Data.Text.Encoding.Base64

This module contains Text-valued combinators for implementing the RFC 4648 specification of the Base64 encoding format. This includes lenient decoding variants, as well as internal and external validation for canonicity.

Encoding

encodeBase64 :: Text -> Text

Encode a Text value in Base64 with padding.

See: RFC-4648 section 4

Examples:

>>> encodeBase64 "Sun"
"U3Vu"

Decoding

decodeBase64 :: Text -> Either Text Text

Decode a padded Base64-encoded Text value.

Note: This function makes sure that decoding is total by deferring to decodeLatin1. This will always round trip for any valid Base64-encoded text value, but it may not round trip for bad inputs. The onus is on the caller to make sure inputs are valid. If unsure, defer to decodeBase64With and pass in a custom decode function.

See: RFC-4648 section 4

Examples:

>>> decodeBase64 "U3Vu"
Right "Sun"

>>> decodeBase64 "U3V"
Left "Base64-encoded bytestring requires padding"

>>> decodebase64 "U3V="
Left "non-canonical encoding detected at offset: 2"

decodeBase64With

Arguments

:: (ByteString -> Either err Text)

convert a bytestring to text (e.g. decodeUtf8')

-> ByteString

Input text to decode

-> Either (Base64Error err) Text

Attempt to decode a Text value as Base64, converting from ByteString to Text according to some encoding function. In practice, This is something like decodeUtf8', which may produce an error.

See: RFC-4648 section 4

Example:

decodeBase64With decodeUtf8'
  :: ByteString -> Either (Base64Error UnicodeException) Text

decodeBase64Lenient :: Text -> Text

Leniently decode a Base64-encoded Text value. This function will not generate parse errors. If input data contains padding chars, then the input will be parsed up until the first pad character.

Note: This is not RFC 4648-compliant.

Examples:

>>> decodeBase64Lenient "U3Vu"
"Sun"

>>> decodeBase64Lenient "U3V"
"Su"

>>> decodebase64Lenient "U3V="
"Su"

Validation

isBase64 :: Text -> Bool

Tell whether a Text value is Base64-encoded.

Examples:

>>> isBase64 "U3Vu"
True

>>> isBase64 "U3V"
False

>>> isBase64 "U3V="
False

isValidBase64 :: Text -> Bool

Tell whether a Text value is a valid Base64 format.

This will not tell you whether or not this is a correct Base64 representation, only that it conforms to the correct shape. To check whether it is a true Base64 encoded Text value, use isBase64.

Examples:

>>> isValidBase64 "U3Vu"
True

>>> isValidBase64 "U3V"
True

>>> isValidBase64 "U3V="
True

>>> isValidBase64 "%"
False