# module_ctx

The context of the module extension containing helper functions and information about pertinent tags across the dependency graph. You get a module_ctx object as an argument to the `implementation` function when you create a module extension.

## Members

- download
- download_and_extract
- execute
- file
- modules
- os
- path
- read
- report_progress
- which

## download

    struct module_ctx.download(url, output='', sha256='', executable=False, allow_fail=False, canonical_id='', auth={}, *, integrity='')

Downloads a file to the output path for the provided url and returns a struct containing `success`, a flag which is `true` if the download completed successfully, and if successful, a hash of the file with the fields `sha256` and `integrity`.

### Parameters

Parameter | Description
--- | ---
`url` | `string; or Iterable of strings`; required List of mirror URLs referencing the same file.
`output` | `string; or Label; or path`; default = '' path to the output file, relative to the repository directory.
`sha256` | default = '' the expected SHA-256 hash of the file downloaded. This must match the SHA-256 hash of the file downloaded. It is a security risk to omit the SHA-256 as remote files can change. At best omitting this field will make your build non-hermetic. It is optional to make development easier but should be set before shipping.
`executable` | default = False set the executable flag on the created file, false by default.
`allow_fail` | default = False If set, indicate the error in the return value instead of raising an error for failed downloads
`canonical_id` | default = '' If set, restrict cache hits to those cases where the file was added to the cache with the same canonical id
`auth` | default = {} An optional dict specifying authentication information for some of the URLs.
`integrity` | default = '' Expected checksum of the file downloaded, in Subresource Integrity format. This must match the checksum of the file downloaded. It is a security risk to omit the checksum as remote files can change. At best omitting this field will make your build non-hermetic. It is optional to make development easier but should be set before shipping.

## download_and_extract

    struct module_ctx.download_and_extract(url, output='', sha256='', type='', stripPrefix='', allow_fail=False, canonical_id='', auth={}, *, integrity='', rename_files={})

Downloads a file to the output path for the provided url, extracts it, and returns a struct containing `success`, a flag which is `true` if the download completed successfully, and if successful, a hash of the file with the fields `sha256` and `integrity`.

### Parameters

Parameter | Description
--- | ---
`url` | `string; or Iterable of strings`; required List of mirror URLs referencing the same file.
`output` | `string; or Label; or path`; default = '' path to the directory where the archive will be unpacked, relative to the repository directory.
`sha256` | default = '' the expected SHA-256 hash of the file downloaded. This must match the SHA-256 hash of the file downloaded. It is a security risk to omit the SHA-256 as remote files can change. At best omitting this field will make your build non-hermetic. It is optional to make development easier but should be set before shipping. If provided, the repository cache will first be checked for a file with the given hash; a download will only be attempted if the file was not found in the cache. After a successful download, the file will be added to the cache.
`type` | default = '' the archive type of the downloaded file. By default, the archive type is determined from the file extension of the URL. If the file has no extension, you can explicitly specify either "zip", "jar", "war", "aar", "tar", "tar.gz", "tgz", "tar.xz", "txz", ".tar.zst", ".tzst", "tar.bz2", ".ar", or ".deb" here.
`stripPrefix` | default = '' a directory prefix to strip from the extracted files. Many archives contain a top-level directory that contains all files in the archive. Instead of needing to specify this prefix over and over in the `build_file`, this field can be used to strip it from extracted files.
`allow_fail` | default = False If set, indicate the error in the return value instead of raising an error for failed downloads
`canonical_id` | default = '' If set, restrict cache hits to those cases where the file was added to the cache with the same canonical id
`auth` | default = {} An optional dict specifying authentication information for some of the URLs.
`integrity` | default = '' Expected checksum of the file downloaded, in Subresource Integrity format. This must match the checksum of the file downloaded. It is a security risk to omit the checksum as remote files can change. At best omitting this field will make your build non-hermetic. It is optional to make development easier but should be set before shipping.
`rename_files` | default = {} An optional dict specifying files to rename during the extraction. Archive entries with names exactly matching a key will be renamed to the value, prior to any directory prefix adjustment. This can be used to extract archives that contain non-Unicode filenames, or which have files that would extract to the same path on case-insensitive filesystems.

## execute

    exec_result module_ctx.execute(arguments, timeout=600, environment={}, quiet=True, working_directory="")

Executes the command given by the list of arguments. The execution time of the command is limited by `timeout` (in seconds, default 600 seconds). This method returns an `exec_result` structure containing the output of the command. The `environment` map can be used to override some environment variables to be passed to the process.

### Parameters

Parameter | Description
--- | ---
`arguments` | required List of arguments, the first element should be the path to the program to execute.
`timeout` | default = 600 maximum duration of the command in seconds (default is 600 seconds).
`environment` | default = {} force some environment variables to be set to be passed to the process.
`quiet` | default = True If stdout and stderr should be printed to the terminal.
`working_directory` | default = "" Working directory for command execution. Can be relative to the repository root or absolute.

## file

    None module_ctx.file(path, content='', executable=True, legacy_utf8=True)

Generates a file in the repository directory with the provided content.

### Parameters

Parameter | Description
--- | ---
`path` | `string; or Label; or path`; required path of the file to create, relative to the repository directory.
`content` | default = '' the content of the file to create, empty by default.
`executable` | default = True set the executable flag on the created file, true by default.
`legacy_utf8` | default = True encode file content to UTF-8, true by default. Future versions will change the default and remove this parameter.

## modules

    list module_ctx.modules

A list of all the Bazel modules in the external dependency graph, each of which is a bazel_module object that exposes all the tags it specified for this module extension. The iteration order of this dictionary is guaranteed to be the same as breadth-first search starting from the root module.

## os

    repository_os module_ctx.os

A struct to access information from the system.

## path

    path module_ctx.path(path)

Returns a path from a string, label or path. If the path is relative, it will resolve relative to the repository directory. If the path is a label, it will resolve to the path of the corresponding file. Note that remote repositories are executed during the analysis phase and thus cannot depends on a target result (the label should point to a non-generated file). If path is a path, it will return that path as is.

### Parameters

Parameter | Description
--- | ---
`path` | `string; or Label; or path`; required string, label or path from which to create a path from

## read

    string module_ctx.read(path)

Reads the content of a file on the filesystem.

### Parameters

Parameter | Description
--- | ---
`path` | `string; or Label; or path`; required path of the file to read from.

## report_progress

    None module_ctx.report_progress(status='')

Updates the progress status for the fetching of this repository or module extension

### Parameters

Parameter | Description
--- | ---
`status` | `string`; default = '' string describing the current status of the fetch progress

## which

    path module_ctx.which(program)

Returns the path of the corresponding program or None if there is no such program in the path.

### Parameters

Parameter | Description
--- | ---
`program` | required Program to find in the path.

May return `None`.