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FileStream F# snippets (#8873)
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‎snippets/fsharp/System.IO/FileOptions/Overview/example.fs

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module example
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//<SNIPPET1>
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open System
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open System.IO;
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open System.Text
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open System.Security.AccessControl;
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try
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// Create a file and write data to it.
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// Create an array of bytes.
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let messageByte = Encoding.ASCII.GetBytes "Here is some data."
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// Specify an access control list (ACL)
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let fs = FileSecurity()
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FileSystemAccessRule(@"DOMAINNAME\AccountName", FileSystemRights.ReadData, AccessControlType.Allow)
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|> fs.AddAccessRule
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// Create a file using the FileStream class.
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let fWrite = new FileStream("test.txt", FileMode.Create, FileSystemRights.Modify, FileShare.None, 8, FileOptions.None, fs)
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// Write the number of bytes to the file.
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byte messageByte.Length
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|> fWrite.WriteByte
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// Write the bytes to the file.
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fWrite.Write(messageByte, 0, messageByte.Length);
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// Close the stream.
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fWrite.Close();
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// Open a file and read the number of bytes.
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let fRead = new FileStream("test.txt", FileMode.Open)
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// The first byte is the string length.
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let length = fRead.ReadByte() |> int
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// Create a new byte array for the data.
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let readBytes = Array.zeroCreate length
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// Read the data from the file.
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fRead.Read(readBytes, 0, readBytes.Length);
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// Close the stream.
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fRead.Close();
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// Display the data.
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printfn $"{Encoding.ASCII.GetString readBytes}"
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printfn "Done writing and reading data."
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with e ->
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printfn $"{e}"
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//</SNIPPET1>

‎snippets/fsharp/System.IO/FileOptions/Overview/fs.fsproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net48</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="example.fs" />
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</ItemGroup>
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</Project>

‎snippets/fsharp/System.IO/FileStream/.ctor/example.fs

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module example
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//<SNIPPET1>
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open System.IO
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open System.Text
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try
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// Create a file and write data to it.
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// Create an array of bytes.
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let messageByte = Encoding.ASCII.GetBytes "Here is some data."
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// Create a file using the FileStream class.
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let fWrite =
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new FileStream("test.txt", FileMode.Create, FileAccess.ReadWrite, FileShare.None, 8, FileOptions.None)
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// Write the number of bytes to the file.
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byte messageByte.Length |> fWrite.WriteByte
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// Write the bytes to the file.
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fWrite.Write(messageByte, 0, messageByte.Length)
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// Close the stream.
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fWrite.Close()
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// Open a file and read the number of bytes.
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let fRead = new FileStream("test.txt", FileMode.Open)
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// The first byte is the string length.
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let length = fRead.ReadByte() |> int
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// Create a new byte array for the data.
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let readBytes = Array.zeroCreate length
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// Read the data from the file.
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fRead.Read(readBytes, 0, readBytes.Length) |> ignore
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// Close the stream.
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fRead.Close()
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// Display the data.
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printfn $"{Encoding.ASCII.GetString readBytes}"
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printfn "Done writing and reading data."
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with e ->
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printfn $"{e}"
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//</SNIPPET1>

‎snippets/fsharp/System.IO/FileStream/.ctor/fs.fsproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net7.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="source.fs" />
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<Compile Include="fstreamlock.fs" />
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<Compile Include="source1.fs" />
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<Compile Include="example.fs" />
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</ItemGroup>
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</Project>

