84 lines
3.3 KiB
ReStructuredText
84 lines
3.3 KiB
ReStructuredText
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Python Storlet Writing and Deployment Guideline
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===============================================
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This is the Python specific storlet writing and deploying guide. This guide complements
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the more general_ guide for writing and deploying storlets which should be read first.
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.. _general: writing_and_deploying_storlets.html
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A python module implementing a storlet looks like this:
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::
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class <Class name>(object):
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def __init__(self, logger):
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self.logger = logger
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def __call__(self, in_files, out_files, params):
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"""
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The function called for storlet invocation
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:param in_files: a list of StorletInputFile
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:param out_files: a list of StorletOutputFile
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:param params: a dict of request parameters
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"""
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Below is a class diagram illustrating the classes behind the in_files, out_files, and logger.
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The diagram lists only the methods that the storlet writer is expected to work with.
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.. image:: images/python_prog_model.jpg
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:height: 960px
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:width: 1216 px
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:scale: 50 %
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:alt: Python Programming Model Class Diagram
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:align: center
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#. The StorletInputFile is used to stream object's data into the storlet.
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StorletInputFile has the same read methods as python FileObject.
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Trying to write to a StorletInputFile yields NotImplemented error.
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Whenever a storlet is invoked, an instance of this class is provided.
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To consume the metadata call the StorletInputFile.get_metadata method.
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#. The StorleOutputFile is used for writing the storlet output.
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StorletOutputFile has the same write methods as python FileObject.
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Trying to read from a StorletOutputFile yields NotImplemented error.
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Whenever a storlet is invoked, an instance of this class is provided.
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Use the StorletInputFile.set_metadata method to set the Object's metadata.
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Note that the storlet must call the StorletInputFile set_metadata method.
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Moreowver, StorletInputFile.set_metadata must be called before writing
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the data.
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#. StorletLogger. The StorletLogger class implements the same log methods as the
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Python logger.
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When invoked via the Swift REST API the __call__ method
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will be called as follows:
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#. The in_files list would include one or more element(s) of type StorleInputFile
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representing the object appearing in the request's URI (and possibly extra resources).
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#. The out_files would include a single element of type StorleOutputFile
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representing the response returned to the user.
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#. The parameters is a dictionary with the execution parameters sent. These parameters can be
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specified in the storlet execution request.
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#. A StorletLogger instance.
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Deploying a Python Storlet
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--------------------------
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Below are specific guidelines for deploying a Python storlet:
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#. The object name of the python module containing the storlet class implemetation
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must end with .py
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#. Any python modules that the class implementation is dependent on should be uploaded as separate .py(s).
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#. The 'X-Object-Meta-Storlet-Main' metadata key shold be of the form: <module_name>.<class_name>. For example,
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if the storlet name is SimpleStorlet and it resides in simple_storlet.py, then the
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'X-Object-Meta-Storlet-Main' metadata key shold be "simple_storlet.SimpleStorlet"
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Deploying a Python Dependency
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-----------------------------
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#. Currently, there is no limitation as to what is being uploaded as a dependency.
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