[Bug] - REST - invalid method returns plaintext error

[lrm25]

Describe the bug
If the method type (e.g. normally GET, PUT, is invalid), versitygw returns this:

HTTP/1.1 400 Bad Request
   Server: VERSITYGW
   Date: Thu, 12 Feb 2026 18:44:06 GMT
   Content-Type: text/plain; charset=utf-8
   Content-Length: 19
   Connection: close
   
   Invalid http method

The error is returned in plaintext. S3 returns this:

HTTP/1.1 400 Bad Request
   Date: Thu, 12 Feb 26 18:47:31 GMT
   Connection: close
   Transfer-Encoding: chunked
   x-amz-id-2: 0vp3gbP+bY8ymlv3nsCGa5EiC8RhZkGLuW7ErRmriUbVrFth0HoNfbpQPJfGxLMA44Sgbq8Lj5EU8t7dHVXSbVof2gPmRKB7hrm2Zq2Jgq+vZH2kF3OQeQ==
   x-amz-request-id: 2CFB9A8897982AAD
   Content-Type: application/xml
   Server: AmazonS3
   
   <?xml version="1.0" encoding="UTF-8"?><Error><Code>BadRequest</Code><Message>An error occurred when parsing the HTTP request.</Message><RequestId>2CFB9A8897982AAD</RequestId><HostId>0vp3gbP+bY8ymlv3nsCGa5EiC8RhZkGLuW7ErRmriUbVrFth0HoNfbpQPJfGxLMA44Sgbq8Lj5EU8t7dHVXSbVof2gPmRKB7hrm2Zq2Jgq+vZH2kF3OQeQ==</HostId></Error>

The versitygw error is actually more clear, but it's in plaintext.

To Reproduce

1. Start versitygw, e.g.: ./versitygw --access=AKIA**** --secret=******** --region=us-east-1 --cert /Users/lukemccrone/devel/versitygw/cert.pem --key /Users/lukemccrone/devel/versitygw/versitygw.pem posix --versioning-dir /tmp/versioning /tmp/gw
2. Create a bucket, e.g.: curl -ks -w %{http_code} -X PUT https://localhost:7070/versity-gwtest-bucket-one-1-20260212154404 -H Authorization: AWS4-HMAC-SHA256 Credential=AKIA6****/20260212/us-east-1/s3/aws4_request,SignedHeaders=host;x-amz-content-sha256;x-amz-date,Signature=ddb2e5e7c773bd8c4b7be2887dade60c206cf76d38e711196833ba03a66bc6d0 -H host: localhost:7070 -H x-amz-content-sha256: UNSIGNED-PAYLOAD -H x-amz-date: 20260212T184405Z -o /Users/lukemccrone/devel/versitygw/versity-gwtest-files/output.txt
3. Send a command with an invalid method to this bucket, e.g.: curl -iks -X INVALID https://localhost:7070/versity-gwtest-bucket-one-1-20260212154404 -H Authorization: AWS4-HMAC-SHA256 Credential=AKIA6****/20260212/us-east-1/s3/aws4_request,SignedHeaders=host;x-amz-content-sha256;x-amz-date,Signature=8bf7e556a6207083f6816079adb9fa6a09347245e1d9421778488cdd83b578ea -H host: localhost:7070 -H x-amz-content-sha256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 -H x-amz-date: 20260212T184406Z

Expected behavior
An XML error is returned.

Server Version
Version : v1.2.0
Build : d214559
BuildTime: 2026-02-11_06:05:08PM
Darwin Lukes-MacBook-Pro.local 24.6.0 Darwin Kernel Version 24.6.0: Mon Jul 14 11:28:30 PDT 2025; root:xnu-11417.140.69~1/RELEASE_ARM64_T6030 arm64

[niksis02]

There is no way we can customize this error. Fiber internally sends a plain text 400 response:
https://github.com/gofiber/fiber/blob/v2.52.11/router.go#L164-L167

[niksis02]

In fiber v3.0.0 a Not Implemented error is returned internally by fiber and there's no outside control over it.
https://github.com/gofiber/fiber/blob/v3.0.0/router.go#L327-L342

Closing this issue, as it's unfixable so far.

[niksis02]

A potential fix/workaround here is to create a PR on fiber to make this error configurable by the global error wrapper after the fiber v3 migration in the gateway.