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GHC 9.10.3 · lts/ghc-9.10.x · c74966e · 2026-09-27

Modulebase64-1.0Haskell2010

Data.ByteString.Lazy.Base64.URL

This module contains ByteString-valued combinators for implementing the RFC 4648 specification of the Base64url encoding format. This includes strictly padded/unpadded and lenient decoding variants, as well as internal and external validation for canonicity.

  • 13 values
  • Packagebase64-1.0
  • Exports13
  • LanguageHaskell2010
  • LicenceBSD-3-Clause
  • SourceURL.hs

Encoding

4 declarations

Decoding

7 declarations

Decode a Base64url encoded ByteString value, either padded or unpadded. The correct decoding function is dispatched based on the existence of padding.

For typed values: - If a padded value is required, use decodeBase64Padded - If an unpadded value is required, use decodeBase64Unpadded

See: RFC-4648 section 4

Examples:
Example1 expression
decodeBase64 $ assertBase64 @'UrlPadded "PDw_Pj4=""<<?>>"
Example1 expression
decodeBase64 $ assertBase64 @'UrlUnpadded "PDw_Pj4""<<?>>"
Example1 expression
decodeBase64 $ assertBase64 @'UrlUnpadded "PDw-Pg""<<>>"

Decode a padded Base64url encoded ByteString value. If its length is not a multiple of 4, then padding chars will be added to fill out the input to a multiple of 4 for safe decoding as Base64url-encoded values are optionally padded.

For a decoder that fails to decode untyped values of incorrect size: - If a padded value is required, use decodeBase64PaddedUntyped - If an unpadded value is required, use decodeBase64UnpaddedUntyped

See: RFC-4648 section 4

Examples:
Example1 expression
decodeBase64Untyped "PDw_Pj4="Right "<<?>>"
Example1 expression
decodeBase64Untyped "PDw_Pj4"Right "<<?>>"
Example1 expression
decodeBase64Untyped "PDw-Pg="Left "Base64-encoded bytestring has invalid padding"
Example1 expression
decodeBase64Untyped "PDw-Pg"Right "<<>>"

Decode an unpadded, untyped Base64url-encoded ByteString value. Input strings are required to be unpadded, and will undergo validation prior to decoding to confirm.

In general, unless unpadded Base64url is explicitly required, it is safer to call decodeBase64Untyped.

See: RFC-4648 section 4

Examples:
Example1 expression
decodeBase64UnpaddedUntyped "PDw_Pj4"Right "<<?>>"
Example1 expression
decodeBase64UnpaddedUntyped "PDw_Pj4="Left "Base64-encoded bytestring has invalid padding"

Decode a padded, untyped Base64url-encoded ByteString value. Input strings are required to be correctly padded, and will be validated prior to decoding to confirm.

In general, unless padded Base64url is explicitly required, it is safer to call decodeBase64.

See: RFC-4648 section 4

Examples:
Example1 expression
decodeBase64PaddedUntyped "PDw_Pj4="Right "<<?>>"
Example1 expression
decodeBase64PaddedUntyped "PDw_Pj4"Left "Base64-encoded bytestring requires padding"

Leniently decode an unpadded, untyped Base64url-encoded ByteString. 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:
Example1 expression
decodeBase64Lenient "PDw_Pj4=""<<?>>"
Example1 expression
decodeBase64Lenient "PDw_%%%$}Pj4""<<?>>"

Validation

2 declarations
valueisBase64Url :: ByteString -> Bool
#

Tell whether an untyped ByteString is Base64url-encoded.

Examples:
Example1 expression
isBase64Url "PDw_Pj4="True
Example1 expression
isBase64Url "PDw_Pj4"True
Example1 expression
isBase64Url "PDw_Pj"False

Tell whether an untyped ByteString is a valid Base64url format.

This will not tell you whether or not this is a correct Base64url representation, only that it conforms to the correct shape. To check whether it is a true Base64 encoded ByteString value, use isBase64Url.

Examples:
Example1 expression
isValidBase64Url "PDw_Pj4="True
Example1 expression
isValidBase64Url "PDw_Pj"True
Example1 expression
isValidBase64Url "%"False