#830 Implement a socket wrapper API for use with LSP connections

test/test_socket_connections.vader

@@ -0,0 +1,90 @@
+Before:
+  let g:can_run_socket_tests = !has('win32')
+  \ && (exists('*ch_close') || exists('*chanclose'))
+
+  if g:can_run_socket_tests
+    call ale#test#SetDirectory('/testplugin/test')
+
+    let g:channel_id_received = 0
+    let g:data_received = ''
+
+    function! WaitForData(expected_data, timeout) abort
+      let l:ticks = 0
+
+      while l:ticks < a:timeout
+        " Sleep first, so we can switch to the callback.
+        let l:ticks += 10
+        sleep 10ms
+
+        if g:data_received is# a:expected_data
+          break
+        endif
+      endwhile
+    endfunction
+
+    function! TestCallback(channel_id, data) abort
+      let g:channel_id_received = a:channel_id
+      let g:data_received .= a:data
+    endfunction
+
+    let g:port = 10347
+    let g:pid = str2nr(system(
+    \ 'python'
+    \ . ' ' . ale#Escape(g:dir . '/dumb_tcp_server.py')
+    \ . ' ' . g:port
+    \))
+  endif
+
+After:
+  if g:can_run_socket_tests
+    call ale#test#RestoreDirectory()
+
+    unlet! g:channel_id_received
+    unlet! g:data_received
+    unlet! g:channel_id
+
+    delfunction WaitForData
+    delfunction TestCallback
+
+    if has_key(g:, 'pid')
+      call system('kill ' . g:pid)
+    endif
+
+    unlet! g:pid
+    unlet! g:port
+  endif
+
+  unlet! g:can_run_socket_tests
+
+Execute(Sending and receiving connections to sockets should work):
+  if g:can_run_socket_tests
+    let g:channel_id = ale#socket#Open(
+    \ '127.0.0.1:' . g:port,
+    \ {'callback': function('TestCallback')}
+    \)
+
+    Assert g:channel_id >= 0, 'The socket was not opened!'
+
+    call ale#socket#Send(g:channel_id, 'hello')
+    call ale#socket#Send(g:channel_id, ' world')
+
+    AssertEqual 1, ale#socket#IsOpen(g:channel_id)
+
+    " Wait up to 1 second for the expected data to arrive.
+    call WaitForData('hello world', 1000)
+
+    AssertEqual g:channel_id, g:channel_id_received
+    AssertEqual 'hello world', g:data_received
+
+    call ale#socket#Close(g:channel_id)
+
+    AssertEqual 0, ale#socket#IsOpen(g:channel_id)
+  endif
+
+  " NeoVim versions which can't connect to sockets should just fail.
+  if has('nvim') && !exists('*chanclose')
+    AssertEqual -1, ale#socket#Open(
+    \ '127.0.0.1:1111',
+    \ {'callback': function('function')}
+    \)
+  endif