HADOOP-18987. Various fixes to FileSystem API docs (#6292)
Contributed by Dieter De Paepe
This commit is contained in:
DieterDP
GitHub
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be13e94843
@ -88,14 +88,13 @@ for example. output streams returned by the S3A FileSystem.
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The stream MUST implement `Abortable` and `StreamCapabilities`.
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```python
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if unsupported:
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if unsupported:
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throw UnsupportedException
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if not isOpen(stream):
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no-op
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StreamCapabilities.hasCapability("fs.capability.outputstream.abortable") == True
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```
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@ -64,13 +64,13 @@ a protected directory, result in such an exception being raised.
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### `boolean isDirectory(Path p)`
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def isDirectory(FS, p)= p in directories(FS)
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def isDir(FS, p) = p in directories(FS)
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### `boolean isFile(Path p)`
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def isFile(FS, p) = p in files(FS)
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def isFile(FS, p) = p in filenames(FS)
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### `FileStatus getFileStatus(Path p)`
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@ -250,7 +250,7 @@ process.
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changes are made to the filesystem, the result of `listStatus(parent(P))` SHOULD
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include the value of `getFileStatus(P)`.
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* After an entry at path `P` is created, and before any other
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* After an entry at path `P` is deleted, and before any other
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changes are made to the filesystem, the result of `listStatus(parent(P))` SHOULD
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NOT include the value of `getFileStatus(P)`.
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@ -305,7 +305,7 @@ that they must all be listed, and, at the time of listing, exist.
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All paths must exist. There is no requirement for uniqueness.
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forall p in paths :
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exists(fs, p) else raise FileNotFoundException
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exists(FS, p) else raise FileNotFoundException
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#### Postconditions
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@ -381,7 +381,7 @@ being completely performed.
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Path `path` must exist:
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exists(FS, path) : raise FileNotFoundException
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if not exists(FS, path) : raise FileNotFoundException
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#### Postconditions
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@ -432,7 +432,7 @@ of data which must be collected in a single RPC call.
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#### Preconditions
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exists(FS, path) else raise FileNotFoundException
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if not exists(FS, path) : raise FileNotFoundException
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### Postconditions
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@ -463,7 +463,7 @@ and 1 for file count.
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#### Preconditions
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exists(FS, path) else raise FileNotFoundException
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if not exists(FS, path) : raise FileNotFoundException
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#### Postconditions
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@ -567,7 +567,7 @@ when writing objects to a path in the filesystem.
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#### Postconditions
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result = integer >= 0
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result = integer >= 0
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The outcome of this operation is usually identical to `getDefaultBlockSize()`,
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with no checks for the existence of the given path.
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@ -591,12 +591,12 @@ on the filesystem.
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#### Preconditions
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if not exists(FS, p) : raise FileNotFoundException
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if not exists(FS, p) : raise FileNotFoundException
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#### Postconditions
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if len(FS, P) > 0: getFileStatus(P).getBlockSize() > 0
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if len(FS, P) > 0 : getFileStatus(P).getBlockSize() > 0
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result == getFileStatus(P).getBlockSize()
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1. The outcome of this operation MUST be identical to the value of
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@ -654,12 +654,12 @@ No ancestor may be a file
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forall d = ancestors(FS, p) :
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if exists(FS, d) and not isDir(FS, d) :
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raise [ParentNotDirectoryException, FileAlreadyExistsException, IOException]
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raise {ParentNotDirectoryException, FileAlreadyExistsException, IOException}
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#### Postconditions
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FS' where FS'.Directories' = FS.Directories + [p] + ancestors(FS, p)
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FS' where FS'.Directories = FS.Directories + [p] + ancestors(FS, p)
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result = True
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@ -688,7 +688,7 @@ The return value is always true—even if a new directory is not created
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The file must not exist for a no-overwrite create:
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if not overwrite and isFile(FS, p) : raise FileAlreadyExistsException
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if not overwrite and isFile(FS, p) : raise FileAlreadyExistsException
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Writing to or overwriting a directory must fail.
