Exceptions Raised by MN and CN APIs
-----------------------------------

.. module:: Exceptions
   :synopsis: Exceptions that are raised by MN, CN, and ITK software.


.. contents::


General
~~~~~~~

All exceptions raised by API methods in DataONE include three basic elements of
information and an optional element ``traceInformation`` as detailed in
:class:`Types.ErrorMessage`, repeated here for convenience.

.. list-table::
   :widths: 2 2 10
   :header-rows: 1

   * - Element
     - Cardinality
     - Description
   * - errorCode
     - 1
     - The error code. This is the HTTP error code (i.e. 4xx). In all cases,
       the HTTP Status Code value in the response headers *should* match this
       value.
   * - detailcode
     - 1
     - A code that can be mapped to a specific location in the source code of
       the implementation. Implemented as a string with dot notation to
       indicate progressive levels of detail.
   * - pid
     - 0..1
     - Required for exceptions that include an identifier in the constructor 
       signature (e.g. NotFound, IdentifierNotUnique, SynchronizationFailed).
   * - nodeId
     - 0..1
     - The node identifier of the machine that raised the exception
   * - description
     - 0..1
     - A human readable message describing what happened
   * - traceInformation
     - 0..1
     - Optional free text providing more information about the error
       condition. The intent of this element is to assist with debugging. Note
       that care should be taken to ensure senstive information is not 
       accidentally exposed through error conditions.


Expressed in xml-schema:

.. code-block:: xml

   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
       <!-- A derived string type with at least length 1 and it must contain non-whitespace -->
       <xs:simpleType name="NonEmptyString">
           <xs:restriction base="xs:string">
               <xs:minLength value="1" />
               <xs:pattern value="[\s]*[\S][\s\S]*" />
           </xs:restriction>
       </xs:simpleType>

       <!-- Exception type for error serialization in DataONE -->
       <xs:complexType name="DataONEException">
           <xs:sequence>
               <xs:element name="description" minOccurs="0" maxOccurs="1" type="xs:string"></xs:element>
               <xs:element name="traceInformation" minOccurs="0" maxOccurs="1" type="xs:anyType"></xs:element>
           </xs:sequence>
           <xs:attribute name="name" type="NonEmptyString" use="required"></xs:attribute>
           <xs:attribute name="errorCode" type="xs:integer" use="required"></xs:attribute>
           <xs:attribute name="detailCode" type="NonEmptyString" use="required"></xs:attribute>
           <xs:attribute name='identifier' type="NonEmptyString" use="optional"></xs:attribute>
           <xs:attribute name='nodeId' type="NonEmptyString" use="optional"></xs:attribute>
       </xs:complexType>
   </xs:schema>



.. _ExceptionCodes:

HTTP Exception Handling Codes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

HTTP error codes of relevance to the DataONE services are repeated here for
convenience. Refer to the `HTTP specification`_ for a complete reference.

.. list-table::
   :widths: 1 2 5
   :header-rows: 1
   
   * - Code
     - Meaning
     - Description
   * - 400
     - Bad Request
     - Bad request if the request REST operation is invalid, serialization is erroneous, mime type is not supported, or resource is not supported.
   * - 401
     - Unauthorized
     - Authentication failure. Credentials are required or were invalid.
   * - 403
     - Forbidden
     - The current user does not have the right to perform the requested action.
   * - 404
     - Not Found
     - The requested resource does not exist.
   * - 405
     - Method not allowed
     - The HTTP method used is not allowed on this resource. Response must include an Allow header indicating valid HTTP methods.
   * - 406
     - Not Acceptable
     - The resource identified by the request is only capable of generating response entities which have content characteristics not acceptable according to the accept headers sent in the request.
   * - 408
     - Request Timeout
     - The client did not produce a request within the time that the server was prepared to wait.
   * - 409
     - Conflict
     - The request could not be completed due to a conflict with the current state of the resource.
   * - 410
     - Gone
     - The resource is known to be permanently deleted (as opposed to 404 which indicates uncertainty about the state of the object).
   * - 413
     - Request Entity Too Large
     - The server is refusing to process a request because the request entity is larger than the server is willing or able to process.
   * - 415
     - Unsupported Media Type
     - The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method. 
   * - 500
     - Internal Server Error
     - The server encountered an unexpected condition which prevented it from fulfilling the request.
   * - 501
     - Not Implemented
     - The server does not support the functionality required  to fulfill the request. This is the appropriate response when the server does not recognize the request method and is not capable of supporting it for any resource.

.. _HTTP specification: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html



Serializing Exceptions
~~~~~~~~~~~~~~~~~~~~~~

