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‎.gitignore

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bin/
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obj/
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out/

‎README.md

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# Example AssemblyLoadContext-using PowerShell Module
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This repository demonstrates a simple example for isolating module dependencies from the rest of PowerShell.
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The `old` directory contains the pre-isolation module,
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and `new` represents the same module after implementing an isolation technique.
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The main purpose of this example is to demonstrate how to use an Assembly Load Context
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in .NET Core/.NET 5 to isolate module dependendies in PowerShell 6+.
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Be warned that the .NET Framework isolation technique is not ideal;
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there's no guarantee that the isolation technique for .NET Framework will work well.

‎new/JsonModule.Cmdlets/DependencyAssemblyLoadContext.cs

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using System;
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using System.Collections.Concurrent;
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using System.IO;
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using System.Reflection;
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using System.Runtime.Loader;
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namespace JsonModule.Cmdlets
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{
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public class DependencyAssemblyLoadContext : AssemblyLoadContext
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{
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private static readonly string s_psHome = Path.GetDirectoryName(Assembly.GetEntryAssembly().Location);
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private static readonly ConcurrentDictionary<string, DependencyAssemblyLoadContext> s_dependencyLoadContexts = new ConcurrentDictionary<string, DependencyAssemblyLoadContext>();
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internal static DependencyAssemblyLoadContext GetForDirectory(string directoryPath)
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{
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return s_dependencyLoadContexts.GetOrAdd(directoryPath, (path) => new DependencyAssemblyLoadContext(path));
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}
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private readonly string _dependencyDirPath;
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public DependencyAssemblyLoadContext(string dependencyDirPath)
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: base(nameof(DependencyAssemblyLoadContext))
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{
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_dependencyDirPath = dependencyDirPath;
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}
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protected override Assembly Load(AssemblyName assemblyName)
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{
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string assemblyFileName = $"{assemblyName.Name}.dll";
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// Make sure we allow other common PowerShell dependencies to be loaded by PowerShell
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// But specifically exclude Newtonsoft.Json since we want to use a different version here
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if (!assemblyName.Name.Equals("Newtonsoft.Json", StringComparison.OrdinalIgnoreCase))
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{
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string psHomeAsmPath = Path.Join(s_psHome, assemblyFileName);
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if (File.Exists(psHomeAsmPath))
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{
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// With this API, returning null means nothing is loaded
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return null;
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}
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}
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// Now try to load the assembly from the dependency directory
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string dependencyAsmPath = Path.Join(_dependencyDirPath, assemblyFileName);
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if (File.Exists(dependencyAsmPath))
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{
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return LoadFromAssemblyPath(dependencyAsmPath);
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}
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return null;
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}
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}
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}

‎new/JsonModule.Cmdlets/JsonModule.Cmdlets.csproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<TargetFrameworks>netcoreapp3.1;net461</TargetFrameworks>
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</PropertyGroup>
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<PropertyGroup Condition="'$(TargetFramework)' == 'net461'">
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<DefineConstants>$(DefineConstants);NETFRAMEWORK</DefineConstants>
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</PropertyGroup>
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<ItemGroup>
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<ProjectReference Include="..\JsonModule.Engine\JsonModule.Engine.csproj" />
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</ItemGroup>
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<ItemGroup Condition="'$(TargetFramework)' == 'net461'">
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<Compile Remove="DependencyAssemblyLoadContext.cs" />
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</ItemGroup>
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<ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.1'">
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<PackageReference Include="System.Management.Automation" Version="7.0.1" />
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</ItemGroup>
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<ItemGroup Condition="'$(TargetFramework)' == 'net461'">
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<PackageReference Include="Microsoft.PowerShell.5.ReferenceAssemblies" Version="1.1.0" />
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</ItemGroup>
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</Project>

