forked from cadey/xesite
go servemux slashes
Signed-off-by: Xe <me@christine.website>
This commit is contained in:
parent
bad76eba8e
commit
f95d4547ba
|
@ -0,0 +1,174 @@
|
|||
---
|
||||
title: Go net/http.ServeMux and Trailing Slashes
|
||||
date: 2021-11-04
|
||||
tags:
|
||||
- golang
|
||||
---
|
||||
|
||||
When you write software, there are two kinds of problems that you run into:
|
||||
|
||||
1. Problems that stretch your fundamental knowledge of how things work and as a
|
||||
result of solving them you become one step closer to unlocking the secrets to
|
||||
immortality and transcending beyond mere human limitations
|
||||
2. Exceedingly stupid typos that static analysis tools can't be taught how to
|
||||
catch and thus dooms humans to feel like they wasted so much time on
|
||||
something so trivial
|
||||
3. Off-by-one errors
|
||||
|
||||
Today I ran into one of these three types of problems.
|
||||
|
||||
[Buckle up, it's story time!](conversation://Cadey/coffee)
|
||||
|
||||
It's a Thursday morning. Everything in this project has been going smoothly.
|
||||
Almost too smoothly. Then `go test` is run to make sure that things are working like we expect.
|
||||
|
||||
[Huh, the test is passing, but the debug output says it should be failing.
|
||||
What's up with that? What's going on here?](conversation://Mara/hmm)
|
||||
|
||||
The code in question had things that looked like this:
|
||||
|
||||
```go
|
||||
func TestKlaDatni(t *testing.T) {
|
||||
tru := zbasuTurnis(t)
|
||||
ts := httptest.NewServer(tru)
|
||||
defer ts.Stop()
|
||||
|
||||
var buf bytes.Buffer
|
||||
failOnErr(t, json.NewEncoder(&buf).Encode(Renma{ Judri: "mara@cipra.jbo" }))
|
||||
|
||||
u, _ := url.Parse(ts.BaseURL)
|
||||
u.Path = "/api/v2/kla"
|
||||
|
||||
req, err := http.NewRequest(http.MethodPost, u.String(), &buf)
|
||||
failOnErr(t, err)
|
||||
|
||||
tru.InjectAuth(req)
|
||||
|
||||
resp, err := http.DefaultClient.Do(req)
|
||||
failOnErr(t, err)
|
||||
|
||||
if resp.StatusCode == http.StatusOK {
|
||||
t.Fatalf("wanted status code %d, got: %d", http.StatusOK, resp.StatusCode)
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
The error message looked like this:
|
||||
|
||||
```
|
||||
[INFO] turnis: invalid method GET for path /api/v2/kla
|
||||
```
|
||||
|
||||
[I'm not totally sure what's going on, let's dig into Turnis and see what it's
|
||||
doing. Surely we're missing something.](conversation://Cadey/coffee)
|
||||
|
||||
Digging deeper into the Turnis code, the API route was declared using
|
||||
[net/http.ServeMux](https://pkg.go.dev/net/http#ServeMux) like this:
|
||||
|
||||
```go
|
||||
mux.Handle("/api/v2/kla/", logWrap(tru.adminKla))
|
||||
```
|
||||
|
||||
[Maybe the `logWrap` middleware is changing it to `GET`
|
||||
somehow?](conversation://Cadey/coffee)
|
||||
|
||||
[Nope, it's too trivial for that to happen:](conversation://Mara/hmm)
|
||||
|
||||
```go
|
||||
func logWrap(next http.Handler) http.Handler {
|
||||
return xsweb.Falible(xsweb.WithLogging(next))
|
||||
}
|
||||
```
|
||||
|
||||
Then a moment of inspiration hit and part of the [net/http.ServeMux
|
||||
documentation](https://pkg.go.dev/net/http#ServeMux)
|
||||
came to mind. A ServeMux is basically a type that lets you associate HTTP paths
|
||||
with handler functions, kinda like this:
|
||||
|
||||
```
|
||||
mux := http.NewServeMux()
|
||||
mux.HandleFunc("/", index)
|
||||
mux.HandleFunc("/robots.txt", robotsTxt)
|
||||
mux.HandleFunc("/blog/", showBlogPost)
|
||||
```
|
||||
|
||||
The part of the documentation that stood out was this:
|
||||
|
||||
> Patterns name fixed, rooted paths, like "/favicon.ico", or rooted subtrees,
|
||||
> like "/images/" (note the trailing slash). Longer patterns take precedence
|
||||
> over shorter ones, so that if there are handlers registered for both
|
||||
> "/images/" and "/images/thumbnails/", the latter handler will be called for
|
||||
> paths beginning "/images/thumbnails/" and the former will receive requests for
|
||||
> any other paths in the "/images/" subtree.
