This is an experimental feature subject to breaking changes in future releases.
The Conan hooks is a feature intended to extend the Conan functionalities and let users customize the client behavior at determined points.
A hook is a Python function that will be executed at certain points of Conan workflow to customize the client behavior without modifying the client sources or the recipe ones. In the hooks reference you can find the full list of hook functions and exhaustive documentation about their arguments.
Hooks can implement any functionality: it could be Conan commands, recipe interactions such as exporting or packaging, or interactions with the remotes.
Here is an example of a simple hook:
from conans import tools def pre_export(output, conanfile, conanfile_path, reference, **kwargs): test = "%s/%s" % (reference.name, reference.version) for field in ["url", "license", "description"]: field_value = getattr(conanfile, field, None) if not field_value: output.error("%s Conanfile doesn't have '%s'. It is recommended to add it as attribute: %s" % (test, field, conanfile_path)) def pre_source(output, conanfile, conanfile_path, **kwargs): conanfile_content = tools.load(conanfile_path) if "def source(self):" in conanfile_content: test = "[IMMUTABLE SOURCES]" valid_content = [".zip", ".tar", ".tgz", ".tbz2", ".txz"] invalid_content = ["git checkout master", "git checkout devel", "git checkout develop"] if "git clone" in conanfile_content and "git checkout" in conanfile_content: fixed_sources = True for invalid in invalid_content: if invalid in conanfile_content: fixed_sources = False else: fixed_sources = False for valid in valid_content: if valid in conanfile_content: fixed_sources = True if not fixed_sources: output.error("%s Source files does not come from and immutable place. Checkout to a " "commit/tag or download a compressed source file for %s" % (test, str(reference)))
This hook checks the recipe content prior to it being exported and prior to downloading the sources. Basically the
pre_export() function checks the attributes of the
conanfile object to see if there is an URL, a license and a description and if missing,
warns the user with a message through the
output. This is done before the recipe is exported to the local cache.
pre_source() function checks if the recipe contains a
source() method (this time it is using the conanfile.py content instead of
conanfile object) and in that case it checks if the download of the sources are likely coming from immutable places (a compressed
file or a determined git checkout). This is done before the source() method of the recipe is called.
Any kind of Python script can be executed. You can create global functions and call them from different hook functions, import from a relative module and warn, error or even raise to abort the Conan client execution.
Other useful task where a hook may come handy are the upload and download actions. There are pre and post functions for every download/upload as a whole and for fine download tasks such as recipe and package downloads/uploads.
For example they can be used to sign the packages (including a file with the signature) when the package is created and check that signature every time they are downloaded.
import os from conans import tools SIGNATURE = "this is my signature" def post_package(output, conanfile, conanfile_path, **kwargs): sign_path = os.path.join(conanfile.package_folder, ".sign") tools.save(sign_path, SIGNATURE) output.success("Package signed successfully") def post_download_package(output, conanfile_path, reference, package_id, remote_name, **kwargs): package_path = os.path.abspath(os.path.join(os.path.dirname(conanfile_path), "..", "package", package_id)) sign_path = os.path.join(package_path, ".sign") content = tools.load(sign_path) if content != SIGNATURE: raise Exception("Wrong signature")
Importing from a module¶
The hook interface should always be placed inside a Python file with the name of the hook and stored in the ~/.conan/hooks folder. However, you can use functionalities from imported modules if you have them installed in your system or if they are installed with Conan:
import requests from conans import tools def post_export(output, conanfile, conanfile_path, reference, **kwargs): cmakelists_path = os.path.join(os.path.dirname(conanfile_path), "CMakeLists.txt") tools.replace_in_file(cmakelists_path, "PROJECT(MyProject)", "PROJECT(MyProject CPP)") r = requests.get('https://api.github.com/events')
You can also import functionalities from a relative module:
hooks ├── custom_module │ ├── custom.py │ └── __init__.py └── my_hook.py
Inside the custom.py from my custom_module there is:
def my_printer(output): output.info("my_printer(): CUSTOM MODULE")
And it can be used in the hook importing the module, just like regular Python:
from custom_module.custom import my_printer def pre_export(output, conanfile, conanfile_path, reference, **kwargs): my_printer(output)
Storage, activation and sharing¶
Hooks are Python files stored under ~/.conan/hooks folder and their file name should be the same used for activation (the .py extension could be indicated or not).
The activation of the hooks is done in the conan.conf section named
[hooks]. The hook names or paths listed under this section will be
... [hooks] attribute_checker.py conan-center.py my_custom_hook/hook.py
They can be easily activated and deactivated from the command line using the conan config set command:
$ conan config set hooks.my_custom_hook/hook # Activates 'my_custom_hook' $ conan config rm hooks.my_custom_hook/hook # Deactivates 'my_custom_hook'
There is also an environment variable CONAN_HOOKS that you can use to declare which hooks should be activated.
Hooks are considered part of the Conan client configuration and can be shared as usual with the conan config install command. However, they can also be managed in isolated Git repositories cloned into the ~/.conan/hooks folder:
$ cd ~/.conan/hooks $ git clone https://github.com/conan-io/hooks.git conan_hooks $ conan config set hooks.conan_hooks/hooks/conan-center.py
This way you can easily change from one version to another.
There are some officially maintained hooks in its own repository in GitHub,
attribute_checker that has been packaged with Conan sources for several versions (although it is
distributed with Conan still, it is no longer maintained and we may remove it in the future, so we encourage you to install
the one in the hooks repository and activate it).
Using the hooks in the official repository is as easy as installing them and activating the ones of interest:
conan config install https://github.com/conan-io/hooks.git -sf hooks -tf hooks conan config set hooks.attribute_checker