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Added symlinks promise type
Ticket: CFE-4541 Signed-off-by: Victor Moene <victor.moene@northern.tech>
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‎promise-types/symlinks/README.md‎

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The `symlink` promise type enables concise policy for symbolic links.
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## Attributes
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| Name | Type | Description | Default |
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|---------------|---------------|-----------------------------------------------------------|---------------|
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| `file` | `string` | Path to file. Cannot be used together with `directory`. | - |
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| `directory` | `string` | Path to directory. Cannot be used together with `file`. | - |
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## Examples
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To create a symlink to the directory `/tmp/my-dir` with the name `/tmp/my-link`, we can do:
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```cfengine3
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bundle agent main
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{
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symlinks:
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"/tmp/my-link"
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directory => "/tmp/my-dir";
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}
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```
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In similar fashion, to create a symlink to the file `/tmp/my-dir` with the name `/tmp/my-link`, we can do:
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```cfengine3
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bundle agent main
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{
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symlinks:
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"/tmp/my-link"
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file => "/tmp/my-file";
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}
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```
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If the path to the file/directory given in the promise is not an absolute, doesn't exist or its type doesn't correspond with the promise's attribute ("file" or "directory"), then the promise will fail.
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Trying to symlink to a file/directory where the link name is the same as an existing file/directory will also make the promise fail.
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Already exisiting symlinks with incorrect target will be corrected according to the policy.
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## Authors
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This software was created by the team at [Northern.tech](https://northern.tech), with many contributions from the community.
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Thanks everyone!
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## Contribute
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Feel free to open pull requests to expand this documentation, add features, or fix problems.
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You can also pick up an existing task or file an issue in [our bug tracker](https://northerntech.atlassian.net/).
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## License
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This software is licensed under the MIT License. See LICENSE in the root of the repository for the full license text.

‎promise-types/symlinks/enable.cf‎

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promise agent symlinks
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# @brief Define symlinks promise type
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{
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path => "$(sys.workdir)/modules/promises/symlinks.py";
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interpreter => "/usr/bin/python3";
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}

‎promise-types/symlinks/example.cf‎

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promise agent symlinks
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# @brief Define symlinks promise type
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{
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path => "$(sys.workdir)/modules/promises/symlinks.py";
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interpreter => "/usr/bin/python3";
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}
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bundle agent main
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{
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symlinks:
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"/tmp/myfilelink"
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file => "tmp/myfile";
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"/tmp/mydirlink"
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directory => "tmp/mydirectory";
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}

‎promise-types/symlinks/symlinks.py‎

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import os
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from cfengine import PromiseModule, ValidationError, Result
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class SymlinksPromiseTypeModule(PromiseModule):
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def __init__(self, **kwargs):
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super(SymlinksPromiseTypeModule, self).__init__(
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name="symlinks_promise_module",
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version="0.0.1",
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**kwargs,
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)
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def is_absolute_dir(v):
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if not os.path.isabs(v):
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raise ValidationError("must be an absolute path, not '{v}'".format(v=v))
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if not os.path.exists(v):
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raise ValidationError("directory must exists")
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if not os.path.isdir(v):
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raise ValidationError("must be a dir")
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def is_absolute_file(v):
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if not os.path.isabs(v):
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raise ValidationError("must be an absolute path, not '{v}'".format(v=v))
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if not os.path.exists(v):
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raise ValidationError("file must exists")
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if not os.path.isfile(v):
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raise ValidationError("must be a file")
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self.add_attribute("directory", str, validator=is_absolute_dir)
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self.add_attribute("file", str, validator=is_absolute_file)
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def validate_promise(self, promiser, attributes, metadata):
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model = self.create_attribute_object(promiser, attributes)
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if not model.file and not model.directory:
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raise ValidationError("missing 'file' or 'directory' attribute")
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if model.file and model.directory:
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raise ValidationError("must specify either 'file' or 'directory', not both")
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def evaluate_promise(self, promiser, attributes, metadata):
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model = self.create_attribute_object(promiser, attributes)
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link_target = model.file if model.file else model.directory
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try:
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os.symlink(link_target, promiser, target_is_directory=bool(model.directory))
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self.log_info("Created symlink '{}' -> '{}'".format(promiser, link_target))
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return Result.REPAIRED
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except FileExistsError:
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if not os.path.islink(promiser):
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self.log_error("Symlink '{}' is already a path".format(promiser))
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return Result.NOT_KEPT
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if os.path.realpath(promiser) != link_target:
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self.log_warning(
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"Symlink '{}' already exists but has wrong target '{}'".format(
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promiser, os.path.realpath(promiser)
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)
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)
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try:
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os.unlink(promiser)
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except FileNotFoundError:
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self.log_error(
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"'{}' is already unlinked from its old target".format(promiser)
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)
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return Result.NOT_KEPT
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except Exception:
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self.log_error(
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"'{}' has wrong target but couldn't be unlinked: {}".format(
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promiser, e
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)
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)
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return Result.NOT_KEPT
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try:
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os.symlink(
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link_target, promiser, target_is_directory=bool(model.directory)
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)
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except FileExistsError:
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self.log_error(
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"Couldn't symlink '{}' to '{}'. A symlink already exists".format(
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link_target, promiser
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)
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)
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return Result.NOT_KEPT
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except FileNotFoundError:
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self.log_error("'{}' doesn't exist".format(link_target))
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return Result.NOT_KEPT
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except Exception as e:
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self.log_error(
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"Couldn't symlink '{}' to '{}': {}".format(
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link_target, promiser, e
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)
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)
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return Result.NOT_KEPT
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self.log_info(
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"Corrected symlink '{}' -> '{}'".format(promiser, link_target)
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)
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return Result.REPAIRED
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return Result.KEPT
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except FileNotFoundError:
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self.log_error("'{}' doesn't exist".format(promiser))
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return Result.NOT_KEPT
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except Exception as e:
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self.log_error(
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"Couldn't symlink '{}' to '{}': {}".format(link_target, promiser, e)
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)
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return Result.NOT_KEPT
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if __name__ == "__main__":
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SymlinksPromiseTypeModule().start()

