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<h2 class="heading"><span>Tortoise and the Hare</span></h2>
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<div class="section" id="tortoise-and-the-hare">
<h1>Tortoise and the Hare<a class="headerlink" href="#tortoise-and-the-hare" title="Permalink to this headline">ΒΆ</a></h1>
<p>Controllers have two methods of talking with Tor...</p>
<ul class="simple">
<li><strong>Synchronous</strong> - Most commonly you make a request to Tor then receive its
reply. The <a class="reference internal" href="../api/control.html#stem.control.Controller.get_info" title="stem.control.Controller.get_info"><tt class="xref py py-func docutils literal"><span class="pre">get_info()</span></tt></a> calls in the <a class="reference external" href="the_little_relay_that_could.html">first
tutorial</a> are an example of this.</li>
<li><strong>Asynchronous</strong> - Controllers can subscribe to be notified when various
kinds of events occur within Tor (see the <a class="reference internal" href="../api/control.html#stem.control.EventType" title="stem.control.EventType"><tt class="xref py py-data docutils literal"><span class="pre">EventType</span></tt></a>).
Stem’s users provide a callback function to
<a class="reference internal" href="../api/control.html#stem.control.Controller.add_event_listener" title="stem.control.Controller.add_event_listener"><tt class="xref py py-func docutils literal"><span class="pre">add_event_listener()</span></tt></a> which is then notified
when the event occurs.</li>
</ul>
<p>Try to avoid lengthy operations within event callbacks. They’re notified by a
single dedicated event thread, and blocking this thread will prevent the
delivery of further events.</p>
<p>With that out of the way lets see an example. The following is a <a class="reference external" href="http://docs.python.org/2/howto/curses.html">curses</a> application that graphs the
bandwidth usage of Tor...</p>
<img alt="../_images/bandwidth_graph_output.png" src="../_images/bandwidth_graph_output.png" />
<p>To do this it listens to <strong>BW events</strong>
(the class for which is a <a class="reference internal" href="../api/response.html#stem.response.events.BandwidthEvent" title="stem.response.events.BandwidthEvent"><tt class="xref py py-class docutils literal"><span class="pre">BandwidthEvent</span></tt></a>). These
are events that Tor emits each second saying the number of bytes downloaded and
uploaded.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">curses</span>
<span class="kn">import</span> <span class="nn">functools</span>
<span class="kn">from</span> <span class="nn">stem.control</span> <span class="kn">import</span> <span class="n">EventType</span><span class="p">,</span> <span class="n">Controller</span>
<span class="kn">from</span> <span class="nn">stem.util</span> <span class="kn">import</span> <span class="n">str_tools</span>
<span class="c"># colors that curses can handle</span>
<span class="n">COLOR_LIST</span> <span class="o">=</span> <span class="p">{</span>
<span class="s">"red"</span><span class="p">:</span> <span class="n">curses</span><span class="o">.</span><span class="n">COLOR_RED</span><span class="p">,</span>
<span class="s">"green"</span><span class="p">:</span> <span class="n">curses</span><span class="o">.</span><span class="n">COLOR_GREEN</span><span class="p">,</span>
<span class="s">"yellow"</span><span class="p">:</span> <span class="n">curses</span><span class="o">.</span><span class="n">COLOR_YELLOW</span><span class="p">,</span>
<span class="s">"blue"</span><span class="p">:</span> <span class="n">curses</span><span class="o">.</span><span class="n">COLOR_BLUE</span><span class="p">,</span>
<span class="s">"cyan"</span><span class="p">:</span> <span class="n">curses</span><span class="o">.</span><span class="n">COLOR_CYAN</span><span class="p">,</span>
<span class="s">"magenta"</span><span class="p">:</span> <span class="n">curses</span><span class="o">.</span><span class="n">COLOR_MAGENTA</span><span class="p">,</span>
<span class="s">"black"</span><span class="p">:</span> <span class="n">curses</span><span class="o">.</span><span class="n">COLOR_BLACK</span><span class="p">,</span>
<span class="s">"white"</span><span class="p">:</span> <span class="n">curses</span><span class="o">.</span><span class="n">COLOR_WHITE</span><span class="p">,</span>
<span class="p">}</span>
<span class="n">GRAPH_WIDTH</span> <span class="o">=</span> <span class="mi">40</span>
<span class="n">GRAPH_HEIGHT</span> <span class="o">=</span> <span class="mi">8</span>
