Add transformBinPath parameter to support weird packaging situations

Author: Nathan Sobo

README.md

@@ -50,6 +50,16 @@ By default, the an appropriate implementation of the watcher is selected for the
 const watcher = new Watcher({pollInterval: 1000});
 ```
 
+### Bin path transformation
+
+If you have a weird packaging situation (for example, this library being archived in an Electron ASAR archive), you may need to modify the path to the subprocess executable. You can pass a `transformBinPath` function to the `Watcher` constructor as a parameter to do so.
+
+```js
+const watcher = new Watcher({
+  transformBinPath: p => p.replace(/\bapp\.asar\b/, "app.asar.unpacked")
+});
+```
+
 ## Project structure
 
 This library spawns a subprocess that speaks a simple line-oriented JSON protocol over stdin and stdout. The Rust source for the subprocess is located in [`subprocess`](./subprocess).

lib/index.js

@@ -1,4 +1,5 @@
 const { spawn } = require("child_process");
+const path = require("path");
 const util = require("util");
 const realpath = util.promisify(require("fs").realpath);
 
@@ -13,15 +14,22 @@ module.exports = class Watcher {
       this.onError = params.onError;
     }
 
-    const args = [];
-    if (params.pollInterval) args.push("--poll-interval", params.pollInterval);
-    this.childProcess = spawn(
-      `${__dirname}/../bin/notify-subprocess-${process.platform}`,
-      args,
-      {
-        stdio: ["pipe", "pipe", "pipe"]
-      }
+    let binPath = path.join(
+      __dirname,
+      "..",
+      "bin",
+      `notify-subprocess-${process.platform}`
     );
+    if (params && typeof params.transformBinPath === "function") {
+      binPath = params.transformBinPath(binPath);
+    }
+
+    const args = [];
+    if (params && params.pollInterval)
+      args.push("--poll-interval", params.pollInterval);
+    this.childProcess = spawn(binPath, args, {
+      stdio: ["pipe", "pipe", "pipe"]
+    });
     this.kill = this.kill.bind(this);
     process.on("exit", this.kill);