External markup renderers can't use in-repo images

[pjanx]

• Gitea version (or commit ref): 1.5.1
• Git version: master
• Operating system: Linux
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant

Description

The logic in modules/markup/markdown's (*Renderer).Image is inaccessible to external renderers. Relative image URLs pass through unchanged and wrong.

I can think of two solutions:

• Expose urlPrefix to the process as an environment variable, such as GITEA_PREFIX_SRC=https://github.com/user/repo/raw/branch/master/subdir/ and GITEA_PREFIX_RAW=/user/repo/raw/branch/master/subdir/. Then you can at least wrap external tools in scripts; asciidoctor just needs to have the imagesdir attribute set appropriately.
• Change all relative image srcs in a PostProcess step to point to a /raw/ location because they are pointless anyway (a brute force solution would be to use <base href=> in the header template).

[pjanx]

Slight generalization of my workaround for nginx, works only for a project's root README:

# Circumventing Gitea issue #5031
# Must not catch POST /user/login, that is an awful surprise
set $redirectable 1;
if ($request_method !~ ^(HEAD|GET)$) {
        set $redirectable 0;
}
if ($request_uri !~ ^(/[^/]+/[^/]+)$) {
        set $redirectable 0;
}
if ($redirectable) {
        return  301 https://$host$request_uri/;
}

#!/bin/sh
external-markup-renderer-invocation | perl -pe '
    # The URL must end with a slash; since <script> does not
    # come through, I had to resolve that in nginx.conf
    s,(<img src=")([^/]*?"),$1raw/branch/master/$2,g'

RENDER_COMMAND = /path/to/that/script

[Eisfunke]

I noticed this too (when using Pandoc as markdown parser) and was just about to open an issue about this.

I would prefer the approach using an environment variable, as this would be more flexible. If there are no objections and I get around to it, I'll try to make a PR doing that.

Also, thanks for the workaround script!