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<h2 class="title"><a name="soap.troubleshooting"></a>12.8. Troubleshooting <span class="acronym">SOAP</span> Web Services
</h2>
</div>
</div>
<div></div>
</div>
<div class="abstract">
<p>Of course, the world of <span class="acronym">SOAP</span> web services is not all happiness and light. Sometimes things go wrong.
</p>
</div>
<p>As you've seen throughout this chapter, <span class="acronym">SOAP</span> involves several layers. There's the HTTP layer, since <span class="acronym">SOAP</span> is sending XML documents to, and receiving XML documents from, an HTTP server. So all the debugging techniques you learned
in <a href="../http_web_services/index.html" title="Chapter 11. HTTP Web Services">Chapter 11, <i>HTTP Web Services</i></a> come into play here. You can <b class="userinput"><tt>import httplib</tt></b> and then set <b class="userinput"><tt>httplib.HTTPConnection.debuglevel = 1</tt></b> to see the underlying HTTP traffic.
</p>
<p>Beyond the underlying HTTP layer, there are a number of things that can go wrong. <span class="application">SOAPpy</span> does an admirable job hiding the <span class="acronym">SOAP</span> syntax from you, but that also means it can be difficult to determine where the problem is when things don't work.
</p>
<p>Here are a few examples of common mistakes that I've made in using <span class="acronym">SOAP</span> web services, and the errors they generated.
</p>
<div class="example"><a name="d0e31615"></a><h3 class="title">Example 12.15. Calling a Method With an Incorrectly Configured Proxy</h3><pre class="screen">
<tt class="prompt">>>> </tt><span class="userinput"><span class='pykeyword'>from</span> SOAPpy <span class='pykeyword'>import</span> SOAPProxy</span>
<tt class="prompt">>>> </tt><span class="userinput">url = <span class='pystring'>'http://services.xmethods.net:80/soap/servlet/rpcrouter'</span></span>
<tt class="prompt">>>> </tt><span class="userinput">server = SOAPProxy(url)</span> <a name="soap.troubleshooting.1.1"></a><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12">
<tt class="prompt">>>> </tt><span class="userinput">server.getTemp(<span class='pystring'>'27502'</span>)</span> <a name="soap.troubleshooting.1.2"></a><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12">
<span class="traceback"><Fault SOAP-ENV:Server.BadTargetObjectURI:
Unable to determine object id from call: is the method element namespaced?>
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "c:\python23\Lib\site-packages\SOAPpy\Client.py", line 453, in __call__
return self.__r_call(*args, **kw)
File "c:\python23\Lib\site-packages\SOAPpy\Client.py", line 475, in __r_call
self.__hd, self.__ma)
File "c:\python23\Lib\site-packages\SOAPpy\Client.py", line 389, in __call
raise p
SOAPpy.Types.faultType: <Fault SOAP-ENV:Server.BadTargetObjectURI:
Unable to determine object id from call: is the method element namespaced?></span>
</pre><div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td width="12" valign="top" align="left"><a href="#soap.troubleshooting.1.1"><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">Did you spot the mistake? You're creating a <tt class="classname">SOAPProxy</tt> manually, and you've correctly specified the service <span class="acronym">URL</span>, but you haven't specified the namespace. Since multiple services may be routed through the same service <span class="acronym">URL</span>, the namespace is essential to determine which service you're trying to talk to, and therefore which method you're really
calling.
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#soap.troubleshooting.1.2"><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">The server responds by sending a <span class="acronym">SOAP</span> Fault, which <span class="application">SOAPpy</span> turns into a <span class="application">Python</span> exception of type <tt class="classname">SOAPpy.Types.faultType</tt>. All errors returned from any <span class="acronym">SOAP</span> server will always be <span class="acronym">SOAP</span> Faults, so you can easily catch this exception. In this case, the human-readable part of the <span class="acronym">SOAP</span> Fault gives a clue to the problem: the method element is not namespaced, because the original <tt class="classname">SOAPProxy</tt> object was not configured with a service namespace.
</td>
</tr>
</table>
</div>
</div>
<p>Misconfiguring the basic elements of the <span class="acronym">SOAP</span> service is one of the problems that <span class="acronym">WSDL</span> aims to solve. The <span class="acronym">WSDL</span> file contains the service <span class="acronym">URL</span> and namespace, so you can't get it wrong. Of course, there are still other things you can get wrong.
