Support SendEmail bindings

Author: penalosa

packages/miniflare/src/plugins/email/index.ts

@@ -5,13 +5,18 @@ import { Service, Worker_Binding } from "../../runtime";
 import {
 getUserBindingServiceName,
 Plugin,
+remoteProxyClientWorker,
+RemoteProxyConnectionString,
 WORKER_BINDING_SERVICE_LOOPBACK,
 } from "../shared";
 
 // Define the mutually exclusive schema
 const EmailBindingOptionsSchema = z
 .object({
 name: z.string(),
+remoteProxyConnectionString: z
+.custom<RemoteProxyConnectionString>()
+.optional(),
 })
 .and(
 z.union([
@@ -53,10 +58,12 @@ export const EMAIL_PLUGIN: Plugin<typeof EmailOptionsSchema> = {
 
 const sendEmailBindings = options.email.send_email;
 
-return sendEmailBindings.map(({ name }) => ({
+return sendEmailBindings.map(({ name, remoteProxyConnectionString }) => ({
 name,
 service: {
-entrypoint: "SendEmailBinding",
+entrypoint: remoteProxyConnectionString
+? undefined
+: "SendEmailBinding",
 name: getUserBindingServiceName(SERVICE_SEND_EMAIL_WORKER_PREFIX, name),
 },
 }));
@@ -67,22 +74,25 @@ export const EMAIL_PLUGIN: Plugin<typeof EmailOptionsSchema> = {
 async getServices(args) {
 const services: Service[] = [];
 
-for (const { name, ...config } of args.options.email?.send_email ?? []) {
+for (const { name, remoteProxyConnectionString, ...config } of args.options
+.email?.send_email ?? []) {
 services.push({
 name: getUserBindingServiceName(SERVICE_SEND_EMAIL_WORKER_PREFIX, name),
-worker: {
-compatibilityDate: "2025-03-17",
-modules: [
-{
-name: "send_email.mjs",
-esModule: SEND_EMAIL_BINDING(),
+worker: remoteProxyConnectionString
+? remoteProxyClientWorker(remoteProxyConnectionString, name)
+: {
+compatibilityDate: "2025-03-17",
+modules: [
+{
+name: "send_email.mjs",
+esModule: SEND_EMAIL_BINDING(),
+},
+],
+bindings: [
+...buildJsonBindings(config),
+WORKER_BINDING_SERVICE_LOOPBACK,
+],
 },
-],
-bindings: [
-...buildJsonBindings(config),
-WORKER_BINDING_SERVICE_LOOPBACK,
-],
-},
 });
 }
 

packages/miniflare/src/workers/shared/remote-proxy-client.worker.ts

@@ -41,8 +41,7 @@ export default class Client extends WorkerEntrypoint<Env> {
 return Reflect.get(target, prop);
 }
 
-const value = Reflect.get(stub, prop);
-return value;
+return Reflect.get(stub, prop);
 },
 });
 }

packages/wrangler/src/config/validation.ts

@@ -2754,6 +2754,7 @@ const validateSendEmailBinding: ValidatorFn = (diagnostics, field, value) => {
 "destination_address",
 "name",
 "binding",
+"experimental_remote",
 ]);
 
 return isValid;

packages/wrangler/src/deployment-bundle/worker.ts

@@ -91,6 +91,7 @@ export interface CfKvNamespace {
  */
 export type CfSendEmailBindings = {
 name: string;
+experimental_remote?: boolean;
 } & (
 | { destination_address?: string }
 | { allowed_destination_addresses?: string[] }

packages/wrangler/src/dev/miniflare.ts

@@ -973,7 +973,13 @@ export function buildMiniflareBindingOptions(
 ]) ?? []
 ),
 email: {
-send_email: bindings.send_email,
+send_email: bindings.send_email?.map((b) => ({
+...b,
+remoteProxyConnectionString:
+b.experimental_remote && remoteProxyConnectionString
+? remoteProxyConnectionString
+: undefined,
+})),
 },
 images:
 bindings.images && (config.imagesLocalMode || remoteBindingsEnabled)

packages/wrangler/src/utils/print-bindings.ts

@@ -213,7 +213,9 @@ export function printBindings(
 destination_address ||
 allowed_destination_addresses?.join(", ") ||
 "unrestricted",
-mode: getMode({ isSimulatedLocally: true }),
+mode: getMode({
+isSimulatedLocally: !emailBinding.experimental_remote,
+}),
 };
 })
 );

packages/wrangler/templates/remoteBindings/proxyServerWorker/index.ts

@@ -1,12 +1,29 @@
 import { receiveRpcOverHttp } from "@cloudflare/jsrpc";
+import { EmailMessage } from "cloudflare:email";
 
+// For most bindings, we expose them as RPC stubs directly to @cloudflare/jsrpc.
+// However, SendEmail bindings need to take EmailMessage as their first parameter, which is not serialisable
+// As such, we reconstruct it before sending it on to the binding.
+// See also packages/miniflare/src/workers/email/email.worker.ts
+function getExposedBinding(b: any) {
+if (b.constructor.name === "SendEmail") {
+return {
+async send(e: ForwardableEmailMessage) {
+// @ts-expect-error EmailMessage::raw is defined in packages/miniflare/src/workers/email/email.worker.ts
+const message = new EmailMessage(e.from, e.to, e["EmailMessage::raw"]);
+return b.send(message);
+},
+};
+}
+return b;
+}
 export default {
 async fetch(request, env) {
 if (request.headers.get("Upgrade")) {
 const url = new URL(request.url);
 return receiveRpcOverHttp(
 request,
-env[url.searchParams.get("MF-Binding")!]
+getExposedBinding(env[url.searchParams.get("MF-Binding")!])
 );
 }
 const targetBinding = request.headers.get("MF-Binding");