Fix RequestHeader parser (valyala#1808)

When FastHTTP receives a header value suffixed or prefixed with tabs, they should be stripped.

header.go

@@ -3298,7 +3298,7 @@ func (s *headerScanner) next() bool {
 	s.key = s.b[:n]
 	normalizeHeaderKey(s.key, s.disableNormalizing)
 	n++
-	for len(s.b) > n && s.b[n] == ' ' {
+	for len(s.b) > n && (s.b[n] == ' ' || s.b[n] == '\t') {
 		n++
 		// the newline index is a relative index, and lines below trimmed `s.b` by `n`,
 		// so the relative newline index also shifted forward. it's safe to decrease
@@ -3352,13 +3352,18 @@ func (s *headerScanner) next() bool {
 	if n > 0 && s.value[n-1] == rChar {
 		n--
 	}
-	for n > 0 && s.value[n-1] == ' ' {
+	for n > 0 && (s.value[n-1] == ' ' || s.value[n-1] == '\t') {
 		n--
 	}
 	s.value = s.value[:n]
 	if isMultiLineValue {
 		s.value, s.b, s.hLen = normalizeHeaderValue(s.value, oldB, s.hLen)
 	}
+
+	for len(s.b) > 0 && (s.b[0] == ' ' || s.b[0] == '\t') {
+		s.b = s.b[1:]
+	}
+
 	return true
 }
 
@@ -3437,6 +3442,7 @@ func normalizeHeaderValue(ov, ob []byte, headerLength int) (nv, nb []byte, nhl i
 	}
 	write := 0
 	shrunk := 0
+	once := false
 	lineStart := false
 	for read := 0; read < length; read++ {
 		c := ov[read]
@@ -3445,10 +3451,17 @@ func normalizeHeaderValue(ov, ob []byte, headerLength int) (nv, nb []byte, nhl i
 			shrunk++
 			if c == nChar {
 				lineStart = true
+				once = false
 			}
 			continue
-		case lineStart && c == '\t':
-			c = ' '
+		case lineStart && (c == '\t' || c == ' '):
+			if !once {
+				c = ' '
+				once = true
+			} else {
+				shrunk++
+				continue
+			}
 		default:
 			lineStart = false
 		}

header_test.go

@@ -67,6 +67,11 @@ func TestResponseHeaderMultiLineValue(t *testing.T) {
 		"Foo: Bar\r\n" +
 		"Multi-Line: one;\r\n two\r\n" +
 		"Values: v1;\r\n v2; v3;\r\n v4;\tv5\r\n" +
+		// issue #1808
+		"WithTabs: \t v1 \t\r\n" +
+		"WithTabs-Start: \t \t v1 \r\n" +
+		"WithTabs-End: v1 \t \t\t\t\r\n" +
+		"WithTabs-Multi-Line: \t v1 \t;\r\n \t v2 \t;\r\n\t v3\r\n" +
 		"\r\n"
 	header := new(ResponseHeader)
 	if _, err := header.parse([]byte(s)); err != nil {