refactoring: moved reverse_proxy to separate package to avoid import cycle

internal/net/http/header_utils.go

@@ -2,6 +2,10 @@ package http
 
 import (
 	"net/http"
+	"net/textproto"
+
+	"github.com/yusing/go-proxy/internal/utils/strutils"
+	"golang.org/x/net/http/httpguts"
 )
 
 const (
@@ -22,6 +26,48 @@ const (
 	HeaderContentLength = "Content-Length"
 )
 
+// Hop-by-hop headers. These are removed when sent to the backend.
+// As of RFC 7230, hop-by-hop headers are required to appear in the
+// Connection header field. These are the headers defined by the
+// obsoleted RFC 2616 (section 13.5.1) and are used for backward
+// compatibility.
+var hopHeaders = []string{
+	"Connection",
+	"Proxy-Connection", // non-standard but still sent by libcurl and rejected by e.g. google
+	"Keep-Alive",
+	"Proxy-Authenticate",
+	"Proxy-Authorization",
+	"Te",      // canonicalized version of "TE"
+	"Trailer", // not Trailers per URL above; https://www.rfc-editor.org/errata_search.php?eid=4522
+	"Transfer-Encoding",
+	"Upgrade",
+}
+
+func UpgradeType(h http.Header) string {
+	if !httpguts.HeaderValuesContainsToken(h["Connection"], "Upgrade") {
+		return ""
+	}
+	return h.Get("Upgrade")
+}
+
+// RemoveHopByHopHeaders removes hop-by-hop headers.
+func RemoveHopByHopHeaders(h http.Header) {
+	// RFC 7230, section 6.1: Remove headers listed in the "Connection" header.
+	for _, f := range h["Connection"] {
+		for _, sf := range strutils.SplitComma(f) {
+			if sf = textproto.TrimString(sf); sf != "" {
+				h.Del(sf)
+			}
+		}
+	}
+	// RFC 2616, section 13.5.1: Remove a set of known hop-by-hop headers.
+	// This behavior is superseded by the RFC 7230 Connection header, but
+	// preserve it for backwards compatibility.
+	for _, f := range hopHeaders {
+		h.Del(f)
+	}
+}
+
 func RemoveHop(h http.Header) {
 	reqUpType := UpgradeType(h)
 	RemoveHopByHopHeaders(h)