[YANG] errors

Hi,

We have been talking about adding two new statements related to
error generation to YANG.

The first statement is 'error'.  It is used to define a named error.
The second statement is 'raise-error'.

For example:

    error no-matches {
      error-tag operation-failed;
      description
        "Generated if the filters return an empty node set.";
    }       

    rpc partial-lock {
      input { ... }
      output { ... }
      raise-error no-matches;
    }

  XML:

    <rpc-error>
      <error-type>application</error-type>
      <error-tag>operation-failed</error-tag>
      <error-severity>error</error-severity>
      <error-app-tag>no-matches</error-app-tag>
    </rpc-error>

The idea is that the error statement is used to define DM-specfic
error messages.  An error is identified by its error-app-tag.  All
errors are defined on the top-level in the module.

The raise-error statement is used to reference an error, either local
in the same module, or imported from some other module.  It will
replace the current error-app-tag/error-message statements in YANG
(can be specified for must, range, length, and pattern).  It can also
be used in the rpc statement, as shown above.

    error bad-ethernet-mtu {
      error-tag invalid-value;
      error-message "An ethernet MTU must be 1500";
    }

    must "ifType != ethernet or " +
         "(ifType == ethernet and ifMTU == 1500)" {
      raise-error bad-ethernet-mtu;
    }

The errors defined for an rpc would be in addition to the standard
errors defined in rfc4741.

Grammar:

    error-stmt = error-keyword sep error-app-tag-str optsep "{"
      ; error-app-tag-str is an identifier 
      error-tag-stmt stmtsep
      [error-message-stmt stmtsep]
      [error-severity-stmt stmtsep]   ; default is error
      [description-stmt stmtsep]
      [reference-stmt stmtsep]
    "}"

  raise-error error-app-tag-ref-str stmtsep

Comments?

/martin

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