Helpers for working with Bytes.Decoders.
Before the release of [elm/bytes], many packages would use List Int
to represent bytes. byteValues aids interaciton between those packages
and Bytes.
import Bytes exposing (Bytes)
import Bytes.Decode
import Bytes.Extra exposing (fromByteValues)
input : Bytes
input =
fromByteValues [ 0x32, 0xFF, 0x53, 0x54, 0x55 ]
Bytes.Decode.decode (byteValues 3) input
--> Just [ 0x32, 0xFF, 0x53 ]One notable use of 24-bit integers is in 24-bit color, a.k.a. "True color".
Decode three bytes into an integer from 0 to 16777215.
Decode three bytes into an integer from -8388608 to 8388607.
Json.Decode.Pipeline provides a neat, scalable way for
decoding JSON. This module provides a few helpers for adopting a similar style
when decoding Bytes.
It is important to note that decoding bytes poses more restrictions than
decoding JSON, as bytes are consumed in order, and a maximum of one time. This
makes an equivalent to Json.Decode.Pipeline.optional difficult to impossible.
import Bytes exposing (Endianness(..))
import Bytes.Decode exposing (Decoder, succeed, andThen, unsignedInt32, string, float64, decode)
import Bytes.Extra exposing (fromByteValues)
type Status = Downloaded | LocallyGenerated
type alias MyData =
{ id: Int
, status : Status
, name: String
, value: Float
}
myDataDecoder : Decoder MyData
myDataDecoder =
succeed MyData
|> andMap (unsignedInt32 BE)
|> hardcoded Downloaded
|> andMap (unsignedInt32 BE |> andThen string)
|> andMap (float64 BE)
decode myDataDecoder (fromByteValues [0,0,0,252,0,0,0,8,116,104,101,95,110,97,109,101,63,224,0,0,0,0,0,0])
--> Just
--> { id = 252
--> , status = Downloaded
--> , name = "the_name"
--> , value = 0.5
--> }andMap behaves in a similar way to Json.Decode.Pipeline.required. It is named andMap to match the naming of similar functions in other packages, and because this package does not provide an equivalent to Json.Decode.Pipeline.optional.
modelDecoder : Decoder Model
modelDecoder =
succeed Model
|> andMap (unsignedInt32 BE)
|> andMap (unsignedInt32 BE |> andThen string)
|> andMap myCustomTypeDecoder
|> andMap myCustomBooleanDecoderA neat way to fill in predetermined information that's not part of the data
being decoded, similar to Json.Decode.Pipeline.hardcoded.
modelDecoder : Decoder Model
modelDecoder =
succeed Model
|> andMap (unsignedInt32 BE)
|> andMap (unsignedInt32 BE |> andThen string)
|> hardcoded []
|> andMap myCustomBooleanDecoder
|> hardcoded SubModel.defaultTake a Decoder (Result err a) and make it fail if it decodes an Err.
Take a Decoder (Maybe a) and make it fail if it decodes to Nothing.
import Bytes.Extra exposing (fromByteValues)
import Bytes.Decode exposing (decode, map, string)
fromByteValues [ 0x30, 0x30, 0x30, 0x31, 0x30 ] -- "00010"
|> decode (onlyJusts (map String.toInt (string 5)))
--> Just 10
Run a decoder a set amount of times, and collect the result in a list.