Add Tor placeholders instructions and fallback

gui/electron/main.js

@@ -46,7 +46,13 @@ function startOnionShare() {
 }
 
 async function runServe (retry = false) {
-  const { torProc, socksPort, controlPort } = await launchTor();
+  let torProc, socksPort, controlPort;
+  try {
+    ({ torProc, socksPort, controlPort } = await launchTor());
+  } catch (err) {
+    dialog.showErrorBox('Tor error', err.message);
+    return;
+  }
 
   const env = { ...process.env,
                 TOR_SOCKS_PORT:   socksPort.toString(),

gui/electron/tor.js

@@ -1,15 +1,39 @@
 const { spawn } = require('child_process');
 const path = require('path');
+const fs = require('fs');
+const which = require('which');
 const getPort = (...args) => import('get-port').then(m => m.default(...args));
 
 async function launchTor() {
   const socks = await getPort();
   const control = await getPort();
   const torBase = path.join(__dirname, '..', '..', 'voxvera', 'resources', 'tor');
-  const exe = path.join(torBase, process.platform,
-                        process.platform === 'win32' ? 'tor.exe' : 'tor');
-  const obfs4 = path.join(torBase, process.platform,
-                         process.platform === 'win32' ? 'obfs4proxy.exe' : 'obfs4proxy');
+  let exe = path.join(torBase, process.platform,
+                      process.platform === 'win32' ? 'tor.exe' : 'tor');
+  let obfs4 = path.join(torBase, process.platform,
+                        process.platform === 'win32' ? 'obfs4proxy.exe' : 'obfs4proxy');
+
+  const missing = p => {
+    try {
+      const data = fs.readFileSync(p, 'utf8');
+      return data.includes('placeholder');
+    } catch (e) {
+      return true;
+    }
+  };
+
+  if (missing(exe)) {
+    const sysTor = which.sync('tor', { nothrow: true });
+    if (sysTor) exe = sysTor;
+  }
+  if (missing(obfs4)) {
+    const sysObfs = which.sync('obfs4proxy', { nothrow: true });
+    if (sysObfs) obfs4 = sysObfs;
+  }
+
+  if (missing(exe) || missing(obfs4)) {
+    throw new Error('Tor or obfs4proxy not found; install them first.');
+  }
 
   const args = [
     'SocksPort', socks,