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<div class="section" id="module-horizon.exceptions">
<span id="horizon-exceptions"></span><h1>Horizon Exceptions<a class="headerlink" href="#module-horizon.exceptions" title="Permalink to this headline">¶</a></h1>
<p>Exceptions raised by the Horizon code and the machinery for handling them.</p>
<dl class="exception">
<dt id="horizon.exceptions.AlreadyExists">
<em class="property">exception </em><tt class="descclassname">horizon.exceptions.</tt><tt class="descname">AlreadyExists</tt><big>(</big><em>name</em>, <em>resource_type</em><big>)</big><a class="reference internal" href="../_modules/horizon/exceptions.html#AlreadyExists"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.AlreadyExists" title="Permalink to this definition">¶</a></dt>
<dd><p>Exception to be raised when trying to create an API resource which
already exists.</p>
</dd></dl>
<dl class="exception">
<dt id="horizon.exceptions.HandledException">
<em class="property">exception </em><tt class="descclassname">horizon.exceptions.</tt><tt class="descname">HandledException</tt><big>(</big><em>wrapped</em><big>)</big><a class="reference internal" href="../_modules/horizon/exceptions.html#HandledException"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.HandledException" title="Permalink to this definition">¶</a></dt>
<dd><p>Used internally to track exceptions that have gone through
<a class="reference internal" href="#horizon.exceptions.handle" title="horizon.exceptions.handle"><tt class="xref py py-func docutils literal"><span class="pre">horizon.exceptions.handle()</span></tt></a> more than once.</p>
</dd></dl>
<dl class="exception">
<dt id="horizon.exceptions.HorizonException">
<em class="property">exception </em><tt class="descclassname">horizon.exceptions.</tt><tt class="descname">HorizonException</tt><a class="reference internal" href="../_modules/horizon/exceptions.html#HorizonException"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.HorizonException" title="Permalink to this definition">¶</a></dt>
<dd><p>Base exception class for distinguishing our own exception classes.</p>
</dd></dl>
<dl class="class">
<dt id="horizon.exceptions.HorizonReporterFilter">
<em class="property">class </em><tt class="descclassname">horizon.exceptions.</tt><tt class="descname">HorizonReporterFilter</tt><a class="reference internal" href="../_modules/horizon/exceptions.html#HorizonReporterFilter"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.HorizonReporterFilter" title="Permalink to this definition">¶</a></dt>
<dd><p>Error report filter that’s always active, even in DEBUG mode.</p>
<dl class="method">
<dt id="horizon.exceptions.HorizonReporterFilter.get_traceback_frame_variables">
<tt class="descname">get_traceback_frame_variables</tt><big>(</big><em>request</em>, <em>tb_frame</em><big>)</big><a class="reference internal" href="../_modules/horizon/exceptions.html#HorizonReporterFilter.get_traceback_frame_variables"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.HorizonReporterFilter.get_traceback_frame_variables" title="Permalink to this definition">¶</a></dt>
<dd><p>Replaces the values of variables marked as sensitive with
stars (<strong>*****</strong>).</p>
</dd></dl>
</dd></dl>
<dl class="exception">
<dt id="horizon.exceptions.Http302">
<em class="property">exception </em><tt class="descclassname">horizon.exceptions.</tt><tt class="descname">Http302</tt><big>(</big><em>location</em>, <em>message=None</em><big>)</big><a class="reference internal" href="../_modules/horizon/exceptions.html#Http302"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.Http302" title="Permalink to this definition">¶</a></dt>
<dd><p>Error class which can be raised from within a handler to cause an
early bailout and redirect at the middleware level.</p>
</dd></dl>
<dl class="exception">
<dt id="horizon.exceptions.NotAuthenticated">
<em class="property">exception </em><tt class="descclassname">horizon.exceptions.</tt><tt class="descname">NotAuthenticated</tt><a class="reference internal" href="../_modules/horizon/exceptions.html#NotAuthenticated"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.NotAuthenticated" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised when a user is trying to make requests and they are not logged in.</p>
<p>The included <a class="reference internal" href="middleware.html#horizon.middleware.HorizonMiddleware" title="horizon.middleware.HorizonMiddleware"><tt class="xref py py-class docutils literal"><span class="pre">HorizonMiddleware</span></tt></a> catches
<tt class="docutils literal"><span class="pre">NotAuthenticated</span></tt> and handles it gracefully by displaying an error
message and redirecting the user to a login page.</p>
</dd></dl>
<dl class="exception">
<dt id="horizon.exceptions.NotAuthorized">
<em class="property">exception </em><tt class="descclassname">horizon.exceptions.</tt><tt class="descname">NotAuthorized</tt><a class="reference internal" href="../_modules/horizon/exceptions.html#NotAuthorized"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.NotAuthorized" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised whenever a user attempts to access a resource which they do not
have permission-based access to (such as when failing the
<a class="reference internal" href="decorators.html#horizon.decorators.require_perms" title="horizon.decorators.require_perms"><tt class="xref py py-func docutils literal"><span class="pre">require_perms()</span></tt></a> decorator).</p>
<p>The included <a class="reference internal" href="middleware.html#horizon.middleware.HorizonMiddleware" title="horizon.middleware.HorizonMiddleware"><tt class="xref py py-class docutils literal"><span class="pre">HorizonMiddleware</span></tt></a> catches