<span class="n">DOWNLOAD_COLOR</span> <span class="o">=</span> <span class="s">"green"</span>
<span class="n">UPLOAD_COLOR</span> <span class="o">=</span> <span class="s">"blue"</span>
<span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
<span class="k">with</span> <span class="n">Controller</span><span class="o">.</span><span class="n">from_port</span><span class="p">(</span><span class="n">port</span> <span class="o">=</span> <span class="mi">9051</span><span class="p">)</span> <span class="k">as</span> <span class="n">controller</span><span class="p">:</span>
<span class="n">controller</span><span class="o">.</span><span class="n">authenticate</span><span class="p">()</span>
<span class="k">try</span><span class="p">:</span>
<span class="c"># This makes curses initialize and call draw_bandwidth_graph() with a</span>
<span class="c"># reference to the screen, followed by additional arguments (in this</span>
<span class="c"># case just the controller).</span>
<span class="n">curses</span><span class="o">.</span><span class="n">wrapper</span><span class="p">(</span><span class="n">draw_bandwidth_graph</span><span class="p">,</span> <span class="n">controller</span><span class="p">)</span>
<span class="k">except</span> <span class="ne">KeyboardInterrupt</span><span class="p">:</span>
<span class="k">pass</span> <span class="c"># the user hit ctrl+c</span>
<span class="k">def</span> <span class="nf">draw_bandwidth_graph</span><span class="p">(</span><span class="n">stdscr</span><span class="p">,</span> <span class="n">controller</span><span class="p">):</span>
<span class="n">window</span> <span class="o">=</span> <span class="n">Window</span><span class="p">(</span><span class="n">stdscr</span><span class="p">)</span>
<span class="c"># (downloaded, uploaded) tuples for the last 40 seconds</span>
<span class="n">bandwidth_rates</span> <span class="o">=</span> <span class="p">[(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">)]</span> <span class="o">*</span> <span class="n">GRAPH_WIDTH</span>
<span class="c"># Making a partial that wraps the window and bandwidth_rates with a function</span>
<span class="c"># for Tor to call when it gets a BW event. This causes the 'window' and</span>
<span class="c"># 'bandwidth_rates' to be provided as the first two arguments whenever</span>
<span class="c"># 'bw_event_handler()' is called.</span>
<span class="n">bw_event_handler</span> <span class="o">=</span> <span class="n">functools</span><span class="o">.</span><span class="n">partial</span><span class="p">(</span><span class="n">_handle_bandwidth_event</span><span class="p">,</span> <span class="n">window</span><span class="p">,</span> <span class="n">bandwidth_rates</span><span class="p">)</span>
<span class="c"># Registering this listener with Tor. Tor reports a BW event each second.</span>
<span class="n">controller</span><span class="o">.</span><span class="n">add_event_listener</span><span class="p">(</span><span class="n">bw_event_handler</span><span class="p">,</span> <span class="n">EventType</span><span class="o">.</span><span class="n">BW</span><span class="p">)</span>
<span class="c"># Pause the main thread until the user hits any key... and no, don't you dare</span>
<span class="c"># ask where the 'any' key is. :P</span>
<span class="n">stdscr</span><span class="o">.</span><span class="n">getch</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">_handle_bandwidth_event</span><span class="p">(</span><span class="n">window</span><span class="p">,</span> <span class="n">bandwidth_rates</span><span class="p">,</span> <span class="n">event</span><span class="p">):</span>
<span class="c"># callback for when tor provides us with a BW event</span>
<span class="n">bandwidth_rates</span><span class="o">.</span><span class="n">insert</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="p">(</span><span class="n">event</span><span class="o">.</span><span class="n">read</span><span class="p">,</span> <span class="n">event</span><span class="o">.</span><span class="n">written</span><span class="p">))</span>
<span class="n">bandwidth_rates</span> <span class="o">=</span> <span class="n">bandwidth_rates</span><span class="p">[:</span><span class="n">GRAPH_WIDTH</span><span class="p">]</span> <span class="c"># truncate old values</span>
<span class="n">_render_graph</span><span class="p">(</span><span class="n">window</span><span class="p">,</span> <span class="n">bandwidth_rates</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">_render_graph</span><span class="p">(</span><span class="n">window</span><span class="p">,</span> <span class="n">bandwidth_rates</span><span class="p">):</span>
