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[Server] Fix: standardize error handling across handlers with MCP specificatio… (#124)

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* fix: standardize error handling across handlers with MCP specification compliance

* Update mcp-elements.md

Co-authored-by: Christopher Hertel <mail@christopher-hertel.de>

* docs: clarify error handling behavior for all element types

* docs: remove unnecessary whitespace in mcp-elements.md

* fix: simplify exception signatures to accept simple messages

* refactor: use specific exceptions in examples for better error handling

* feat: throw exceptions from reference provider instead of returning null

---------

Co-authored-by: Christopher Hertel <mail@christopher-hertel.de>
This commit is contained in:
Kyrian Obikwelu 2025-10-30 17:30:58 +01:00 • committed by GitHub
commit ca18caf29d
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GPG key ID: B5690EEEBB952194
4 changed files with 278 additions and 185 deletions
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19
src/Server/Handler/Request/CallToolHandler.php
View file

@ -13,9 +13,9 @@ namespace Mcp\Server\Handler\Request;
use Mcp\Capability\Registry\ReferenceHandlerInterface;
use Mcp\Capability\Registry\ReferenceProviderInterface;
use Mcp\Exception\ExceptionInterface;
use Mcp\Exception\ToolCallException;
use Mcp\Exception\ToolNotFoundException;
use Mcp\Schema\Content\TextContent;
use Mcp\Schema\JsonRpc\Error;
use Mcp\Schema\JsonRpc\Request;
use Mcp\Schema\JsonRpc\Response;
@ -59,9 +59,6 @@ final class CallToolHandler implements RequestHandlerInterface
try {
$reference = $this->referenceProvider->getTool($toolName);
if (null === $reference) {
throw new ToolNotFoundException($request);
}
$arguments['_session'] = $session;
@ -77,17 +74,19 @@ final class CallToolHandler implements RequestHandlerInterface
]);
return new Response($request->getId(), $result);
} catch (ToolNotFoundException $e) {
$this->logger->error('Tool not found', ['name' => $toolName]);
return new Error($request->getId(), Error::METHOD_NOT_FOUND, $e->getMessage());
} catch (ToolCallException|ExceptionInterface $e) {
} catch (ToolCallException $e) {
$this->logger->error(\sprintf('Error while executing tool "%s": "%s".', $toolName, $e->getMessage()), [
'tool' => $toolName,
'arguments' => $arguments,
]);
return Error::forInternalError('Error while executing tool', $request->getId());
$errorContent = [new TextContent($e->getMessage())];
return new Response($request->getId(), CallToolResult::error($errorContent));
} catch (ToolNotFoundException $e) {
$this->logger->error('Tool not found', ['name' => $toolName]);
return new Error($request->getId(), Error::METHOD_NOT_FOUND, $e->getMessage());
} catch (\Throwable $e) {
$this->logger->error('Unhandled error during tool execution', [
'name' => $toolName,

57
src/Server/Handler/Request/CompletionCompleteHandler.php
View file

@ -13,10 +13,14 @@ namespace Mcp\Server\Handler\Request;
use Mcp\Capability\Completion\ProviderInterface;
use Mcp\Capability\Registry\ReferenceProviderInterface;
use Mcp\Exception\PromptNotFoundException;
use Mcp\Exception\ResourceNotFoundException;
use Mcp\Schema\JsonRpc\Error;
use Mcp\Schema\JsonRpc\Request;
use Mcp\Schema\JsonRpc\Response;
use Mcp\Schema\PromptReference;
use Mcp\Schema\Request\CompletionCompleteRequest;
use Mcp\Schema\ResourceReference;
use Mcp\Schema\Result\CompletionCompleteResult;
use Mcp\Server\Session\SessionInterface;
use Psr\Container\ContainerInterface;
@ -51,41 +55,38 @@ final class CompletionCompleteHandler implements RequestHandlerInterface
$name = $request->argument['name'] ?? '';
$value = $request->argument['value'] ?? '';
$reference = match ($request->ref->type) {
'ref/prompt' => $this->referenceProvider->getPrompt($request->ref->name),
'ref/resource' => $this->referenceProvider->getResourceTemplate($request->ref->uri),
default => null,
};
if (null === $reference) {
return new Response($request->getId(), new CompletionCompleteResult([]));
}
$providers = $reference->completionProviders;
$provider = $providers[$name] ?? null;
if (null === $provider) {
return new Response($request->getId(), new CompletionCompleteResult([]));
}
if (\is_string($provider)) {
if (!class_exists($provider)) {
return Error::forInternalError('Invalid completion provider', $request->getId());
}
$provider = $this->container?->has($provider) ? $this->container->get($provider) : new $provider();
}
if (!$provider instanceof ProviderInterface) {
return Error::forInternalError('Invalid completion provider type', $request->getId());
}
try {
$reference = match (true) {
$request->ref instanceof PromptReference => $this->referenceProvider->getPrompt($request->ref->name),
$request->ref instanceof ResourceReference => $this->referenceProvider->getResource($request->ref->uri),
};
$providers = $reference->completionProviders;
$provider = $providers[$name] ?? null;
if (null === $provider) {
return new Response($request->getId(), new CompletionCompleteResult([]));
}
if (\is_string($provider)) {
if (!class_exists($provider)) {
return Error::forInternalError('Invalid completion provider', $request->getId());
}
$provider = $this->container?->has($provider) ? $this->container->get($provider) : new $provider();
}
if (!$provider instanceof ProviderInterface) {
return Error::forInternalError('Invalid completion provider type', $request->getId());
}
$completions = $provider->getCompletions($value);
$total = \count($completions);
$hasMore = $total > 100;
$paged = \array_slice($completions, 0, 100);
return new Response($request->getId(), new CompletionCompleteResult($paged, $total, $hasMore));
} catch (\Throwable) {
} catch (PromptNotFoundException|ResourceNotFoundException $e) {
return Error::forResourceNotFound($e->getMessage(), $request->getId());
} catch (\Throwable $e) {
return Error::forInternalError('Error while handling completion request', $request->getId());
}
}

