HADOOP-18987. Various fixes to FileSystem API docs (#6292)

Contributed by Dieter De Paepe

hadoop-common-project/hadoop-common/src/site/markdown/filesystem/abortable.md

@@ -88,14 +88,13 @@ for example. output streams returned by the S3A FileSystem.
 The stream MUST implement `Abortable` and `StreamCapabilities`.
 
 ```python
- if unsupported:
+if unsupported:
   throw UnsupportedException
 
 if not isOpen(stream):
   no-op
 
 StreamCapabilities.hasCapability("fs.capability.outputstream.abortable") == True
-
 ```
 
 

hadoop-common-project/hadoop-common/src/site/markdown/filesystem/filesystem.md

@@ -64,13 +64,13 @@ a protected directory, result in such an exception being raised.
 
 ### `boolean isDirectory(Path p)`
 
-    def isDirectory(FS, p)= p in directories(FS)
+    def isDir(FS, p) = p in directories(FS)
 
 
 ### `boolean isFile(Path p)`
 
 
-    def isFile(FS, p) = p in files(FS)
+    def isFile(FS, p) = p in filenames(FS)
 
 
 ### `FileStatus getFileStatus(Path p)`
@@ -250,7 +250,7 @@ process.
  changes are made to the filesystem, the result of `listStatus(parent(P))` SHOULD
  include the value of `getFileStatus(P)`.
 
-* After an entry at path `P` is created, and before any other
+* After an entry at path `P` is deleted, and before any other
  changes are made to the filesystem, the result of `listStatus(parent(P))` SHOULD
  NOT include the value of `getFileStatus(P)`.
 
@@ -305,7 +305,7 @@ that they must all be listed, and, at the time of listing, exist.
 All paths must exist. There is no requirement for uniqueness.
 
     forall p in paths :
-      exists(fs, p) else raise FileNotFoundException
+      exists(FS, p) else raise FileNotFoundException
 
 #### Postconditions
 
@@ -381,7 +381,7 @@ being completely performed.
 
 Path `path` must exist:
 
-    exists(FS, path) : raise FileNotFoundException
+    if not exists(FS, path) : raise FileNotFoundException
 
 #### Postconditions
 
@@ -432,7 +432,7 @@ of data which must be collected in a single RPC call.
 
 #### Preconditions
 
-    exists(FS, path) else raise FileNotFoundException
+    if not exists(FS, path) : raise FileNotFoundException
 
 ### Postconditions
 
@@ -463,7 +463,7 @@ and 1 for file count.
 
 #### Preconditions
 
-    exists(FS, path) else raise FileNotFoundException
+    if not exists(FS, path) : raise FileNotFoundException
 
 #### Postconditions
 
@@ -567,7 +567,7 @@ when writing objects to a path in the filesystem.
 #### Postconditions
 
 
-    result = integer  >= 0
+    result = integer >= 0
 
 The outcome of this operation is usually identical to `getDefaultBlockSize()`,
 with no checks for the existence of the given path.
@@ -591,12 +591,12 @@ on the filesystem.
 
 #### Preconditions
 
-    if not exists(FS, p) :  raise FileNotFoundException
+    if not exists(FS, p) : raise FileNotFoundException
 
 
 #### Postconditions
 
-    if len(FS, P) > 0:  getFileStatus(P).getBlockSize() > 0
+    if len(FS, P) > 0 :  getFileStatus(P).getBlockSize() > 0
     result == getFileStatus(P).getBlockSize()
 
 1. The outcome of this operation MUST be identical to the value of
@@ -654,12 +654,12 @@ No ancestor may be a file
 
     forall d = ancestors(FS, p) : 
         if exists(FS, d) and not isDir(FS, d) :
-            raise [ParentNotDirectoryException, FileAlreadyExistsException, IOException]
+            raise {ParentNotDirectoryException, FileAlreadyExistsException, IOException}
 
 #### Postconditions
 
 
-    FS' where FS'.Directories' = FS.Directories + [p] + ancestors(FS, p)
+    FS' where FS'.Directories = FS.Directories + [p] + ancestors(FS, p)
     result = True
 
 
@@ -688,7 +688,7 @@ The return value is always true—even if a new directory is not created
 
 The file must not exist for a no-overwrite create:
 
-    if not overwrite and isFile(FS, p)  : raise FileAlreadyExistsException
+    if not overwrite and isFile(FS, p) : raise FileAlreadyExistsException
 
 Writing to or overwriting a directory must fail.
 
