feat: askpass bridge from git prompts to a callback

Co-Authored-By: Claude

src/askpass.test.ts

@@ -0,0 +1,25 @@
+import { afterEach, expect, test } from "vitest";
+import { execFile } from "node:child_process";
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { promisify } from "node:util";
+import { AskpassBridge } from "./askpass";
+
+const run = promisify(execFile);
+let bridge: AskpassBridge | undefined;
+afterEach(() => bridge?.stop());
+
+test("helper script round-trips a prompt to onPrompt and returns the answer", async () => {
+  const dir = mkdtempSync(join(tmpdir(), "jp-ask-"));
+  bridge = new AskpassBridge({
+    dir,
+    onPrompt: async (p) => (p.includes("Password") ? "s3cret" : "alice"),
+  });
+  const env = await bridge.start();
+  const { stdout } = await run(env.GIT_ASKPASS, ["Password for 'https://x':"], {
+    env: { ...process.env, JEKYLL_ASKPASS_SOCK: env.JEKYLL_ASKPASS_SOCK },
+  });
+  expect(stdout.trim()).toBe("s3cret");
+  rmSync(dir, { recursive: true, force: true });
+});

src/askpass.ts

@@ -0,0 +1,60 @@
+import { createServer, Server } from "node:net";
+import { chmodSync, writeFileSync } from "node:fs";
+import { join } from "node:path";
+
+export class AskpassBridge {
+  private server?: Server;
+  private sock = "";
+  private script = "";
+
+  constructor(private opts: { dir: string; onPrompt: (prompt: string) => Promise<string> }) {}
+
+  async start(): Promise<{
+    GIT_ASKPASS: string;
+    SSH_ASKPASS: string;
+    SSH_ASKPASS_REQUIRE: string;
+    JEKYLL_ASKPASS_SOCK: string;
+  }> {
+    this.sock = join(this.opts.dir, "askpass.sock");
+    this.script = join(this.opts.dir, "askpass.sh");
+
+    this.server = createServer({ allowHalfOpen: true }, (conn) => {
+      let buf = "";
+      conn.on("data", (d) => (buf += d.toString()));
+      conn.on("end", async () => {
+        const answer = await this.opts.onPrompt(buf.replace(/\n$/, ""));
+        conn.end(answer.endsWith("\n") ? answer : answer + "\n");
+      });
+    });
+    await new Promise<void>((res) => this.server!.listen(this.sock, res));
+
+    // Helper: send argv[1] (the prompt) to the socket, print the reply.
+    // Uses a Node one-liner for reliable EOF signalling across platforms
+    // (nc -U without -N hangs on BSD-derived netcat; socat may also vary).
+    // Protocol: client writes prompt + "\n", server replies with answer + "\n" and closes.
+    // allowHalfOpen ensures the client can still receive after calling end().
+    const sh = [
+      "#!/bin/sh",
+      'node -e "' +
+        "const n=require('net'),s=process.env.JEKYLL_ASKPASS_SOCK,p=process.argv[1];" +
+        "const c=n.createConnection({path:s,allowHalfOpen:true},()=>{c.end(p+'\\n')});" +
+        "c.on('data',d=>process.stdout.write(d));" +
+        '" -- "$1"',
+      "",
+    ].join("\n");
+    writeFileSync(this.script, sh);
+    chmodSync(this.script, 0o755);
+
+    return {
+      GIT_ASKPASS: this.script,
+      SSH_ASKPASS: this.script,
+      SSH_ASKPASS_REQUIRE: "force",
+      JEKYLL_ASKPASS_SOCK: this.sock,
+    };
+  }
+
+  stop(): void {
+    this.server?.close();
+    this.server = undefined;
+  }
+}