DAP4 Error Response

The DAP4 protocol returns error information using an Error response. If a request for any of the three basic responses cannot be completed then an Error response is returned in its place.

Schema

The normative XML representation for the Error Response is defined by the following RELAX-NG schema.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0" xmlns:doc="http://www.example.com/annotation" datatypeLibrary="http://xml.opendap.org/datatypes/dap4" ns="http://xml.opendap.org/ns/DAP/4.0#">
    <start>
        <ref name="errorresponse"/>
    </start>
    <define name="errorresponse">
        <element name="Error">
            <optional>
                <element name="code">
                    <attribute name="protocol">
                        <data type="text"/>
                    </attribute>
                    <data type="dap4_integer"/>
                </element>
            </optional>
            <optional>
                <interleave>
                    <element name="Message">
                        <text/>
                    </element>
                    <element name="Context">
                        <text/>
                    </element>
                    <element name="OtherInformation">
                        <text/>
                    </element>
                </interleave>
            </optional>
        </element>
    </define>
</grammar>

The Error element has one optional attribute: the httpcode which is a standard HTTP protocol return code indicating the general class of error. When possible, this code should match the return code in the HTTP headers for the response.

The body of the <Error> element may contain any or all of the following inner elements each containing arbitrary text.

1. <code> — An numerically valued error code. For this code to have any real meaning to must be associated with a protocol, such as HTTP, via the protocol attribute.
2. <Message> — A short informative message describing the error.
3. <Context> — Information describing the context in which the error occurred: position of a parse error in a constraint expression, for example.
4. <OtherInformation> — Arbitrary additional text information: a Java stack trace, for example.

Error Response Resource Role

DAP4 Error Responses are identified by the resource role:

http://services.opendap.org/dap4/error

Normative Encoding of the Error Response

The normative XML representation for the Error Response is defined in Appendix x "Normative XML Encoding of the Error Response". The media type for the normative XML representation is:

application/vnd.opendap.dap4.error.xml

Examples

Not Found

<?xml version="1.0" encoding="UTF-8"?>
<dap4:Error xmlns:dap4="http://xml.opendap.org/ns/DAP/4.0#">
    <code protocol="http">404</code>
    <Message>Unable to locate requested resource</Message>
</dap4:Error>