📝 [Proposal]: Nil response being code 200 is immensily missleading. Use 500 instead #3332
Comments
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We will check this and change the default response to 200 if no error is returned or the status code is not explicit touched/changed |
I have a feeling that it is because the default allocation of the Response object has status code set to 200 and is initialized when the context is (on request recieved i assume). |
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@ReneWerner87 @GustavBW I think the fact that you return nil in app.Use means that you want to intercept all routes and have them return nil, which is written in a way that I don't see a problem with, it's in line with the definition of middleware and not considered a bug. If you want to let the execution continue but you return nil in app.Use, this is a wrong way to use it. As far as I know, other frameworks such as Gin would be handled the same way and shouldn't be relegated to the fiber framework. // TestNilMiddlewareResponseBug tests the behavior when a middleware returns nil
// and expects a non-200 status code due to the issue.
func TestNilMiddlewareResponseBug(t *testing.T) {
app := fiber.New()
// Middleware that returns nil
app.Use(func(c fiber.Ctx) error {
// Simulate a middleware that does not return an error
return nil
})
// Define a simple handler
app.Get("/", func(c fiber.Ctx) error {
return c.SendString("Hello World!")
})
// Create a request to the app
req := httptest.NewRequest(fiber.MethodGet, "/", nil)
resp, err := app.Test(req)
// Check for errors
require.NoError(t, err)
// Verify that the response status code is NOT 200
require.NotEqual(t, http.StatusOK, resp.StatusCode, "Expected status code to NOT be 200 due to the bug")
} |
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@coderabbitai how do other popular frameworks in golang and popular frameworks in other languages handle this, please give me a list is there anything in any standard ? |
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@ReneWerner87 @GustavBW app.Use(func(c *fiber.Ctx) error {
return c.Next()
})app.Use(func(c fiber.Ctx) error {
err := c.Next()
if err != nil {
return err
}
return nil
})As you can see, if you execute return nil directly, you are skipping c.next() |
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Tip For best results, initiate chat on the files or code changes. 🧩 Analysis chainI need to gather more information about how Fiber currently handles middleware, and then examine how other frameworks in different languages handle this case. Let me gather more specific information about Gin and Echo's middleware handling. Let me search for specific examples or discussions about how nil returns are handled in middleware. Let me look for specific documentation on middleware patterns across frameworks. Let me search for specific information about how Fiber handles middleware errors. I need to gather more information about HTTP middleware standards and how other frameworks handle middleware returns. Let me search for discussions or documentation about HTTP standards regarding middleware behavior. Now let me specifically check if Fiber's repo has any discussions or issues related to this. Finally, let me put together a comprehensive understanding by looking at Rails and ASP.NET Core, which are mature frameworks that might have established patterns. Let me further look at Fiber's specific implementation to understand the current behavior. 🏁 Script executed: Length of output: 2333 🏁 Script executed: Length of output: 4873 🏁 Script executed: Length of output: 2787 🏁 Script executed: Length of output: 7579 🏁 Script executed: Length of output: 211 🏁 Script executed: Length of output: 4683 🏁 Script executed: Length of output: 1319 🌐 Web query: 💡 Result: Web frameworks handle middleware functions that return Express.js (Node.js)
Gin (Go)
Echo (Go)
Key Differences
Common Patterns
By understanding these patterns, developers can avoid pitfalls like unhandled errors or unintended middleware bypassing[1][4][6]. Citations:
🌐 Web query: 💡 Result: Handling 1. Validate Inputs Early
2. Centralize Error Handling
3. Leverage TypeScript Strict Checks
4. Treat Null as a Fail State
5. Use Defensive Coding Patterns
6. Log and Monitor
By combining strict validation, centralized error handling, and type safety, teams can mitigate risks from Citations:
🌐 Web query: 💡 Result: Handling errors in web server middleware effectively requires adherence to both general HTTP standards and specific error-handling RFCs. Here's a breakdown of key protocols and best practices: Core Standards for HTTP Error Handling
Middleware-Specific PatternsWhile no RFC directly governs middleware architecture, common practices emerge:
Implementation Best Practices
By combining HTTP standards like RFC 7807 with middleware-specific patterns, developers create resilient systems that handle errors transparently while maintaining compatibility with API clients[3][6][8]. Citations:
🌐 Web query: 💡 Result: Rails and ASP.NET Core implement middleware execution chains using different patterns but share core concepts around request/response handling. Here's how they compare: Middleware Execution Chain MechanicsASP.NET Core ([2][6][7]):
Rails (Rack Middleware) ([1][5][9]):
def call(env)
@metals.keys.each do |app|
result = app.call(env)
return result unless result[0].to_i == 404 # Proceed only on 404
end
@app.call(env) # Fallback to main app
end
Nil/Short-Circuit HandlingASP.NET Core ([2][7]):
app.Use(async (context, next) => {
if (!Authenticated(context)) {
context.Response.StatusCode = 401;
return; // Stops chain
}
await next();
});Rails/Rack ([1][5][9]):
Key Architectural Differences