<span class="n">window</span><span class="o">.</span><span class="n">erase</span><span class="p">()</span>
<span class="n">download_rates</span> <span class="o">=</span> <span class="p">[</span><span class="n">entry</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="k">for</span> <span class="n">entry</span> <span class="ow">in</span> <span class="n">bandwidth_rates</span><span class="p">]</span>
<span class="n">upload_rates</span> <span class="o">=</span> <span class="p">[</span><span class="n">entry</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="k">for</span> <span class="n">entry</span> <span class="ow">in</span> <span class="n">bandwidth_rates</span><span class="p">]</span>
<span class="c"># show the latest values at the top</span>
<span class="n">label</span> <span class="o">=</span> <span class="s">"Downloaded (</span><span class="si">%s</span><span class="s">/s):"</span> <span class="o">%</span> <span class="n">str_tools</span><span class="o">.</span><span class="n">get_size_label</span><span class="p">(</span><span class="n">download_rates</span><span class="p">[</span><span class="mi">0</span><span class="p">],</span> <span class="mi">1</span><span class="p">)</span>
<span class="n">window</span><span class="o">.</span><span class="n">addstr</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="n">label</span><span class="p">,</span> <span class="n">DOWNLOAD_COLOR</span><span class="p">,</span> <span class="n">curses</span><span class="o">.</span><span class="n">A_BOLD</span><span class="p">)</span>
<span class="n">label</span> <span class="o">=</span> <span class="s">"Uploaded (</span><span class="si">%s</span><span class="s">/s):"</span> <span class="o">%</span> <span class="n">str_tools</span><span class="o">.</span><span class="n">get_size_label</span><span class="p">(</span><span class="n">upload_rates</span><span class="p">[</span><span class="mi">0</span><span class="p">],</span> <span class="mi">1</span><span class="p">)</span>
<span class="n">window</span><span class="o">.</span><span class="n">addstr</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">GRAPH_WIDTH</span> <span class="o">+</span> <span class="mi">7</span><span class="p">,</span> <span class="n">label</span><span class="p">,</span> <span class="n">UPLOAD_COLOR</span><span class="p">,</span> <span class="n">curses</span><span class="o">.</span><span class="n">A_BOLD</span><span class="p">)</span>
<span class="c"># draw the graph bounds in KB</span>
<span class="n">max_download_rate</span> <span class="o">=</span> <span class="nb">max</span><span class="p">(</span><span class="n">download_rates</span><span class="p">)</span>
<span class="n">max_upload_rate</span> <span class="o">=</span> <span class="nb">max</span><span class="p">(</span><span class="n">upload_rates</span><span class="p">)</span>
<span class="n">window</span><span class="o">.</span><span class="n">addstr</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="s">"</span><span class="si">%4i</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">max_download_rate</span> <span class="o">/</span> <span class="mi">1024</span><span class="p">),</span> <span class="n">DOWNLOAD_COLOR</span><span class="p">)</span>
<span class="n">window</span><span class="o">.</span><span class="n">addstr</span><span class="p">(</span><span class="n">GRAPH_HEIGHT</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="s">" 0"</span><span class="p">,</span> <span class="n">DOWNLOAD_COLOR</span><span class="p">)</span>
<span class="n">window</span><span class="o">.</span><span class="n">addstr</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="n">GRAPH_WIDTH</span> <span class="o">+</span> <span class="mi">7</span><span class="p">,</span> <span class="s">"</span><span class="si">%4i</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">max_upload_rate</span> <span class="o">/</span> <span class="mi">1024</span><span class="p">),</span> <span class="n">UPLOAD_COLOR</span><span class="p">)</span>
<span class="n">window</span><span class="o">.</span><span class="n">addstr</span><span class="p">(</span><span class="n">GRAPH_HEIGHT</span><span class="p">,</span> <span class="n">GRAPH_WIDTH</span> <span class="o">+</span> <span class="mi">7</span><span class="p">,</span> <span class="s">" 0"</span><span class="p">,</span> <span class="n">UPLOAD_COLOR</span><span class="p">)</span>
<span class="c"># draw the graph</span>