‎snippets/fsharp/System.IO/FileStream/.ctor/fstreamlock.fs

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module fstreamlock
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// <Snippet1>
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open System
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open System.IO
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open System.Text
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let uniEncoding = UnicodeEncoding()
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let lastRecordText = "The last processed record number was: "
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let textLength = uniEncoding.GetByteCount lastRecordText
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let mutable recordNumber = 13
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let byteCount = string recordNumber |> uniEncoding.GetByteCount
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do
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// <Snippet2>
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use fileStream =
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new FileStream("Test#@@#.dat", FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.ReadWrite)
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// </Snippet2>
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// <Snippet3>
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// Write the original file data.
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if fileStream.Length = 0 then
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let tempString = lastRecordText + string recordNumber
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fileStream.Write(uniEncoding.GetBytes tempString, 0, uniEncoding.GetByteCount tempString)
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// </Snippet3>
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// Allow the user to choose the operation.
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let mutable consoleInput = 'R'
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let readText = int fileStream.Length |> Array.zeroCreate
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while consoleInput <> 'X' do
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printf "\nEnter 'R' to read, 'W' to write, 'L' to lock, 'U' to unlock, anything else to exit: "
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let mutable tempString = stdin.ReadLine()
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if tempString.Length = 0 then
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consoleInput <- 'X'
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else
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consoleInput <- Char.ToUpper tempString[0]
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match consoleInput with
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| 'R' ->
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// Read data from the file and
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// write it to the console.
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try
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fileStream.Seek(0, SeekOrigin.Begin) |> ignore
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fileStream.Read(readText, 0, int fileStream.Length) |> ignore
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tempString <- String(uniEncoding.GetChars readText, 0, readText.Length)
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printfn $"{tempString}"
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recordNumber <- tempString.IndexOf ':' + 2 |> tempString.Substring |> Int32.Parse
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// Catch the IOException generated if the
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// specified part of the file is locked.
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with :? IOException as e ->
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printfn
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$"{e.GetType().Name}: The read operation could not be performed because the specified part of the file is locked."
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// <Snippet4>
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| 'W' ->
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// Update the file.
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try
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fileStream.Seek(textLength, SeekOrigin.Begin) |> ignore
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fileStream.Read(readText, textLength - 1, byteCount) |> ignore
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tempString <- String(uniEncoding.GetChars readText, textLength - 1, byteCount)
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recordNumber <- Int32.Parse tempString + 1
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fileStream.Seek(textLength, SeekOrigin.Begin) |> ignore
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fileStream.Write(string recordNumber |> uniEncoding.GetBytes, 0, byteCount)
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fileStream.Flush()
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printfn "Record has been updated."
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// </Snippet4>
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// <Snippet6>
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// Catch the IOException generated if the
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// specified part of the file is locked.
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with :? IOException as e ->
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printfn
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$"{e.GetType().Name}: The write operation could not be performed because the specified part of the file is locked."
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// </Snippet6>
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// Lock the specified part of the file.
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| 'L' ->
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try
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fileStream.Lock(textLength - 1 |> int64, byteCount)
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printfn "The specified part of file has been locked."
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with :? IOException as e ->
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printfn $"{e.GetType().Name}: The specified part of file is already locked."
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// <Snippet5>
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// Unlock the specified part of the file.
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| 'U' ->
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try
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fileStream.Unlock(textLength - 1 |> int64, byteCount)
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printfn "The specified part of file has been unlocked."
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with :? IOException as e ->
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printfn $"{e.GetType().Name}: The specified part of file is not locked by the current process."
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// </Snippet5>
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// Exit the program.
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| _ -> consoleInput <- 'X'
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// </Snippet1>

‎snippets/fsharp/System.IO/FileStream/.ctor/source.fs

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module source
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// <Snippet1>
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open System
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open System.IO
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let fileName = "Test#@@#.dat"
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// Create random data to write to the file.
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let dataArray = Array.zeroCreate 100000
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Random.Shared.NextBytes dataArray
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do
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use fileStream = new FileStream(fileName, FileMode.Create)
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// Write the data to the file, byte by byte.
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for i = 0 to dataArray.Length - 1 do
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fileStream.WriteByte dataArray[i]
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// Set the stream position to the beginning of the file.
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fileStream.Seek(0, SeekOrigin.Begin) |> ignore
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// Read and verify the data.
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for i in 0L .. fileStream.Length - 1L do
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if dataArray[int i] <> (fileStream.ReadByte() |> byte) then
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printfn "Error writing data."
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exit 1
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printfn $"The data was written to {fileStream.Name} and verified."
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// </Snippet1>

