Add strong typing to background messages

scripts/excmds_macros.py

@@ -68,7 +68,7 @@ def get_block(lines):
     """next(lines) contains an open brace: return all the lines up to close brace.
 
     Moves the lines iterator, so useful for consuming a block.
-    
+
     """
     brace_balance = 0
     block = ""
@@ -139,7 +139,7 @@ def background(lines, context):
                    return Messaging.message(
                        "excmd_background",
                        "{sig.name}",
-                       [{message_params}],
+                       {message_params}
                    )
                }}\n""".format(**locals()))
 

src/background.ts

@@ -2,7 +2,7 @@
 
 /* tslint:disable:import-spacing */
 
-import "@src/lib/browser_proxy_background"
+import * as proxy_background from "@src/lib/browser_proxy_background"
 
 import * as controller from "@src/lib/controller"
 import * as perf from "@src/perf"
@@ -55,8 +55,6 @@ controller.setExCmds({
     "text": EditorCmds,
     "hint": HintingCmds
 })
-messaging.addListener("excmd_background", messaging.attributeCaller(excmds_background))
-messaging.addListener("controller_background", messaging.attributeCaller(controller))
 
 // {{{ tri.contentLocation
 // When loading the background, use the active tab to know what the current content url is
@@ -165,10 +163,19 @@ browser.tabs.onCreated.addListener(
 
 // An object to collect all of our statistics in one place.
 const statsLogger: perf.StatsLogger = new perf.StatsLogger()
-messaging.addListener(
-    "performance_background",
-    messaging.attributeCaller(statsLogger),
-)
+export const messages = {
+    excmd_background: excmds_background,
+    controller_background: controller,
+    performance_background: statsLogger,
+    download_background: {
+        downloadUrl: download_background.downloadUrl,
+        downloadUrlAs: download_background.downloadUrlAs,
+    },
+    browser_proxy_background: {shim: proxy_background.shim}
+}
+export type Messages = typeof messages
+
+messaging.setupListener(messages)
 // Listen for statistics from the background script and store
 // them. Set this one up to log directly to the statsLogger instead of
 // going through messaging.

src/background/download_background.ts

@@ -146,14 +146,3 @@ export async function downloadUrlAs(url: string, saveAs: string) {
         browser.downloads.onChanged.addListener(onDownloadComplete)
     })
 }
-
-import * as Messaging from "@src/lib/messaging"
-
-// Get messages from content
-Messaging.addListener(
-    "download_background",
-    Messaging.attributeCaller({
-        downloadUrl,
-        downloadUrlAs,
-    }),
-)

src/excmds.ts

@@ -839,9 +839,9 @@ export async function restart() {
 //#content
 export async function saveas(...filename: string[]) {
     if (filename.length > 0) {
-        return Messaging.message("download_background", "downloadUrlAs", [window.location.href, filename.join(" ")])
+        return Messaging.message("download_background", "downloadUrlAs", window.location.href, filename.join(" "))
     } else {
-        return Messaging.message("download_background", "downloadUrl", [window.location.href, true])
+        return Messaging.message("download_background", "downloadUrl", window.location.href, true)
     }
 }
 
@@ -3962,7 +3962,7 @@ export async function hint(option?: string, selectors?: string, ...rest: string[
             selectHints = hinting.pipe_elements(
                 elems,
                 elem => {
-                    Messaging.message("download_background", "downloadUrl", [new URL(elem[attr], window.location.href).href, saveAs])
+                    Messaging.message("download_background", "downloadUrl", new URL(elem[attr], window.location.href).href, saveAs)
                     return elem
                 },
                 rapid,
@@ -4074,7 +4074,7 @@ export function rot13(n: number) {
  */
 //#content
 export function run_exstr(...commands: string[]) {
-    return Messaging.message("controller_background", "acceptExCmd", commands)
+    return Messaging.message("controller_background", "acceptExCmd", commands.join(""))
 }
 
