diff --git a/contrib_bots/lib/virtual_fs.py b/contrib_bots/lib/virtual_fs.py
new file mode 100644
index 0000000..7a116f9
--- /dev/null
+++ b/contrib_bots/lib/virtual_fs.py
@@ -0,0 +1,232 @@
+# See readme.md for instructions on running this code.
+
+import re
+import os
+
+class VirtualFsHandler(object):
+    def usage(self):
+        return get_help()
+
+    def triage_message(self, message):
+        # return True iff we want to (possibly) response to this message
+        if message['type'] != 'stream':
+            return False
+
+        original_content = message['content']
+        return original_content.startswith('fs ')
+
+    def handle_message(self, message, client, state_handler):
+        assert self.triage_message(message)
+
+        original_content = message['content']
+        command = original_content[len('fs '):]
+        stream = message['display_recipient']
+        topic = message['subject']
+
+        state = state_handler.get_state()
+        if state is None:
+            state = {}
+
+        if stream not in state:
+            state[stream] = fs_new()
+
+        fs = state[stream]
+        fs, msg = fs_command(fs, command)
+        state[stream] = fs
+        state_handler.set_state(state)
+
+        client.send_message(dict(
+            type='stream',
+            to=stream,
+            subject=topic,
+            content=msg,
+        ))
+
+
+def get_help():
+    return '''
+The "fs" commands implement a virtual file system for a stream.
+The locations of text are persisted for the lifetime of the bot
+running, and if you rename a stream, you will lose the info.
+
+Example commands:
+
+```
+fs mkdir: create a directory
+fs ls: list a directory
+fs write: write text
+fs read: read text
+fs rm: remove a file
+```
+
+Use commands like `fs help write` for more details on specific
+commands.
+'''
+
+def test():
+    fs = fs_new()
+    assert is_directory(fs, '/')
+
+    for cmd, expected_response in sample_conversation():
+        fs, msg = fs_command(fs, cmd)
+        if msg != expected_response:
+            raise AssertionError('''
+                cmd: %s
+                expected: %s
+                but got : %s
+                ''' % (cmd, expected_response, msg))
+
+def sample_conversation():
+    return [
+        ('write /foo contents of /foo', 'file written'),
+        ('read /foo', 'contents of /foo'),
+        ('write /bar Contents: bar bar', 'file written'),
+        ('read /bar', 'Contents: bar bar'),
+        ('write /bar invalid', 'ERROR: file already exists'),
+        ('rm /bar', 'removed'),
+        ('rm /bar', 'ERROR: file does not exist'),
+        ('write /bar new bar', 'file written'),
+        ('read /bar', 'new bar'),
+        ('write /yo/invalid whatever', 'ERROR: /yo is not a directory'),
+        ('mkdir /yo', 'directory created'),
+        ('ls /yo', 'WARNING: directory is empty'),
+        ('read /yo/nada', 'ERROR: file does not exist'),
+        ('write /yo whatever', 'ERROR: file already exists'),
+        ('write /yo/apple red', 'file written'),
+        ('read /yo/apple', 'red'),
+        ('mkdir /yo/apple', 'ERROR: file already exists'),
+        ('ls /invalid', 'ERROR: file does not exist'),
+        ('ls /foo', 'ERROR: /foo is not a directory'),
+        ('ls /', '* /bar\n* /foo\n* /yo'),
+        ('invalid command', 'ERROR: unrecognized command'),
+        ('write', 'ERROR: syntax: write <path> <some_text>'),
+        ('help', get_help()),
