Codec.CBOR.Decoding · cborg-0.2.10.0

Decode primitive operations

4 declarations

newtypenewtype Decoder s a

A continuation-based decoder, used for decoding values that were previously encoded using the Codec.CBOR.Encoding module. As Decoder has a Monad instance, you can easily write Decoders monadically for building your deserialisation logic.

Instances4Monad, Functor, MonadFail, Applicative

Monad (Decoder s)Defined in cborg-0.2.10.0 · Codec.CBOR.Decoding
Functor (Decoder s)Defined in cborg-0.2.10.0 · Codec.CBOR.Decoding
MonadFail (Decoder s)Defined in cborg-0.2.10.0 · Codec.CBOR.Decoding
Applicative (Decoder s)Defined in cborg-0.2.10.0 · Codec.CBOR.Decoding

datadata DecodeAction s a

#

An action, representing a step for a decoder to taken and a continuation to invoke with the expected value.

Constructors

ConsumeWord (Word# -> ST s (DecodeAction s a))
ConsumeWord8 (Word# -> ST s (DecodeAction s a))
ConsumeWord16 (Word# -> ST s (DecodeAction s a))
ConsumeWord32 (Word# -> ST s (DecodeAction s a))
ConsumeNegWord (Word# -> ST s (DecodeAction s a))
ConsumeInt (Int# -> ST s (DecodeAction s a))
ConsumeInt8 (Int# -> ST s (DecodeAction s a))
ConsumeInt16 (Int# -> ST s (DecodeAction s a))
ConsumeInt32 (Int# -> ST s (DecodeAction s a))
ConsumeListLen (Int# -> ST s (DecodeAction s a))
ConsumeMapLen (Int# -> ST s (DecodeAction s a))
ConsumeTag (Word# -> ST s (DecodeAction s a))
ConsumeInteger (Integer -> ST s (DecodeAction s a))
ConsumeFloat (Float# -> ST s (DecodeAction s a))
ConsumeDouble (Double# -> ST s (DecodeAction s a))
ConsumeBytes (ByteString -> ST s (DecodeAction s a))
ConsumeByteArray (ByteArray -> ST s (DecodeAction s a))
ConsumeString (Text -> ST s (DecodeAction s a))
ConsumeUtf8ByteArray (ByteArray -> ST s (DecodeAction s a))
ConsumeBool (Bool -> ST s (DecodeAction s a))
ConsumeSimple (Word# -> ST s (DecodeAction s a))
ConsumeBytesIndef (ST s (DecodeAction s a))
ConsumeStringIndef (ST s (DecodeAction s a))
ConsumeListLenIndef (ST s (DecodeAction s a))
ConsumeMapLenIndef (ST s (DecodeAction s a))
ConsumeNull (ST s (DecodeAction s a))
ConsumeListLenOrIndef (Int# -> ST s (DecodeAction s a))
ConsumeMapLenOrIndef (Int# -> ST s (DecodeAction s a))
ConsumeBreakOr (Bool -> ST s (DecodeAction s a))
PeekTokenType (TokenType -> ST s (DecodeAction s a))
PeekAvailable (Int# -> ST s (DecodeAction s a))
PeekByteOffset (Int# -> ST s (DecodeAction s a))
ConsumeWordCanonical (Word# -> ST s (DecodeAction s a))
ConsumeWord8Canonical (Word# -> ST s (DecodeAction s a))
ConsumeWord16Canonical (Word# -> ST s (DecodeAction s a))
ConsumeWord32Canonical (Word# -> ST s (DecodeAction s a))
ConsumeNegWordCanonical (Word# -> ST s (DecodeAction s a))
ConsumeIntCanonical (Int# -> ST s (DecodeAction s a))
ConsumeInt8Canonical (Int# -> ST s (DecodeAction s a))
ConsumeInt16Canonical (Int# -> ST s (DecodeAction s a))
ConsumeInt32Canonical (Int# -> ST s (DecodeAction s a))
ConsumeListLenCanonical (Int# -> ST s (DecodeAction s a))
ConsumeMapLenCanonical (Int# -> ST s (DecodeAction s a))
ConsumeTagCanonical (Word# -> ST s (DecodeAction s a))
ConsumeIntegerCanonical (Integer -> ST s (DecodeAction s a))
ConsumeFloat16Canonical (Float# -> ST s (DecodeAction s a))
ConsumeFloatCanonical (Float# -> ST s (DecodeAction s a))
ConsumeDoubleCanonical (Double# -> ST s (DecodeAction s a))
ConsumeBytesCanonical (ByteString -> ST s (DecodeAction s a))
ConsumeByteArrayCanonical (ByteArray -> ST s (DecodeAction s a))
ConsumeStringCanonical (Text -> ST s (DecodeAction s a))
ConsumeUtf8ByteArrayCanonical (ByteArray -> ST s (DecodeAction s a))
ConsumeSimpleCanonical (Word# -> ST s (DecodeAction s a))
Fail String
Done a

valueliftST :: ST s a -> Decoder s a

#

Lift an ST action into a Decoder. Useful for, e.g., leveraging in-place mutation to efficiently build a deserialised value.

