purescript-parsing-dataview

Primitive parsers for DataViews on JavaScript ArrayBuffers with the package purescript-parsing.

With this package, the input stream support of purescript-parsing is similar to the built-in stream support of Megaparsec:

Stream type	purescript-parsing	Megaparsec
UTF-16 strings	String	Text < v2.0
UTF-8 strings		Text ≥ v2.0
Listy strings	Token	String
Binary blobs	DataView	ByteString

Usage examples

Parse values out of a dataview :: Data.ArrayBuffer.Types.DataView. All DataView parsing must be done in an Effect context. The result will be Either a parse error or the parsed value.

Parse two numbers

Parse two big-endian IEEE 754 double-precision Numbers.

import Text.Parsing.Parser (runParserT)
import Text.Parsing.Parser.DataView (anyFloat64be)

do
  result <- runParserT dataview do
    float1 <- anyFloat64be
    float2 <- anyFloat64be
    pure $ Tuple float1 float2

Parse an array

Parse an array of n 32-bit big-endian signed Ints.

import Text.Parsing.Parser (runParserT)
import Text.Parsing.Parser.DataView (anyUint32be)
import Data.Unfoldable (replicateA)

do
  result <- runParserT dataview $ replicateA n anyInt32be

Parse UTF-8

Parse a UTF-8 String with a length prefix.

We give this as an example, rather than supporting it in the library, because it depends on Data.TextDecoding.decodeUtf8.

import Control.Monad.Trans.Class (lift)
import Data.ArrayBuffer.Types (DataView, Uint8Array)
import Data.ArrayBuffer.DataView (buffer, byteOffset, byteLength)
import Data.ArrayBuffer.Typed (part)
import Effect (Effect, liftEffect)
import Text.Parsing.Parser (runParserT, fail)
import Text.Parsing.Parser.DataView (anyUint32be, takeN)
import Data.UInt (toInt)
import Data.Text.Decoding (decodeUtf8)


-- Make a `Uint8Array` Typed Array from a `DataView`. We can do this
-- for the case of `Uint8` because byte arrays are always aligned.
mkUint8Array :: DataView -> Effect Uint8Array
mkUint8Array dv = part (buffer dv) (byteOffset dv) (byteLength dv)

do
  result <- runParserT dataview do
    -- Parse a 32-bit big-endian length prefix for the length
    -- of the UTF-8 string in bytes.
    length      <- anyUint32be
    stringview  <- takeN $ toInt length
    stringarray <- lift $ liftEffect $ mkUint8Array stringview
    case decodeUtf8 stringarray of
      Left err -> fail $ show err
      Right s  -> pure s

Serialization

This package is for reading (DataViews on) ArrayBuffers, not writing them. See the package arraybuffer-builder for a way to serialize and build ArrayBuffers.

References

Development

Run the tests with the development spago file:

spago -x spago-dev.dhall test

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