How to enable online-mode for build-commands?

[sequencerr]

2. if you re-read the documentation you will learn that the build is offline. Which is exactly what is happening.

Originally posted by @hfiguiere in flatpak/flatpak#2855 (comment)

https://docs.flatpak.org/en/latest/flatpak-builder-command-reference.html

Permissions:
Builds have the --allow=devel and --allow=multiarch permissions that regular flatpak runs don't have by default. This limits the syscall filtering that is normally done so development tools like debuggers work. Otherwise the build sandbox is very limited, for example there is no network access.

Though devel feature is only about developer tools, I don't understand why network mentioned in that context. I have network connection to sources: type: git for example, to resolve dns github.com and download repo, but not to wget [something] in build-commands.
devel: Allow system calls used by development-oriented tools such as perf, strace and gdb.

flatpak-builder doesn't have --allow flag
https://docs.flatpak.org/en/latest/flatpak-command-reference.html#flatpak-run
and flatpak run --allow=devel org.flatpak.Builder doesn't help

Other that I can't find anything in docs/reference about network isolation during build.

[TingPing]

build-options:
  build-args: ['--share=network']

[TingPing]

but not to wget [something] in build-commands.

In case it wasn't obvious, you would do this with:

sources:
  - type: archive
    url: ...
    sha256: ...

Using wget doesn't make sense.

[sequencerr]

Thank you!

but not to wget [something] in build-commands.

In case it wasn't obvious, you would do this with:

sources:
  - type: archive
    url: ...
    sha256: ...

Using wget doesn't make sense.

It was example of course. I need some build system tools like maven or gradle to install packages while building.

[sequencerr]

BTW: you also need to remove --sandbox flag from flatpak-builder cli.

[TingPing]

There are some scripts that generate a static list of downloads for tools like gradle: https://github.com/flatpak/flatpak-builder-tools

If you want to publish on Flathub you'd have to use them. But for your own usage it might not be worth it.