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@ -698,7 +698,7 @@ No ancestor may be a file
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forall d = ancestors(FS, p) :
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if exists(FS, d) and not isDir(FS, d) :
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raise [ParentNotDirectoryException, FileAlreadyExistsException, IOException]
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raise {ParentNotDirectoryException, FileAlreadyExistsException, IOException}
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FileSystems may reject the request for other
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reasons, such as the FS being read-only (HDFS),
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@ -712,8 +712,8 @@ For instance, HDFS may raise an `InvalidPathException`.
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#### Postconditions
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FS' where :
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FS'.Files'[p] == []
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ancestors(p) is-subset-of FS'.Directories'
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FS'.Files[p] == []
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ancestors(p) subset-of FS'.Directories
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result = FSDataOutputStream
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@ -734,7 +734,7 @@ The behavior of the returned stream is covered in [Output](outputstream.html).
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clients creating files with `overwrite==true` to fail if the file is created
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by another client between the two tests.
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* The S3A and potentially other Object Stores connectors not currently change the `FS` state
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* The S3A and potentially other Object Stores connectors currently don't change the `FS` state
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until the output stream `close()` operation is completed.
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This is a significant difference between the behavior of object stores
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and that of filesystems, as it allows >1 client to create a file with `overwrite=false`,
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@ -762,15 +762,15 @@ The behavior of the returned stream is covered in [Output](outputstream.html).
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#### Implementation Notes
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`createFile(p)` returns a `FSDataOutputStreamBuilder` only and does not make
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change on filesystem immediately. When `build()` is invoked on the `FSDataOutputStreamBuilder`,
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changes on the filesystem immediately. When `build()` is invoked on the `FSDataOutputStreamBuilder`,
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the builder parameters are verified and [`create(Path p)`](#FileSystem.create)
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is invoked on the underlying filesystem. `build()` has the same preconditions
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and postconditions as [`create(Path p)`](#FileSystem.create).
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* Similar to [`create(Path p)`](#FileSystem.create), files are overwritten
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by default, unless specify `builder.overwrite(false)`.
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by default, unless specified by `builder.overwrite(false)`.
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* Unlike [`create(Path p)`](#FileSystem.create), missing parent directories are
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not created by default, unless specify `builder.recursive()`.
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not created by default, unless specified by `builder.recursive()`.
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### <a name='FileSystem.append'></a> `FSDataOutputStream append(Path p, int bufferSize, Progressable progress)`
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@ -780,14 +780,14 @@ Implementations without a compliant call SHOULD throw `UnsupportedOperationExcep
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if not exists(FS, p) : raise FileNotFoundException
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if not isFile(FS, p) : raise [FileAlreadyExistsException, FileNotFoundException, IOException]
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if not isFile(FS, p) : raise {FileAlreadyExistsException, FileNotFoundException, IOException}
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#### Postconditions
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FS' = FS
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result = FSDataOutputStream
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Return: `FSDataOutputStream`, which can update the entry `FS.Files[p]`
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Return: `FSDataOutputStream`, which can update the entry `FS'.Files[p]`
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by appending data to the existing list.
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The behavior of the returned stream is covered in [Output](outputstream.html).
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@ -813,7 +813,7 @@ Implementations without a compliant call SHOULD throw `UnsupportedOperationExcep
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#### Preconditions
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if not isFile(FS, p)) : raise [FileNotFoundException, IOException]
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if not isFile(FS, p)) : raise {FileNotFoundException, IOException}
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This is a critical precondition. Implementations of some FileSystems (e.g.
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Object stores) could shortcut one round trip by postponing their HTTP GET
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@ -842,7 +842,7 @@ The result MUST be the same for local and remote callers of the operation.
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symbolic links
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1. HDFS throws `IOException("Cannot open filename " + src)` if the path
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exists in the metadata, but no copies of any its blocks can be located;
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exists in the metadata, but no copies of its blocks can be located;
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-`FileNotFoundException` would seem more accurate and useful.
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### `FSDataInputStreamBuilder openFile(Path path)`
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@ -861,7 +861,7 @@ Implementations without a compliant call MUST throw `UnsupportedOperationExcepti
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let stat = getFileStatus(Path p)
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let FS' where:
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(FS.Directories', FS.Files', FS.Symlinks')
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(FS'.Directories, FS.Files', FS'.Symlinks)
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p' in paths(FS') where:
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exists(FS, stat.path) implies exists(FS', p')
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@ -931,16 +931,16 @@ metadata in the `PathHandle` to detect references from other namespaces.