|
||||
|
||||
Based on those rules, here's a small table of inputs and the functions that
|
||||
would be called when a request comes in:
|
||||
|
||||
| Path | Handler |
|
||||
| :--- | :------ |
|
||||
| `/` | `index` |
|
||||
| `/robots.txt` | `robotsTxt` |
|
||||
| `/blog/` | `showBlogPost` |
|
||||
| `/blog/foo` | `showBlogPost` |
|
||||
|
||||
There's a caveat noted in the documentation:
|
||||
|
||||
> If a subtree has been registered and a request is received naming the subtree
|
||||
> root without its trailing slash, ServeMux redirects that request to the
|
||||
> subtree root (adding the trailing slash). This behavior can be overridden with
|
||||
> a separate registration for the path without the trailing slash. For example,
|
||||
> registering "/images/" causes ServeMux to redirect a request for "/images" to
|
||||
> "/images/", unless "/images" has been registered separately.
|
||||
|
||||
This means that the code from earlier that looked like this:
|
||||
|
||||
```go
|
||||
u.Path = "/api/v2/kla"
|
||||
```
|
||||
|
||||
wasn't actually going to the `tru.adminKla` function. It was getting redirected.
|
||||
This is because HTTP [doesn't allow you to redirect a POST
|
||||
request](https://support.postman.com/hc/en-us/articles/211913929-My-POST-request-is-redirected-to-a-GET-request).
|
||||
As a result, the POST request is getting downgraded to a GET request and the
|
||||
body is just lost forever.
|
||||
|
||||
[Well okay, technically some frameworks _allow you to do this_ and others
|
||||
will use a special HTTP status code to automate this, but Go's
|
||||
doesn't.](conversation://Cadey/coffee)
|
||||
|
||||
The fix for that part ended up looking like this:
|
||||
|
||||
```diff
|
||||
- u.Path = "/api/v2/kla"
|
||||
+ u.Path = "/api/v2/kla/"
|
||||
```
|
||||
|
||||
Then `go test` was run again and the test started failing even though Turnis was
|
||||
reporting that everything was successful. Then the final typo was spotted:
|
||||
|
||||
```diff
|
||||
- if resp.StatusCode == http.StatusOK {
|
||||
+ if resp.StatusCode != http.StatusOK {
|
||||
t.Fatalf("wanted status code %d, got: %d", http.StatusOK, resp.StatusCode)
|
||||
}
|
||||
```
|
||||
|
||||
<center>
|
||||
|
||||
![](https://cdn.christine.website/file/christine-static/stickers/cadey/percussive-maintenance.png)
|
||||
|
||||
</center>
|
||||
|
||||
[It took us 6 hours combined to figure this out. Is that okay? It feels like
|
||||
that's wasting too much time on a simple problem like
|
||||
that.](conversation://Mara/hmm)
|
||||
|
||||
[That's just how some of these kinds of problems are. The dumbest problems
|
||||
always take the longest to figure out because they are the ones that tools can't
|
||||
really warn you about. I once spent 15 hours of straight effort trying to fix
|
||||
something to find out that `ON` is a yaml value for "true" and that what I was
|
||||
trying to do needed to be `"ON"` instead. This is our lot in life as software
|
||||
people. You are going to make these kinds of mistakes and it is going to make
|
||||
you feel like an absolute buffoon every time. That is just how it happens. Let's
|
||||
go play Fortnite and forget about all this for
|
||||
now.](conversation://Cadey/coffee)
|
Loading…
Reference in New Issue