feat: add buildCopyCommand for safe clipboard command construction

Uses validateClipboardCmd to reject untrusted input and properly escapes
single quotes in text to prevent shell injection.

tailscalectl/lib.js

@@ -32,6 +32,12 @@ function validateClipboardCmd(cmd) {
     return typeof cmd === "string" && safeClipboardCmds.includes(cmd)
 }
 
+function buildCopyCommand(text, clipboardCmd) {
+    if (!validateClipboardCmd(clipboardCmd)) return null
+    var escaped = text.replace(/'/g, "'\\''")
+    return ["sh", "-c", "printf '%s' '" + escaped + "' | " + clipboardCmd]
+}
+
 function errorMessage(cmd) {
     var messages = {
         "up": "Failed to connect to Tailscale",
@@ -46,5 +52,5 @@ function errorMessage(cmd) {
 
 // CommonJS export for Node.js tests (ignored by QML)
 if (typeof module !== "undefined" && module.exports) {
-    module.exports = { parsePeers, makeExitNodeCommand, findActiveExitNode, errorMessage, validateClipboardCmd }
+    module.exports = { parsePeers, makeExitNodeCommand, findActiveExitNode, errorMessage, validateClipboardCmd, buildCopyCommand }
 }

test/lib.test.js

@@ -1,7 +1,7 @@
 import { test } from "node:test"
 import assert from "node:assert"
 import lib from "../tailscalectl/lib.js"
-const { parsePeers, makeExitNodeCommand, findActiveExitNode, errorMessage, validateClipboardCmd } = lib
+const { parsePeers, makeExitNodeCommand, findActiveExitNode, errorMessage, validateClipboardCmd, buildCopyCommand } = lib
 
 test("parsePeers extracts exitNode from ExitNodeOption", () => {
     const peerMap = {
@@ -96,3 +96,23 @@ test("validateClipboardCmd rejects empty and falsy inputs", () => {
     assert.strictEqual(validateClipboardCmd(null), false)
     assert.strictEqual(validateClipboardCmd(undefined), false)
 })
+
+// --- buildCopyCommand ---
+
+test("buildCopyCommand returns safe command for whitelisted clipboard tool", () => {
+    const cmd = buildCopyCommand("hello", "wl-copy")
+    assert.ok(Array.isArray(cmd))
+    assert.strictEqual(cmd[0], "sh")
+    assert.strictEqual(cmd[1], "-c")
+})
+
+test("buildCopyCommand returns null for invalid clipboard command", () => {
+    assert.strictEqual(buildCopyCommand("hello", "rm -rf /"), null)
+    assert.strictEqual(buildCopyCommand("hello", ""), null)
+    assert.strictEqual(buildCopyCommand("hello", null), null)
+})
+
+test("buildCopyCommand safely handles text with special characters", () => {
+    const cmd = buildCopyCommand("it's a 'test' with \"quotes\" and\nnewlines", "wl-copy")
+    assert.ok(Array.isArray(cmd))
+})