valuegetDecodeAction :: Decoder s a -> ST s (DecodeAction s a)

#

Given a Decoder, give us the DecodeAction

Read input tokens

valuedecodeWord :: Decoder s Word

#

Decode a Word.

valuedecodeWord8 :: Decoder s Word8

#

Decode a Word8.

valuedecodeWord16 :: Decoder s Word16

#

Decode a Word16.

valuedecodeWord32 :: Decoder s Word32

#

Decode a Word32.

valuedecodeWord64 :: Decoder s Word64

#

Decode a Word64.

valuedecodeNegWord :: Decoder s Word

#

Decode a negative Word.

valuedecodeNegWord64 :: Decoder s Word64

#

Decode a negative Word64.

valuedecodeInt :: Decoder s Int

#

Decode an Int.

valuedecodeInt8 :: Decoder s Int8

#

Decode an Int8.

valuedecodeInt16 :: Decoder s Int16

#

Decode an Int16.

valuedecodeInt32 :: Decoder s Int32

#

Decode an Int32.

valuedecodeInt64 :: Decoder s Int64

#

Decode an Int64.

valuedecodeInteger :: Decoder s Integer

#

Decode an Integer.

valuedecodeFloat :: Decoder s Float

#

Decode a Float.

valuedecodeDouble :: Decoder s Double

#

Decode a Double.

valuedecodeBytes :: Decoder s ByteString

#

Decode a string of bytes as a ByteString.

valuedecodeBytesIndef :: Decoder s ()

#

Decode a token marking the beginning of an indefinite length set of bytes.

valuedecodeByteArray :: Decoder s ByteArray

#

Decode a string of bytes as a ByteArray.

Also note that this will eagerly copy the content out of the input to ensure that the input does not leak in the event that the ByteArray is live but not forced.

valuedecodeString :: Decoder s Text

#

Decode a textual string as a piece of Text.

valuedecodeStringIndef :: Decoder s ()

#

Decode a token marking the beginning of an indefinite length string.

valuedecodeUtf8ByteArray :: Decoder s ByteArray

#

Decode a textual string as UTF-8 encoded ByteArray. Note that the result is not validated to be well-formed UTF-8.

Also note that this will eagerly copy the content out of the input to ensure that the input does not leak in the event that the ByteArray is live but not forced.

valuedecodeListLen :: Decoder s Int

#

Decode the length of a list.

valuedecodeListLenIndef :: Decoder s ()

#

Decode a token marking the beginning of a list of indefinite length.

valuedecodeMapLen :: Decoder s Int

#

Decode the length of a map.

valuedecodeMapLenIndef :: Decoder s ()

#

Decode a token marking the beginning of a map of indefinite length.

valuedecodeTag :: Decoder s Word

#

Decode an arbitrary tag and return it as a Word.

valuedecodeTag64 :: Decoder s Word64

#

Decode an arbitrary 64-bit tag and return it as a Word64.

valuedecodeBool :: Decoder s Bool

#

Decode a bool.

valuedecodeNull :: Decoder s ()

#

Decode a nullary value, and return a unit value.

valuedecodeSimple :: Decoder s Word8

#

Decode a simple CBOR value and give back a Word8. You probably don't ever need to use this.

Specialised Read input token operations

valuedecodeWordOf

:: Word
Expected value of the decoded word
-> Decoder s ()

#

Attempt to decode a word with decodeWord, and ensure the word is exactly as expected, or fail.

valuedecodeListLenOf :: Int -> Decoder s ()

#

Attempt to decode a list length using decodeListLen, and ensure it is exactly the specified length, or fail.

Branching operations

valuedecodeListLenOrIndef :: Decoder s (Maybe Int)

#

Attempt to decode a token for the length of a finite, known list, or an indefinite list. If Nothing is returned, then an indefinite length list occurs afterwords. If Just x is returned, then a list of length x is encoded.

valuedecodeMapLenOrIndef :: Decoder s (Maybe Int)

#

Attempt to decode a token for the length of a finite, known map, or an indefinite map. If Nothing is returned, then an indefinite length map occurs afterwords. If Just x is returned, then a map of length x is encoded.

valuedecodeBreakOr :: Decoder s Bool

#

Attempt to decode a Break token, and if that was successful, return True. If the token was of any other type, return False.

Inspecting the token type

valuepeekTokenType :: Decoder s TokenType

#

Peek at the current token we're about to decode, and return a TokenType specifying what it is.

datadata TokenType

#

The type of a token, which a decoder can ask for at an arbitrary time.

