1 files changed, 117 insertions, 0 deletions
diff --git a/third_party/protobuf/csharp/README.md b/third_party/protobuf/csharp/README.md
new file mode 100644
index 0000000000..65d2311fff
--- /dev/null
+++ b/third_party/protobuf/csharp/README.md
@@ -0,0 +1,117 @@
+This directory contains the C# Protocol Buffers runtime library.
+
+Usage
+=====
+
+The easiest way how to use C# protobufs is via the `Google.Protobuf`
+NuGet package. Just add the NuGet package to your VS project.
+
+You will also want to install the `Google.Protobuf.Tools` NuGet package, which
+contains precompiled version of `protoc.exe` and a copy of well known `.proto`
+files under the package's `tools` directory.
+
+To generate C# files from your `.proto` files, invoke `protoc` with the 
+`--csharp_out` option.
+
+Supported platforms
+===================
+
+The runtime library is built as a portable class library, supporting:
+
+- .NET 4.5
+- Windows 8
+- Windows Phone Silverlight 8
+- Windows Phone 8.1
+- .NET Core
+
+You should be able to use Protocol Buffers in Visual Studio 2012 and
+all later versions. This includes all code generated by `protoc`,
+which only uses features from C# 3 and earlier.
+
+Building
+========
+
+Open the `src/Google.Protobuf.sln` solution in Visual Studio 2015 or
+later.
+
+Although *users* of this project are only expected to have Visual
+Studio 2012 or later, *developers* of the library are required to
+have Visual Studio 2015 or later, as the library uses C# 6 features
+in its implementation. These features have no impact when using the
+compiled code - they're only relevant when building the
+`Google.Protobuf` assembly.
+
+Testing
+=======
+
+The unit tests use [NUnit 3](https://github.com/nunit/nunit). Vanilla NUnit doesn't 
+support .NET Core, so to run the tests you'll need to use 
+[dotnet-test-nunit](https://github.com/nunit/dotnet-test-nunit). 
+`dotnet-test-nunit` can also run tests for .NET 4.5+, so to run the tests 
+for both .NET Core and .NET 4.5, you can simply open the 
+`Package Manager Console` in Visual Studio and execute:
+```
+dotnet test Google.Protobuf.Test
+```
+
+.NET 3.5
+========
+
+We don't officially support .NET 3.5. However, there has been some effort 
+to make enabling .NET 3.5 support relatively painless in case you require it. 
+There's no guarantee that this will continue in the future, so rely on .NET 
+3.5 support at your peril.
+
+To enable .NET 3.5 support:
+
+1. Modify [src/Google.Protobuf/project.json](src/Google.Protobuf/project.json) to add `"net35": {}` to `"frameworks"`.
+2. Modify [src/Google.Protobuf.Test/project.json](src/Google.Protobuf/project.json):
+  1. Add `"net35": {}` to `"frameworks"`.
+  2. `dotnet-test-nunit` doesn't support .NET 3.5, so remove it from 
+  the project-wide `"dependencies"` and add it to the framework-specific 
+  dependencies under `"net451"` and `"netcoreapp1.0"`.
+
+Note that `dotnet-test-nunit` doesn't support .NET 3.5. You can instead run the 
+tests with [NUnit 3 console](https://github.com/nunit/nunit-console) 
+by running something like: 
+```
+nunit3-console.exe "Google.Protobuf.Test\bin\Debug\net35\win7-x64\Google.Protobuf.Test.dll" --inprocess
+```
+
+The exact path may differ depending on your environment (e.g., the `win7-x64` 
+directory may be called something else). The `--inprocess` flag seems to be a 
+necessary workaround for a bug in NUnit; otherwise, you'll receive 
+an error "Exception has been thrown by the target of an invocation" 
+([possibly related issue](https://github.com/nunit/nunit/issues/1480)).
+
+If you still want to run the .NET 4.5 and .NET Core tests, you can do so by 
+specifying the framework when using `dotnet-test-nunit`, i.e. from 
+`Package Manager Console` in Visual Studio:
+```
+dotnet test Google.Protobuf.Test --framework netcoreapp1.0
+dotnet test Google.Protobuf.Test --framework net451
+```
+
+History of C# protobufs
+=======================
+
+This subtree was originally imported from https://github.com/jskeet/protobuf-csharp-port
+and represents the latest development version of C# protobufs, that will now be developed
+and maintained by Google. All the development will be done in open, under this repository
+(https://github.com/google/protobuf).
+
+The previous project differs from this project in a number of ways:
+
+- The old code only supported proto2; the new code only supports
+proto3 (so no unknown fields, no required/optional distinction, no
+extensions)
+- The old code was based on immutable message types and builders for
+them
+- The old code did not support maps or `oneof`
+- The old code had its own JSON representation, whereas the new code
+uses the standard protobuf JSON representation
+- The old code had no notion of the "well-known types" which have
+special support in the new code
+- The old project supported some older platforms (such as older
+versions of Silverlight) which are not currently supported in the
+new project