Mercurial > repos > shellac > sam_consensus_v3
annotate env/lib/python3.9/site-packages/boto/file/README @ 0:4f3585e2f14b draft default tip
"planemo upload commit 60cee0fc7c0cda8592644e1aad72851dec82c959"
author | shellac |
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date | Mon, 22 Mar 2021 18:12:50 +0000 |
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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 |