error                     { return nil }
+func (noBody) WriteTo(io.Writer) (int64, error) { return 0, nil }
+
+var (
+	// verify that an io.Copy from NoBody won't require a buffer:
+	_ io.WriterTo   = NoBody
+	_ io.ReadCloser = NoBody
+)

src/net/http/readrequest_test.go

@@ -25,7 +25,7 @@ type reqTest struct {
 }
 
 var noError = ""
-var noBody = ""
+var noBodyStr = ""
 var noTrailer Header = nil
 
 var reqTests = []reqTest{
@@ -95,7 +95,7 @@ var reqTests = []reqTest{
 			RequestURI:    "/",
 		},
 
-		noBody,
+		noBodyStr,
 		noTrailer,
 		noError,
 	},
@@ -121,7 +121,7 @@ var reqTests = []reqTest{
 			RequestURI:    "//user@host/is/actually/a/path/",
 		},
 
-		noBody,
+		noBodyStr,
 		noTrailer,
 		noError,
 	},
@@ -131,7 +131,7 @@ var reqTests = []reqTest{
 		"GET ../../../../etc/passwd HTTP/1.1\r\n" +
 			"Host: test\r\n\r\n",
 		nil,
-		noBody,
+		noBodyStr,
 		noTrailer,
 		"parse ../../../../etc/passwd: invalid URI for request",
 	},
@@ -141,7 +141,7 @@ var reqTests = []reqTest{
 		"GET  HTTP/1.1\r\n" +
 			"Host: test\r\n\r\n",
 		nil,
-		noBody,
+		noBodyStr,
 		noTrailer,
 		"parse : empty url",
 	},
@@ -227,7 +227,7 @@ var reqTests = []reqTest{
 			RequestURI:    "www.google.com:443",
 		},
 
-		noBody,
+		noBodyStr,
 		noTrailer,
 		noError,
 	},
@@ -251,7 +251,7 @@ var reqTests = []reqTest{
 			RequestURI:    "127.0.0.1:6060",
 		},
 
-		noBody,
+		noBodyStr,
 		noTrailer,
 		noError,
 	},
@@ -275,7 +275,7 @@ var reqTests = []reqTest{
 			RequestURI:    "/_goRPC_",
 		},
 
-		noBody,
+		noBodyStr,
 		noTrailer,
 		noError,
 	},
@@ -299,7 +299,7 @@ var reqTests = []reqTest{
 			RequestURI:    "*",
 		},
 
-		noBody,
+		noBodyStr,
 		noTrailer,
 		noError,
 	},
@@ -323,7 +323,7 @@ var reqTests = []reqTest{
 			RequestURI:    "*",
 		},
 
-		noBody,
+		noBodyStr,
 		noTrailer,
 		noError,
 	},
@@ -350,7 +350,7 @@ var reqTests = []reqTest{
 			RequestURI: "/",
 		},
 
-		noBody,
+		noBodyStr,
 		noTrailer,
 		noError,
 	},
@@ -376,7 +376,7 @@ var reqTests = []reqTest{
 			RequestURI: "/",
 		},
 
-		noBody,
+		noBodyStr,
 		noTrailer,
 		noError,
 	},
@@ -397,7 +397,7 @@ var reqTests = []reqTest{
 			ContentLength: -1,
 			Close:         true,
 		},
-		noBody,
+		noBodyStr,
 		noTrailer,
 		noError,
 	},

src/net/http/request.go

@@ -771,10 +771,14 @@ func NewRequest(method, urlStr string, body io.Reader) (*Request, error) {
 		// For client requests, Request.ContentLength of 0
 		// means either actually 0, or unknown. The only way
 		// to explicitly say that the ContentLength is zero is
-		// to set the Body to nil.
+		// to set the Body to nil. But turns out too much code
+		// depends on NewRequest returning a non-nil Body,
+		// so we use a well-known ReadCloser variable instead
+		// and have the http package also treat that sentinel
+		// variable to mean explicitly zero.
 		if req.ContentLength == 0 {
-			req.Body = nil
-			req.GetBody = nil
+			req.Body = NoBody
+			req.GetBody = func() (io.ReadCloser, error) { return NoBody, nil }
 		}
 	}
 
