httpraw: fix overrwrite/empty val bugs in Header.Set/SetBytes (#159)

http/httpraw/header.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"io"
 	"slices"
-	"unsafe"
 )
 
 const (
@@ -250,7 +249,7 @@ func (h *Header) Body() ([]byte, error) {
 // SetBytes is equivalent to [Header.Set] but with a []byte value. Does not keep reference to value slice.
 // Calling SetBytes Mangles the buffer.
 func (h *Header) SetBytes(key string, value []byte) {
-	h.Set(key, unsafe.String(&value[0], len(value)))
+	h.Set(key, b2s(value))
 }
 
 // Set sets a key-value pair in the HTTP header.
@@ -258,10 +257,10 @@ func (h *Header) SetBytes(key string, value []byte) {
 func (h *Header) Set(key, value string) {
 	hb := &h.hbuf
 	var useKv *argsKV
-	for i := len(hb.headers); len(hb.headers) > 0 && i <= 0; i++ {
+	for i := 0; i < len(hb.headers); i++ {
 		// Search for key-value with largest buffer for value to store value reusing buffer.
 		gotkv := &hb.headers[i]
-		if b2s(hb.musttoken(gotkv.key)) == key {
+		if gotkv.isValid() && b2s(hb.musttoken(gotkv.key)) == key {
 			if useKv == nil {
 				useKv = gotkv
 			} else if gotkv.value.len > useKv.value.len {

http/httpraw/header_test.go

@@ -208,3 +208,35 @@ func TestCopyNormalizedHeaderValue(t *testing.T) {
 		}
 	}
 }
+
+func TestHeaderSetOverwrite(t *testing.T) {
+	var h Header
+	h.Reset(nil)
+	h.SetMethod("GET")
+	h.SetRequestURI("/")
+	h.SetProtocol("HTTP/1.1")
+
+	h.Set("Host", "first.example.com")
+	h.Set("Host", "second.example.com")
+
+	got := string(h.Get("Host"))
+	if got != "second.example.com" {
+		t.Errorf("want Host %q, got %q", "second.example.com", got)
+	}
+	req, err := h.AppendRequest(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n := strings.Count(string(req), "Host:"); n != 1 {
+		t.Errorf("want 1 Host field in request, got %d:\n%s", n, req)
+	}
+}
+
+func TestHeaderSetBytesEmptyValue(t *testing.T) {
+	var h Header
+	h.Reset(nil)
+	h.SetBytes("X-Empty", nil)
+	if got := h.Get("X-Empty"); len(got) != 0 {
+		t.Errorf("want empty value, got %q", got)
+	}
+}