SizeFS is a mock filesystem for creating files of particular sizes with specified contents.
Project description
A mock Filesystem that exists in memory only and allows for the creation of files of a size specified by the filename.
For example, reading a file named 128M+1B will return a file of 128 Megabytes plus 1 byte, reading a file named 128M-1B will return a file of 128 Megabytes minus 1 byte
Within the filesystem one level of folders may be created. Each of these folders can have its extended attributes set to determine the default contents of each file within the folder. The attributes of individual files may be overridden, and, when mounted as a filesystem using fuse, should be set using ‘xattr’ for OS X, or ‘attr’ for Linux. The attributes are described below in the ‘Extended Usage’ section.
Files may only be created within the folders and can only be named with a valid size descriptor. The names of the files should be a number followed by one of the letters B, K, M, G, T, P or E (to mean bytes, kilobytes, megabytes …). Optionally an addition or subtraction may be specified to modify the base size of the file.
Examples of valid filenames:
100K - A 100 kilobyte file. 4M - A 4 megabyte file. 2G-1B - A file 1 byte smaller than 2 gigabytes. 100K+10K - A file 10 kilobytes larger than 100 kilobytes. 10E - A ten exabyte file (yes really!)
File contents are generated as they are read, so it is entirely possible to ‘create’ files that are larger than any available RAM or HD storage. This can be very useful for testing large external storage systems, and the +/- operations are useful for exploring file size limitations without having to specify a file size as a huge number of bytes. The contents of each file are specified by a set of regular expressions that are initially inherited from the containing folder.
Example Usage
Create Size File objects in memory:
from sizefs import SizeFS sfs = SizeFS() sfs.read('/1B', 1, 0, None) sfs.read('/2B', 2, 0, None) sfs.read('/2K', 1024, 0, None) sfs.read('/128K', 1024*128, 0, None) sfs.read('/4G', 4*1024*1024, 0, None)
The folder structure is used to determine the content of the files:
sfs.read('/zeros/5B', 5, 0, None).read(0, 5) out> 00000 sfs.read('/ones/5B', 5, 0, None).read(0, 5) out> 11111 sfs.read('/alpha_num/5B', 5, 0, None).read(0, 5) out> TMdEv
Folders can be created to manipulate the data:
sfs.mkdir('/regex1', None) sfs.setxattr('/regex1', 'filler', '0', None) print sfs.read('/alpha_num/5B', 5, 0, None).read(0, 5) out> 00000 sfs.mkdir('/regex2', None) sfs.setxattr('/regex2', 'filler', '1', None) print sfs.read('/regex2/5B', 5, 0, None).read(0, 5) out> 11111 sfs.mkdir('/regex3', None) sfs.setxattr('/regex3', 'filler', '[a-zA-Z0-9]', None) print sfs.read('/regex3/5B', 5, 0, None).read(0, 5) out> 1JAbd
Files can be added to SizeFS using sfs.create:
sfs.mkdir('/regex3', None) sfs.setxattr('/regex3', 'filler', '[a-zA-Z0-9]', None) sfs.create('/regex3/5B', None) print sfs.read('/regex3/5B', 5, 0, None) out> aS8yG sfs.create('/regex3/128K', None) print len(sfs.read('/regex3/128K', 128*1024, 0, None)) out> 131072 sfs.create('/regex3/128K-1B', None) print len(sfs.read('/regex3/128K-1B', 128*1024, 0, None)) out> 131071 sfs.create('/regex3/128K+1B', None) print len(sfs.read('/alphanum/128K+1B', 128*1024+1, 0, None)) out> 131073
File content can be generated that matches a regex pattern by adding a directory
sfs.mkdir('/regex1') sfs.setxattr('/regex1','filler','a(bcd)*e{4}[a-z03]*') sfs.create('/regex1','128K') print len(sfs.open('regex1/128KB').read(0, 128*1024)) out> 131072 sfs.create('/regex1','128K-1B') print len(sfs.open('regex1/128K-1B').read(0, 128*1024-1)) out> 131071 sfs.create('/regex1','128K+1B') print len(sfs.open('regex1/128KB+1B').read(0, 128*1024+1)) out> 131073
Extended Usage
We can set up to 5 properties:
prefix - defined pattern for the start of a file (default = "") suffix - defined pattern for the end of a file (default = "") filler - repeating pattern to fill file content (default = 0) padder - single character to fill between content and footer (default = 0) max_random - the largest number a + or * will resolve to
Where ‘prefix’, ‘suffix’, ‘filler’, and ‘padder’ conform to the following grammar:
<Regex> ::= <Pattern> <Pattern> ::= <Expression> | <Expression> <Pattern> <Expression> ::= <Char> [<Multiplier>] | "(" <Pattern> ")" [<Multiplier>] | "[" <Set> "]" [<Multiplier>] <Multiplier> ::= "*" | "+" | "?" | '{' <Num> '}' <Set> ::= <Char> | <Char> "-" <Char> | <Set> <Set>
If the requested file sizes are too small for the combination of header, footer and some padding, then a warning will be logged, but the file will still return as much content as possible to fill the exact file size requested.
The file contents will always match the following pattern:
^prefix(filler)*(padder)*suffix$
The generator will always produce a string containing the prefix and suffix if a file of sufficient size is requested. Following that, the generator will fill the remaining space with ‘filler’ generated as many times as can be contained. If a filler pattern is generated that does not fit within the remaining space the remainder is filled using the (possibly incomplete) padder pattern. The padder pattern will only be used if a complete filler pattern will not fit in the space remaining.
‘max_random’ is used to define the largest random repeat factor of any + or * operators.
Random seeks within a file may produce inconsistent results for general file contents, however prefix and suffix will always be consistent with the requested pattern.
Testing
Requires nose
From the command line:
nosetests
Mounting as a filesystem
Mac Mounting - http://osxfuse.github.com/
From the command line:
python ./sizefs.py <mount_point>
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