@@ -698,7 +698,7 @@ No ancestor may be a file
 
     forall d = ancestors(FS, p) : 
         if exists(FS, d) and not isDir(FS, d) :
-            raise [ParentNotDirectoryException, FileAlreadyExistsException, IOException]
+            raise {ParentNotDirectoryException, FileAlreadyExistsException, IOException}
 
 FileSystems may reject the request for other
 reasons, such as the FS being read-only  (HDFS),
@@ -712,8 +712,8 @@ For instance, HDFS may raise an `InvalidPathException`.
 #### Postconditions
 
     FS' where :
-       FS'.Files'[p] == []
-       ancestors(p) is-subset-of FS'.Directories'
+       FS'.Files[p] == []
+       ancestors(p) subset-of FS'.Directories
 
     result = FSDataOutputStream
 
@@ -734,7 +734,7 @@ The behavior of the returned stream is covered in [Output](outputstream.html).
  clients creating files with `overwrite==true` to fail if the file is created
  by another client between the two tests.
 
-* The S3A and potentially other Object Stores connectors not currently change the `FS` state
+* The S3A and potentially other Object Stores connectors currently don't change the `FS` state
 until the output stream `close()` operation is completed.
 This is a significant difference between the behavior of object stores
 and that of filesystems, as it allows >1 client to create a file with `overwrite=false`,
@@ -762,15 +762,15 @@ The behavior of the returned stream is covered in [Output](outputstream.html).
 #### Implementation Notes
 
 `createFile(p)` returns a `FSDataOutputStreamBuilder` only and does not make
-change on filesystem immediately. When `build()` is invoked on the `FSDataOutputStreamBuilder`,
+changes on the filesystem immediately. When `build()` is invoked on the `FSDataOutputStreamBuilder`,
 the builder parameters are verified and [`create(Path p)`](#FileSystem.create)
 is invoked on the underlying filesystem. `build()` has the same preconditions
 and postconditions as [`create(Path p)`](#FileSystem.create).
 
 * Similar to [`create(Path p)`](#FileSystem.create), files are overwritten
-by default, unless specify `builder.overwrite(false)`.
+by default, unless specified by `builder.overwrite(false)`.
 * Unlike [`create(Path p)`](#FileSystem.create), missing parent directories are
-not created by default, unless specify `builder.recursive()`.
+not created by default, unless specified by `builder.recursive()`.
 
 ### <a name='FileSystem.append'></a> `FSDataOutputStream append(Path p, int bufferSize, Progressable progress)`
 
@@ -780,14 +780,14 @@ Implementations without a compliant call SHOULD throw `UnsupportedOperationExcep
 
     if not exists(FS, p) : raise FileNotFoundException
 
-    if not isFile(FS, p) : raise [FileAlreadyExistsException, FileNotFoundException, IOException]
+    if not isFile(FS, p) : raise {FileAlreadyExistsException, FileNotFoundException, IOException}
 
 #### Postconditions
 
     FS' = FS
     result = FSDataOutputStream
 
-Return: `FSDataOutputStream`, which can update the entry `FS.Files[p]`
+Return: `FSDataOutputStream`, which can update the entry `FS'.Files[p]`
 by appending data to the existing list.
 
 The behavior of the returned stream is covered in [Output](outputstream.html).
@@ -813,7 +813,7 @@ Implementations without a compliant call SHOULD throw `UnsupportedOperationExcep
 
 #### Preconditions
 
-    if not isFile(FS, p)) : raise [FileNotFoundException, IOException]
+    if not isFile(FS, p)) : raise {FileNotFoundException, IOException}
 
 This is a critical precondition. Implementations of some FileSystems (e.g.
 Object stores) could shortcut one round trip by postponing their HTTP GET
@@ -842,7 +842,7 @@ The result MUST be the same for local and remote callers of the operation.
 symbolic links
 
 1. HDFS throws `IOException("Cannot open filename " + src)` if the path
-exists in the metadata, but no copies of any its blocks can be located;
+exists in the metadata, but no copies of its blocks can be located;
 -`FileNotFoundException` would seem more accurate and useful.
 
 ### `FSDataInputStreamBuilder openFile(Path path)`
@@ -861,7 +861,7 @@ Implementations without a compliant call MUST throw `UnsupportedOperationExcepti
 
     let stat = getFileStatus(Path p)
     let FS' where:
-      (FS.Directories', FS.Files', FS.Symlinks')
+      (FS'.Directories, FS.Files', FS'.Symlinks)
       p' in paths(FS') where:
         exists(FS, stat.path) implies exists(FS', p')
 
@@ -931,16 +931,16 @@ metadata in the `PathHandle` to detect references from other namespaces.
 
