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finished HTTP Web Services chapter

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Mark Pilgrim
2009-06-10 11:44:01 -04:00
parent 0444160ed1
commit ec0b90cd84
1 changed files with 54 additions and 27 deletions
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http-web-services.html
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@@ -684,18 +684,19 @@ Updates the authenticating user&#8217;s status. Requires the <code>status</code
<samp class=p>>>> </samp><kbd class=pp>h = httplib2.Http('.cache')</kbd>
<samp class=p>>>> </samp><kbd class=pp>data = {'status': 'Test update from Python 3'}</kbd>
<a><samp class=p>>>> </samp><kbd class=pp>h.add_credentials('diveintomark', '<var>MY_SECRET_PASSWORD</var>')</kbd> <span class=u>&#x2460;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>resp, content = h.request('https://identi.ca/api/statuses/update.xml',</kbd> <span class=u>&#x2461;</span></a>
<samp class=p>>>> </samp><kbd class=pp>resp, content = h.request('https://identi.ca/api/statuses/update.xml',</kbd>
<a><samp class=p>... </samp><kbd class=pp> 'POST',</kbd> <span class=u>&#x2462;</span></a>
<a><samp class=p>... </samp><kbd class=pp> urlencode(data),</kbd> <span class=u>&#x2463;</span></a>
<a><samp class=p>... </samp><kbd class=pp> headers={'Content-Type': 'application/x-www-form-urlencoded'})</kbd> <span class=u>&#x2464;</span></a></pre>
<ol>
<li>This is how <code>httplib2</code> handles authentication. Store your username and password with the <code>add_credentials()</code> method. When <code>httplib2</code> tries to issue the request, the server will respond with a <code>401 Authentication Required</code>, and it will list which authentication methods it supports. <code>httplib2</code> will automatically format the appropriate FIXME
<li>
<li>
<li>
<li>
<li>This is how <code>httplib2</code> handles authentication. Store your username and password with the <code>add_credentials()</code> method. When <code>httplib2</code> tries to issue the request, the server will respond with a <code>401 Unauthorized</code> status code, and it will list which authentication methods it supports (in the <code>WWW-Authenticate</code> header). <code>httplib2</code> will automatically construct an <code>Authorization</code> header and re-request the <abbr>URL</abbr>.
<li>The second parameter is the type of <abbr>HTTP</abbr> request, in this case <code>POST</code>.
<li>The third parameter is the <i>payload</i> to send to the server. We&#8217;re sending the <abbr>URL</abbr>-encoded dictionary with a status message.
<li>Finally, we need to tell the server that the payload is <abbr>URL</abbr>-encoded data.
</ol>
<p>This is what goes over the wire:
<pre class=screen>
# continued from the previous example
<samp>send: b'POST /api/statuses/update.xml HTTP/1.1
@@ -706,32 +707,37 @@ content-type: application/x-www-form-urlencoded
user-agent: Python-httplib2/$Rev: 259 $
status=Test+update+from+Python+3'
reply: 'HTTP/1.1 401 Unauthorized'
send: b'POST /api/statuses/update.xml HTTP/1.1
<a>reply: 'HTTP/1.1 401 Unauthorized' <span class=u>&#x2460;</span></a>
<a>send: b'POST /api/statuses/update.xml HTTP/1.1 <span class=u>&#x2461;</span></a>
Host: identi.ca
Accept-Encoding: identity
Content-Length: 32
content-type: application/x-www-form-urlencoded
authorization: Basic SECRET_HASH_CONSTRUCTED_BY_HTTPLIB2
<a>authorization: Basic SECRET_HASH_CONSTRUCTED_BY_HTTPLIB2 <span class=u>&#x2462;</span></a>
user-agent: Python-httplib2/$Rev: 259 $
status=Test+update+from+Python+3'
reply: 'HTTP/1.1 200 OK'</samp></pre>
<a>reply: 'HTTP/1.1 200 OK' <span class=u>&#x2463;</span></a></samp></pre>
<ol>
<li>FIXME
<li>After the first request, the server responds with a <code>401 Unauthorized</code> status code. <code>httplib2</code> will never send authentication headers unless the server explicitly asks for them. This is how the server asks for them.
<li><code>httplib2</code> immediately turns around and requests the same <abbr>URL</abbr> a second time.
<li>This time, it includes the username and password that you added with the <code>add_credentials()</code> method.
<li>It worked!
</ol>
<p>What does the server send back after a successful request? That depends entirely on the web service <abbr>API</abbr>. In some protocols (like the <a href=http://www.ietf.org/rfc/rfc5023.txt>Atom Publishing Protocol</a>), the server sends back a <code>201 Created</code> status code and the location of the newly created resource in the <code>Location</code> header. Identi.ca sends back a <code>200 OK</code> and an <abbr>XML</abbr> document containing information about the newly created resource.
<pre class=screen>
# continued from the previous example
<samp class=p>>>> </samp><kbd class=pp>print(content.decode('utf-8'))</kbd>
<a><samp class=p>>>> </samp><kbd class=pp>print(content.decode('utf-8'))</kbd> <span class=u>&#x2460;</span></a>
<samp class=pp>&lt;?xml version="1.0" encoding="UTF-8"?>
&lt;status>
&lt;text>Test update from Python 3&lt;/text>
<a> &lt;text>Test update from Python 3&lt;/text> <span class=u>&#x2461;</span></a>
&lt;truncated>false&lt;/truncated>
&lt;created_at>Wed Jun 10 03:53:46 +0000 2009&lt;/created_at>
&lt;in_reply_to_status_id>&lt;/in_reply_to_status_id>
&lt;source>api&lt;/source>
&lt;id>5131472&lt;/id>
<a> &lt;id>5131472&lt;/id> <span class=u>&#x2462;</span></a>
&lt;in_reply_to_user_id>&lt;/in_reply_to_user_id>
&lt;in_reply_to_screen_name>&lt;/in_reply_to_screen_name>
&lt;favorited>false&lt;/favorited>
@@ -763,48 +769,69 @@ reply: 'HTTP/1.1 200 OK'</samp></pre>
&lt;/user>
&lt;/status></samp></pre>
<ol>
<li>FIXME
<li>Remember, the data returned by <code>httplib2</code> is always <a href=strings.html#byte-arrays>bytes</a>, not a string. To convert it to a string, you need to decode it using the proper character encoding. Identi.ca&#8217;s <abbr>API</abbr> always returns results in UTF-8, so that part is easy.
