http.go

var httpClient = &http.Client{
	Timeout: defaultHTTPTimeout,

	// There is a bug in Go's HTTP/2 implementation that occasionally causes it
	// to send an empty body when it receives a `GOAWAY` message from a server:
	//
	//     https://github.com/golang/go/issues/32441
	//
	// This is particularly problematic for this library because the empty body
	// results in no parameters being sent, which usually results in a 400,
	// which is a status code expressly not covered by retry logic.
	//
	// The bug seems to be somewhat tricky to fix and hasn't seen any traction
	// lately, so for now we're mitigating by disabling HTTP/2 in stripe-go by
	// default. Users who like to live dangerously can still re-enable it by
	// specifying a custom HTTP client. When the bug above is fixed, we can
	// turn it back on.
	//
	// The particular methodology here for disabling HTTP/2 is a little
	// confusing at first glance, but is recommended by the `net/http`
	// documentation ("Programs that must disable HTTP/2 can do so by setting
	// Transport.TLSNextProto (for clients) ... to a non-nil, empty map.")
	//
	// Note that the test suite still uses HTTP/2 to run as it specifies its
	// own HTTP client with it enabled. See `testing/testing.go`.
	//
	// (Written 2019/07/24.)
	Transport: &http.Transport{
		TLSNextProto: make(map[string]func(string, *tls.Conn) http.RoundTripper),
	},
}