net/http: remove badStringError, make some unexported structs non-comparable

Reduces binary size by 4K, not counting the http2 changes (in CL
231119) that'll be bundled into this package in the future.

Updates golang/go#38782

Change-Id: Id360348707e076b8310a8f409e412d68dd2394b2
Reviewed-on: https://go-review.googlesource.com/c/go/+/231118
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/http/http.go

@@ -16,6 +16,11 @@ import (
 	"golang.org/x/net/http/httpguts"
 )
 
+// incomparable is a zero-width, non-comparable type. Adding it to a struct
+// makes that struct also non-comparable, and generally doesn't add
+// any size (as long as it's first).
+type incomparable [0]func()
+
 // maxInt64 is the effective "infinite" value for the Server and
 // Transport's byte-limiting readers.
 const maxInt64 = 1<<63 - 1

src/net/http/proxy_test.go

@@ -35,7 +35,7 @@ func TestCacheKeys(t *testing.T) {
 			}
 			proxy = u
 		}
-		cm := connectMethod{proxy, tt.scheme, tt.addr, false}
+		cm := connectMethod{proxyURL: proxy, targetScheme: tt.scheme, targetAddr: tt.addr}
 		if got := cm.key().String(); got != tt.key {
 			t.Fatalf("{%q, %q, %q} cache key = %q; want %q", tt.proxy, tt.scheme, tt.addr, got, tt.key)
 		}

src/net/http/request.go

@@ -83,12 +83,7 @@ var (
 	ErrMissingContentLength = &ProtocolError{"missing ContentLength in HEAD response"}
 )
 
-type badStringError struct {
-	what string
-	str  string
-}
-
-func (e *badStringError) Error() string { return fmt.Sprintf("%s %q", e.what, e.str) }
+func badStringError(what, val string) error { return fmt.Errorf("%s %q", what, val) }
 
 // Headers that Request.Write handles itself and should be skipped.
 var reqWriteExcludeHeader = map[string]bool{
@@ -1025,14 +1020,14 @@ func readRequest(b *bufio.Reader, deleteHostHeader bool) (req *Request, err erro
 	var ok bool
 	req.Method, req.RequestURI, req.Proto, ok = parseRequestLine(s)
 	if !ok {
-		return nil, &badStringError{"malformed HTTP request", s}
+		return nil, badStringError("malformed HTTP request", s)
 	}
 	if !validMethod(req.Method) {
-		return nil, &badStringError{"invalid method", req.Method}
+		return nil, badStringError("invalid method", req.Method)
 	}
 	rawurl := req.RequestURI
 	if req.ProtoMajor, req.ProtoMinor, ok = ParseHTTPVersion(req.Proto); !ok {
-		return nil, &badStringError{"malformed HTTP version", req.Proto}
+		return nil, badStringError("malformed HTTP version", req.Proto)
 	}
 
 	// CONNECT requests are used two different ways, and neither uses a full URL:

src/net/http/response.go

@@ -166,7 +166,7 @@ func ReadResponse(r *bufio.Reader, req *Request) (*Response, error) {
 		return nil, err
 	}
 	if i := strings.IndexByte(line, ' '); i == -1 {
-		return nil, &badStringError{"malformed HTTP response", line}
+		return nil, badStringError("malformed HTTP response", line)
 	} else {
 		resp.Proto = line[:i]
 		resp.Status = strings.TrimLeft(line[i+1:], " ")
@@ -176,15 +176,15 @@ func ReadResponse(r *bufio.Reader, req *Request) (*Response, error) {
 		statusCode = resp.Status[:i]
 	}
 	if len(statusCode) != 3 {
-		return nil, &badStringError{"malformed HTTP status code", statusCode}
+		return nil, badStringError("malformed HTTP status code", statusCode)
 	}
 	resp.StatusCode, err = strconv.Atoi(statusCode)
 	if err != nil || resp.StatusCode < 0 {
-		return nil, &badStringError{"malformed HTTP status code", statusCode}
+		return nil, badStringError("malformed HTTP status code", statusCode)
 	}
 	var ok bool
 	if resp.ProtoMajor, resp.ProtoMinor, ok = ParseHTTPVersion(resp.Proto); !ok {
-		return nil, &badStringError{"malformed HTTP version", resp.Proto}
+		return nil, badStringError("malformed HTTP version", resp.Proto)
 	}
 
 	// Parse the response headers.

