Add the ssh_key_from_memory optional feature.

[JMLX42]

Fix for https://github.com/alexcrichton/git2-rs/issues/320

This is done through a feature that will enable the GIT_SSH_MEMORY_CREDENTIALS flag when building libgit2-sys.

This feature is optional so that the current behavior is unchanged.

[alexcrichton]

Thanks! It looks like though this is defined by libgit2's build system if it detects a symbol in libssh2, and maybe the detection is broken? Are you sure the libssh2 build you're using has the libssh2_userauth_publickey_frommemory symbol?

[JMLX42]

Are you sure the libssh2 build you're using has the libssh2_userauth_publickey_frommemory symbol?

When I enable the feature, everything works as expected.
So I'm guessing it does, yes.

[alexcrichton]

In that case perhaps this should be enabled unconditionally? Assuming that we put it on ourselves to find an appropriate libssh2 build?

[JMLX42]

In that case perhaps this should be enabled unconditionally? Assuming that we put it on ourselves to find an appropriate libssh2 build?

Maybe. I made it optional because I don't know what would happen if someone uses it with a system libssh2 that does not support it.

In my case I'm also using the ssh2 crate. So I'm guessing the system's libssh2 is not used when I use git2-rs?

[alexcrichton]

Hm yeah the API there seems to have been added 4 years ago, so it seems fine to unconditionally enable this.

[JMLX42]

Hm yeah the API there seems to have been added 4 years ago, so it seems fine to unconditionally enable this.

Does that mean I remove the cargo "feature" thing, or make it enabled by default?

[alexcrichton]

Indeed!

[JMLX42]

@alexcrichton Here you go!

[alexcrichton]

Thanks!