Add Sender module

pkg/sender/transport.go

@@ -0,0 +1,50 @@
+package sender
+
+import (
+	"crypto/tls"
+	"net"
+	"net/http"
+	"time"
+)
+
+type HTTPTransport struct{}
+
+type protoCtxKey struct{}
+
+const (
+	HTTPProto1 = "HTTP/1.1"
+	HTTPProto2 = "HTTP/2.0"
+)
+
+// h1OnlyTransport mimics `http.DefaultTransport`, but with HTTP/2 disabled.
+var h1OnlyTransport = &http.Transport{
+	Proxy: http.ProxyFromEnvironment,
+	DialContext: (&net.Dialer{
+		Timeout:   30 * time.Second,
+		KeepAlive: 30 * time.Second,
+	}).DialContext,
+	MaxIdleConns:          100,
+	IdleConnTimeout:       90 * time.Second,
+	TLSHandshakeTimeout:   10 * time.Second,
+	ExpectContinueTimeout: 1 * time.Second,
+
+	// Disable HTTP/2.
+	TLSNextProto: map[string]func(string, *tls.Conn) http.RoundTripper{},
+}
+
+// RountTrip implements http.RoundTripper. Based on a context value on the
+// HTTP request, it switches between using `http.DefaultTransport` (which attempts
+// HTTP/2) and a HTTP/1.1 only transport that's based off `http.DefaultTransport`.
+func (t *HTTPTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	proto, ok := req.Context().Value(protoCtxKey{}).(string)
+
+	if ok && proto == HTTPProto1 {
+		return h1OnlyTransport.RoundTrip(req)
+	}
+
+	return http.DefaultTransport.RoundTrip(req)
+}
+
+func isValidProto(proto string) bool {
+	return proto == HTTPProto1 || proto == HTTPProto2
+}