‎snippets/fsharp/System.IO/FileStream/.ctor/source1.fs

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module source1
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// <Snippet1>
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open System
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open System.IO
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open System.Threading
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// Maintain state information to be passed to
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// EndWriteCallback and EndReadCallback.
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type State(fStream: FileStream, writeArray: byte[], manualEvent: ManualResetEvent) =
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// readArray stores data that is read from the file.
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let readArray = Array.zeroCreate writeArray.Length
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member _.FStream = fStream
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member _.WriteArray = writeArray
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member _.ReadArray = readArray
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member _.ManualEvent = manualEvent
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// When BeginRead is finished reading data from the file, the
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// EndReadCallback method is called to end the asynchronous
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// read operation and then verify the data.
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// <Snippet4>
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let endReadCallback (asyncResult: IAsyncResult) =
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let tempState = asyncResult.AsyncState :?> State
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let readCount = tempState.FStream.EndRead asyncResult
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let mutable i = 0
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let mutable errored = false
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while i < readCount do
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if tempState.ReadArray[i] <> tempState.WriteArray[i] then
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printfn "Error writing data."
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tempState.FStream.Close()
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errored <- true
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i <- readCount
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i <- i + 1
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printfn $"The data was written to {tempState.FStream.Name} and verified."
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tempState.FStream.Close()
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// Signal the main thread that the verification is finished.
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tempState.ManualEvent.Set() |> ignore
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// </Snippet4>
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// When BeginWrite is finished writing data to the file, the
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// EndWriteCallback method is called to end the asynchronous
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// write operation and then read back and verify the data.
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// <Snippet3>
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let endWriteCallback (asyncResult: IAsyncResult) =
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let tempState = asyncResult.AsyncState :?> State
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let fStream = tempState.FStream
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fStream.EndWrite asyncResult
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// Asynchronously read back the written data.
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fStream.Position <- 0
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let asyncResult =
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fStream.BeginRead(tempState.ReadArray, 0, tempState.ReadArray.Length, AsyncCallback endReadCallback, tempState)
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// Concurrently do other work, such as
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// logging the write operation.
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()
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// </Snippet3>
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// <Snippet2>
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// Create a synchronization object that gets
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// signaled when verification is complete.
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let manualEvent = new ManualResetEvent false
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// Create random data to write to the file.
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let writeArray = Array.zeroCreate 100000
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Random.Shared.NextBytes writeArray
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let fStream =
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new FileStream("Test#@@#.dat", FileMode.Create, FileAccess.ReadWrite, FileShare.None, 4096, true)
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// Check that the FileStream was opened asynchronously.
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if fStream.IsAsync then "" else "not "
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|> printfn "fStream was %sopened asynchronously."
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// Asynchronously write to the file.
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let asyncResult =
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fStream.BeginWrite(
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writeArray,
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0,
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writeArray.Length,
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AsyncCallback endWriteCallback,
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State(fStream, writeArray, manualEvent)
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)
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// Concurrently do other work and then wait
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// for the data to be written and verified.
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manualEvent.WaitOne(5000, false) |> ignore
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// </Snippet2>
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// </Snippet1>

‎snippets/fsharp/System.IO/FileStream/CanRead/fs.fsproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net7.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="source.fs" />
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</ItemGroup>
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</Project>

‎snippets/fsharp/System.IO/FileStream/CanRead/source.fs

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module source
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// <Snippet1>
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open System.IO
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let fs = new FileStream("MyFile.txt", FileMode.OpenOrCreate, FileAccess.Read)
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if fs.CanRead && fs.CanWrite then
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printfn "MyFile.txt can be both written to and read from."
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else if fs.CanRead then
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printfn "MyFile.txt is not writable."
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// </Snippet1>

‎snippets/fsharp/System.IO/FileStream/CanSeek/fs.fsproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net7.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="fstream canseek.fs" />
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</ItemGroup>
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</Project>

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