</p>
<div class="example"><a name="d0e31701"></a><h3 class="title">Example 12.16. Calling a Method With the Wrong Arguments</h3><pre class="screen">
<tt class="prompt">>>> </tt><span class="userinput">wsdlFile = <span class='pystring'>'http://www.xmethods.net/sd/2001/TemperatureService.wsdl'</span></span>
<tt class="prompt">>>> </tt><span class="userinput">server = WSDL.Proxy(wsdlFile)</span>
<tt class="prompt">>>> </tt><span class="userinput">temperature = server.getTemp(27502)</span> <a name="soap.troubleshooting.2.1"></a><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12">
<span class="traceback"><Fault SOAP-ENV:Server: Exception while handling service request:
services.temperature.TempService.getTemp(int) -- no signature match> <a name="soap.troubleshooting.2.2"></a><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12">
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "c:\python23\Lib\site-packages\SOAPpy\Client.py", line 453, in __call__
return self.__r_call(*args, **kw)
File "c:\python23\Lib\site-packages\SOAPpy\Client.py", line 475, in __r_call
self.__hd, self.__ma)
File "c:\python23\Lib\site-packages\SOAPpy\Client.py", line 389, in __call
raise p
SOAPpy.Types.faultType: <Fault SOAP-ENV:Server: Exception while handling service request:
services.temperature.TempService.getTemp(int) -- no signature match></span>
</pre><div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td width="12" valign="top" align="left"><a href="#soap.troubleshooting.2.1"><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">Did you spot the mistake? It's a subtle one: you're calling <tt class="function">server.getTemp</tt> with an integer instead of a string. As you saw from introspecting the <span class="acronym">WSDL</span> file, the <tt class="function">getTemp()</tt> <span class="acronym">SOAP</span> function takes a single argument, <tt class="varname">zipcode</tt>, which must be a string. <tt class="classname">WSDL.Proxy</tt> will <span class="emphasis"><em>not</em></span> coerce datatypes for you; you need to pass the exact datatypes that the server expects.
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#soap.troubleshooting.2.2"><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">Again, the server returns a <span class="acronym">SOAP</span> Fault, and the human-readable part of the error gives a clue as to the problem: you're calling a <tt class="function">getTemp</tt> function with an integer value, but there is no function defined with that name that takes an integer. In theory, <span class="acronym">SOAP</span> allows you to <span class="emphasis"><em>overload</em></span> functions, so you could have two functions in the same <span class="acronym">SOAP</span> service with the same name and the same number of arguments, but the arguments were of different datatypes. This is why
it's important to match the datatypes exactly, and why <tt class="classname">WSDL.Proxy</tt> doesn't coerce datatypes for you. If it did, you could end up calling a completely different function! Good luck debugging
that one. It's much easier to be picky about datatypes and fail as quickly as possible if you get them wrong.
</td>
</tr>
</table>
</div>
</div>
<p>It's also possible to write <span class="application">Python</span> code that expects a different number of return values than the remote function actually returns.
</p>
<div class="example"><a name="d0e31779"></a><h3 class="title">Example 12.17. Calling a Method and Expecting the Wrong Number of Return Values</h3><pre class="screen">
<tt class="prompt">>>> </tt><span class="userinput">wsdlFile = <span class='pystring'>'http://www.xmethods.net/sd/2001/TemperatureService.wsdl'</span></span>
<tt class="prompt">>>> </tt><span class="userinput">server = WSDL.Proxy(wsdlFile)</span>
<tt class="prompt">>>> </tt><span class="userinput">(city, temperature) = server.getTemp(27502)</span> <a name="soap.troubleshooting.3.1"></a><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12">
<span class="traceback">Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: unpack non-sequence</span>
</pre><div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td width="12" valign="top" align="left"><a href="#soap.troubleshooting.3.1"><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">Did you spot the mistake? <tt class="function">server.getTemp</tt> only returns one value, a float, but you've written code that assumes you're getting two values and trying to assign them
to two different variables. Note that this does not fail with a <span class="acronym">SOAP</span> fault. As far as the remote server is concerned, nothing went wrong at all. The error only occurred <span class="emphasis"><em>after</em></span> the <span class="acronym">SOAP</span> transaction was complete, <tt class="classname">WSDL.Proxy</tt> returned a float, and your local <span class="application">Python</span> interpreter tried to accomodate your request to split it into two different variables. Since the function only returned
one value, you get a <span class="application">Python</span> exception trying to split it, not a <span class="acronym">SOAP</span> Fault.
