Fetch image immediately before presenting/sending

Closes #1

herald/index.js

@@ -53,15 +53,15 @@ function killViewerProcess() {
   return viewerProcess.then(lose, lose);
 }
 
-function startViewerProcess(location, duration) {
+async function startViewerProcess(imageStream, duration) {
   // defer to the termination of any existing viewer process
   if (viewerProcess) {
-    return killViewerProcess().then(
-      startViewerProcess.bind(null, location, duration));
+    await killViewerProcess();
+    return startViewerProcess(imageStream, duration);
   }
 
   // set up a new viewer process
-  viewerProcess = asDesktopUser`feh -F ${location}`;
+  viewerProcess = asDesktopUser({input: imageStream})`feh -F -`;
 
   // log any errors, except the one we're expecting
   viewerProcess.catch(logNonSigTermErrors);
@@ -70,20 +70,23 @@ function startViewerProcess(location, duration) {
   if (duration) {
     viewerTimeout = setTimeout(killViewerProcess, duration);
   }
+}
 
-  // ensure that we're returning a resolved Promise context,
-  // whether this was called from killViewerProcess.then or not
-  return Promise.resolve();
+async function fetchAndDisplay(location, duration) {
+  const res = await fetch(location);
+  if (!res.ok) throw new Error(
+    `HTTP error fetching image: ${response.status} ${response.statusText}`);
+  return startViewerProcess(res.body, duration);
 }
 
 app.post('/present/still', (req, res, next) => {
   return Promise.all([
     // wake the display
     asDesktopUser`xset dpms force on`,
     // present the still
-    startViewerProcess(req.query.location, req.query.duration)
+    fetchAndDisplay(req.query.location, req.query.duration)
 
-    ].map(p=>p.catch(next))).then(()=>res.send());
+    ].map(p => p.catch(next))).then(() => res.send());
 });
 
 app.listen(80);

sentinel/index.js

@@ -61,8 +61,11 @@ const mailer = EMAIL_RECIPIENT && nodemailer.createTransport({
   },
 });
 
-function sendEmailNotification() {
+async function sendEmailNotification() {
   const cid = uuid();
+  const res = await fetch(SNAP_URL);
+  if (!res.ok) throw new Error(
+    `HTTP error fetching image: ${response.status} ${response.statusText}`);
   return mailer.sendMail({
     from: {name: EMAIL_SENDER_NAME, address: EMAIL_SENDER_ADDRESS},
     to: EMAIL_RECIPIENT,
@@ -72,7 +75,7 @@ function sendEmailNotification() {
     html: `<img src="cid:${cid}">`,
     attachments: [{
       filename: EMAIL_ATTACHMENT_FILENAME,
-      path: SNAP_URL,
+      content: res.body,
       cid }]
   });
 }