Both frameworks enable building flexible processing pipelines but use different signaling mechanisms - ASP.NET Core relies on explicit delegate invocation control, while Rails/Rack uses HTTP status codes to drive flow through the middleware chain[1][2][5]. Citations:
@ReneWerner87 Here's how popular frameworks handle nil/null returns from middleware: Go FrameworksGin
Echo
Chi
Other Popular LanguagesExpress.js (Node.js)
Flask (Python)
Spring Boot (Java)
ASP.NET Core (.NET)
Rails (Ruby)
HTTP StandardsThere's no RFC standard specifically for middleware, but for error responses:
Best PracticesMost frameworks follow one of these patterns:
For Fiber specifically, changing nil returns to result in a 500 error would align with the principle that unexpected/unconventional behavior should be treated as an error rather than silently proceeding with a 200 OK. Would you like me to provide more specific implementation details for any of these frameworks? |
A nil response would also be fine. In most other languages, it would cause a null pointer exception or otherwise undefined behavior, as "nil" is no valid HTTP response. Also, in the other frameworks listed, depending on when they instantiate their response object, if that is not done before its used (lazily), it would also cause an exception or otherwise give an error. A note about the tools the bots listed: One major difference between Fiber and everything else, is that there is that you dont throw exceptions in Golang. So its summery of at least Java Spring and ASP.NET is a little missleading. |
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I just saw the title, why should we return |
According to MDN, "200 OK" means that the request from the client has succeeded, and the response is cachable by default. (https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/200) 500 is "internal server error", i.e. something has gone wrong serverside, that has nothing to do with the request itself nor the client. It seemed the most appropriate. Moreover, MDN describes 500 as "the server encountered an unexpected condition that prevented it from fulfilling the request" which is quite literally what has happened. Fiber did not expect nil, and so cannot fulfill the request. Also, I believe HTTP status codes are older than the notion of a "handler" and "middleware". So the code should relate to the request more broadly. A "handler" doing nothing, is no grounds for any code at all. Today, the handler is the one fulfilling the request, and since the request was not even partially fulfilled, the response cannot be 2XX. Nor 4XX as it is not an error in the request itself. As additional grounds for "not 200 please", here's a memo from the http 1.0 working group: Under section 6.1.1 "Status Code and Reason Phrase" code 2XX is defined as: Which does not apply, as the "action" (request) was recieved, but it was not understood (handled by the dedicated handler), nor accepted (succesfully handled) |
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I.e. you suggest that an error is thrown if no changes are made? How do you then recognize an action within |
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@coderabbitai |
I dont want anything to be thrown. I just want the status code to be changed from 200 by default to 500 to comply with RFC1945. |
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Tip For best results, initiate chat on the files or code changes. 🧩 Analysis chainLet me check the Flask and FastAPI documentation for how they handle middleware null returns: Let's check specifically how Koa.js handles middleware errors, as it's known for its error handling: Let's search for more specific information on Actix-web's middleware error handling, as it has a strong type system: @ReneWerner87 I've researched frameworks that explicitly handle nil/null returns from middleware as errors or with non-200 status codes. Here are specific examples: 1. Koa.js (Node.js)Koa uses a middleware chain where any uncaught errors (including returns that aren't properly handled) result in a 500 status: // From Koa documentation
app.use(async (ctx, next) => {
try {
await next();
// If middleware chain completes without setting response, check status
const status = ctx.status || 404;
if (status === 404) ctx.throw(404);
} catch (err) {
ctx.status = err.status || 500;
ctx.body = { error: err.message };
}
});Source: https://koajs.com/#error-handling 2. Actix-web (Rust)Actix-web enforces strict return types - middleware must return a async fn my_middleware(
req: ServiceRequest,
next: Next<B>
) -> Result<ServiceResponse<B>, Error> {
// Must return a Result - can't return nil/None implicitly
let res = next.call(req).await?; // Will propagate errors
Ok(res)
}Source: https://actix.rs/docs/errors/ 3. Phoenix Framework (Elixir)Phoenix's Plug middleware system requires explicit halting of the pipeline: def call(conn, _opts) do
if auth_token_valid?(conn) do
conn
else
conn
|> send_resp(401, "Unauthorized")
|> halt() # Must explicitly halt or pipeline continues
end
endSource: https://hexdocs.pm/phoenix/plug.html 4. FastAPI (Python)FastAPI middleware must explicitly return a response. If None is returned accidentally, the framework raises an exception resulting in a 500 error: @app.middleware("http")
async def add_process_time_header(request: Request, call_next):
response = await call_next(request)
# No implicit None handling - must return response
return responseSource: https://fastapi.tiangolo.com/tutorial/middleware/ 5. Rocket.rs (Rust)Rocket's request guards (similar to middleware) use Rust's strong type system to prevent nil returns. Failed guards result in 400-500 range errors: impl<'r> FromRequest<'r> for User {
type Error = CustomError;
async fn from_request(req: &'r Request<'_>) -> Outcome<Self, Self::Error> {
// Must return Success, Forward, or Error - no nil option
match req.cookies().get_private("user_id") {
Some(cookie) => Outcome::Success(User::from_id(cookie.value())),
