Dependency error: Phoenix with gun

odohMei7

I am new to phoenix and want to use it with gun to subscribe to websockets. But when I try this in a phoenix project, I get a dependency error. As a minimal example do the following:

$ mix phx.new --version
Phoenix v1.5.3
$ mix phx.new test --no-ecto
[...]

Then I add gun to the dependencies:

  defp deps do
    [
      {:phoenix, "~> 1.5.3"},
      {:phoenix_html, "~> 2.11"},
      {:phoenix_live_reload, "~> 1.2", only: :dev},
      {:phoenix_live_dashboard, "~> 0.2.0"},
      {:telemetry_metrics, "~> 0.4"},
      {:telemetry_poller, "~> 0.4"},
      {:gettext, "~> 0.11"},
      {:jason, "~> 1.0"},
      {:plug_cowboy, "~> 2.0"},
      {:gun, "~> 1.3.2"},
    ]
  end

But when I do mix deps.get I get the following error:

Resolving Hex dependencies...

Failed to use "cowlib" because
  gun (version 1.3.2) requires ~> 2.6.0
  mix.lock specifies 2.9.1

** (Mix) Hex dependency resolution failed, change the version requirements of your dependencies or unlock them (by using mix deps.update or mix deps.unlock). If you are unable to resolve the conflicts you can try overriding with {:dependency, "~> 1.0", override: true}

What should I do? Thanks in advance.

22 comments

/phoenix #dependencies #cowlib

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2020-07-01 20:58:25 UTC

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LostKobrakai

You can probably unlock cowlib and do a mix deps.get again and it should resolve. Unless you really have some code depending on cowlib > 2.6.

Post #1

odohMei7

Thank you but how exactly can I unlock something? I have never done that before.

And is this a bug? Or how would you use pheonix with gun?

Post #2

LostKobrakai

This is not a bug. You installed phoenix, which then fetched the latest version of cowlib and locks the version in mix.lock (this happens for all your dependencies). gun however needs an earlier version of cowlib. You’re however unlikely to be using cowlib directly (transitive dependency) and it seems non of your direct dependencies actually conflicts with the version constraint of gun, so you should be able to safely do mix deps.unlock cowlib, mix deps.get. This will remove the lock on the currently installed version of cowlib and allow mix to resolve the selected version under those new constraints with gun.

Post #3

odohMei7

OK thanks for the explanation. But it now produces a slightly different error for the minimal example from the beginning ot this thread (the 2.6.0 is green and the 2.9.1 red now)

$ mix deps.unlock cowlib
$ mix deps.get
Resolving Hex dependencies...

Failed to use "cowlib" (version 2.6.0) because
  cowboy (version 2.8.0) requires ~> 2.9.1
  gun (version 1.3.2) requires ~> 2.6.0

** (Mix) Hex dependency resolution failed, change the version requirements of your dependencies or unlock them (by using mix deps.update or mix deps.unlock). If you are unable to resolve the conflicts you can try overriding with {:dependency, "~> 1.0", override: true}

Does it have to do something with Mix phx.new deps error - cowlib - the dependency does not match the requirement ?

Post #4

LostKobrakai

Ok, seems like there’s no version of phoenix 1.5, which depends on a cowboy/cowlib low enough to fulfill gun’s requirement. You could try to set the cowlib version in your mix.exs with override: true, but I’m not sure how much cowlib has changed.

Post #5

odohMei7

Maybe I am wrong but does this mean that gun is outdated and should not depend on old cowlib, i.e. one (=the maintainers of gun) should release a new version of gun to resolve this issue?

I will try to override cowlib to a lower version.

Post #6

LostKobrakai

Essentially you’re correct. The changes for http → http2 (and upcoming http3) did result in a bunch of updates on the cowboy/cowlib site of things and gun wasn’t updated. There seems to be work for gun 2.0 on github though.

Post #7

odohMei7

So now I have

  defp deps do
    [
      {:phoenix, "~> 1.5.3"},
      {:phoenix_html, "~> 2.11"},
      {:phoenix_live_reload, "~> 1.2", only: :dev},
      {:phoenix_live_dashboard, "~> 0.2.0"},
      {:telemetry_metrics, "~> 0.4"},
      {:telemetry_poller, "~> 0.4"},
      {:gettext, "~> 0.11"},
      {:jason, "~> 1.0"},
      {:plug_cowboy, "~> 2.0"},
      {:cowlib, "~> 2.6.0", override: true},
      {:gun, "~> 1.3.2"},
    ]
  end

And it seems to work:

$ mix deps.get
Resolving Hex dependencies...
Dependency resolution completed:
Unchanged:
  cowboy 2.8.0
  file_system 0.2.8
  gettext 0.18.0
  jason 1.2.1
  mime 1.3.1
  phoenix 1.5.3
  phoenix_html 2.14.2
  phoenix_live_dashboard 0.2.6
  phoenix_live_reload 1.2.4
  phoenix_live_view 0.13.3
  phoenix_pubsub 2.0.0
  plug 1.10.3
  plug_cowboy 2.3.0
  plug_crypto 1.1.2
  ranch 1.7.1
  telemetry 0.4.2
  telemetry_metrics 0.5.0
  telemetry_poller 0.5.1
New:
  cowlib 2.6.0
  gun 1.3.2
* Updating cowlib (Hex package)
* Getting gun (Hex package)
$ mix compile
===> Compiling cowlib
===> Compiling cowboy
===> Compiling gun
==> plug_cowboy
Compiling 6 files (.ex)
Generated plug_cowboy app
==> phoenix
Compiling 66 files (.ex)
Generated phoenix app
==> phoenix_live_reload
Compiling 4 files (.ex)
Generated phoenix_live_reload app
==> phoenix_live_view
Compiling 18 files (.ex)
Generated phoenix_live_view app
==> phoenix_live_dashboard
Compiling 33 files (.ex)
Generated phoenix_live_dashboard app
==> test
Compiling 13 files (.ex)
Generated test app

But can this override cause any problems? Or am I on the safe side whenever it compiles as it apparently did?

Post #8

benwilson512

Author of Craft GraphQL APIs in Elixir with Absinthe

Yes. Cowlib could work differently than gun expects, and there can be bugs at runtime. It is quite possible that it isn’t possible to use Phoenix 1.5 and gun 1.3 together at all.

Post #9