From 89189212dda85b981adb2f50f082831d0b3f46cc Mon Sep 17 00:00:00 2001
From: Gabriel Augendre <gabriel@augendre.info>
Date: Tue, 17 Oct 2023 18:35:36 +0200
Subject: [PATCH] add gin method not allowed post

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 content/posts/gin-method-not-allowed/gin.jpg  |   3 +
 content/posts/gin-method-not-allowed/index.md | 108 ++++++++++++++++++
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 create mode 100644 content/posts/gin-method-not-allowed/gin.jpg
 create mode 100644 content/posts/gin-method-not-allowed/index.md

diff --git a/content/posts/gin-method-not-allowed/gin.jpg b/content/posts/gin-method-not-allowed/gin.jpg
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+version https://git-lfs.github.com/spec/v1
+oid sha256:9edd5ff40286c1983780f40648851c16d8cd7b11e1b1807b7cadc1adb94eeefc
+size 1916946
diff --git a/content/posts/gin-method-not-allowed/index.md b/content/posts/gin-method-not-allowed/index.md
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+---
+title: "Gin Method Not Allowed"
+date: 2023-10-17T18:29:45+02:00
+draft: false
+tags: ["go", "gin", "golang", "http", "ovh", "ovhcloud"]
+
+# Keep them short
+description: "By default `gin` returns a 404 for an incorrect HTTP verb sent to a handled path. This can be fixed."
+summary: "By default `gin` returns a 404 for an incorrect HTTP verb sent to a handled path. This can be fixed."
+
+cover:
+  image: "gin.jpg"
+  relative: true
+  alt: "Gin & Tonic"
+  caption: 'Gin & Tonic from Vlad Tchompalov sur (Unsplash)'
+  hidden: false  # applies only on single view
+
+# showToc: true
+# TocOpen: false
+---
+
+TL;DR: by default `gin` returns a 404 for an incorrect HTTP verb sent to a handled path. Double-check the method you're using.
+
+## 📖 Context
+At OVHcloud, we use [`gin-gonic/gin`](https://github.com/gin-gonic/gin) as the go-to HTTP web framework for our internal services.
+
+The default behavior when receiving a request for a path that's handled but with an incorrect HTTP verb is to reply with `404 Not Found`. 
+That's confusing because this status code is more often used when a path is not handled at all.
+
+{{< highlight go "linenos=inline" >}}
+package main
+
+import "github.com/gin-gonic/gin"
+
+func main() {
+	router := gin.Default()
+	router.GET("/hello", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{"hello": "gin"})
+	})
+	router.Run("localhost:8080")
+}
+{{< /highlight >}}
+
+```shell
+$ # existing path
+$ curl -i http://localhost:8080/foo
+HTTP/1.1 200 OK
+Content-Type: application/json; charset=utf-8
+Date: Tue, 17 Oct 2023 15:59:49 GMT
+Content-Length: 15
+
+{"hello":"gin"}⏎
+
+$ # wrong method
+$ curl -i -X POST http://localhost:8080/foo
+HTTP/1.1 404 Not Found
+Content-Type: text/plain
+Date: Tue, 17 Oct 2023 16:00:03 GMT
+Content-Length: 18
+
+404 page not found⏎
+
+$ # non-existent path
+$ curl -i http://localhost:8080/bar
+HTTP/1.1 404 Not Found
+Content-Type: text/plain
+Date: Tue, 17 Oct 2023 16:00:17 GMT
+Content-Length: 18
+
+404 page not found⏎
+```
+
+## 👨🏻‍🔧 Fixing the issue
+The router can be configured to handle these cases, but it needs to be manually enabled:
+
+{{< highlight go "linenos=inline,hl_lines=7" >}}
+package main
+
+import "github.com/gin-gonic/gin"
+
+func main() {
+	router := gin.Default()
+	router.HandleMethodNotAllowed = true
+	router.GET("/hello", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{"hello": "gin"})
+	})
+	router.Run("localhost:8080")
+}
+{{< /highlight >}}
+
+```shell
+$ # wrong method
+$ curl -i -X POST http://localhost:8080/foo
+HTTP/1.1 405 Method Not Allowed
+Content-Type: text/plain
+Date: Tue, 17 Oct 2023 16:00:53 GMT
+Content-Length: 22
+
+405 method not allowed⏎
+```
+
+As far as I can tell, this boolean isn't documented on the [docs website](https://gin-gonic.com/docs/), but it has a [doc comment](https://github.com/gin-gonic/gin/blob/a481ee2897af1e368de5c919fbeb21b89aa26fc7/gin.go#L105-L111) attached.
+
+## 👀 Going further
+As you can see, the response still misses the `Allow` header that should document the allowed methods on the endpoint.
+
+A PR was opened in 2020 to fix this and maintainers seemed OK to merge it, but it had conflicts and the original author wasn't responsive ;
+so I opened [a new one](https://github.com/gin-gonic/gin/pull/3759). I hope it will get merged soon!