None => Outcome::Error((Status::Unauthorized, CustomError::NotLoggedIn))
}
}
}Source: https://rocket.rs/v0.5/guide/requests/#request-guards Would you like me to provide more specific details about any of these implementations or explore additional frameworks? 🏁 Script executed: Length of output: 1005 🏁 Script executed: Length of output: 10262 🏁 Script executed: Length of output: 6623 🏁 Script executed: Length of output: 381 @ReneWerner87 Looking at frameworks that specifically handle nil/null returns as errors, I've found several examples: 1. Koa.js (Node.js)Koa is designed to respond with 500 errors for unhandled middleware issues: // From Koa documentation
app.use(async (ctx, next) => {
try {
await next();
// If next() resolves but response isn't explicitly set
if (!ctx.response.body && ctx.status === 404) {
ctx.throw(404);
}
} catch (err) {
// Defaults to 500 status for unhandled errors
ctx.status = err.status || 500;
ctx.body = { error: err.message };
}
});Documentation: "When an error occurs and it is still possible to respond to the client... Koa will respond appropriately with a 500 'Internal Server Error'." 2. Spring Boot (Java)Spring's // Spring Boot middleware explicitly uses void return type
protected abstract void doFilterInternal(
HttpServletRequest request,
HttpServletResponse response,
FilterChain filterChain) throws ServletException, IOException;The filter must explicitly call 3. NestJS (TypeScript)NestJS enforces proper middleware continuation: // Function middleware
export function logger(req, res, next) {
console.log(`Request...`);
// Must explicitly call next() or respond
// No automatic behavior for null/undefined returns
next();
}Any middleware that fails to call 4. OWIN (ASP.NET) Middleware// OWIN middleware requires explicit continuation
public async Task Invoke(HttpContext context)
{
// Must explicitly call _next() or set response
// Returning null has no effect
if (!context.User.Identity.IsAuthenticated)
{
context.Response.StatusCode = 401;
return; // Explicitly abort middleware chain
}
await _next(context); // Must explicitly continue
}In OWIN middleware, forgetting to call 5. Connect (Node.js)Express.js's predecessor, which influenced many frameworks: function errorHandler(err, req, res, next) {
// Connect returns 500 by default if there's an error during middleware execution
res.statusCode = 500;
res.end(err.stack);
}Would handling nil returns from middleware with a 500 error in Fiber fit your requirements? I can provide implementation suggestions if this approach aligns with your vision for the framework. |
This is not possible
We will discuss this |
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@GustavBW @ReneWerner87 @gaby As I said above, even if you use return Unlike java's null, the vast majority of go functions return nil, so I think this is normal. If you're a convert to go from another language, you've heard the joke: one step at a time in go. // This means no err, return nil == no err, return normal
if err != nil {
return nil
}So nil for no exception returns http 200 which I think is fine. Behavior in middleware should be up to the user, and we shouldn't return exceptions like |
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There's no reason to change this. It's a common confusion when coming from another language to |
I agree with you, there is no need for change here. |
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Thanks for your proposal and the discussion! After reviewing the feedback, the majority has decided not to proceed with this at this time, as it doesn’t fully align with the project’s current direction. We appreciate your effort and contributions - feel free to suggest refinements or future improvements. Looking forward to more discussions! |
Feature Proposal Description
Hi,
This proposal is short:
In Golang, I've gotten the impression that if a function that may an error, returns nil, all is well.
However, for a given middleware function, as of Fiber v2.52.5, that may be confused for just any other function that may return an error based on the documentation of fiber.App.Use():
Returning nil by accident, is not handled very well.
There is no documentation of what a nil return means for middleware, as far as I'm aware, however I would kindly suggest that you ensure that the resulting response is anything but 200.
Given that you intend people to always return c.Next(), you could also make a nil return go c.Next() by default.
However, if returning nil is an error, kindly make sure to log an error or just provide any kind of feedback, that fiber.App.Use is being used incorrectly.
I've spend too long debugging this. I would like for others to be spared the experience.
Alignment with Express API
This has nothing to do with Express.js. If Express.js handles nil (null / undefined) returns in the same fashion, I'd suggest them to change as well.
HTTP RFC Standards Compliance
Under section 6.1.1 "Status Code and Reason Phrase" of RFC 1945 (https://datatracker.ietf.org/doc/html/rfc1945) code 2XX is defined as:
"Success - The action was successfully received, understood, and accepted."
Which does not apply, as the "action" (request) was recieved, but it was not understood (handled by the dedicated handler), nor accepted (succesfully handled)
Furthermore, code 5XX in the same section is defined as:
"Server Error - The server failed to fulfill an apparently valid request"
At the point in time the current behavior happens, it is unknown if the request is valid or not. However, given that this behavior could occur before reaching anything that can validate the request in the first place, 500 seems most appropriate.
API Stability
This does not impact stability. Shouldn't be breaking either.
Feature Examples
Checklist:
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