Detect PuTTY Link on Windows and show error [GH-1518]

CHANGELOG.md

@@ -40,6 +40,7 @@ IMPROVEMENTS:
   - Specify the default provider with the `VAGRANT_DEFAULT_PROVIDER`
     environmental variable. [GH-1478]
   - Invalid settings are now caught and shown in a user-friendly way. [GH-1484]
+  - Detect PuTTY Link SSH client on Windows and show an error. [GH-1518]
 
 BUG FIXES:
 

lib/vagrant/errors.rb

@@ -411,6 +411,10 @@ module Vagrant
       error_key(:ssh_host_down)
     end
 
+    class SSHIsPuttyLink < VagrantError
+      error_key(:ssh_is_putty_link)
+    end
+
     class SSHKeyBadOwner < VagrantError
       error_key(:ssh_key_bad_owner)
     end

lib/vagrant/util/ssh.rb

@@ -3,6 +3,7 @@ require "log4r"
 require "vagrant/util/file_mode"
 require "vagrant/util/platform"
 require "vagrant/util/safe_exec"
+require "vagrant/util/subprocess"
 require "vagrant/util/which"
 
 module Vagrant
@@ -60,7 +61,8 @@ module Vagrant
       def self.exec(ssh_info, opts={})
         # Ensure the platform supports ssh. On Windows there are several programs which
         # include ssh, notably git, mingw and cygwin, but make sure ssh is in the path!
-        if !Which.which("ssh")
+        ssh_path = Which.which("ssh")
+        if !ssh_path
           if Platform.windows?
             raise Errors::SSHUnavailableWindows,
               :host => ssh_info[:host],
@@ -72,6 +74,19 @@ module Vagrant
           raise Errors::SSHUnavailable
         end
 
+        # On Windows, we need to detect whether SSH is actually "plink"
+        # underneath the covers. In this case, we tell the user.
+        if Platform.windows?
+          r = Subprocess.execute(ssh_path)
+          if r.stdout.include?("PuTTY Link")
+            raise Errors::SSHIsPuttyLink,
+              :host => ssh_info[:host],
+              :port => ssh_info[:port],
+              :username => ssh_info[:username],
+              :key_path => ssh_info[:private_key_path]
+          end
+        end
+
         # If plain mode is enabled then we don't do any authentication (we don't
         # set a user or an identity file)
         plain_mode = opts[:plain_mode]

templates/locales/en.yml

@@ -364,6 +364,16 @@ en:
         While attempting to connect with SSH, a "host is down" (EHOSTDOWN)
         error was received. Please verify your SSH settings are correct
         and try again.
+      ssh_is_putty_link: |-
+        The `ssh` executable found in the PATH is a PuTTY Link SSH client.
+        Vagrant is only compatible with OpenSSH SSH clients. Please install
+        an OpenSSH SSH client or manually SSH in using your existing client
+        using the information below.
+
+        Host: %{host}
+        Port: %{port}
+        Username: %{username}
+        Private key: %{key_path}
       ssh_key_bad_owner: |-
         The private key to connect to the machine via SSH must be owned
         by the user running Vagrant. This is a strict requirement from