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Frequently Asked Questions

  1. How do I fix invalid entitlements?
  2. ob thunk update or ob deploy update fails
  3. How do I fix Ambiguous module name errors?
  4. What does ob run actually do?

How do I fix invalid entitlements?

You probably did not set ios.bundleIdentifier correctly in default.nix. When this happens you'll see an error something like this:

2018-11-25 09:34:22.438 ios-deploy[58106:8521046] [ !! ] Error 0xe8008016: The executable was signed with invalid entitlements. AMDeviceSecureInstallApplication(0, device, url, options, install_callback, 0)

Fixing the value of ios.bundleIdentifier should fix the error.

ob thunk update or ob deploy update fails

Whenever an ob command fails, try re-running it with -v.

If you're using a private repo, and you get a failure in nix-prefetch-url, you may need to unpack and repack the thunk. Here's some example output that shows this issue:

Starting Obelisk </nix/store/j8wls8a89xr6s1a47lg6g83gnbdrfd0l-obelisk-command-0.1/bin/.ob-wrapped> args=["deploy","update","-v"] logging-level=Debug
Creating process: 'nix-build' './.obelisk/impl' '-A' 'command' '--no-out-link'
✔ Built  on ./.obelisk/impl [command]
Handing off to /nix/store/j8wls8a89xr6s1a47lg6g83gnbdrfd0l-obelisk-command-0.1/bin/ob
Starting Obelisk </nix/store/j8wls8a89xr6s1a47lg6g83gnbdrfd0l-obelisk-command-0.1/bin/.ob-wrapped> args=["--no-handoff","deploy","update","-v"] logging-level=Debug
Creating process: 'git' 'ls-remote' '--exit-code' '--symref' 'https://github.com/obsidiansystems/some-private-repo.git' 'refs/heads/master'
git ls-remote maps: (fromList [],fromList [(GitRef_Branch "master","8546dfc8be9653f20bb26214e0991dbb957cb290")])
Latest commit in branch master from remote repo https://github.com/obsidiansystems/some-private-repo.git is 8546dfc8be9653f20bb26214e0991dbb957cb290
Creating process: 'nix-prefetch-url' '--unpack' '--type' 'sha256' 'https://github.com/obsidiansystems/some-private-repo/archive/8546dfc8be9653f20bb26214e0991dbb957cb290.tar.gz'
error: unable to download 'https://github.com/obsidiansystems/some-private-repo/archive/8546dfc8be9653f20bb26214e0991dbb957cb290.tar.gz': HTTP error 404
Process exited with code 1; 'nix-prefetch-url' '--unpack' '--type' 'sha256' 'https://github.com/obsidiansystems/some-private-repo/archive/8546dfc8be9653f20bb26214e0991dbb957cb290.tar.gz'
nix-prefetch-url: Failed to determine sha256 hash of URL https://github.com/obsidiansystems/some-private-repo/archive/8546dfc8be9653f20bb26214e0991dbb957cb290.tar.gz
✖ Updating thunk ./src to latest

And here's how you can fix it:

ob thunk unpack $SOME_THUNK
ob thunk pack $SOME_THUNK

Substitute the directory of your thunk for $SOME_THUNK. In the case of ob deploy update, $SOME_THUNK will be src in the deployment directory.

(Based on issue #351).

How do I fix Ambiguous module name errors?

Since obelisk places the common/backend/frontend modules packages into the same ghci, and ghci doesn't "sandbox" them, it is possible to have conflicting module errors inside ob repl/watch/run that do not appear when doing a cabal build.

You can disambiguate this via PackageImports. For instance, if you see

error:
    Ambiguous module name ‘Crypto.Hash’:
      it was found in multiple packages:
      cryptohash-0.11.9 cryptonite-0.25

then specify the package you want in the import, e.g: import "cryptonite" Crypto.Hash

What does ob run actually do?

Short version:

ob run starts a ghcid process which tries to build your project within a carefully crafted nix-shell with all the project's dependencies and,

  • either displays compilation errors/warnings,
  • or starts the Obelisk server, which serves:
    • your backend's route handlers,
    • the static assets,
    • the JSaddle frontend code (while opening its websocket).

Longer version:

Assuming we are in a project created with ob init, ob run calls (see lib/command/src/Obelisk/Command.hs):

nix-shell --pure -A shells.ghc --run 'ob --no-handoff internal run-static-io <real-run-function>'

where

  • shells.ghc is defined in ./default.nix by importing ./.obelisk/impl/default.nix which is default.nix in the present (Obelisk) repository,
  • run-static-io is a logging-enabled command wrapper (cf. runObelisk in lib/command/src/Obelisk/App.hs).

In this case, it runs the function Obelisk.Command.Command.run (defined in lib/command/src/Obelisk/Command/Run.hs).

  • It creates a GHCi config from a Nix expression which:
    • loads three packages: backend, common, frontend,
    • obtains a free port number.
  • Then runs ghcid
    • with a command that reruns Obelisk.Run.run at each restart (option --test).

It is defined in lib/run/src/Obelisk/Run.hs:

  • It creates a thread which starts the main backend. This runs runSnapWithCommandLineArgs and passes routes:
    • to the backend (result of the _backend_run field of your implementation of the Backend fullRoute frontendRoute record),
    • or to serveDefaultObeliskApp (lib/backend/src/Obelisk/Backend.hs) to serve static assets.
  • Starts runWidget which itself runs runSettingsSocket (the “TCP listen loop”):
    • it binds to TCP socket, and
    • creates the HTTP connection manager ( newManager)
    • calls obeliskApp which
      • has a route to serve the JSaddle frontend,
      • runs the frontend (on the server), to produce pre-rendered pages,
      • starts the JSaddle web-socket,
      • “falls back” to proxying the backend (fallbackProxy).