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### `FSDataInputStream open(PathHandle handle, int bufferSize)`
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Implementaions without a compliant call MUST throw `UnsupportedOperationException`
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Implementations without a compliant call MUST throw `UnsupportedOperationException`
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#### Preconditions
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let fd = getPathHandle(FileStatus stat)
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if stat.isdir : raise IOException
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let FS' where:
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(FS.Directories', FS.Files', FS.Symlinks')
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p' in FS.Files' where:
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FS.Files'[p'] = fd
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(FS'.Directories, FS.Files', FS'.Symlinks)
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p' in FS'.Files where:
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FS'.Files[p'] = fd
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if not exists(FS', p') : raise InvalidPathHandleException
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The implementation MUST resolve the referent of the `PathHandle` following
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@ -951,7 +951,7 @@ encoded in the `PathHandle`.
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#### Postconditions
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result = FSDataInputStream(0, FS.Files'[p'])
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result = FSDataInputStream(0, FS'.Files[p'])
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The stream returned is subject to the constraints of a stream returned by
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`open(Path)`. Constraints checked on open MAY hold to hold for the stream, but
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@ -1006,7 +1006,7 @@ A directory with children and `recursive == False` cannot be deleted
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If the file does not exist the filesystem state does not change
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if not exists(FS, p):
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if not exists(FS, p) :
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FS' = FS
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result = False
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@ -1089,7 +1089,7 @@ Some of the object store based filesystem implementations always return
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false when deleting the root, leaving the state of the store unchanged.
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if isRoot(p) :
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FS ' = FS
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FS' = FS
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result = False
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This is irrespective of the recursive flag status or the state of the directory.
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@ -1152,7 +1152,7 @@ has been calculated.
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Source `src` must exist:
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exists(FS, src) else raise FileNotFoundException
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if not exists(FS, src) : raise FileNotFoundException
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`dest` cannot be a descendant of `src`:
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@ -1162,7 +1162,7 @@ This implicitly covers the special case of `isRoot(FS, src)`.
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`dest` must be root, or have a parent that exists:
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isRoot(FS, dest) or exists(FS, parent(dest)) else raise IOException
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if not (isRoot(FS, dest) or exists(FS, parent(dest))) : raise IOException
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The parent path of a destination must not be a file:
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@ -1240,7 +1240,8 @@ There is no consistent behavior here.
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The outcome is no change to FileSystem state, with a return value of false.
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FS' = FS; result = False
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FS' = FS
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result = False
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*Local Filesystem*
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@ -1319,28 +1320,31 @@ Implementations without a compliant call SHOULD throw `UnsupportedOperationExcep
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All sources MUST be in the same directory:
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for s in sources: if parent(S) != parent(p) raise IllegalArgumentException
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for s in sources:
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if parent(s) != parent(p) : raise IllegalArgumentException
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All block sizes must match that of the target:
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for s in sources: getBlockSize(FS, S) == getBlockSize(FS, p)
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for s in sources:
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getBlockSize(FS, s) == getBlockSize(FS, p)
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No duplicate paths:
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not (exists p1, p2 in (sources + [p]) where p1 == p2)
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let input = sources + [p]
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not (exists i, j: i != j and input[i] == input[j])
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HDFS: All source files except the final one MUST be a complete block:
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for s in (sources[0:length(sources)-1] + [p]):
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(length(FS, s) mod getBlockSize(FS, p)) == 0
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(length(FS, s) mod getBlockSize(FS, p)) == 0
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#### Postconditions
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FS' where:
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(data(FS', T) = data(FS, T) + data(FS, sources[0]) + ... + data(FS, srcs[length(srcs)-1]))
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and for s in srcs: not exists(FS', S)
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(data(FS', p) = data(FS, p) + data(FS, sources[0]) + ... + data(FS, sources[length(sources)-1]))
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for s in sources: not exists(FS', s)
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HDFS's restrictions may be an implementation detail of how it implements
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@ -1360,7 +1364,7 @@ Implementations without a compliant call SHOULD throw `UnsupportedOperationExcep
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if not exists(FS, p) : raise FileNotFoundException
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if isDir(FS, p) : raise [FileNotFoundException, IOException]
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if isDir(FS, p) : raise {FileNotFoundException, IOException}
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if newLength < 0 || newLength > len(FS.Files[p]) : raise HadoopIllegalArgumentException
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@ -1369,8 +1373,7 @@ Truncate cannot be performed on a file, which is open for writing or appending.