<li>There&#8217;s the text of the status message we just published.
<li>There&#8217;s the unique identifier for the new status message. Identi.ca uses this to construct a <abbr>URL</abbr> for viewing the message on the web.
</ol>
<p>FIXME
<p>And here it is:
<p class=c><img class=fr src=i/identica-screenshot.png alt="screenshot showing published status on identi.ca" width=740 height=449>
<p class=c><img class=fr src=i/identica-screenshot.png alt="screenshot showing published status message on Identi.ca" width=740 height=449>
<p class=a>&#x2042;
<h2 id=beyond-post>Beyond HTTP POST</h2>
<p>FIXME
<p><abbr>HTTP</abbr> isn&#8217;t limited to <code>GET</code> and <code>POST</code>. Those are certainly the most common types of requests, especially in web browsers. But web service <abbr>API</abbr>s can go beyond <code>GET</code> and <code>POST</code>, and <code>httplib2</code> is ready.
<pre class=screen>
# continued from the previous example
<samp class=p>>>> </samp><kbd class=pp>from xml.etree import ElementTree as etree</kbd>
<samp class=p>>>> </samp><kbd class=pp>tree = etree.fromstring(content)</kbd>
<samp class=p>>>> </samp><kbd class=pp>status_id = tree.findtext('id')</kbd>
<a><samp class=p>>>> </samp><kbd class=pp>tree = etree.fromstring(content)</kbd> <span class=u>&#x2460;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>status_id = tree.findtext('id')</kbd> <span class=u>&#x2461;</span></a>
<samp class=p>>>> </samp><kbd class=pp>status_id</kbd>
<samp class=pp>'5131472'</samp>
<samp class=p>>>> </samp><kbd class=pp>resp, deleted_content = h.request('https://identi.ca/api/statuses/destroy/{0}.xml'.format(status_id), 'DELETE')</kbd>
<samp>send: b'DELETE /api/statuses/destroy/5131472.xml HTTP/1.1
<a><samp class=p>>>> </samp><kbd class=pp>url = 'https://identi.ca/api/statuses/destroy/{0}.xml'.format(status_id)</kbd> <span class=u>&#x2462;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>resp, deleted_content = h.request(url, 'DELETE')</kbd> <span class=u>&#x2463;</span></a></pre>
<ol>
<li>The server returned <abbr>XML</abbr>, right? You know <a href=xml.html#xml-parse>how to parse <abbr>XML</abbr></a>.
<li>The <code>findtext()</code> method finds the first instance of the given expression and extracts its text content. In this case, we&#8217;re just looking for an <code>&lt;id></code> element.
<li>Based on the text content of the <code>&lt;id></code> element, we can construct a <abbr>URL</abbr> to delete the status message we just published.
<li>To delete a message, you simply issue an <abbr>HTTP</abbr> <code>DELETE</code> request to that <abbr>URL</abbr>.
</ol>
<p>This is what goes over the wire:
<pre class=screen>
<samp><a>send: b'DELETE /api/statuses/destroy/5131472.xml HTTP/1.1 <span class=u>&#x2460;</span></a>
Host: identi.ca
Accept-Encoding: identity
user-agent: Python-httplib2/$Rev: 259 $
'
reply: 'HTTP/1.1 401 Unauthorized'
send: b'DELETE /api/statuses/destroy/5131472.xml HTTP/1.1
<a>reply: 'HTTP/1.1 401 Unauthorized' <span class=u>&#x2461;</span></a>
<a>send: b'DELETE /api/statuses/destroy/5131472.xml HTTP/1.1 <span class=u>&#x2462;</span></a>
Host: identi.ca
Accept-Encoding: identity
authorization: Basic SECRET_HASH_CONSTRUCTED_BY_HTTPLIB2
<a>authorization: Basic SECRET_HASH_CONSTRUCTED_BY_HTTPLIB2 <span class=u>&#x2463;</span></a>
user-agent: Python-httplib2/$Rev: 259 $
'
reply: 'HTTP/1.1 200 OK'</samp>
<a>reply: 'HTTP/1.1 200 OK' <span class=u>&#x2464;</span></a></samp>
<samp class=p>>>> </samp><kbd class=pp>resp.status</kbd>
<samp class=pp>200</samp></pre>
<ol>
<li>FIXME
<li>&#8220;Delete this status message, please.&#8221;
<li>&#8220;I&#8217;m sorry, Dave, I&#8217;m afraid I can&#8217;t do that.&#8221;
<li>&#8220;Delete this status message, please&hellip;
<li>&hellip;here&#8217;s my username and password.&#8221;
<li>&#8220;Consider it done!&#8221;
</ol>
<p>And just like that, poof, it&#8217;s gone.
<p class=c><img class=fr src=i/identica-deleted.png alt="screenshot showing deleted message on Identi.ca" width=740 height=449>
<p class=a>&#x2042;
<h2 id=furtherreading>Further Reading</h2>