state/api/watcher: Refactor API watchers

state/api/params/apierror.go

 // Copyright 2013 Canonical Ltd.
 // Licensed under the AGPLv3, see LICENCE file for details.
 
 package params
 
 import (
         "fmt"
 
         "launchpad.net/juju-core/rpc"
 )
 
+// Error is the type of error returned by any call to the state API
 type Error struct {
         Message string
         Code    string
 }
 
 func (e *Error) Error() string {
         return e.Message
 }
 
 func (e *Error) ErrorCode() string {
@@ skipping 40 matching lines @@
         }
         // We use our own error type rather than rpc.ServerError
         // because we don't want the code or the "server error" prefix
         // within the error message. Also, it's best not to make clients
         // know that we're using the rpc package.
         return &Error{
                 Message: rerr.Message,
                 Code:    rerr.Code,
         }
 }