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#### Postconditions
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FS' where:
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len(FS.Files[p]) = newLength
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len(FS'.Files[p]) = newLength
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Return: `true`, if truncation is finished and the file can be immediately
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opened for appending, or `false` otherwise.
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@ -1399,7 +1402,7 @@ Source and destination must be different
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if src = dest : raise FileExistsException
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```
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Destination and source must not be descendants one another
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Destination and source must not be descendants of one another
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```python
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if isDescendant(src, dest) or isDescendant(dest, src) : raise IOException
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```
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@ -1429,7 +1432,7 @@ Given a base path on the source `base` and a child path `child` where `base` is
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```python
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def final_name(base, child, dest):
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is base = child:
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if base == child:
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return dest
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else:
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return dest + childElements(base, child)
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@ -1557,7 +1560,7 @@ while (iterator.hasNext()) {
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As raising exceptions is an expensive operation in JVMs, the `while(hasNext())`
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loop option is more efficient. (see also [Concurrency and the Remote Iterator](#RemoteIteratorConcurrency)
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for a dicussion on this topic).
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for a discussion on this topic).
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Implementors of the interface MUST support both forms of iterations; authors
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of tests SHOULD verify that both iteration mechanisms work.
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@ -55,7 +55,7 @@ with access functions:
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file as returned by `FileSystem.getFileStatus(Path p)`
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forall p in dom(FS.Files[p]) :
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len(data(FSDIS)) == FS.getFileStatus(p).length
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len(data(FSDIS)) == FS.getFileStatus(p).length
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### `Closeable.close()`
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@ -259,8 +259,8 @@ Examples: `RawLocalFileSystem` , `HttpFSFileSystem`
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If the operation is supported and there is a new location for the data:
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FSDIS' = (pos, data', true)
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result = True
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FSDIS' = (pos, data', true)
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result = True
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The new data is the original data (or an updated version of it, as covered
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in the Consistency section below), but the block containing the data at `offset`
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@ -268,7 +268,7 @@ is sourced from a different replica.
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If there is no other copy, `FSDIS` is not updated; the response indicates this:
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result = False
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result = False
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Outside of test methods, the primary use of this method is in the {{FSInputChecker}}
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class, which can react to a checksum error in a read by attempting to source
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@ -108,21 +108,21 @@ such as `rename`.
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## Defining the Filesystem
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A filesystem `FS` contains a set of directories, a dictionary of paths and a dictionary of symbolic links
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A filesystem `FS` contains directories (a set of paths), files (a mapping of a path to a list of bytes) and symlinks (a set of paths mapping to paths)
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(Directories:Set[Path], Files:[Path:List[byte]], Symlinks:Set[Path])
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(Directories:Set[Path], Files:Map[Path:List[byte]], Symlinks:Map[Path:Path])
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Accessor functions return the specific element of a filesystem
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def FS.Directories = FS.Directories
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def directories(FS) = FS.Directories
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def files(FS) = FS.Files
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def symlinks(FS) = FS.Symlinks
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def symlinks(FS) = keys(FS.Symlinks)
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def filenames(FS) = keys(FS.Files)
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The entire set of a paths finite subset of all possible Paths, and functions to resolve a path to data, a directory predicate or a symbolic link:
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def paths(FS) = FS.Directories + filenames(FS) + FS.Symlinks)
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def paths(FS) = FS.Directories + filenames(FS) + symlinks(FS)
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A path is deemed to exist if it is in this aggregate set:
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@ -169,10 +169,10 @@ in a set, hence no children with duplicate names.
