Adding ssh support to the Visual Studio 2015 Git plug-in

Some background

Visual Studio 2015 includes a Git plug-in that allows to version control software using Git. The plug-in allows to publish/clone from a shared Git repository, but is currently limited to repositories that support the http/https protocol.

Many users are requesting support for the ssh protocol, but the requirement is still under evaluation:
http://visualstudio.uservoice.com/forums/121579-visual-studio/suggestions/3801342-add-support-for-ssh-keys-as-alternate-authenticati

Anyhow the plug-in is based on libgit2, which optionally supports the ssh protocol. The next section describes how to rebuild libgit2 in order to enable ssh support.

Rebuilding the Git plug-in with ssh support

Visual Studio 2015 includes the source code used for compiling libgit2. It is compressed in the zip file:
C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\Extensions\4ygda0r0.oxa\libgit2-src.zip

The folder 4ygda0r0.oxa in the above path could change from installation to installation; anyhow it is enough searching for libgit2-src.zip in:
C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\Extensions

To build the source code it is necessary to:

1. download cmake binaries, available at http://www.cmake.org/
2. download the python interpreter, required by cmake and available at https://www.python.org
3. download libssh2 source, available at http://www.libssh2.org/
4. have installed Visual Studio 2015 with support for native C++ development

I think that any recent version of cmake and libssh2 should work. Anyhow, for building my own libgit2, I used the following versions:

1. cmake 3.3.0 (while the link points to the cmake installer, the web site distributes also a zip version of the cmake binaries. In case you prefer to download this version, it is enough to unzip it and add the bin folder to the PATH)
2. python 2.7.10
3. libssh2 1.6.0

After installing cmake and python, unzip both the libgit2 source and the libssh2 source in two separate folders. Lets assume they are respectively c:\dev\libgit2 and c:\dev\libssh2.

To configure libgit2 for the build, open a Visual Studio 2015 command prompt configured for native 32 bit builds (from the Start Menu: Visuals Studio 2015 -> VS2015 x86 Native Tools Command Prompt) and execute the following commands:

cd c:\dev\libgit2
mkdir build
cd build
cmake -DEMBED_SSH_PATH=C:/dev/libssh2 -DSTDCALL=ON ..

The cmake command options are required in order to:

1. the first option implies that we want to build using libssh2 and provides the path of the library. It is important to specify the path using the slash instead of the back slash;
2. the second option specifies the calling convention, that must be stdcall in order to generate a library that interacts properly with Visual Studio

After executing the cmake command, the build folder contains a Visual Studio 2015 solution and some projects. Open the solution, change the configuration from Debug to Release and build the git2 project.

Visual Studio will generate a Release folder under build, containing git2.dll. In order to "install" the new library execute the following steps:

1. close Visual Studio so that the git2 library is not in use and locked
2. go into the folder: C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\Extensions\4ygda0r0.oxa
3. Rename the file git2-msvstfs.dll to keep a copy of the original library
4. copy the just built git2.dll into the folder, naming it git2-msvstfs.dll.

After executing the above steps, the new libgit2 with ssh support is now in place. Start Visual Studio 2015 and configure a remote repository using the ssh protocol. It is important to specify both the username and password in the ssh URL as in this example:

ssh://user:password@githost/path/to/repository

This is necessary because Visual Studio 2015, when calling the Git library, does not provide a callback to retrieve username and password. The libgit2 library could be modified to open a standard Windows dialog to collect this information if it is not part of the URL, but possibly this will be the subject of a future post.

Visual Studio 2015 is now able to interact with your ssh Git repository.