neovim/runtime/lua/vim/_core/server.lua

-- For "--listen", ":restart", and related remote/server functionality.

local M = {}

--- Called by builtin serverlist(). Returns the combined server list (own + peers).
---
---@class vim.ServerInfo
---@field addr string Server address (socket path, named pipe, or TCP host:port).
---@field pid integer PID of the Nvim process.
---@field own boolean True if this server belongs to the current Nvim instance.
---@field active integer Timestamp of last user activity.

--- @param opts? table Options:
---              - opts.peer (boolean): If true, also discover peer servers.
---              - opts.info (boolean): If true, return a list of |vim.ServerInfo| dicts
---                instead of a list of addresses. Implies peer=true.
--- @param addrs string[] Internal ("own") addresses, from server_address_list.
--- @return string[]|vim.ServerInfo[]
function M.serverlist(opts, addrs)
  if type(opts) ~= 'table' then
    return addrs
  end

  local want_info = opts.info == true
  if opts.peer ~= true and not want_info then
    return addrs
  end

  local seen = {} ---@type table<string, true>
  for _, a in ipairs(addrs) do
    seen[a] = true
  end

  local peers ---@type string[]|vim.ServerInfo[]
  if want_info then
    local self_pid = vim.fn.getpid()
    local self_active = vim.v.useractive
    peers = vim.tbl_map(function(addr) ---@param addr vim.ServerInfo
      return {
        addr = addr,
        pid = self_pid,
        own = true,
        active = self_active,
      }
    end, addrs)
  else
    peers = addrs
  end

  -- Discover peer servers in stdpath("run").
  -- TODO: track TCP servers, somehow.
  -- TODO: support Windows named pipes.
  local root = vim.fs.normalize(vim.fn.stdpath('run') .. '/..')
  local socket_paths = vim.fs.find(function(name, _)
    return name:match('nvim.*')
  end, { path = root, type = 'socket', limit = math.huge })

  for _, socket in ipairs(socket_paths) do
    if not seen[socket] then
      local ok, chan = pcall(vim.fn.sockconnect, 'pipe', socket, { rpc = true })
      if ok and chan and chan > 0 then
        -- Check that the server is responding
        -- TODO: do we need a timeout or error handling here?
        local ok_rpc, peer_info = pcall(
          vim.fn.rpcrequest,
          chan,
          'nvim_exec_lua',
          [[return { pid = vim.fn.getpid(), active = vim.v.useractive, }]],
          {}
        )

        if ok_rpc and type(peer_info) == 'table' then
          ---@cast peer_info vim.ServerInfo
          seen[socket] = true
          if want_info then
            table.insert(peers, {
              addr = socket,
              pid = peer_info.pid,
              own = false,
              active = peer_info.active,
            })
          else
            table.insert(peers, socket)
          end
        end
        pcall(vim.fn.chanclose, chan)
      end
    end
  end

  return peers
end

-- (Windows only) Canonical --listen address persisted across restarts.
M.restart_canonical_addr = nil ---@type string?

--- (Windows only)
--- Called on the new server via nvim_exec_lua RPC from the old server (:restart).
--- Windows named pipes can't be rebound immediately, so the new server starts on a
--- temporary bootstrap address and polls until the canonical address is reclaimable.
--- @param canonical_addr string  The original --listen address to reclaim.
--- @param expected_uis   integer Number of UIs expected to reattach (0 = don't wait).
function M.rebind_after_restart(canonical_addr, expected_uis)
  M.restart_canonical_addr = canonical_addr
  local bootstrap_addr = vim.v.servername -- Temporary autogenerated address.
  local poll_ms = 50
  local max_wait_ms = 30000
  local timer = assert(vim.uv.new_timer())

  -- Poll until the canonical address can be reclaimed (or timeout).
  local poll_elapsed = 0
  timer:start(poll_ms, poll_ms, function()
    vim.schedule(function()
      if timer:is_closing() then
        return
      end
      poll_elapsed = poll_elapsed + poll_ms
      if poll_elapsed >= max_wait_ms then
        timer:stop()
        timer:close()
        return
      end
      if not vim.list_contains(vim.fn.serverlist(), canonical_addr) then
        local ok = vim._with({ log_level = 5 }, function()
          return pcall(vim.fn.serverstart, canonical_addr)
        end)
        if not ok then
          return -- pipe still held by old server; retry next tick
        end
      end

      -- Wait for UIs to reattach, then retire the bootstrap address.
      local elapsed = 0
      timer:stop()
      timer:start(poll_ms, poll_ms, function()
        vim.schedule(function()
          if timer:is_closing() then
            return
          end
          elapsed = elapsed + poll_ms
          local all_uis = expected_uis <= 0 or #vim.api.nvim_list_uis() >= expected_uis
          if all_uis or elapsed >= max_wait_ms then
            if canonical_addr ~= bootstrap_addr then
              vim._with({ log_level = 5 }, function()
                pcall(vim.fn.serverstop, bootstrap_addr)
              end)
            end
            timer:stop()
            timer:close()
          end
        end)
      end)
    end)
  end)
end

-- Called by ex_restart(). Saves the current session and calls ex_restart() (again) with the
-- updated arguments.
--
-- TODO: https://github.com/neovim/neovim/issues/34204
--
--- @param eap vim._core.ExCmdArgs
--- @param extra { quit_cmd: string }
function M.ex_session_restart(eap, extra)
  local after_cmd = eap.args -- User-provided [command].
  assert(not after_cmd:find(']==]'))

  -- Use custom +cmd if given.
  local quit_cmd = extra.quit_cmd == '' and 'qall' or extra.quit_cmd

  -- Preserve v:this_session in the restarted Nvim.
  local this_session = vim.v.this_session
  assert(not this_session:find(']==]'))

  -- Nvim temp "root dir": "/tmp/…/nvim.<user>/"
  local tmproot = vim.fs.abspath(vim.fs.dirname(vim.fs.dirname(vim.fn.tempname())))
  assert(not tmproot:find(']==]'))
  local fd, session = vim.uv.fs_mkstemp(vim.fs.joinpath(tmproot, 'restart_session_XXXXXX'))
  if not fd then
    error('Failed to get temporary filename for restart session')
  end
  vim.uv.fs_close(fd)

  -- Write session
  local session_arg = vim.fn.fnameescape(session)
  vim.cmd('%argdelete')
  vim.cmd.mksession { session_arg, bang = true }

  -- Lua commands to restore the session and remove the session file
  local after_list = {}
  table.insert(after_list, ('vim.cmd("source %s")'):format(session_arg))
  table.insert(after_list, ('pcall(vim.fs.rm, [==[%s]==])'):format(session))
  table.insert(after_list, ('vim.v.this_session = [==[%s]==]'):format(this_session))
  if after_cmd ~= '' then
    table.insert(after_list, ('vim.cmd([==[%s]==])'):format(after_cmd))
  end
  local after = 'lua ' .. table.concat(after_list, ';')

  -- Restart Neovim and run our Lua commands
  local success, msg = pcall(function()
    -- "+:::" dummy prefix tells the C handler that this is actually a non-bang restart.
    -- Then v:startreason (if any) can be preserved.
    vim.cmd.restart { '+:::', quit_cmd, after, bang = true }
  end)

  if not success then
    vim.fs.rm(session, { force = true })
    error(msg)
  end
end

return M