<tt class="docutils literal"><span class="pre">NotAuthorized</span></tt> and handles it gracefully by displaying an error
message and redirecting the user to a login page.</p>
</dd></dl>
<dl class="exception">
<dt id="horizon.exceptions.NotFound">
<em class="property">exception </em><tt class="descclassname">horizon.exceptions.</tt><tt class="descname">NotFound</tt><a class="reference internal" href="../_modules/horizon/exceptions.html#NotFound"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.NotFound" title="Permalink to this definition">¶</a></dt>
<dd><p>Generic error to replace all “Not Found”-type API errors.</p>
</dd></dl>
<dl class="exception">
<dt id="horizon.exceptions.RecoverableError">
<em class="property">exception </em><tt class="descclassname">horizon.exceptions.</tt><tt class="descname">RecoverableError</tt><a class="reference internal" href="../_modules/horizon/exceptions.html#RecoverableError"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.RecoverableError" title="Permalink to this definition">¶</a></dt>
<dd><p>Generic error to replace any “Recoverable”-type API errors.</p>
</dd></dl>
<dl class="exception">
<dt id="horizon.exceptions.ServiceCatalogException">
<em class="property">exception </em><tt class="descclassname">horizon.exceptions.</tt><tt class="descname">ServiceCatalogException</tt><big>(</big><em>service_name</em><big>)</big><a class="reference internal" href="../_modules/horizon/exceptions.html#ServiceCatalogException"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.ServiceCatalogException" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised when a requested service is not available in the <tt class="docutils literal"><span class="pre">ServiceCatalog</span></tt>
returned by Keystone.</p>
</dd></dl>
<dl class="exception">
<dt id="horizon.exceptions.WorkflowError">
<em class="property">exception </em><tt class="descclassname">horizon.exceptions.</tt><tt class="descname">WorkflowError</tt><a class="reference internal" href="../_modules/horizon/exceptions.html#WorkflowError"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.WorkflowError" title="Permalink to this definition">¶</a></dt>
<dd><p>Exception to be raised when something goes wrong in a workflow.</p>
</dd></dl>
<dl class="exception">
<dt id="horizon.exceptions.WorkflowValidationError">
<em class="property">exception </em><tt class="descclassname">horizon.exceptions.</tt><tt class="descname">WorkflowValidationError</tt><a class="reference internal" href="../_modules/horizon/exceptions.html#WorkflowValidationError"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.WorkflowValidationError" title="Permalink to this definition">¶</a></dt>
<dd><p>Exception raised during workflow validation if required data is missing,
or existing data is not valid.</p>
</dd></dl>
<dl class="function">
<dt id="horizon.exceptions.check_message">
<tt class="descclassname">horizon.exceptions.</tt><tt class="descname">check_message</tt><big>(</big><em>keywords</em>, <em>message</em><big>)</big><a class="reference internal" href="../_modules/horizon/exceptions.html#check_message"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.check_message" title="Permalink to this definition">¶</a></dt>
<dd><p>Checks an exception for given keywords and raises a new <tt class="docutils literal"><span class="pre">ActionError</span></tt>
with the desired message if the keywords are found. This allows selective
control over API error messages.</p>
</dd></dl>
<dl class="function">
<dt id="horizon.exceptions.handle">
<tt class="descclassname">horizon.exceptions.</tt><tt class="descname">handle</tt><big>(</big><em>request</em>, <em>message=None</em>, <em>redirect=None</em>, <em>ignore=False</em>, <em>escalate=False</em>, <em>log_level=None</em>, <em>force_log=None</em><big>)</big><a class="reference internal" href="../_modules/horizon/exceptions.html#handle"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#horizon.exceptions.handle" title="Permalink to this definition">¶</a></dt>
<dd><p>Centralized error handling for Horizon.</p>
<p>Because Horizon consumes so many different APIs with completely
different <tt class="docutils literal"><span class="pre">Exception</span></tt> types, it’s necessary to have a centralized
place for handling exceptions which may be raised.</p>
<p>Exceptions are roughly divided into 3 types:</p>
<ol class="arabic simple">
<li><tt class="docutils literal"><span class="pre">UNAUTHORIZED</span></tt>: Errors resulting from authentication or authorization
problems. These result in being logged out and sent to the login screen.</li>
<li><tt class="docutils literal"><span class="pre">NOT_FOUND</span></tt>: Errors resulting from objects which could not be
located via the API. These generally result in a user-facing error
message, but are otherwise returned to the normal code flow. Optionally
a redirect value may be passed to the error handler so users are
returned to a different view than the one requested in addition to the
error message.</li>
<li>RECOVERABLE: Generic API errors which generate a user-facing message
but drop directly back to the regular code flow.</li>
</ol>
<p>All other exceptions bubble the stack as normal unless the <tt class="docutils literal"><span class="pre">ignore</span></tt>
argument is passed in as <tt class="docutils literal"><span class="pre">True</span></tt>, in which case only unrecognized
errors are bubbled.</p>
<p>If the exception is not re-raised, an appropriate wrapper exception
class indicating the type of exception that was encountered will be
returned.</p>
</dd></dl>
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