+        ('help ls', 'syntax: ls <path>'),
+        ('help invalid_command', get_help()),
+    ]
+
+REGEXES = dict(
+    command='(ls|mkdir|read|rm|write)',
+    path='(\S+)',
+    some_text='(.+)',
+)
+
+def get_commands():
+    return {
+        'help': (fs_help, ['command']),
+        'ls': (fs_ls, ['path']),
+        'mkdir': (fs_mkdir, ['path']),
+        'read': (fs_read, ['path']),
+        'rm': (fs_rm, ['path']),
+        'write': (fs_write, ['path', 'some_text']),
+    }
+
+def fs_command(fs, cmd):
+    if cmd.strip() == 'help':
+        return fs, get_help()
+
+    cmd_name = cmd.split()[0]
+    commands = get_commands()
+    if cmd_name not in commands:
+        return fs, 'ERROR: unrecognized command'
+
+    f, arg_names = commands[cmd_name]
+    partial_regexes = [cmd_name] + [REGEXES[a] for a in arg_names]
+    regex = ' '.join(partial_regexes)
+    m = re.match(regex, cmd)
+    if m:
+        return f(fs, *m.groups())
+    elif cmd_name == 'help':
+        return fs, get_help()
+    else:
+        return fs, 'ERROR: ' + syntax_help(cmd_name)
+
+def syntax_help(cmd_name):
+    commands = get_commands()
+    f, arg_names = commands[cmd_name]
+    arg_syntax = ' '.join('<' + a + '>' for a in arg_names)
+    return 'syntax: %s %s' % (cmd_name, arg_syntax)
+
+def fs_new():
+    fs = {
+        '/': directory([])
+    }
+    return fs
+
+def fs_help(fs, cmd_name):
+    return fs, syntax_help(cmd_name)
+
+def fs_mkdir(fs, fn):
+    if fn in fs:
+        return fs, 'ERROR: file already exists'
+    dir_path = os.path.dirname(fn)
+    if not is_directory(fs, dir_path):
+        msg = 'ERROR: %s is not a directory' % (dir_path,)
+        return fs, msg
+    new_fs = fs.copy()
+    new_dir = directory({fn}.union(fs[dir_path]['fns']))
+    new_fs[dir_path] = new_dir
+    new_fs[fn] = directory([])
+    msg = 'directory created'
+    return new_fs, msg
+
+def fs_ls(fs, fn):
+    if fn not in fs:
+        msg = 'ERROR: file does not exist'
+        return fs, msg
+    if not is_directory(fs, fn):
+        return fs, 'ERROR: %s is not a directory' % (fn,)
+    fns = fs[fn]['fns']
+    if not fns:
+        return fs, 'WARNING: directory is empty'
+    msg = '\n'.join('* ' + fn for fn in sorted(fns))
+    return fs, msg
+
+def fs_rm(fs, fn):
+    if fn not in fs:
+        msg = 'ERROR: file does not exist'
+        return fs, msg
+    new_fs = fs.copy()
+    new_fs.pop(fn)
+    msg = 'removed'
+    return new_fs, msg
+
+def fs_write(fs, fn, content):
+    if fn in fs:
+        msg = 'ERROR: file already exists'
+        return fs, msg
+    dir_path = os.path.dirname(fn)
+    if not is_directory(fs, dir_path):
+        msg = 'ERROR: %s is not a directory' % (dir_path,)
+        return fs, msg
+    new_fs = fs.copy()
+    new_dir = directory({fn}.union(fs[dir_path]['fns']))
+    new_fs[dir_path] = new_dir
+    new_fs[fn] = text_file(content)
+    msg = 'file written'
+    return new_fs, msg
+
+def fs_read(fs, fn):
+    if fn not in fs:
+        msg = 'ERROR: file does not exist'
+        return fs, msg
+    val = fs[fn]['content']
+    return fs, val
+
+def directory(fns):
+    return dict(kind='dir', fns=set(fns))
+
+def text_file(content):
+    return dict(kind='text', content=content)
+
+def is_directory(fs, fn):
+    if fn not in fs:
+        return False
+    return fs[fn]['kind'] == 'dir'
+
+handler_class = VirtualFsHandler
+
+if __name__ == '__main__':
+    # We eventually want to test bots with a "real" testing
+    # framework.
+    test()