 ### `FSDataInputStream open(PathHandle handle, int bufferSize)`
 
-Implementaions without a compliant call MUST throw `UnsupportedOperationException`
+Implementations without a compliant call MUST throw `UnsupportedOperationException`
 
 #### Preconditions
 
     let fd = getPathHandle(FileStatus stat)
     if stat.isdir : raise IOException
     let FS' where:
-      (FS.Directories', FS.Files', FS.Symlinks')
-      p' in FS.Files' where:
-        FS.Files'[p'] = fd
+      (FS'.Directories, FS.Files', FS'.Symlinks)
+      p' in FS'.Files where:
+        FS'.Files[p'] = fd
     if not exists(FS', p') : raise InvalidPathHandleException
 
 The implementation MUST resolve the referent of the `PathHandle` following
@@ -951,7 +951,7 @@ encoded in the `PathHandle`.
 
 #### Postconditions
 
-    result = FSDataInputStream(0, FS.Files'[p'])
+    result = FSDataInputStream(0, FS'.Files[p'])
 
 The stream returned is subject to the constraints of a stream returned by
 `open(Path)`. Constraints checked on open MAY hold to hold for the stream, but
@@ -1006,7 +1006,7 @@ A directory with children and `recursive == False` cannot be deleted
 
 If the file does not exist the filesystem state does not change
 
-    if not exists(FS, p):
+    if not exists(FS, p) :
         FS' = FS
         result = False
 
@@ -1089,7 +1089,7 @@ Some of the object store based filesystem implementations always return
 false when deleting the root, leaving the state of the store unchanged.
 
     if isRoot(p) :
-        FS ' = FS
+        FS' = FS
         result = False
 
 This is irrespective of the recursive flag status or the state of the directory.
@@ -1152,7 +1152,7 @@ has been calculated.
 
 Source `src` must exist:
 
-    exists(FS, src) else raise FileNotFoundException
+    if not exists(FS, src) : raise FileNotFoundException
 
 `dest` cannot be a descendant of `src`:
 
@@ -1162,7 +1162,7 @@ This implicitly covers the special case of `isRoot(FS, src)`.
 
 `dest` must be root, or have a parent that exists:
 
-    isRoot(FS, dest) or exists(FS, parent(dest)) else raise IOException
+    if not (isRoot(FS, dest) or exists(FS, parent(dest))) : raise IOException
 
 The parent path of a destination must not be a file:
 
@@ -1240,7 +1240,8 @@ There is no consistent behavior here.
 
 The outcome is no change to FileSystem state, with a return value of false.
 
-    FS' = FS; result = False
+    FS' = FS
+    result = False
 
 *Local Filesystem*
 
@@ -1319,28 +1320,31 @@ Implementations without a compliant call SHOULD throw `UnsupportedOperationExcep
 
 All sources MUST be in the same directory:
 
-    for s in sources: if parent(S) != parent(p) raise IllegalArgumentException
+    for s in sources:
+        if parent(s) != parent(p) : raise IllegalArgumentException
 
 All block sizes must match that of the target:
 
-    for s in sources: getBlockSize(FS, S) == getBlockSize(FS, p)
+    for s in sources:
+        getBlockSize(FS, s) == getBlockSize(FS, p)
 
 No duplicate paths:
 
-    not (exists p1, p2 in (sources + [p]) where p1 == p2)
+    let input = sources + [p]
+    not (exists i, j: i != j and input[i] == input[j])
 
 HDFS: All source files except the final one MUST be a complete block:
 
     for s in (sources[0:length(sources)-1] + [p]):
-      (length(FS, s) mod getBlockSize(FS, p)) == 0
+        (length(FS, s) mod getBlockSize(FS, p)) == 0
 
 
 #### Postconditions
 
 
     FS' where:
-     (data(FS', T) = data(FS, T) + data(FS, sources[0]) + ... + data(FS, srcs[length(srcs)-1]))
-     and for s in srcs: not exists(FS', S)
+        (data(FS', p) = data(FS, p) + data(FS, sources[0]) + ... + data(FS, sources[length(sources)-1]))
+        for s in sources: not exists(FS', s)
 
 
 HDFS's restrictions may be an implementation detail of how it implements
@@ -1360,7 +1364,7 @@ Implementations without a compliant call SHOULD throw `UnsupportedOperationExcep
 
     if not exists(FS, p) : raise FileNotFoundException
 
-    if isDir(FS, p) : raise [FileNotFoundException, IOException]
+    if isDir(FS, p) : raise {FileNotFoundException, IOException}
 
     if newLength < 0 || newLength > len(FS.Files[p]) : raise HadoopIllegalArgumentException
 
@@ -1369,8 +1373,7 @@ Truncate cannot be performed on a file, which is open for writing or appending.
 