<span class="k">for</span> <span class="n">col</span> <span class="ow">in</span> <span class="nb">xrange</span><span class="p">(</span><span class="n">GRAPH_WIDTH</span><span class="p">):</span>
<span class="n">col_height</span> <span class="o">=</span> <span class="n">GRAPH_HEIGHT</span> <span class="o">*</span> <span class="n">download_rates</span><span class="p">[</span><span class="n">col</span><span class="p">]</span> <span class="o">/</span> <span class="nb">max</span><span class="p">(</span><span class="n">max_download_rate</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="nb">xrange</span><span class="p">(</span><span class="n">col_height</span><span class="p">):</span>
<span class="n">window</span><span class="o">.</span><span class="n">addstr</span><span class="p">(</span><span class="n">GRAPH_HEIGHT</span> <span class="o">-</span> <span class="n">row</span><span class="p">,</span> <span class="n">col</span> <span class="o">+</span> <span class="mi">6</span><span class="p">,</span> <span class="s">" "</span><span class="p">,</span> <span class="n">DOWNLOAD_COLOR</span><span class="p">,</span> <span class="n">curses</span><span class="o">.</span><span class="n">A_STANDOUT</span><span class="p">)</span>
<span class="n">col_height</span> <span class="o">=</span> <span class="n">GRAPH_HEIGHT</span> <span class="o">*</span> <span class="n">upload_rates</span><span class="p">[</span><span class="n">col</span><span class="p">]</span> <span class="o">/</span> <span class="nb">max</span><span class="p">(</span><span class="n">max_upload_rate</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="nb">xrange</span><span class="p">(</span><span class="n">col_height</span><span class="p">):</span>
<span class="n">window</span><span class="o">.</span><span class="n">addstr</span><span class="p">(</span><span class="n">GRAPH_HEIGHT</span> <span class="o">-</span> <span class="n">row</span><span class="p">,</span> <span class="n">col</span> <span class="o">+</span> <span class="n">GRAPH_WIDTH</span> <span class="o">+</span> <span class="mi">12</span><span class="p">,</span> <span class="s">" "</span><span class="p">,</span> <span class="n">UPLOAD_COLOR</span><span class="p">,</span> <span class="n">curses</span><span class="o">.</span><span class="n">A_STANDOUT</span><span class="p">)</span>
<span class="n">window</span><span class="o">.</span><span class="n">refresh</span><span class="p">()</span>
<span class="k">class</span> <span class="nc">Window</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="sd">"""</span>
<span class="sd"> Simple wrapper for the curses standard screen object.</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">stdscr</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_stdscr</span> <span class="o">=</span> <span class="n">stdscr</span>
<span class="c"># Mappings of names to the curses color attribute. Initially these all</span>
<span class="c"># reference black text, but if the terminal can handle color then</span>
<span class="c"># they're set with that foreground color.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_colors</span> <span class="o">=</span> <span class="nb">dict</span><span class="p">([(</span><span class="n">color</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span> <span class="k">for</span> <span class="n">color</span> <span class="ow">in</span> <span class="n">COLOR_LIST</span><span class="p">])</span>
<span class="c"># allows for background transparency</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">curses</span><span class="o">.</span><span class="n">use_default_colors</span><span class="p">()</span>
<span class="k">except</span> <span class="n">curses</span><span class="o">.</span><span class="n">error</span><span class="p">:</span>
<span class="k">pass</span>
<span class="c"># makes the cursor invisible</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">curses</span><span class="o">.</span><span class="n">curs_set</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="k">except</span> <span class="n">curses</span><span class="o">.</span><span class="n">error</span><span class="p">:</span>
<span class="k">pass</span>
<span class="c"># initializes colors if the terminal can handle them</span>
<span class="k">try</span><span class="p">:</span>
<span class="k">if</span> <span class="n">curses</span><span class="o">.</span><span class="n">has_colors</span><span class="p">():</span>
<span class="n">color_pair</span> <span class="o">=</span> <span class="mi">1</span>
<span class="k">for</span> <span class="n">name</span><span class="p">,</span> <span class="n">foreground</span> <span class="ow">in</span> <span class="n">COLOR_LIST</span><span class="o">.</span><span class="n">items</span><span class="p">():</span>