</td>
</tr>
</table>
</div>
</div>
<p>What about Google's web service? The most common problem I've had with it is that I forget to set the application key properly.</p>
<div class="example"><a name="d0e31834"></a><h3 class="title">Example 12.18. Calling a Method With An Application-Specific Error</h3><pre class="screen">
<tt class="prompt">>>> </tt><span class="userinput"><span class='pykeyword'>from</span> SOAPpy <span class='pykeyword'>import</span> WSDL</span>
<tt class="prompt">>>> </tt><span class="userinput">server = WSDL.Proxy(r<span class='pystring'>'/path/to/local/GoogleSearch.wsdl'</span>)</span>
<tt class="prompt">>>> </tt><span class="userinput">results = server.doGoogleSearch(<span class='pystring'>'foo'</span>, <span class='pystring'>'mark'</span>, 0, 10, False, <span class='pystring'>""</span>,</span> <a name="soap.troubleshooting.4.1"></a><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12">
<tt class="prompt">... </tt><span class="userinput">False, <span class='pystring'>""</span>, <span class='pystring'>"utf-8"</span>, <span class='pystring'>"utf-8"</span>)</span>
<span class="traceback"><Fault SOAP-ENV:Server: <a name="soap.troubleshooting.4.2"></a><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12">
Exception from service object: Invalid authorization key: foo:
<SOAPpy.Types.structType detail at 14164616>:
{'stackTrace':
'com.google.soap.search.GoogleSearchFault: Invalid authorization key: foo
at com.google.soap.search.QueryLimits.lookUpAndLoadFromINSIfNeedBe(
QueryLimits.java:220)
at com.google.soap.search.QueryLimits.validateKey(QueryLimits.java:127)
at com.google.soap.search.GoogleSearchService.doPublicMethodChecks(
GoogleSearchService.java:825)
at com.google.soap.search.GoogleSearchService.doGoogleSearch(
GoogleSearchService.java:121)
at sun.reflect.GeneratedMethodAccessor13.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.soap.server.RPCRouter.invoke(RPCRouter.java:146)
at org.apache.soap.providers.RPCJavaProvider.invoke(
RPCJavaProvider.java:129)
at org.apache.soap.server.http.RPCRouterServlet.doPost(
RPCRouterServlet.java:288)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:760)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at com.google.gse.HttpConnection.runServlet(HttpConnection.java:237)
at com.google.gse.HttpConnection.run(HttpConnection.java:195)
at com.google.gse.DispatchQueue$WorkerThread.run(DispatchQueue.java:201)
Caused by: com.google.soap.search.UserKeyInvalidException: Key was of wrong size.
at com.google.soap.search.UserKey.<init>(UserKey.java:59)
at com.google.soap.search.QueryLimits.lookUpAndLoadFromINSIfNeedBe(
QueryLimits.java:217)
... 14 more
'}>
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "c:\python23\Lib\site-packages\SOAPpy\Client.py", line 453, in __call__
return self.__r_call(*args, **kw)
File "c:\python23\Lib\site-packages\SOAPpy\Client.py", line 475, in __r_call
self.__hd, self.__ma)
File "c:\python23\Lib\site-packages\SOAPpy\Client.py", line 389, in __call
raise p
SOAPpy.Types.faultType: <Fault SOAP-ENV:Server: Exception from service object:
Invalid authorization key: foo:
<SOAPpy.Types.structType detail at 14164616>:
{'stackTrace':
'com.google.soap.search.GoogleSearchFault: Invalid authorization key: foo
at com.google.soap.search.QueryLimits.lookUpAndLoadFromINSIfNeedBe(
QueryLimits.java:220)
at com.google.soap.search.QueryLimits.validateKey(QueryLimits.java:127)
at com.google.soap.search.GoogleSearchService.doPublicMethodChecks(
GoogleSearchService.java:825)
at com.google.soap.search.GoogleSearchService.doGoogleSearch(
GoogleSearchService.java:121)
at sun.reflect.GeneratedMethodAccessor13.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.soap.server.RPCRouter.invoke(RPCRouter.java:146)
at org.apache.soap.providers.RPCJavaProvider.invoke(
RPCJavaProvider.java:129)
at org.apache.soap.server.http.RPCRouterServlet.doPost(
RPCRouterServlet.java:288)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:760)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at com.google.gse.HttpConnection.runServlet(HttpConnection.java:237)
at com.google.gse.HttpConnection.run(HttpConnection.java:195)
at com.google.gse.DispatchQueue$WorkerThread.run(DispatchQueue.java:201)
Caused by: com.google.soap.search.UserKeyInvalidException: Key was of wrong size.
at com.google.soap.search.UserKey.<init>(UserKey.java:59)
at com.google.soap.search.QueryLimits.lookUpAndLoadFromINSIfNeedBe(
QueryLimits.java:217)
... 14 more
'}></span>
</pre><div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td width="12" valign="top" align="left"><a href="#soap.troubleshooting.4.1"><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">Can you spot the mistake? There's nothing wrong with the calling syntax, or the number of arguments, or the datatypes. The
problem is application-specific: the first argument is supposed to be my application key, but <tt class="literal">foo</tt> is not a valid Google key.
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#soap.troubleshooting.4.2"><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">The Google server responds with a <span class="acronym">SOAP</span> Fault and an incredibly long error message, which includes a complete Java stack trace. Remember that <span class="emphasis"><em>all</em></span> <span class="acronym">SOAP</span> errors are signified by <span class="acronym">SOAP</span> Faults: errors in configuration, errors in function arguments, and application-specific errors like this. Buried in there
somewhere is the crucial piece of information: <tt class="literal">Invalid authorization key: foo</tt>.
</td>
</tr>
</table>
</div>
</div>
<div class="furtherreading">
<h3>Further Reading on Troubleshooting <span class="acronym">SOAP</span></h3>
<ul>
<li><a href="http://www-106.ibm.com/developerworks/webservices/library/ws-pyth17.html">New developments for <span class="application">SOAPpy</span></a> steps through trying to connect to another <span class="acronym">SOAP</span> service that doesn't quite work as advertised.
</li>
</ul>
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