src/net/http/server.go

@@ -629,6 +629,7 @@ func (srv *Server) newConn(rwc net.Conn) *conn {
 }
 
 type readResult struct {
+	_   incomparable
 	n   int
 	err error
 	b   byte // byte read, if n == 1

src/net/http/transfer.go

@@ -310,7 +310,7 @@ func (t *transferWriter) writeHeader(w io.Writer, trace *httptrace.ClientTrace)
 			k = CanonicalHeaderKey(k)
 			switch k {
 			case "Transfer-Encoding", "Trailer", "Content-Length":
-				return &badStringError{"invalid Trailer key", k}
+				return badStringError("invalid Trailer key", k)
 			}
 			keys = append(keys, k)
 		}
@@ -637,7 +637,7 @@ func (t *transferReader) fixTransferEncoding() error {
 		te[len(te)-1] = encoding
 	}
 	if len(te) > 1 {
-		return &badStringError{"too many transfer encodings", strings.Join(te, ",")}
+		return badStringError("too many transfer encodings", strings.Join(te, ","))
 	}
 	if len(te) > 0 {
 		// RFC 7230 3.3.2 says "A sender MUST NOT send a
@@ -791,7 +791,7 @@ func fixTrailer(header Header, te []string) (Header, error) {
 			switch key {
 			case "Transfer-Encoding", "Trailer", "Content-Length":
 				if err == nil {
-					err = &badStringError{"bad trailer key", key}
+					err = badStringError("bad trailer key", key)
 					return
 				}
 			}
@@ -1055,7 +1055,7 @@ func parseContentLength(cl string) (int64, error) {
 	}
 	n, err := strconv.ParseInt(cl, 10, 64)
 	if err != nil || n < 0 {
-		return 0, &badStringError{"bad Content-Length", cl}
+		return 0, badStringError("bad Content-Length", cl)
 	}
 	return n, nil
 

src/net/http/transfer_test.go

@@ -290,7 +290,7 @@ func TestFixTransferEncoding(t *testing.T) {
 		},
 		{
 			hdr:     Header{"Transfer-Encoding": {"chunked, chunked", "identity", "chunked"}},
-			wantErr: &badStringError{"too many transfer encodings", "chunked,chunked"},
+			wantErr: badStringError("too many transfer encodings", "chunked,chunked"),
 		},
 		{
 			hdr:     Header{"Transfer-Encoding": {"chunked"}},

src/net/http/transport.go

@@ -518,7 +518,7 @@ func (t *Transport) roundTrip(req *Request) (*Response, error) {
 	}
 	if !isHTTP {
 		req.closeBody()
-		return nil, &badStringError{"unsupported protocol scheme", scheme}
+		return nil, badStringError("unsupported protocol scheme", scheme)
 	}
 	if req.Method != "" && !validMethod(req.Method) {
 		req.closeBody()
@@ -1696,6 +1696,7 @@ var _ io.ReaderFrom = (*persistConnWriter)(nil)
 //	https://proxy.com|http            https to proxy, http to anywhere after that
 //
 type connectMethod struct {
+	_            incomparable
 	proxyURL     *url.URL // nil for no proxy, else full proxy URL
 	targetScheme string   // "http" or "https"
 	// If proxyURL specifies an http or https proxy, and targetScheme is http (not https),
@@ -2250,6 +2251,7 @@ func newReadWriteCloserBody(br *bufio.Reader, rwc io.ReadWriteCloser) io.ReadWri
 // the concrete type for a Response.Body on the 101 Switching
 // Protocols response, as used by WebSockets, h2c, etc.
 type readWriteCloserBody struct {
+	_  incomparable
 	br *bufio.Reader // used until empty
 	io.ReadWriteCloser
 }
@@ -2350,11 +2352,13 @@ func (pc *persistConn) wroteRequest() bool {
 // responseAndError is how the goroutine reading from an HTTP/1 server
 // communicates with the goroutine doing the RoundTrip.
 type responseAndError struct {
+	_   incomparable
 	res *Response // else use this response (see res method)
 	err error
 }
 
 type requestAndChan struct {
+	_   incomparable
 	req *Request
 	ch  chan responseAndError // unbuffered; always send in select on callerGone
 
@@ -2687,6 +2691,7 @@ func (es *bodyEOFSignal) condfn(err error) error {
 // gzipReader wraps a response body so it can lazily
 // call gzip.NewReader on the first call to Read
 type gzipReader struct {
+	_    incomparable
 	body *bodyEOFSignal // underlying HTTP/1 response body framing
 	zr   *gzip.Reader   // lazily-initialized gzip reader
 	zerr error          // any error from gzip.NewReader; sticky