DAP4: DAP4 Error Responses

From OPeNDAP Documentation

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1 Background

It must be expected that any DAP4 server will encounter unrecoverable errors when processing a DAP4 request. Thus the DAP4 protocol must be prepared to communicate such errors from the server to the requesting client.

2 Proposal

The multipart mime proposal is to be extended so that at any point, the sequence of parts can be terminated with an error part describing the error and ending the request.

The proposed format for an error part is as follows.

--<<boundary>>
   Content-Type: text/xml; charset=UTF-8
   Content-Transfer-Encoding: binary
   Content-Description: error
       <<Error Body>>

The error body contains information using a T.B.D. xml document structure. It is proposed that the error body contain at least the following information.

  1. An error code (an integer) – provides a short characterization of the error. The set of error codes will be defined and extended as needed.
  2. An error message – provides a detailed characterization of the error.
  3. Positional information – where appropriate, this provides a "pointer" into some text document that shows where the error was detected. Possible documents include the DDX and the constraint expression. The positional information will include, as appropriate, a document reference, (optionally) a line number, and a character number either within the line or within the document as a whole.
  4. Context information – provide additional information that will help to isolate the error and its cause. A java stack trace would be an example of this.
  5. Other information – Any other arbitrary text information thought useful by the error detector.

The error code and error message are the only required elements. The structure of the "other information" is undefined, but should look like a legal, if unvalidated, xml document.

Dennis Heimbigner