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| [[Category:Libraries]]
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| Data Encodings (dataenc): A collection of data encoding algorithms.
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| == Data encodings library ==
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| The data encodings library strives to provide implementations in Haskell of every major data encoding, and a few minor ones as well. Currently the following encodings are implemented:
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| * Base16 (<hask>Codec.Binary.Base16</hask>)
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| * Base32 (<hask>Codec.Binary.Base32</hask>)
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| * Base32Hex (<hask>Codec.Binary.Base32Hex</hask>)
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| * Base64 (<hask>Codec.Binary.Base64</hask>)
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| * Base64Url (<hask>Codec.Binary.Base64Url</hask>)
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| * Uuencode (<hask>Codec.Binary.Uu</hask>)
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| In some cases the encodings also specify headers and footers for the encoded data. Implementation of that is left for the user of the library.
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| == The API ==
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| === Main API ===
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| The module <hask>Codec.Binary.DataEncoding</hask> provides a type that collects the functions for an individual encoding:
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| <haskell>
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| data DataCodec = DataCodec {
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| encode :: [Word8] -> String,
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| decode :: String -> Maybe [Word8],
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| decode' :: String -> [Maybe Word8],
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| chop :: Int -> String -> [String],
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| unchop :: [String] -> String
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| }
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| </haskell>
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| It also exposes instances of this type for each encoding:
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| <haskell>
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| base16 :: DataCodec
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| base32 :: DataCodec
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| base32Hex :: DataCodec
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| base64 :: DataCodec
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| base64Url :: DataCodec
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| uu :: DataCodec
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| </haskell>
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| <b>NB</b> There is no instance for yEncoding since the functions in that module have slightly different type signatures.
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| === Secondary API ===
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| Each individual encoding module is also exposed and offers four functions:
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|
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| <haskell>
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| encode :: [Word8] -> String
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| decode :: String -> Maybe [Word8]
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| decode' :: String -> [Maybe Word8]
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| chop :: Int -> String -> [String]
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| unchop :: [String] -> String
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| </haskell>
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|
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| == Description of the encodings ==
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| === Base16 ===
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| Implemented as it's defined in [http://tools.ietf.org/html/rfc4648 RFC 4648].
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| Each four bit nibble of an octet is encoded as a character in the set 0-9,A-F.
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| === Base32 ===
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| Implemented as it's defined in [http://tools.ietf.org/html/rfc4648 RFC 4648].
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| Five octets are expanded into eight so that only the five least significant bits are used. Each is then encoded into a 32-character encoding alphabet.
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| === Base32Hex ===
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| Implemented as it's defined in [http://tools.ietf.org/html/rfc4648 RFC 4648].
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| Just like Base32 but with a different encoding alphabet. Unlike Base64 and Base32, data encoded with Base32Hex maintains its sort order when the encoded data is compared bit wise.
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| === Base64 ===
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| Implemented as it's defined in [http://tools.ietf.org/html/rfc4648 RFC 4648].
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| Three octets are expanded into four so that only the six least significant bits are used. Each is then encoded into a 64-character encoding alphabet.
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| === Base64Url ===
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| Implemented as it's defined in [http://tools.ietf.org/html/rfc4648 RFC 4648].
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| Just like Base64 but with a different encoding alphabet. The encoding alphabet is made URL and filename safe by substituting <tt>+</tt> and <tt>/</tt> for <tt>-</tt> and <tt>_</tt> respectively.
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| === Uuencode ===
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| Unfortunately uuencode is badly specified and there are in fact several differing implementations of it. This implementation attempts to encode data in the same way as the <tt>uuencode</tt> utility found in [http://www.gnu.org/software/sharutils/ GNU's sharutils]. The workings of <hask>chop</hask> and <hask>unchop</hask> also follow how sharutils split and unsplit encoded lines.
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| === yEncoding ===
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| Implemented as it's defined in [http://yence.sourceforge.net/docs/protocol/version1_3_draft.html the 1.3 draft].
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| == Downloading ==
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| The current release is available from [http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dataenc HackageDB].
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| See [[#Contributing]] below for how to get the development version.
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| == Example of use ==
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| The package [http://hackage.haskell.org/cgi-bin/hackage-scripts/package/omnicodec omnicodec] contains two command line tools for encoding and decoding data.
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| == Contributing ==
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| Retrieve the source code using darcs like this:
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| darcs get http://code.haskell.org/dataenc/devo dataenc
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| Send any patches to magnus@therning.org
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