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annotate venv/lib/python2.7/site-packages/boto/file/README @ 0:d67268158946 draft

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planemo upload commit a3f181f5f126803c654b3a66dd4e83a48f7e203b
author bcclaywell
date Mon, 12 Oct 2015 17:43:33 -0400
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1 Handling of file:// URIs:
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2
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3 This directory contains code to map basic boto connection, bucket, and key
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4 operations onto files in the local filesystem, in support of file://
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5 URI operations.
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6
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7 Bucket storage operations cannot be mapped completely onto a file system
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8 because of the different naming semantics in these types of systems: the
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9 former have a flat name space of objects within each named bucket; the
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10 latter have a hierarchical name space of files, and nothing corresponding to
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11 the notion of a bucket. The mapping we selected was guided by the desire
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12 to achieve meaningful semantics for a useful subset of operations that can
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13 be implemented polymorphically across both types of systems. We considered
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14 several possibilities for mapping path names to bucket + object name:
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15
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16 1) bucket = the file system root or local directory (for absolute vs
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17 relative file:// URIs, respectively) and object = remainder of path.
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18 We discarded this choice because the get_all_keys() method doesn't make
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19 sense under this approach: Enumerating all files under the root or current
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20 directory could include more than the caller intended. For example,
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21 StorageUri("file:///usr/bin/X11/vim").get_all_keys() would enumerate all
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22 files in the file system.
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23
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24 2) bucket is treated mostly as an anonymous placeholder, with the object
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25 name holding the URI path (minus the "file://" part). Two sub-options,
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26 for object enumeration (the get_all_keys() call):
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27 a) disallow get_all_keys(). This isn't great, as then the caller must
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28 know the URI type before deciding whether to make this call.
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29 b) return the single key for which this "bucket" was defined.
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30 Note that this option means the app cannot use this API for listing
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31 contents of the file system. While that makes the API less generally
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32 useful, it avoids the potentially dangerous/unintended consequences
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33 noted in option (1) above.
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34
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35 We selected 2b, resulting in a class hierarchy where StorageUri is an abstract
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36 class, with FileStorageUri and BucketStorageUri subclasses.
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37
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38 Some additional notes:
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39
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40 BucketStorageUri and FileStorageUri each implement these methods:
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41 - clone_replace_name() creates a same-type URI with a
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42 different object name - which is useful for various enumeration cases
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43 (e.g., implementing wildcarding in a command line utility).
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44 - names_container() determines if the given URI names a container for
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45 multiple objects/files - i.e., a bucket or directory.
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46 - names_singleton() determines if the given URI names an individual object
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47 or file.
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48 - is_file_uri() and is_cloud_uri() determine if the given URI is a
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49 FileStorageUri or BucketStorageUri, respectively