Add health checking.

render.py

@@ -1,3 +1,4 @@
+import json
 import math
 import os
 import StringIO
@@ -14,6 +15,7 @@ class App(flask.Flask):
     def __init__(self, *args, **kwargs):
         super(App, self).__init__(*args, **kwargs)
         self.last = 0
+        self.health = (0, False, "unknown")
 
 
 app = App(__name__)
@@ -70,6 +72,31 @@ class Renderer(object):
 def index():
     return flask.render_template('index.html')
 
+def healthcheck():
+    last_checked, last_status, last_details = app.health
+    if time.time() - last_checked < 1:
+        return last_status, last_details
+    output = subprocess.check_output(['lpstat', '-p', '-d'])
+    mark = False
+    for line in output.split('\n'):
+        line = line.strip()
+        if line.startswith('printer DYMO_LabelWriter_450'):
+            mark = True
+            continue
+        if mark:
+            if line.startswith('Ready to print'):
+                app.health = (time.time(), True, line)
+                return True, line
+            else:
+                app.health = (time.time(), False, line)
+                return False, line
+        mark = False
+
+@app.route('/health')
+def health():
+    ok, details = healthcheck()
+    return json.dumps({'ok': ok, 'details': details})
+
 @app.route('/stuff/preview/<int:size>/')
 def stuff_preview(size):
     text = flask.request.args.get('text')
@@ -84,6 +111,8 @@ def stuff_preview(size):
 DELAY = 5
 @app.route('/stuff/print/<int:size>/', methods=['POST'])
 def stuff_print(size):
+    if not healthcheck()[0]:
+        return 'Printer is down.'
     last = app.last
     print last, time.time() - last
     if time.time() - last < DELAY:

templates/index.html

@@ -44,6 +44,7 @@ body {
         <div class="container">
             <div class="page-header">
                 <h1>Hackerspace Printing System For Printing Labels</h1>
+                <h4>System status: <span class="label label-default" id="systemstatus">unknown</span></h4>
             </div>
             <h3>Box 'o Stuff Label <small>For SAMLA boxes with common equipment</small></h3>
             <div class="row">
@@ -114,6 +115,19 @@ $(document).ready(function() {
         print();
     });
     generatePreview();
+    var updateStatus = function() {
+        $.getJSON("/health", function(data) {
+            if (data.ok) {
+                $("#systemstatus").attr("class", "label label-success");
+                $("#systemstatus").html(data.details);
+            } else {
+                $("#systemstatus").attr("class", "label label-danger");
+                $("#systemstatus").html(data.details);
+            }
+        });
+    };
+    updateStatus();
+    setInterval(updateStatus, 1000);
 });
         </script>
     </body>