<span class="n">background</span> <span class="o">=</span> <span class="o">-</span><span class="mi">1</span> <span class="c"># allows for default (possibly transparent) background</span>
<span class="n">curses</span><span class="o">.</span><span class="n">init_pair</span><span class="p">(</span><span class="n">color_pair</span><span class="p">,</span> <span class="n">foreground</span><span class="p">,</span> <span class="n">background</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_colors</span><span class="p">[</span><span class="n">name</span><span class="p">]</span> <span class="o">=</span> <span class="n">curses</span><span class="o">.</span><span class="n">color_pair</span><span class="p">(</span><span class="n">color_pair</span><span class="p">)</span>
<span class="n">color_pair</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="k">except</span> <span class="n">curses</span><span class="o">.</span><span class="n">error</span><span class="p">:</span>
<span class="k">pass</span>
<span class="k">def</span> <span class="nf">addstr</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">y</span><span class="p">,</span> <span class="n">x</span><span class="p">,</span> <span class="n">msg</span><span class="p">,</span> <span class="n">color</span> <span class="o">=</span> <span class="bp">None</span><span class="p">,</span> <span class="n">attr</span> <span class="o">=</span> <span class="n">curses</span><span class="o">.</span><span class="n">A_NORMAL</span><span class="p">):</span>
<span class="c"># Curses throws an error if we try to draw a message that spans out of the</span>
<span class="c"># window's bounds (... seriously?), so doing our best to avoid that.</span>
<span class="k">if</span> <span class="n">color</span> <span class="ow">is</span> <span class="ow">not</span> <span class="bp">None</span><span class="p">:</span>
<span class="k">if</span> <span class="n">color</span> <span class="ow">not</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">_colors</span><span class="p">:</span>
<span class="n">recognized_colors</span> <span class="o">=</span> <span class="s">", "</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_colors</span><span class="o">.</span><span class="n">keys</span><span class="p">())</span>
<span class="k">raise</span> <span class="ne">ValueError</span><span class="p">(</span><span class="s">"The '</span><span class="si">%s</span><span class="s">' color isn't recognized: </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">color</span><span class="p">,</span> <span class="n">recognized_colors</span><span class="p">))</span>
<span class="n">attr</span> <span class="o">|=</span> <span class="bp">self</span><span class="o">.</span><span class="n">_colors</span><span class="p">[</span><span class="n">color</span><span class="p">]</span>
<span class="n">max_y</span><span class="p">,</span> <span class="n">max_x</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">_stdscr</span><span class="o">.</span><span class="n">getmaxyx</span><span class="p">()</span>
<span class="k">if</span> <span class="n">max_x</span> <span class="o">></span> <span class="n">x</span> <span class="ow">and</span> <span class="n">max_y</span> <span class="o">></span> <span class="n">y</span><span class="p">:</span>
<span class="k">try</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_stdscr</span><span class="o">.</span><span class="n">addstr</span><span class="p">(</span><span class="n">y</span><span class="p">,</span> <span class="n">x</span><span class="p">,</span> <span class="n">msg</span><span class="p">[:</span><span class="n">max_x</span> <span class="o">-</span> <span class="n">x</span><span class="p">],</span> <span class="n">attr</span><span class="p">)</span>
<span class="k">except</span><span class="p">:</span>
<span class="k">pass</span> <span class="c"># maybe an edge case while resizing the window</span>
<span class="k">def</span> <span class="nf">erase</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_stdscr</span><span class="o">.</span><span class="n">erase</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">refresh</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_stdscr</span><span class="o">.</span><span class="n">refresh</span><span class="p">()</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">'__main__'</span><span class="p">:</span>
<span class="n">main</span><span class="p">()</span>
</pre></div>
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