Using Utf8JsonReader from System.Text.Json with FSharp

High-performance JSON parsing with System.Text.Json and F#

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// Example translated to F# from 
// https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/use-utf8jsonreader
#r "nuget:System.Text.Json"

open System
open System.Text
open System.Text.Json

let options = JsonReaderOptions(
                AllowTrailingCommas = true, 
                CommentHandling = JsonCommentHandling.Skip)

let readJson (jsonUtf8Bytes:ReadOnlySpan<byte>) =
    let reader = Utf8JsonReader(jsonUtf8Bytes, options)

    while reader.Read() do
        Console.WriteLine reader.TokenType
        match reader.TokenType with
        | JsonTokenType.PropertyName
        | JsonTokenType.String ->
            let text = reader.GetString()
            Console.Write " "
            Console.Write text
        | JsonTokenType.Number ->
            let intValue = reader.GetInt32()
            Console.Write " "
            Console.Write intValue
        | JsonTokenType.None | JsonTokenType.Null | JsonTokenType.Comment 
        | JsonTokenType.True | JsonTokenType.False
        | JsonTokenType.StartObject | JsonTokenType.EndObject
        | JsonTokenType.StartArray  | JsonTokenType.EndArray 
        | _ -> () // Other token types elided for brevity

    Console.WriteLine()

let sampleJson = 
    let jsonBytes = 
        """{ "x": 3 }""" 
        |> Encoding.UTF8.GetBytes
    readJson (System.ReadOnlySpan jsonBytes)

namespace System

namespace System.Text

namespace System.Text.Json

val options : JsonReaderOptions

[<Struct>]
type JsonReaderOptions =
  val ``<AllowTrailingCommas>k__BackingField`` : bool
  member AllowTrailingCommas : bool
  member CommentHandling : JsonCommentHandling
  member MaxDepth : int

type JsonCommentHandling =
  | Disallow = 0uy
  | Skip = 1uy
  | Allow = 2uy

field JsonCommentHandling.Skip: JsonCommentHandling = 1uy

val readJson : jsonUtf8Bytes:ReadOnlySpan<byte> -> unit

val jsonUtf8Bytes : ReadOnlySpan<byte>

Multiple items
val byte : value:'T -> byte (requires member op_Explicit)

--------------------
[<Struct>]
type byte = Byte

--------------------
type byte<'Measure> =
byte

val reader : Utf8JsonReader

Utf8JsonReader.Read() : bool

type Console =
  static member Beep : unit -> unit + 1 overload
  static member CheckNonNull : obj: obj * paramName: string -> unit
  static member Clear : unit -> unit
  static member CreateOutputWriter : outputStream: Stream -> TextWriter
  static member EnsureInitialized<'T (requires reference type)> : field: byref<'T> * initializer: Func<'T> -> 'T
  static member HandleBreakEvent : controlKey: ConsoleSpecialKey -> bool
  static member MoveBufferArea : sourceLeft: int * sourceTop: int * sourceWidth: int * sourceHeight: int * targetLeft: int * targetTop: int -> unit + 1 overload
  static member OpenStandardError : unit -> Stream + 1 overload
  static member OpenStandardInput : unit -> Stream + 1 overload
  static member OpenStandardOutput : unit -> Stream + 1 overload
  ...

Console.WriteLine() : unit
   (+0 other overloads)
Console.WriteLine(value: string) : unit
   (+0 other overloads)
Console.WriteLine(value: obj) : unit
   (+0 other overloads)
Console.WriteLine(value: uint64) : unit
   (+0 other overloads)
Console.WriteLine(value: int64) : unit
   (+0 other overloads)
Console.WriteLine(value: uint32) : unit
   (+0 other overloads)
Console.WriteLine(value: int) : unit
   (+0 other overloads)
Console.WriteLine(value: float32) : unit
   (+0 other overloads)
Console.WriteLine(value: float) : unit
   (+0 other overloads)
Console.WriteLine(value: decimal) : unit
   (+0 other overloads)

property Utf8JsonReader.TokenType: JsonTokenType with get

field JsonTokenType.PropertyName: JsonTokenType = 5uy

field JsonTokenType.String: JsonTokenType = 7uy

val text : string

Utf8JsonReader.GetString() : string

Console.Write(value: string) : unit
   (+0 other overloads)
Console.Write(value: obj) : unit
   (+0 other overloads)
Console.Write(value: uint64) : unit
   (+0 other overloads)
Console.Write(value: int64) : unit
   (+0 other overloads)
Console.Write(value: uint32) : unit
   (+0 other overloads)
Console.Write(value: int) : unit
   (+0 other overloads)
Console.Write(value: float32) : unit
   (+0 other overloads)
Console.Write(value: decimal) : unit
   (+0 other overloads)
Console.Write(value: float) : unit
   (+0 other overloads)
Console.Write(buffer: char []) : unit
   (+0 other overloads)

field JsonTokenType.Number: JsonTokenType = 8uy

val intValue : int

Utf8JsonReader.GetInt32() : int

field JsonTokenType.None: JsonTokenType = 0uy

field JsonTokenType.Null: JsonTokenType = 11uy

field JsonTokenType.Comment: JsonTokenType = 6uy

field JsonTokenType.True: JsonTokenType = 9uy

field JsonTokenType.False: JsonTokenType = 10uy

field JsonTokenType.StartObject: JsonTokenType = 1uy

field JsonTokenType.EndObject: JsonTokenType = 2uy

field JsonTokenType.StartArray: JsonTokenType = 3uy

field JsonTokenType.EndArray: JsonTokenType = 4uy

val sampleJson : unit

val jsonBytes : byte []

type Encoding =
  interface ICloneable
  new : unit -> unit + 2 overloads
  member Clone : unit -> obj
  member DecodeFirstRune : bytes: ReadOnlySpan<byte> * value: byref<Rune> * bytesConsumed: byref<int> -> OperationStatus
  member EncodeRune : value: Rune * bytes: Span<byte> * bytesWritten: byref<int> -> OperationStatus
  member Equals : value: obj -> bool
  member GetBestFitBytesToUnicodeData : unit -> char []
  member GetBestFitUnicodeToBytesData : unit -> char []
  member GetByteCount : chars: char [] -> int + 6 overloads
  member GetByteCountFast : pChars: nativeptr<char> * charsLength: int * fallback: EncoderFallback * charsConsumed: byref<int> -> int
  ...

property Encoding.UTF8: Encoding with get

Encoding.GetBytes(s: string) : byte []
Encoding.GetBytes(chars: char []) : byte []
Encoding.GetBytes(chars: ReadOnlySpan<char>, bytes: Span<byte>) : int
Encoding.GetBytes(s: string, index: int, count: int) : byte []
Encoding.GetBytes(chars: char [], index: int, count: int) : byte []
Encoding.GetBytes(chars: nativeptr<char>, charCount: int, bytes: nativeptr<byte>, byteCount: int) : int
Encoding.GetBytes(s: string, charIndex: int, charCount: int, bytes: byte [], byteIndex: int) : int
Encoding.GetBytes(chars: char [], charIndex: int, charCount: int, bytes: byte [], byteIndex: int) : int

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More information

Link:	http://fssnip.net/8a9
Posted:	5 months ago
Author:	Tuomas Hietanen
Tags:	json , parsing , reader , text