 #### Postconditions
 
-    FS' where:
-        len(FS.Files[p]) = newLength
+    len(FS'.Files[p]) = newLength
 
 Return: `true`, if truncation is finished and the file can be immediately
 opened for appending, or `false` otherwise.
@@ -1399,7 +1402,7 @@ Source and destination must be different
 if src = dest : raise FileExistsException
 ```
 
-Destination and source must not be descendants one another
+Destination and source must not be descendants of one another
 ```python
 if isDescendant(src, dest) or isDescendant(dest, src) : raise IOException
 ```
@@ -1429,7 +1432,7 @@ Given a base path on the source `base` and a child path `child` where `base` is
 
 ```python
 def final_name(base, child, dest):
-    is base = child:
+    if base == child:
         return dest
     else:
         return dest + childElements(base, child)
@@ -1557,7 +1560,7 @@ while (iterator.hasNext()) {
 
 As raising exceptions is an expensive operation in JVMs, the `while(hasNext())`
 loop option is more efficient. (see also [Concurrency and the Remote Iterator](#RemoteIteratorConcurrency)
-for a dicussion on this topic).
+for a discussion on this topic).
 
 Implementors of the interface MUST support both forms of iterations; authors
 of tests SHOULD verify that both iteration mechanisms work.

hadoop-common-project/hadoop-common/src/site/markdown/filesystem/fsdatainputstream.md

@@ -55,7 +55,7 @@ with access functions:
 file as returned by `FileSystem.getFileStatus(Path p)`
 
     forall p in dom(FS.Files[p]) :
-    len(data(FSDIS)) == FS.getFileStatus(p).length
+        len(data(FSDIS)) == FS.getFileStatus(p).length
 
 
 ### `Closeable.close()`
@@ -259,8 +259,8 @@ Examples: `RawLocalFileSystem` , `HttpFSFileSystem`
 
 If the operation is supported and there is a new location for the data:
 
-        FSDIS' = (pos, data', true)
-        result = True
+    FSDIS' = (pos, data', true)
+    result = True
 
 The new data is the original data (or an updated version of it, as covered
 in the Consistency section below), but the block containing the data at `offset`
@@ -268,7 +268,7 @@ is sourced from a different replica.
 
 If there is no other copy, `FSDIS` is  not updated; the response indicates this:
 
-        result = False
+    result = False
 
 Outside of test methods, the primary use of this method is in the {{FSInputChecker}}
 class, which can react to a checksum error in a read by attempting to source

hadoop-common-project/hadoop-common/src/site/markdown/filesystem/model.md

@@ -108,21 +108,21 @@ such as `rename`.
 ## Defining the Filesystem
 
 
-A filesystem `FS` contains a set of directories, a dictionary of paths and a dictionary of symbolic links
+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)
 
-    (Directories:Set[Path], Files:[Path:List[byte]], Symlinks:Set[Path])
+    (Directories:Set[Path], Files:Map[Path:List[byte]], Symlinks:Map[Path:Path])
 
 
 Accessor functions return the specific element of a filesystem
 
-    def FS.Directories  = FS.Directories
+    def directories(FS)  = FS.Directories
     def files(FS) = FS.Files
-    def symlinks(FS) = FS.Symlinks
+    def symlinks(FS) = keys(FS.Symlinks)
     def filenames(FS) = keys(FS.Files)
 
 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:
 
-    def paths(FS) = FS.Directories + filenames(FS) + FS.Symlinks)
+    def paths(FS) = FS.Directories + filenames(FS) + symlinks(FS)
 
 A path is deemed to exist if it is in this aggregate set:
 
@@ -169,10 +169,10 @@ in a set, hence no children with duplicate names.
 A path *D* is a descendant of a path *P* if it is the direct child of the
 path *P* or an ancestor is a direct child of path *P*:
 
-    def isDescendant(P, D) = parent(D) == P where isDescendant(P, parent(D))
+    def isDescendant(P, D) = parent(D) == P or isDescendant(P, parent(D))
 
 The descendants of a directory P are all paths in the filesystem whose
-path begins with the path P -that is their parent is P or an ancestor is P
+path begins with the path P, i.e. their parent is P or an ancestor is P
 
     def descendants(FS, D) = {p for p in paths(FS) where isDescendant(D, p)}
 
@@ -181,7 +181,7 @@ path begins with the path P -that is their parent is P or an ancestor is P
 
 A path MAY refer to a file that has data in the filesystem; its path is a key in the data dictionary
 
-    def isFile(FS, p) =  p in FS.Files
+    def isFile(FS, p) =  p in keys(FS.Files)
 
 
 ### Symbolic references
@@ -193,6 +193,10 @@ A path MAY refer to a symbolic link:
 
 ### File Length
 
+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

hadoop-common-project/hadoop-common/src/site/markdown/filesystem/notation.md

@@ -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']