RESTXQ: User-friendly error messages

[ChristianGruen]

Values of an HTTP request will be assigned to the parameters of the invoked function. If the assignment fails, the returned error message should be more intuitive:

• Right now, it indicates what went wrong during the variable assignment in XQuery.
• The returned message should rather indicate how the request can be rewritten by the client to be successfully processed.

Examples

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RESTXQ function:

declare %rest:path("page") %rest:query-param("param", "{$p}")
  function page:x($p as xs:string) { };

HTTP Request: http://localhost/page

Returned error:

Stopped at F:/webapp/x.xqm, 6/10:
[XPTY0004] Cannot convert empty-sequence() to xs:string: ().

Better alternatives:

• Query parameter "param" must be of type xs:string, found: () as empty-sequence().
• Query parameter "param" must be of type xs:string. Found: ().
• Query parameter "param" cannot be converted to xs:string: ().
• "param" could not be assigned to $p: empty-sequence() found, xs:string expected.

---

RESTXQ function:

declare %rest:path("browse/{$n}")
  function page:x($n as xs:integer) { };

HTTP Request: http://localhost/browse/INVALID

Returned error:

Stopped at F:/webapp/x.xqm, 5/10:
[FORG0001] Cannot convert xs:untypedAtomic to xs:integer: "INVALID".

Better alternatives:

• Path segment must be of type xs:integer, found: INVALID as xs:untypedAtomic.
• Path segment must be of type xs:integer. Found: INVALID.
• Path segment cannot be converted to xs:integer: INVALID.
• Path segment could not be assigned to $n: xs:untypedAtomic found, xs:integer expected.

---

A similar observation applies to requests for which more than one endpoint is found:

RESTXQ function:

declare %rest:path("a") function page:a1() { };
declare %rest:path("a") function page:a2() { };

HTTP Request: http://localhost/browse/a

Returned error:

Stopped at F:/webapp/x.xqm, 5/10:
[basex:restxq] Several functions found for path "b":
- page:x
- page:z

It might not be necessary to return information on the XQuery code.