Instances5Bounded, Enum, Eq, Ord, Show

Bounded TokenTypeDefined in cborg-0.2.10.0 · Codec.CBOR.Decoding
Enum TokenTypeDefined in cborg-0.2.10.0 · Codec.CBOR.Decoding
Eq TokenTypeDefined in cborg-0.2.10.0 · Codec.CBOR.Decoding
Ord TokenTypeDefined in cborg-0.2.10.0 · Codec.CBOR.Decoding
Show TokenTypeDefined in cborg-0.2.10.0 · Codec.CBOR.Decoding

Special operations

valuepeekAvailable :: Decoder s Int

#

Peek and return the length of the current buffer that we're running our decoder on.

typetype ByteOffset = Int64

#

A 0-based offset within the overall byte sequence that makes up the input to the Decoder.

This is an Int64 since Decoder is incremental and can decode more data than fits in memory at once. This is also compatible with the result type of length.

valuepeekByteOffset :: Decoder s ByteOffset

#

Get the current ByteOffset in the input byte sequence of the Decoder.

The Decoder does not provide any facility to get at the input data directly (since that is tricky with an incremental decoder). The next best is this primitive which can be used to keep track of the offset within the input bytes that makes up the encoded form of a term.

By keeping track of the byte offsets before and after decoding a subterm (a pattern captured by decodeWithByteSpan) and if the overall input data is retained then this is enables later retrieving the span of bytes for the subterm.

valuedecodeWithByteSpan :: Decoder s a -> Decoder s (a, ByteOffset, ByteOffset)

#

This captures the pattern of getting the byte offsets before and after decoding a subterm.

!before <- peekByteOffset
x <- decode
!after  <- peekByteOffset

Canonical CBOR

https://tools.ietf.org/html/rfc7049#section-3.9

In general in CBOR there can be multiple representations for the same value, for example the integer 0 can be represented in 8, 16, 32 or 64 bits. This library always encoded values in the shortest representation but on decoding allows any valid encoding. For some applications it is useful or important to only decode the canonical encoding. The decoder primitives here are to allow applications to implement canonical decoding.

It is important to note that achieving a canonical representation is not simply about using these primitives. For example consider a typical CBOR encoding of a Haskell Set data type. This will be encoded as a CBOR list of the set elements. A typical implementation might be:

encodeSet = encodeList . Set.toList
decodeSet = fmap Set.fromList . decodeList

This does not enforce a canonical encoding. The decoder above will allow set elements in any order. The use of Set.fromList forgets the order. To enforce that the decoder only accepts the canonical encoding it will have to check that the elements in the list are strictly increasing. Similar issues arise in many other data types, wherever there is redundancy in the external representation.

The decoder primitives in this section are not much more expensive than their normal counterparts. If checking the canonical encoding property is critical then a technique that is more expensive but easier to implement and test is to decode normally, re-encode and check the serialised bytes are the same.

valuedecodeWordCanonical :: Decoder s Word

#

Decode canonical representation of a Word.

valuedecodeWord8Canonical :: Decoder s Word8

#

Decode canonical representation of a Word8.

valuedecodeWord16Canonical :: Decoder s Word16

#

Decode canonical representation of a Word16.

valuedecodeWord32Canonical :: Decoder s Word32

#

Decode canonical representation of a Word32.

valuedecodeWord64Canonical :: Decoder s Word64

#

Decode canonical representation of a Word64.

valuedecodeNegWordCanonical :: Decoder s Word

#

Decode canonical representation of a negative Word.

valuedecodeNegWord64Canonical :: Decoder s Word64

#

Decode canonical representation of a negative Word64.

valuedecodeIntCanonical :: Decoder s Int

#

Decode canonical representation of an Int.

valuedecodeInt8Canonical :: Decoder s Int8

#

Decode canonical representation of an Int8.

valuedecodeInt16Canonical :: Decoder s Int16

#

Decode canonical representation of an Int16.

valuedecodeInt32Canonical :: Decoder s Int32

#

Decode canonical representation of an Int32.

valuedecodeInt64Canonical :: Decoder s Int64

#

Decode canonical representation of an Int64.

valuedecodeBytesCanonical :: Decoder s ByteString

#

Decode canonical representation of a string of bytes as a ByteString.

valuedecodeByteArrayCanonical :: Decoder s ByteArray

#

Decode canonical representation of a string of bytes as a ByteArray.

Also note that this will eagerly copy the content out of the input to ensure that the input does not leak in the event that the ByteArray is live but not forced.

valuedecodeStringCanonical :: Decoder s Text

#

Decode canonical representation of a textual string as a piece of Text.

valuedecodeUtf8ByteArrayCanonical :: Decoder s ByteArray

#

Decode canonical representation of a textual string as UTF-8 encoded ByteArray. Note that the result is not validated to be well-formed UTF-8.

Also note that this will eagerly copy the content out of the input to ensure that the input does not leak in the event that the ByteArray is live but not forced.