Data.Text.Encoding

Copyright	(c) 2009 2010 2011 Bryan O'Sullivan (c) 2009 Duncan Coutts (c) 2008 2009 Tom Harper
License	BSD-style
Maintainer	[email protected]
Portability	portable
Safe Haskell	Trustworthy
Language	Haskell2010

Decoding ByteStrings to Text

All of the single-parameter functions for decoding bytestrings encoded in one of the Unicode Transformation Formats (UTF) operate in a strict mode: each will throw an exception if given invalid input.

Each function has a variant, whose name is suffixed with -With, that gives greater control over the handling of decoding errors. For instance, decodeUtf8 will throw an exception, but decodeUtf8With allows the programmer to determine what to do on a decoding error.

decodeASCII :: ByteString -> Text Source

Deprecated. Decode a ByteString containing 7-bit ASCII encoded text.

decodeLatin1 :: ByteString -> Text Source

Decode a ByteString containing Latin-1 (aka ISO-8859-1) encoded text.

decodeLatin1 is semantically equivalent to Data.Text.pack . Data.ByteString.Char8.unpack

decodeUtf8 :: ByteString -> Text Source

Decode a ByteString containing UTF-8 encoded text that is known to be valid.

If the input contains any invalid UTF-8 data, an exception will be thrown that cannot be caught in pure code. For more control over the handling of invalid data, use decodeUtf8' or decodeUtf8With.

decodeUtf16LE :: ByteString -> Text Source

Decode text from little endian UTF-16 encoding.

If the input contains any invalid little endian UTF-16 data, an exception will be thrown. For more control over the handling of invalid data, use decodeUtf16LEWith.

decodeUtf16BE :: ByteString -> Text Source

Decode text from big endian UTF-16 encoding.

If the input contains any invalid big endian UTF-16 data, an exception will be thrown. For more control over the handling of invalid data, use decodeUtf16BEWith.

decodeUtf32LE :: ByteString -> Text Source

Decode text from little endian UTF-32 encoding.

If the input contains any invalid little endian UTF-32 data, an exception will be thrown. For more control over the handling of invalid data, use decodeUtf32LEWith.

decodeUtf32BE :: ByteString -> Text Source

Decode text from big endian UTF-32 encoding.

If the input contains any invalid big endian UTF-32 data, an exception will be thrown. For more control over the handling of invalid data, use decodeUtf32BEWith.

Catchable failure

decodeUtf8' :: ByteString -> Either UnicodeException Text Source

Decode a ByteString containing UTF-8 encoded text.

If the input contains any invalid UTF-8 data, the relevant exception will be returned, otherwise the decoded text.

Controllable error handling

decodeUtf8With :: OnDecodeError -> ByteString -> Text Source

Decode a ByteString containing UTF-8 encoded text.

NOTE: The replacement character returned by OnDecodeError MUST be within the BMP plane; surrogate code points will automatically be remapped to the replacement char U+FFFD (since 0.11.3.0), whereas code points beyond the BMP will throw an error (since 1.2.3.1); For earlier versions of text using those unsupported code points would result in undefined behavior.

decodeUtf16LEWith :: OnDecodeError -> ByteString -> Text Source

Decode text from little endian UTF-16 encoding.

decodeUtf16BEWith :: OnDecodeError -> ByteString -> Text Source

Decode text from big endian UTF-16 encoding.

decodeUtf32LEWith :: OnDecodeError -> ByteString -> Text Source

Decode text from little endian UTF-32 encoding.

decodeUtf32BEWith :: OnDecodeError -> ByteString -> Text Source

Decode text from big endian UTF-32 encoding.

Stream oriented decoding

The streamDecodeUtf8 and streamDecodeUtf8With functions accept a ByteString that represents a possibly incomplete input (e.g. a packet from a network stream) that may not end on a UTF-8 boundary.

1. The maximal prefix of Text that could be decoded from the given input.
2. The suffix of the ByteString that could not be decoded due to insufficient input.
3. A function that accepts another ByteString. That string will be assumed to directly follow the string that was passed as input to the original function, and it will in turn be decoded.

To help understand the use of these functions, consider the Unicode string "hi ☃". If encoded as UTF-8, this becomes "hi \xe2\x98\x83"; the final '☃' is encoded as 3 bytes.

Now suppose that we receive this encoded string as 3 packets that are split up on untidy boundaries: ["hi \xe2", "\x98", "\x83"]. We cannot decode the entire Unicode string until we have received all three packets, but we would like to make progress as we receive each one.

ghci> let s0@(Some _ _ f0) = streamDecodeUtf8 "hi \xe2"
ghci> s0
Some "hi " "\xe2" _

We use the continuation f0 to decode our second packet.

ghci> let s1@(Some _ _ f1) = f0 "\x98"
ghci> s1
Some "" "\xe2\x98"

We could not give f0 enough input to decode anything, so it returned an empty string. Once we feed our second continuation f1 the last byte of input, it will make progress.

ghci> let s2@(Some _ _ f2) = f1 "\x83"
ghci> s2
Some "\x2603" "" _

If given invalid input, an exception will be thrown by the function or continuation where it is encountered.

streamDecodeUtf8 :: ByteString -> Decoding Source

Decode, in a stream oriented way, a ByteString containing UTF-8 encoded text that is known to be valid.

If the input contains any invalid UTF-8 data, an exception will be thrown (either by this function or a continuation) that cannot be caught in pure code. For more control over the handling of invalid data, use streamDecodeUtf8With.

Since: text-1.0.0.0

streamDecodeUtf8With :: OnDecodeError -> ByteString -> Decoding Source

Decode, in a stream oriented way, a ByteString containing UTF-8 encoded text.

Since: text-1.0.0.0

data Decoding Source

A stream oriented decoding result.

Since: text-1.0.0.0

Encoding Text to ByteStrings

encodeUtf8 :: Text -> ByteString Source

Encode text using UTF-8 encoding.

encodeUtf16LE :: Text -> ByteString Source

Encode text using little endian UTF-16 encoding.

encodeUtf16BE :: Text -> ByteString Source

Encode text using big endian UTF-16 encoding.

encodeUtf32LE :: Text -> ByteString Source

Encode text using little endian UTF-32 encoding.

encodeUtf32BE :: Text -> ByteString Source

Encode text using big endian UTF-32 encoding.

Encoding Text using ByteString Builders

encodeUtf8Builder :: Text -> Builder Source

Encode text to a ByteString Builder using UTF-8 encoding.

Since: text-1.1.0.0

encodeUtf8BuilderEscaped :: BoundedPrim Word8 -> Text -> Builder Source

Encode text using UTF-8 encoding and escape the ASCII characters using a BoundedPrim.

Use this function is to implement efficient encoders for text-based formats like JSON or HTML.

Since: text-1.1.0.0