 // }}}

src/lib/browser_proxy.ts

@@ -7,11 +7,11 @@ const browserProxy = new Proxy(Object.create(null), {
             {
                 get(_, func) {
                     return (...args) =>
-                        message("browser_proxy_background", "shim", [
+                        message("browser_proxy_background", "shim",
                             api,
                             func,
                             args,
-                        ])
+                        )
                 },
             },
         )

src/lib/browser_proxy_background.ts

@@ -1,11 +1,5 @@
 /** Shim to access BG browser APIs from content. */
 
-function shim(api, func, args) {
+export function shim(api, func, args) {
     return browser[api][func](...args)
 }
-
-import { addListener, attributeCaller, MessageType } from "@src/lib/messaging"
-addListener(
-    "browser_proxy_background" as MessageType,
-    attributeCaller({ shim }),
-)

src/lib/messaging.ts

@@ -1,4 +1,5 @@
 import { browserBg, activeTabId, ownTabId, getContext } from "@src/lib/webext"
+import * as Messages from "@src/message_protocols"
 import Logger from "@src/lib/logging"
 const logger = new Logger("messaging")
 
@@ -65,9 +66,48 @@ export function attributeCaller(obj) {
     return handler
 }
 
+interface TypedMessage<Root, Type extends keyof Root, Command extends keyof Root[Type]> {
+    type: Type
+    command: Command
+    args: Parameters<Root[Type][Command]>
+}
+
+function backgroundHandler<
+    Root,
+    Type extends keyof Root,
+    Command extends keyof Root[Type]
+    >(root: Root,
+      message: TypedMessage<Root, Type, Command>,
+      sender: browser.runtime.MessageSender,
+    ): ReturnType<Root[Type][Command]> {
+    return root[message.type][message.command](...message.args)
+}
+
+export function setupListener<Root>(root: Root) {
+    browser.runtime.onMessage.addListener((message: any, sender: browser.runtime.MessageSender) => {
+        if (message.type in root) {
+            if (!(message.command in root[message.type]))
+                throw new Error(`missing handler in protocol ${message.type} ${message.command}`)
+            if (!Array.isArray(message.args))
+                throw new Error(`wrong arguments in protocol ${message.type} ${message.command}`)
+            return backgroundHandler(root, message, sender)
+        }
+    });
+}
+
 /** Send a message to non-content scripts */
-export async function message(type: NonTabMessageType, command, args?) {
-    return browser.runtime.sendMessage({ type, command, args } as Message)
+export async function message<
+    Type extends keyof Messages.Background,
+    Command extends keyof Messages.Background[Type],
+    F extends ((...args: any) => any) & Messages.Background[Type][Command]
+  >(type: Type, command: Command, ...args: Parameters<F>) {
+    const message: TypedMessage<Messages.Background, Type, Command> = {
+        type,
+        command,
+        args
+    }
+
+    return browser.runtime.sendMessage<typeof message, ReturnType<F>>(message)
 }
 
 /** Message the active tab of the currentWindow */

src/message_protocols.ts

@@ -0,0 +1,3 @@
+// This file re-exports types for message protocols for background, content and commandline contexts
+
+export { Messages as Background } from "@src/background"

src/newtab.ts

@@ -47,6 +47,6 @@ window.addEventListener("load", _ => {
 // Periodically nag people about updates.
 window.addEventListener("load", _ => {
     if (config.get("update", "nag") === true) {
-        Messaging.message("controller_background", "acceptExCmd", ["updatecheck auto_polite"])
+        Messaging.message("controller_background", "acceptExCmd", "updatecheck auto_polite")
     }
 })

src/perf.ts

@@ -416,7 +416,5 @@ class MetricName {
 }
 
 function sendStats(list: PerformanceEntryList) {
-    messaging.message("performance_background", "receiveStatsJson", [
-        JSON.stringify(list),
-    ])
+    messaging.message("performance_background", "receiveStatsJson", JSON.stringify(list))
 }