From 31a380115a0f05d9709e016e349fbf91f1c20e2a Mon Sep 17 00:00:00 2001
From: Richard Maw <richard.maw@codethink.co.uk>
Date: Thu, 30 Jan 2014 16:12:34 +0000
Subject: Connect to ephemeral port when debugging

Rather than use a random, possibly used port, have the server connect
to an ephemeral port and report via a file, which port it connected to.
---
 lorry-controller-webapp               | 31 +++++++++++++++++++++++++------
 yarns.webapp/900-implementations.yarn | 15 ++++++---------
 2 files changed, 31 insertions(+), 15 deletions(-)

diff --git a/lorry-controller-webapp b/lorry-controller-webapp
index 6acbac0..9064d17 100755
--- a/lorry-controller-webapp
+++ b/lorry-controller-webapp
@@ -20,6 +20,7 @@ import logging
 import os
 import sqlite3
 import time
+import wsgiref.simple_server
 
 import bottle
 import cliapp
@@ -132,11 +133,12 @@ class WEBAPP(cliapp.Application):
             ['wsgi'],
             'run in wsgi mode (default is debug mode, for development)')
 
-        self.settings.integer(
-            ['debug-port'],
-            'listen on PORT when in debug mode (i.e., not running under WSGI)',
-            metavar='PORT',
-            default=8888)
+        self.settings.string(
+            ['debug-port-file'],
+            'write listening port to FILE when in debug mode '
+            '(i.e., not running under WSGI)',
+            metavar='FILE',
+            default='webapp.port')
 
         self.settings.string(
             ['debug-host'],
@@ -182,10 +184,27 @@ class WEBAPP(cliapp.Application):
         if self.settings['wsgi']:
             WSGIServer(webapp).run()
         else:
+            server_port_file = self.settings['debug-port-file']
+            class DebugServer(wsgiref.simple_server.WSGIServer):
+                '''WSGI-like server that uses an ephemeral port.
+
+                Rather than use a specified port, or default, the
+                DebugServer connects to an ephemeral port and writes
+                its number to debug-port-file, so a non-racy temporary
+                port can be used.
+
+                '''
+
+                def __init__(self, (host, port), *args, **kwargs):
+                    wsgiref.simple_server.WSGIServer.__init__(
+                        self, (host, 0), *args, **kwargs)
+                    with open(server_port_file, 'w') as f:
+                        f.write(str(self.server_port) + '\n')
+
             bottle.run(
                 webapp,
                 host=self.settings['debug-host'],
-                port=self.settings['debug-port'],
+                server_class=DebugServer,
                 quiet=True,
                 debug=True)
 
diff --git a/yarns.webapp/900-implementations.yarn b/yarns.webapp/900-implementations.yarn
index 7bfb6bb..19d4cfc 100644
--- a/yarns.webapp/900-implementations.yarn
+++ b/yarns.webapp/900-implementations.yarn
@@ -24,14 +24,6 @@ but the shell doesn't wait for it to terminate. This way, WEBAPP will
 be running until it crashes or is explicitly killed.
 
     IMPLEMENTS GIVEN a running WEBAPP
-    # Pick a random port beyond 1024 (i.e., an unreserved one).
-    port=0
-    while [ "$port" -le 1024 ]
-    do
-        port=$RANDOM
-    done
-    echo "$port" > "$DATADIR/webapp.port"
-
     start-stop-daemon -S -x "$SRCDIR/lorry-controller-webapp" \
         -b -p "$DATADIR/webapp.pid" -m --verbose \
         -- \
@@ -39,7 +31,12 @@ be running until it crashes or is explicitly killed.
         --log-level debug \
         --log "$DATADIR/webapp.log" \
         --debug-host 127.0.0.1 \
-        --debug-port "$port"
+        --debug-port-file "$DATADIR/webapp.port"
+
+    while [ ! -e "$DATADIR/webapp.port" ]; do
+        sleep 1
+    done
+    port=$(cat "$DATADIR/webapp.port")
 
     # Wait for the WEBAPP to actually be ready, i.e., that it's
     # listening on its assigned port.
-- 
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