Don't allow \r in header names (#1789)

* Don't allow \r in header names

From RFC 9112:

  A sender MUST NOT generate a bare CR (a CR character not immediately
  followed by LF) within any protocol elements other than the content.
  A recipient of such a bare CR MUST consider that element to be invalid
  or replace each bare CR with SP before processing the element or forwarding
  the message.

net/http seems to completely error on this, so let's do the same.

Fixes #1785

* Validate the full header field

bytesconv_table_gen.go

@@ -98,7 +98,7 @@ func main() {
 		return a
 	}()
 
-	tcharTable := func() [128]byte {
+	validHeaderFieldByteTable := func() [128]byte {
 		// Should match net/textproto's validHeaderFieldByte(c byte) bool
 		// Defined by RFC 9110 5.6.2
 		//      tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
@@ -125,7 +125,7 @@ func main() {
 	fmt.Fprintf(w, "const toUpperTable = %q\n", toUpperTable)
 	fmt.Fprintf(w, "const quotedArgShouldEscapeTable = %q\n", quotedArgShouldEscapeTable)
 	fmt.Fprintf(w, "const quotedPathShouldEscapeTable = %q\n", quotedPathShouldEscapeTable)
-	fmt.Fprintf(w, "const tcharTable = %q\n", tcharTable)
+	fmt.Fprintf(w, "const validHeaderFieldByteTable = %q\n", validHeaderFieldByteTable)
 
 	if err := os.WriteFile("bytesconv_table.go", w.Bytes(), 0o660); err != nil {
 		log.Fatal(err)

header.go

@@ -548,7 +548,7 @@ func (h *ResponseHeader) AddTrailerBytes(trailer []byte) error {
 // validHeaderFieldByte returns true if c is a valid tchar as defined
 // by section 5.6.2 of [RFC9110].
 func validHeaderFieldByte(c byte) bool {
-	return c < 128 && tcharTable[c] == 1
+	return c < 128 && validHeaderFieldByteTable[c] == 1
 }
 
 // VisitHeaderParams calls f for each parameter in the given header bytes.
@@ -2947,8 +2947,17 @@ func (h *ResponseHeader) parseHeaders(buf []byte) (int, error) {
 	s.disableNormalizing = h.disableNormalizing
 	var err error
 	var kv *argsKV
+
+outer:
 	for s.next() {
 		if len(s.key) > 0 {
+			for _, ch := range s.key {
+				if !validHeaderFieldByte(ch) {
+					err = fmt.Errorf("invalid header key %q", s.key)
+					continue outer
+				}
+			}
+
 			switch s.key[0] | 0x20 {
 			case 'c':
 				if caseInsensitiveCompare(s.key, strContentType) {
@@ -3035,13 +3044,15 @@ func (h *RequestHeader) parseHeaders(buf []byte) (int, error) {
 	s.b = buf
 	s.disableNormalizing = h.disableNormalizing
 	var err error
+
+outer:
 	for s.next() {
 		if len(s.key) > 0 {
-			// Spaces between the header key and colon are not allowed.
-			// See RFC 7230, Section 3.2.4.
-			if bytes.IndexByte(s.key, ' ') != -1 || bytes.IndexByte(s.key, '\t') != -1 {
-				err = fmt.Errorf("invalid header key %q", s.key)
-				continue
+			for _, ch := range s.key {
+				if !validHeaderFieldByte(ch) {
+					err = fmt.Errorf("invalid header key %q", s.key)
+					continue outer
+				}
 			}
 
 			if h.disableSpecialHeader {

header_test.go

@@ -154,6 +154,19 @@ func TestResponseHeaderMultiLinePanicked(t *testing.T) {
 	}
 }
 
+func TestRequestHeaderLooseBackslashR(t *testing.T) {
+	t.Parallel()
+
+	s := "GET / HTTP/1.1\r\n" +
+		"Host: go.dev\r\n" +
+		"\rFoo: bar\r\n" +
+		"\r\n"
+	header := new(RequestHeader)
+	if _, err := header.parse([]byte(s)); err == nil {
+		t.Fatal("expected error, got <nil>")
+	}
+}
+
 func TestResponseHeaderEmptyValueFromHeader(t *testing.T) {
 	t.Parallel()