18
src/Server/Handler/Request/GetPromptHandler.php
View file

@ -13,7 +13,6 @@ namespace Mcp\Server\Handler\Request;
use Mcp\Capability\Registry\ReferenceHandlerInterface;
use Mcp\Capability\Registry\ReferenceProviderInterface;
use Mcp\Exception\ExceptionInterface;
use Mcp\Exception\PromptGetException;
use Mcp\Exception\PromptNotFoundException;
use Mcp\Schema\JsonRpc\Error;
@ -56,9 +55,6 @@ final class GetPromptHandler implements RequestHandlerInterface
try {
$reference = $this->referenceProvider->getPrompt($promptName);
if (null === $reference) {
throw new PromptNotFoundException($request);
}
$arguments['_session'] = $session;
@ -67,18 +63,18 @@ final class GetPromptHandler implements RequestHandlerInterface
$formatted = $reference->formatResult($result);
return new Response($request->getId(), new GetPromptResult($formatted));
} catch (PromptGetException $e) {
$this->logger->error(\sprintf('Error while handling prompt "%s": "%s".', $promptName, $e->getMessage()));
return Error::forInternalError($e->getMessage(), $request->getId());
} catch (PromptNotFoundException $e) {
$this->logger->error('Prompt not found', ['prompt_name' => $promptName]);
return new Error($request->getId(), Error::METHOD_NOT_FOUND, $e->getMessage());
} catch (PromptGetException|ExceptionInterface $e) {
$this->logger->error('Error while handling prompt', ['prompt_name' => $promptName]);
return Error::forInternalError('Error while handling prompt: '.$e->getMessage(), $request->getId());
return Error::forResourceNotFound($e->getMessage(), $request->getId());
} catch (\Throwable $e) {
$this->logger->error('Error while handling prompt', ['prompt_name' => $promptName]);
$this->logger->error(\sprintf('Unexpected error while handling prompt "%s": "%s".', $promptName, $e->getMessage()));
return Error::forInternalError('Error while handling prompt: '.$e->getMessage(), $request->getId());
return Error::forInternalError('Error while handling prompt', $request->getId());
}
}
}

12
src/Server/Handler/Request/ReadResourceHandler.php
View file

@ -15,6 +15,7 @@ use Mcp\Capability\Registry\ReferenceHandlerInterface;
use Mcp\Capability\Registry\ReferenceProviderInterface;
use Mcp\Capability\Registry\ResourceTemplateReference;
use Mcp\Exception\ResourceNotFoundException;
use Mcp\Exception\ResourceReadException;
use Mcp\Schema\JsonRpc\Error;
use Mcp\Schema\JsonRpc\Request;
use Mcp\Schema\JsonRpc\Response;
@ -56,9 +57,6 @@ final class ReadResourceHandler implements RequestHandlerInterface
try {
$reference = $this->referenceProvider->getResource($uri);
if (null === $reference) {
throw new ResourceNotFoundException($request);
}
$arguments = [
'uri' => $uri,
@ -77,12 +75,16 @@ final class ReadResourceHandler implements RequestHandlerInterface
}
return new Response($request->getId(), new ReadResourceResult($formatted));
} catch (ResourceReadException $e) {
$this->logger->error(\sprintf('Error while reading resource "%s": "%s".', $uri, $e->getMessage()));
return Error::forInternalError($e->getMessage(), $request->getId());
} catch (ResourceNotFoundException $e) {
$this->logger->error('Resource not found', ['uri' => $uri]);
return new Error($request->getId(), Error::RESOURCE_NOT_FOUND, $e->getMessage());
return Error::forResourceNotFound($e->getMessage(), $request->getId());
} catch (\Throwable $e) {
$this->logger->error(\sprintf('Error while reading resource "%s": "%s".', $uri, $e->getMessage()));
$this->logger->error(\sprintf('Unexpected error while reading resource "%s": "%s".', $uri, $e->getMessage()));
return Error::forInternalError('Error while reading resource', $request->getId());
}