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 body of the <Error> element may contain any or all of the following inner elements:

1. <code> — An numerically valued error code. This code must be associated with a protocol, such as HTTP, via the protocol attribute. It is not a requirement that the protocol over which the originating request and subsequent Error response where transmitted be the same as the protocol identified by the value of the protocol attribute.
2. <Message> — A short informative text message describing the error.
3. <Context> — Textual 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>

Parse Error

<?xml version="1.0" encoding="UTF-8"?>
<dap4:Error xmlns:dap4="http://xml.opendap.org/ns/DAP/4.0#">
    <code protocol="http">400</code>
    <Message>Bad DAP4 Request Syntax</Message>
    <Context>
        The constraint expression "?u[3][lat<66]" failed to parse at the sub expression "lat<66". 
         Relational syntax expressions are not supported for array subsetting operations.
    </Context>
</dap4:Error>