Make pipe read timeout configurable via idleTimeout metadata

The 30s hardcoded readTimeout in Pipe() caused all CONNECT tunnel
connections to be hard-closed after 30s of inactivity, breaking
WebSocket and long-polling connections through the proxy.

Pipe() now accepts a WithReadTimeout(d) option. When d is 0 (the
default) no read deadline is set, relying on TCP keepalives or context
cancellation to detect dead connections instead.

The HTTP handler exposes this as the idleTimeout metadata key.

Fixes: https://github.com/go-gost/x/issues/91

handler/http/metadata.go

@@ -21,6 +21,7 @@ const (
 
 type metadata struct {
 	readTimeout     time.Duration
+	idleTimeout     time.Duration
 	keepalive       bool
 	compression     bool
 	probeResistance *probeResistance
@@ -57,6 +58,11 @@ func (h *httpHandler) parseMetadata(md mdata.Metadata) error {
 		h.md.readTimeout = 0
 	}
 
+	h.md.idleTimeout = mdutil.GetDuration(md, "idleTimeout")
+	if h.md.idleTimeout < 0 {
+		h.md.idleTimeout = 0
+	}
+
 	if m := mdutil.GetStringMapString(md, "http.header", "header"); len(m) > 0 {
 		hd := http.Header{}
 		for k, v := range m {