net/http/httputil: make DumpRequest and DumpRequestOut recognize http.NoBody

Fixes #18506

Change-Id: I6b0b107296311178938609e878e1ef47a30a463f
Reviewed-on: https://go-review.googlesource.com/34814Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/http/httputil/dump.go

@@ -18,11 +18,16 @@ import (
 	"time"
 )
 
-// One of the copies, say from b to r2, could be avoided by using a more
-// elaborate trick where the other copy is made during Request/Response.Write.
-// This would complicate things too much, given that these functions are for
-// debugging only.
+// drainBody reads all of b to memory and then returns two equivalent
+// ReadClosers yielding the same bytes.
+//
+// It returns an error if the initial slurp of all bytes fails. It does not attempt
+// to make the returned ReadClosers have identical error-matching behavior.
 func drainBody(b io.ReadCloser) (r1, r2 io.ReadCloser, err error) {
+	if b == http.NoBody {
+		// No copying needed. Preserve the magic sentinel meaning of NoBody.
+		return http.NoBody, http.NoBody, nil
+	}
 	var buf bytes.Buffer
 	if _, err = buf.ReadFrom(b); err != nil {
 		return nil, b, err

src/net/http/httputil/dump_test.go

@@ -184,6 +184,18 @@ var dumpTests = []dumpTest{
 		WantDump: "POST /v2/api/?login HTTP/1.1\r\n" +
 			"Host: passport.myhost.com\r\n\r\n",
 	},
+
+	// Issue 18506: make drainBody recognize NoBody. Otherwise
+	// this was turning into a chunked request.
+	{
+		Req: *mustNewRequest("POST", "http://example.com/foo", http.NoBody),
+
+		WantDumpOut: "POST /foo HTTP/1.1\r\n" +
+			"Host: example.com\r\n" +
+			"User-Agent: Go-http-client/1.1\r\n" +
+			"Content-Length: 0\r\n" +
+			"Accept-Encoding: gzip\r\n\r\n",
+	},
 }
 
 func TestDumpRequest(t *testing.T) {