zf2 JSON-RPC server how to return custom error - zend-framework2

Question

I'm looking for the proper way to return a custom error from a JSON-RPC exposed class.
JSON-RPC has a special format for reporting error conditions. All errors need to provide, minimally, an error message and error code; optionally, they can provide additional data, such as a backtrace.
Error codes are derived from those recommended by the XML-RPC EPI project. Zend\Json\Server appropriately assigns the code based on the error condition. For application exceptions, the code ‘-32000’ is used.
I will use the divide method of the sample code from documentation to explain:
<?php
/**
* Calculator - sample class to expose via JSON-RPC
*/
class Calculator
{
/**
* Return sum of two variables
*
* #param int $x
* #param int $y
* #return int
*/
public function add($x, $y)
{
return $x + $y;
}
/**
* Return difference of two variables
*
* #param int $x
* #param int $y
* #return int
*/
public function subtract($x, $y)
{
return $x - $y;
}
/**
* Return product of two variables
*
* #param int $x
* #param int $y
* #return int
*/
public function multiply($x, $y)
{
return $x * $y;
}
/**
* Return the division of two variables
*
* #param int $x
* #param int $y
* #return float
*/
public function divide($x, $y)
{
if ($y == 0) {
// Say "y must not be zero" in proper JSON-RPC error format
// e.g. something like {"error":{"code":-32600,"message":"Invalid Request","data":null},"id":null}
} else {
return $x / $y;
}
}
}
$server = new Zend\Json\Server\Server();
$server->setClass('Calculator');
if ('GET' == $_SERVER['REQUEST_METHOD']) {
// Indicate the URL endpoint, and the JSON-RPC version used:
$server->setTarget('/json-rpc.php')
->setEnvelope(Zend\Json\Server\Smd::ENV_JSONRPC_2);
// Grab the SMD
$smd = $server->getServiceMap();
// Return the SMD to the client
header('Content-Type: application/json');
echo $smd;
return;
}
$server->handle();
p.s. Yes I tried Google search.

Answer 1

Disclaimer: I have no experience in using Zend\Json\Server whatsoever :)
If you talk about an error response, I can correlate that to the Server::fault() method (also available on Github). So I assume if fault() is called and injected into the respones, it would return the response with error messages according to your referred recommended XML-RPC server standard.
The handler method proxies the actual work to _handle() (linked to the source) where a try/catch is encapsuling the dispatching to the (in your case) Calculator class.
The fault is called based on the exception message and exception code. As such I think it's simply throwing an exception and setting the right message/code there:
use Zend\Json\Server\Error;
class Calculator
{
public function divide($x, $y)
{
if (0 === $y) {
throw new InvalidArgumentException(
'Denominator must be a non-zero numerical',
Error::ERROR_INVALID_PARAMS
);
}
// Rest here
}
// Rest here
}
PS. I also changed your error code here, as to me, it feels -32602 (invalid params) is more appropriate than -32600 (invalid request.