‎promise-types/symlinks/test.cf‎

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body common control
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{
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inputs => { "$(sys.libdir)/stdlib.cf" };
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version => "1.0";
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bundlesequence => { "init", "test", "check", "cleanup"};
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}
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#######################################################
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bundle agent init
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{
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files:
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"/tmp/my-file"
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create => "true";
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"/tmp/my-dir/."
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create => "true";
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"/tmp/other-dir/."
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create => "true";
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"/tmp/replaced-link"
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link_from => ln_s("/tmp/other-dir");
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"/tmp/already-existing-link"
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link_from => ln_s("/tmp/other-dir");
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}
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#######################################################
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promise agent symlinks
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{
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path => "$(this.promise_dirname)/symlinks.py";
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interpreter => "/usr/bin/python3";
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}
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body classes outcome(arg)
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{
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promise_kept => { "$(arg)_kept" };
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promise_repaired => { "$(arg)_repaired" };
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}
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bundle agent test
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{
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meta:
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"description" -> { "CFE-4541" }
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string => "Test the symlinks promise module";
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symlinks:
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"/tmp/file-link"
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file => "/tmp/my-file",
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classes => outcome("created_file");
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"/tmp/dir-link"
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directory => "/tmp/my-dir",
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classes => outcome("created_dir");
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"/tmp/replaced-link"
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directory => "/tmp/my-dir",
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classes => outcome("corrected");
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"/tmp/already-existing-link"
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directory => "/tmp/other-dir",
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classes => outcome("didnothing");
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}
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#######################################################
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bundle agent check
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{
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vars:
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"my_file_stat"
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string => filestat("/tmp/file-link", "linktarget");
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"my_dir_stat"
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string => filestat("/tmp/dir-link", "linktarget");
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"replaced_link_stat"
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string => filestat("/tmp/replaced-link", "linktarget");
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"already_existing_link_stat"
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string => filestat("/tmp/already-existing-link", "linktarget");
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classes:
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"ok"
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expression => and (
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strcmp("$(my_file_stat)", "/tmp/my-file"),
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strcmp("$(my_dir_stat)", "/tmp/my-dir"),
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strcmp("$(replaced_link_stat)", "/tmp/my-dir"),
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strcmp("$(already_existing_link_stat)", "/tmp/other-dir"),
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"created_file_repaired",
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"created_dir_repaired",
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"corrected_repaired",
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"didnothing_kept"
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);
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reports:
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ok::
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"$(this.promise_filename) Pass";
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!ok::
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"$(this.promise_filename) FAIL";
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}
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# #######################################################
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bundle agent cleanup
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{
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files:
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"/tmp/file-link"
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delete => tidy;
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"/tmp/dir-link"
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delete => tidy;
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"/tmp/my-file"
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delete => tidy;
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"/tmp/my-dir/."
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delete => tidy;
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"/tmp/other-dir/."
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delete => tidy;
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"/tmp/replaced-link"
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delete => tidy;
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"/tmp/already-existing-link"
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delete => tidy;
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}

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