From b230502084d628938cd50818d3d336f9f911d48d Mon Sep 17 00:00:00 2001
From: Johan Brandhorst <johan.brandhorst@gmail.com>
Date: Fri, 3 Aug 2018 10:22:27 +0100
Subject: [PATCH] net/http: support configuring fetch options

The default WASM RoundTripper is implemented using
the browser Fetch API. Some options don't readily map to
existing http.Request options, so we use the precedent
set by the TrailerPrefix constant to allow a user to configure
the "mode" and "credentials" options by supplying them
as headers in the http.Request.

Updates #26769
---
 src/net/http/roundtrip_js.go | 38 +++++++++++++++++++++++++++++-------
 1 file changed, 31 insertions(+), 7 deletions(-)

diff --git a/src/net/http/roundtrip_js.go b/src/net/http/roundtrip_js.go
index cb4a4392b5..8ef29dd509 100644
--- a/src/net/http/roundtrip_js.go
+++ b/src/net/http/roundtrip_js.go
@@ -17,17 +17,27 @@ import (
 	"syscall/js"
 )
 
+// ModeHeader is a Request.Header map key that, if present,
+// signals that the map entry is actually an option to the Fetch API mode setting.
+// Valid values are: "cors", "no-cors", "same-origin", "navigate"
+// The default is "same-origin".
+//
+// Reference: https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch#Parameters
+const ModeHeader = "Fetch:Mode"
+
+// CredentialsHeader is a Request.Header map key that, if present,
+// signals that the map entry is actually an option to the Fetch API credentials setting.
+// Valid values are: "omit", "same-origin", "include"
+// The default is "same-origin".
+//
+// Reference: https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch#Parameters
+const CredentialsHeader = "Fetch:Credentials"
+
 // RoundTrip implements the RoundTripper interface using the WHATWG Fetch API.
 func (t *Transport) RoundTrip(req *Request) (*Response, error) {
 	if useFakeNetwork() {
 		return t.roundTrip(req)
 	}
-	headers := js.Global().Get("Headers").New()
-	for key, values := range req.Header {
-		for _, value := range values {
-			headers.Call("append", key, value)
-		}
-	}
 
 	ac := js.Global().Get("AbortController")
 	if ac != js.Undefined() {
@@ -40,12 +50,26 @@ func (t *Transport) RoundTrip(req *Request) (*Response, error) {
 	opt := js.Global().Get("Object").New()
 	// See https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch
 	// for options available.
-	opt.Set("headers", headers)
 	opt.Set("method", req.Method)
 	opt.Set("credentials", "same-origin")
+	if h := req.Header.Get(CredentialsHeader); h != "" {
+		opt.Set("credentials", h)
+		req.Header.Del(CredentialsHeader)
+	}
+	if h := req.Header.Get(ModeHeader); h != "" {
+		opt.Set("credentials", h)
+		req.Header.Del(ModeHeader)
+	}
 	if ac != js.Undefined() {
 		opt.Set("signal", ac.Get("signal"))
 	}
+	headers := js.Global().Get("Headers").New()
+	for key, values := range req.Header {
+		for _, value := range values {
+			headers.Call("append", key, value)
+		}
+	}
+	opt.Set("headers", headers)
 
 	if req.Body != nil {
 		// TODO(johanbrandhorst): Stream request body when possible.