1 files changed, 52 insertions, 0 deletions
diff --git a/extension/src/webext-bridge/internal/post-message.ts b/extension/src/webext-bridge/internal/post-message.ts
new file mode 100644
index 0000000..9db4424
--- /dev/null
+++ b/extension/src/webext-bridge/internal/post-message.ts
@@ -0,0 +1,52 @@
+import type { InternalMessage } from '../types'
+import { getMessagePort } from './message-port'
+
+export interface EndpointWontRespondError {
+  type: 'error'
+  transactionID: string
+}
+
+export const usePostMessaging = (thisContext: 'window' | 'content-script') => {
+  let allocatedNamespace: string
+  let messagingEnabled = false
+  let onMessageCallback: (
+    msg: InternalMessage | EndpointWontRespondError
+  ) => void
+  let portP: Promise<MessagePort>
+
+  return {
+    enable: () => (messagingEnabled = true),
+    onMessage: (cb: typeof onMessageCallback) => (onMessageCallback = cb),
+    postMessage: async(msg: InternalMessage | EndpointWontRespondError) => {
+      if (thisContext !== 'content-script' && thisContext !== 'window')
+        throw new Error('Endpoint does not use postMessage')
+
+      if (!messagingEnabled)
+        throw new Error('Communication with window has not been allowed')
+
+      ensureNamespaceSet(allocatedNamespace)
+
+      return (await portP).postMessage(msg)
+    },
+    setNamespace: (nsps: string) => {
+      if (allocatedNamespace)
+        throw new Error('Namespace once set cannot be changed')
+
+      allocatedNamespace = nsps
+      portP = getMessagePort(thisContext, nsps, ({ data }) =>
+        onMessageCallback?.(data),
+      )
+    },
+  }
+}
+
+function ensureNamespaceSet(namespace: string) {
+  if (typeof namespace !== 'string' || namespace.trim().length === 0) {
+    throw new Error(
+      'webext-bridge uses window.postMessage to talk with other "window"(s) for message routing'
+        + 'which is global/conflicting operation in case there are other scripts using webext-bridge. '
+        + 'Call Bridge#setNamespace(nsps) to isolate your app. Example: setNamespace(\'com.facebook.react-devtools\'). '
+        + 'Make sure to use same namespace across all your scripts whereever window.postMessage is likely to be used`',
+    )
+  }
+}