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A path *D* is a descendant of a path *P* if it is the direct child of the
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path *P* or an ancestor is a direct child of path *P*:
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def isDescendant(P, D) = parent(D) == P where isDescendant(P, parent(D))
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def isDescendant(P, D) = parent(D) == P or isDescendant(P, parent(D))
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The descendants of a directory P are all paths in the filesystem whose
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path begins with the path P -that is their parent is P or an ancestor is P
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path begins with the path P, i.e. their parent is P or an ancestor is P
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def descendants(FS, D) = {p for p in paths(FS) where isDescendant(D, p)}
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@ -181,7 +181,7 @@ path begins with the path P -that is their parent is P or an ancestor is P
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A path MAY refer to a file that has data in the filesystem; its path is a key in the data dictionary
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def isFile(FS, p) = p in FS.Files
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def isFile(FS, p) = p in keys(FS.Files)
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### Symbolic references
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@ -193,6 +193,10 @@ A path MAY refer to a symbolic link:
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### File Length
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Files store data:
|
||||
|
||||
def data(FS, p) = files(FS)[p]
|
||||
|
||||
The length of a path p in a filesystem FS is the length of the data stored, or 0 if it is a directory:
|
||||
|
||||
def length(FS, p) = if isFile(p) : return length(data(FS, p)) else return 0
|
||||
@ -215,9 +219,9 @@ This may differ from the local user account name.
|
||||
A path cannot refer to more than one of a file, a directory or a symbolic link
|
||||
|
||||
|
||||
FS.Directories ^ keys(data(FS)) == {}
|
||||
FS.Directories ^ symlinks(FS) == {}
|
||||
keys(data(FS))(FS) ^ symlinks(FS) == {}
|
||||
directories(FS) ^ filenames(FS) == {}
|
||||
directories(FS) ^ symlinks(FS) == {}
|
||||
filenames(FS) ^ symlinks(FS) == {}
|
||||
|
||||
|
||||
This implies that only files may have data.
|
||||
@ -248,7 +252,7 @@ For all files in an encrypted zone, the data is encrypted, but the encryption
|
||||
type and specification are not defined.
|
||||
|
||||
forall f in files(FS) where inEncyptionZone(FS, f):
|
||||
isEncrypted(data(f))
|
||||
isEncrypted(data(FS, f))
|
||||
|
||||
|
||||
## Notes
|
||||
|
||||
@ -80,15 +80,15 @@ are used as the basis for this syntax as it is both plain ASCII and well-known.
|
||||
|
||||
##### Lists
|
||||
|
||||
* A list *L* is an ordered sequence of elements `[e1, e2, ... en]`
|
||||
* A list *L* is an ordered sequence of elements `[e1, e2, ... e(n)]`
|
||||
* The size of a list `len(L)` is the number of elements in a list.
|
||||
* Items can be addressed by a 0-based index `e1 == L[0]`
|
||||
* Python slicing operators can address subsets of a list `L[0:3] == [e1,e2]`, `L[:-1] == en`
|
||||
* Python slicing operators can address subsets of a list `L[0:3] == [e1,e2,e3]`, `L[:-1] == [e1, ... e(n-1)]`
|
||||
* Lists can be concatenated `L' = L + [ e3 ]`
|
||||
* Lists can have entries removed `L' = L - [ e2, e1 ]`. This is different from Python's
|
||||
`del` operation, which operates on the list in place.
|
||||
* The membership predicate `in` returns true iff an element is a member of a List: `e2 in L`
|
||||
* List comprehensions can create new lists: `L' = [ x for x in l where x < 5]`
|
||||
* List comprehensions can create new lists: `L' = [ x for x in L where x < 5]`
|
||||
* for a list `L`, `len(L)` returns the number of elements.
|
||||
|
||||
|
||||
@ -130,7 +130,7 @@ Strings are lists of characters represented in double quotes. e.g. `"abc"`
|
||||
|
||||
All system state declarations are immutable.
|
||||
|
||||
The suffix "'" (single quote) is used as the convention to indicate the state of the system after an operation:
|
||||
The suffix "'" (single quote) is used as the convention to indicate the state of the system after a mutating operation:
|
||||
|
||||
L' = L + ['d','e']
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user