‎new/JsonModule.Cmdlets/JsonModuleInitializer.cs

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using System.IO;
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using System.Management.Automation;
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using System.Reflection;
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#if NETFRAMEWORK
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using System;
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#else
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using System.Runtime.Loader;
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#endif
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namespace JsonModule.Cmdlets
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{
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public class JsonModuleInitializer : IModuleAssemblyInitializer
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{
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private static string s_binBasePath = Path.GetFullPath(
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Path.Combine(
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Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location),
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".."));
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private static string s_binCommonPath = Path.Combine(s_binBasePath, "Common");
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#if NETFRAMEWORK
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private static string s_binFrameworkPath = Path.Combine(s_binBasePath, "Framework");
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#else
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private static string s_binCorePath = Path.Join(s_binBasePath, "Core");
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#endif
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public void OnImport()
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{
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#if NETFRAMEWORK
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AppDomain.CurrentDomain.AssemblyResolve += ResolveAssembly_NetFramework;
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#else
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AssemblyLoadContext.Default.Resolving += ResolveAssembly_NetCore;
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#endif
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}
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#if NETFRAMEWORK
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private static Assembly ResolveAssembly_NetFramework(object sender, ResolveEventArgs args)
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{
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// In .NET Framework, we must try to resolve ALL assemblies under the dependency dir here
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// This essentially means we are combining the .NET Core ALC and resolve events into one here
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// Note that:
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// - This is not a recommended usage of Assembly.LoadFile()
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// - Even doing this will not bypass the GAC
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// Parse the assembly name to get the file name
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var asmName = new AssemblyName(args.Name);
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var dllFileName = $"{asmName.Name}.dll";
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// Look for the DLL in our .NET Framework directory
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string frameworkAsmPath = Path.Combine(s_binFrameworkPath, dllFileName);
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if (File.Exists(frameworkAsmPath))
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{
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return LoadAssemblyFile_NetFramework(frameworkAsmPath);
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}
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// Now look in the dependencies directory to resolve .NET Standard dependencies
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string commonAsmPath = Path.Combine(s_binCommonPath, dllFileName);
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if (File.Exists(commonAsmPath))
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{
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return LoadAssemblyFile_NetFramework(commonAsmPath);
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}
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// We've run out of places to look
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return null;
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}
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private static Assembly LoadAssemblyFile_NetFramework(string assemblyPath)
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{
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return Assembly.LoadFile(assemblyPath);
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}
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#else
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private static Assembly ResolveAssembly_NetCore(
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AssemblyLoadContext assemblyLoadContext,
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AssemblyName assemblyName)
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{
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// In .NET Core, PowerShell deals with assembly probing so our logic is much simpler
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// We only care about our Engine assembly
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if (!assemblyName.Name.Equals("JsonModule.Engine"))
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{
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return null;
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}
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// Now load the Engine assembly through the dependency ALC, and let it resolve further dependencies automatically
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return DependencyAssemblyLoadContext.GetForDirectory(s_binCommonPath).LoadFromAssemblyName(assemblyName);
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}
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#endif
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}
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}

‎new/JsonModule.Cmdlets/OutJsonCommand.cs

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using System.Collections.Generic;
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using System.IO;
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using System.Management.Automation;
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using JsonModule.Engine;
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namespace JsonModule.Cmdlets
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{
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[Cmdlet(VerbsData.Out, "Json")]
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public class OutJsonCommand : PSCmdlet
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{
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private List<object> _values;
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public OutJsonCommand()
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{
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_values = new List<object>();
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}
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[Parameter(Mandatory = true)]
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[ValidateNotNullOrEmpty]
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public string OutFile { get; set; }
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[Parameter(Mandatory = true, ValueFromPipeline = true)]
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public object[] Value { get; set; }
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protected override void ProcessRecord()
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{
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_values.AddRange(Value);
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}
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protected override void EndProcessing()
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{
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if (_values.Count == 0)
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{
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return;
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}
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using (FileStream fileStream = new FileStream(GetUnresolvedProviderPathFromPSPath(OutFile), FileMode.Create, FileAccess.Write, FileShare.None))
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{
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new JsonWriter().WriteToStream(fileStream, _values.Count > 1 ? _values : _values[0]);
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}
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}
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}
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}

‎new/JsonModule.Engine/JsonModule.Engine.csproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<TargetFramework>netstandard2.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
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</ItemGroup>
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</Project>

‎new/JsonModule.Engine/JsonWriter.cs

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using System.IO;
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using Newtonsoft.Json;
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namespace JsonModule.Engine
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{
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public class JsonWriter
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{
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public static string NewtonsoftName { get; } = typeof(JsonConvert).Assembly.FullName;
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public void WriteToStream(Stream stream, object value)
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{
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using (var textWriter = new StreamWriter(stream))
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using (var jsonWriter = new JsonTextWriter(textWriter){ Formatting = Formatting.Indented })
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{
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new JsonSerializer().Serialize(jsonWriter, value);
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}
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}
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}
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}