All error messages in DataONE are serialized in XML. In the future, DataONE
interfaces may support additional serialization formats such as HTML and JSON,
and the serialization format will be selected through normal HTTP content
negotiation procedures (RFC2616_). 

An example of an XML serialized error message:

.. code-block:: xml

  <error name='NotFound'
         errorCode='404' 
         detailCode='1020.1' 
         pid='123XYZ'
         nodeId='urn:node:DEMO1'>
    <description>The specified object does not exist on this node.</description>
    <traceInformation>
      method: mn.get
      hint: http://cn.dataone.org/cn/resolve/123XYZ
    </traceInformation>
  </error>

Note that the *detailCode*, *pid*, and *nodeId* attributes are optional. The
*description* element is optional but strongly recommended, and
*traceInformation* is optional though especially useful during development and
testing.

.. 
    Exceptions can be serialized in different formats that vary according to
    where the error occurs and what caller the error message is being sent to. Four
    common serialization formats will be HTML, XML, JSON, and Log. The general
    approach for serializing error messages is indicated by way of example below.
    For errors raised in response to a HTTP call (e.g. through the REST interface),
    the error should be serialized in the format indicated in the request Accept
    header, defaulting to HTML.

    Examples of a :exc:`Exceptions.NotFound` error raised by a request to
    :func:`MNRead.get` object ``123XYZ`` from a Member Node. The trace
    information contains ``{'method':'mn.get'}``.

    In HTML:

    .. code-block:: html

      <html>
        <head>
          <meta http-equiv="content-type" content="text/html;charset=utf-8" />
          <title>Error: 404 Not Found (1020.1)</title>
        </head>
        <body>
          <p>
            <dl>
              <dt>Error</dt>
              <dd class='erroName'>NotFound</dd>
              <dt>Code</dt>
              <dd class='errorCode'>404</dd>
              <dt>Detail Code</dt>
              <dd class='detailCode'>1020.1</dd>
              <dt>Identifier</dt>
              <dd class='pid'>123XYZ</dd>
              <dt>Node Identifier</dt>
              <dd class='nodeId'>c3p0</dd>
            </dl>
          </p>
          <p class='description'>The specified object does not exist on this node.</p>
          <pre class='traceInformation'>
            method: mn.get
            hint: Please try resolving http://cn.dataone.org/cn/resolve/123XYZ
          </pre>
        </body>
      </html>


    In XML:

    In JSON::

      {
        'name': 'NotFound',
        'errorCode':404,
        'detailCode': '1020.1',
        'pid': '123XYZ',
        'nodeId': 'c3p0',
        'description': 'The specified object does not exist on this node.',
        'traceInformation': 'method: mn.get
          hint: http://cn.dataone.org/cn/resolve/123XYZ'
      }


    Log message body. This type of representation is presented here as a
    suggestion. The actual log representation may differ according to the actual
    implementation::

      [detail:1020.1][pid:123XYZ, nodeId:c3p0, method:mn.get]The specified object does not exist on this node.


.. _RFC2616: http://tools.ietf.org/html/rfc2616


The Exceptions
~~~~~~~~~~~~~~

.. include:: generated/generated_exception_summary.txt

.. include:: generated/generated_exceptions.txt