Content of text file with "LP" after 34 bytes not show in the repository view due to Golang's http.DetectContentType

[mg-cloud]

Description

I have encounter an issue on the web interface with some basic text file not displayed in the repository content preview.
You have the message "[View Raw]" to download the file as for a binary instead of the content displayed.

After some test, I found that the following 2 lines pasted on demo.gitea.com reproduced the problem.

# syntax=docker/dockerfile:1
ARG ALP

I stored two text file on https://demo.gitea.com/mg-cloud/gitea-issue-raw with, one OK et one KO just by changing the last letter for P to E (adding a space, a new line seems to solve the issue as well).
Test KO
Test OK

See screenshot below.

Gitea Version

1.26.0+dev-209-g26602fd207 on demo.gitea.com

Can you reproduce the bug on the Gitea demo site?

Yes

Log Gist

No response

Screenshots

Screenshoot with the file not displayed

Screenshoot of a correct display with a character changed

Git Version

No response

Operating System

No response

How are you running Gitea?

Problem reproduced on demo.gitea.com

Database

None

[wxiaoguang]

The real difference is the last new line \n

[mg-cloud]

The real difference is the last new line \n

You're right, I missed that. However I removed the extra line at the end with the same result (see the last commit).

[wxiaoguang]

Without last new line, the file is detected as this type: (see next comment)

[wxiaoguang]

Well .... not related to the new line.

Golang's code only try to find the "LP" substring, that's why you change the "LP" to other string then the problem would disappear.

https://github.com/golang/go/blob/28147b528312055b535c6a69d0d4492bd502e1b0/src/net/http/sniff.go#L166-L173