‎new/JsonModule.psd1

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@{
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# Script module or binary module file associated with this manifest.
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RootModule = if ($PSEdition -eq 'Core')
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{
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'Core/JsonModule.Cmdlets.dll'
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}
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else
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{
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'Framework/JsonModule.Cmdlets.dll'
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}
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# Version number of this module.
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ModuleVersion = '0.0.1'
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# Supported PSEditions
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CompatiblePSEditions = @('Core', 'Desktop')
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# ID used to uniquely identify this module
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GUID = '228638a3-fe17-46ec-a093-edfc555a75f1'
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# Author of this module
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Author = 'Me'
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# Company or vendor of this module
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CompanyName = 'Unknown'
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# Copyright statement for this module
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Copyright = '(c) Me. All rights reserved.'
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# Description of the functionality provided by this module
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# Description = ''
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# Minimum version of the PowerShell engine required by this module
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PowerShellVersion = '5.1'
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# Minimum version of Microsoft .NET Framework required by this module. This prerequisite is valid for the PowerShell Desktop edition only.
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DotNetFrameworkVersion = '4.6.1'
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# Functions to export from this module, for best performance, do not use wildcards and do not delete the entry, use an empty array if there are no functions to export.
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FunctionsToExport = @()
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# Cmdlets to export from this module, for best performance, do not use wildcards and do not delete the entry, use an empty array if there are no cmdlets to export.
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CmdletsToExport = 'Out-Json'
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# Variables to export from this module
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VariablesToExport = @()
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# Aliases to export from this module, for best performance, do not use wildcards and do not delete the entry, use an empty array if there are no aliases to export.
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AliasesToExport = @()
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# Private data to pass to the module specified in RootModule/ModuleToProcess. This may also contain a PSData hashtable with additional module metadata used by PowerShell.
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PrivateData = @{
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PSData = @{
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} # End of PSData hashtable
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} # End of PrivateData hashtable
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}
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‎new/build.ps1

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param(
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[ValidateSet('Debug', 'Release')]
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[string]
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$Configuration = 'Debug'
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)
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$netCore = 'netcoreapp3.1'
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$netFramework = 'net461'
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$outPath = "$PSScriptRoot/out/JsonModule"
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$commonPath = "$outPath/Common"
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$corePath = "$outPath/Core"
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$frameworkPath = "$outPath/Framework"
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if (Test-Path $outPath)
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{
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Remove-Item -Path $outPath -Recurse
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}
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New-Item -Path $outPath -ItemType Directory
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New-Item -Path $commonPath -ItemType Directory
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New-Item -Path $corePath -ItemType Directory
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New-Item -Path $frameworkPath -ItemType Directory
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Push-Location "$PSScriptRoot/JsonModule.Engine"
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try
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{
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dotnet publish
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}
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finally
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{
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Pop-Location
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}
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Push-Location "$PSScriptRoot/JsonModule.Cmdlets"
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try
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{
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dotnet publish -f $netCore
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dotnet publish -f $netFramework
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}
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finally
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{
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Pop-Location
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}
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$commonFiles = [System.Collections.Generic.HashSet[string]]::new()
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Copy-Item -Path "$PSScriptRoot/JsonModule.psd1" -Destination $outPath
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Get-ChildItem -Path "$PSScriptRoot/JsonModule.Engine/bin/$Configuration/netstandard2.0/publish" |
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Where-Object { $_.Extension -in '.dll','.pdb' } |
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ForEach-Object { [void]$commonFiles.Add($_.Name); Copy-Item -LiteralPath $_.FullName -Destination $commonPath }
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Get-ChildItem -Path "$PSScriptRoot/JsonModule.Cmdlets/bin/$Configuration/$netCore/publish" |
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Where-Object { $_.Extension -in '.dll','.pdb' -and -not $commonFiles.Contains($_.Name) } |
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ForEach-Object { Copy-Item -LiteralPath $_.FullName -Destination $corePath }
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Get-ChildItem -Path "$PSScriptRoot/JsonModule.Cmdlets/bin/$Configuration/$netFramework/publish" |
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Where-Object { $_.Extension -in '.dll','.pdb' -and -not $commonFiles.Contains($_.Name) } |
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ForEach-Object { Copy-Item -LiteralPath $_.FullName -Destination $frameworkPath }

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