@@ -1252,7 +1256,7 @@ func (r *Request) isReplayable() bool {
 // outgoingLength reports the Content-Length of this outgoing (Client) request.
 // It maps 0 into -1 (unknown) when the Body is non-nil.
 func (r *Request) outgoingLength() int64 {
-	if r.Body == nil {
+	if r.Body == nil || r.Body == NoBody {
 		return 0
 	}
 	if r.ContentLength != 0 {

src/net/http/request_test.go

@@ -511,7 +511,7 @@ func TestNewRequestContentLength(t *testing.T) {
 		if req.ContentLength != tt.want {
 			t.Errorf("test[%d]: ContentLength(%T) = %d; want %d", i, tt.r, req.ContentLength, tt.want)
 		}
-		if (req.ContentLength == 0) != (req.Body == nil) {
+		if (req.ContentLength == 0) != (req.Body == NoBody) {
 			t.Errorf("test[%d]: ContentLength = %d but Body non-nil is %v", i, req.ContentLength, req.Body != nil)
 		}
 	}

src/net/http/response.go

@@ -261,7 +261,7 @@ func (r *Response) Write(w io.Writer) error {
 		if n == 0 {
 			// Reset it to a known zero reader, in case underlying one
 			// is unhappy being read repeatedly.
-			r1.Body = eofReader
+			r1.Body = NoBody
 		} else {
 			r1.ContentLength = -1
 			r1.Body = struct {

src/net/http/server.go

@@ -1776,7 +1776,7 @@ func registerOnHitEOF(rc io.ReadCloser, fn func()) {
 // requestBodyRemains reports whether future calls to Read
 // on rc might yield more data.
 func requestBodyRemains(rc io.ReadCloser) bool {
-	if rc == eofReader {
+	if rc == NoBody {
 		return false
 	}
 	switch v := rc.(type) {
@@ -2702,24 +2702,6 @@ func (globalOptionsHandler) ServeHTTP(w ResponseWriter, r *Request) {
 	}
 }
 
-type eofReaderWithWriteTo struct{}
-
-func (eofReaderWithWriteTo) WriteTo(io.Writer) (int64, error) { return 0, nil }
-func (eofReaderWithWriteTo) Read([]byte) (int, error)         { return 0, io.EOF }
-
-// eofReader is a non-nil io.ReadCloser that always returns EOF.
-// It has a WriteTo method so io.Copy won't need a buffer.
-var eofReader = &struct {
-	eofReaderWithWriteTo
-	io.Closer
-}{
-	eofReaderWithWriteTo{},
-	ioutil.NopCloser(nil),
-}
-
-// Verify that an io.Copy from an eofReader won't require a buffer.
-var _ io.WriterTo = eofReader
-
 // initNPNRequest is an HTTP handler that initializes certain
 // uninitialized fields in its *Request. Such partially-initialized
 // Requests come from NPN protocol handlers.
@@ -2734,7 +2716,7 @@ func (h initNPNRequest) ServeHTTP(rw ResponseWriter, req *Request) {
 		*req.TLS = h.c.ConnectionState()
 	}
 	if req.Body == nil {
-		req.Body = eofReader
+		req.Body = NoBody
 	}
 	if req.RemoteAddr == "" {
 		req.RemoteAddr = h.c.RemoteAddr().String()

src/net/http/transfer.go

@@ -367,12 +367,12 @@ func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
 	switch {
 	case chunked(t.TransferEncoding):
 		if noBodyExpected(t.RequestMethod) {
-			t.Body = eofReader
+			t.Body = NoBody
 		} else {
 			t.Body = &body{src: internal.NewChunkedReader(r), hdr: msg, r: r, closing: t.Close}
 		}
 	case realLength == 0:
-		t.Body = eofReader
+		t.Body = NoBody
 	case realLength > 0:
 		t.Body = &body{src: io.LimitReader(r, realLength), closing: t.Close}
 	default:
@@ -382,7 +382,7 @@ func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
 			t.Body = &body{src: r, closing: t.Close}
 		} else {
 			// Persistent connection (i.e. HTTP/1.1)
-			t.Body = eofReader
+			t.Body = NoBody
 		}
 	}