Adds ant task to update fallback directories in RS

build.xml

@@ -322,6 +322,14 @@
     </untar>
   </target>
 
+  <target name="update-fallback-dir-list"
+          description="Update the fallback directory list used by Relay Search">
+    <exec executable="bash">
+      <arg value="-c"/>
+      <arg value="python3 src/main/python/fallback_dir.py | tee src/main/resources/web/js/rs/fallback_dir.js"/>
+    </exec>
+  </target>
+
   <!-- The following line adds the common targets and properties
        for Metrics' Java Projects.
   -->

src/main/python/fallback_dir.py

@@ -0,0 +1,31 @@
+import json
+import re
+import urllib.request
+
+response = urllib.request.urlopen("https://gitweb.torproject.org/tor.git/plain/src/app/config/fallback_dirs.inc")
+lines = [x.decode("ascii") for x in response.readlines()]
+
+fingerprints = []
+for line in lines:
+    if line.startswith("\""):
+        m = re.search('(?<=id=)\w+', line)
+        if m:
+            fingerprints.append(m.group(0))
+
+print("""
+
+/*
+This file is generated by src/main/python/fallback_dir.py.
+
+To update run:
+
+ant update-fallback-dir-list
+*/
+
+var fallbackDirs = %s;
+
+function IsFallbackDir(fingerprint) {
+  return $.inArray(fingerprint, fallbackDirs) > -1;
+}
+""" % (json.dumps(fingerprints)))
+