CGI example for redbean web server

.init.lua

local MAXTIME = 5 -- sec
local function cgi(cmd, opts)
  if not cmd or not cmd[1] then error('missing command') end
  if not opts then opts = {} end
  local nph = opts.nph
  local maxtime = opts.maxtime or MAXTIME
  local env = {}
  local envu = opts.env or {}
  local envd = #envu > 0 and envu or {
    SERVER_ADDR = FormatIp(GetServerAddr()),
    SERVER_PORT = select(2, GetServerAddr()),
    SERVER_SOFTWARE = "redbean", -- fm.getBrand()
    REMOTE_HOST = GetHost(),
    REMOTE_ADDR = FormatIp(GetRemoteAddr()),
    REMOTE_INDENT = ParseUrl(GetUrl()).user,
    REQUEST_SCHEME = GetScheme(),
    REQUEST_METHOD = GetMethod(),
    GATEWAY_INTERFACE = "CGI/1.1",
    SERVER_PROTOCOL = ("HTTP/%01.1f"):format(GetHttpVersion()/10),
    QUERY_STRING = EncodeUrl({params = ParseUrl(GetUrl()).params}):sub(2),
    REQUEST_URI = (function(u) return EncodeUrl({params = u.params, path = u.path})end)(ParseUrl(GetUrl())),
    HTTPS = GetSslIdentity() and "on" or nil,
    PATH_INFO = GetPath(),
    PATH_TRANSLATED = GetEffectivePath(),
    CONTENT_TYPE = GetHeader("Content-Type"),
    CONTENT_LENGTH = GetHeader("Content-Length"),
  }
  if #envu == 0 then
    -- provide all the headers
    for k, v in pairs(GetHeaders()) do envd["HTTP_"..k:upper()] = v end
    -- overwrite all defaults
    for k, v in pairs(envu) do envd[k] = v end
    -- convert to strings unless the value is false
    for k, v in pairs(envd) do if v then table.insert(env, k.."="..v) end end
  end
  local rfd1, wfd1 = unix.pipe(unix.O_CLOEXEC)
  local rfd2, wfd2 = unix.pipe(unix.O_CLOEXEC)
  local pid = unix.fork()
  if pid == 0 then  -- forked child
    assert(unix.close(GetClientFd()))  -- close client fd to not send anything
    assert(unix.dup(rfd2, 0))  -- redirect stdin
    assert(unix.dup(wfd1, 1))  -- redirect stdout
    assert(unix.dup(wfd1, 2))  -- redirect stderr
    assert(unix.close(wfd1))
    assert(unix.close(rfd1))
    assert(unix.close(wfd2))
    assert(unix.close(rfd2))
    assert(unix.sigaction(unix.SIGQUIT, unix.exit))
    unix.execve(cmd[1], cmd, env)
    unix.exit(127)
  else
    unix.write(wfd2, GetBody())
    local isactive = true
    local header = true
    local done = false
    assert(unix.sigaction(unix.SIGALRM, function() isactive = false end))
    assert(unix.setitimer(unix.ITIMER_REAL, 0, 0, maxtime, 0))
    local cfd = GetClientFd()
    while true do
      -- block for a bit until there is output from the launched process
      local se = (unix.poll({[rfd1] = unix.POLLIN}, maxtime*1000/10) or {})[rfd1] or 0
      if se & (unix.POLLHUP + unix.POLLERR) > 0 then break end

      -- check if the client is (still) writable
      local re = (unix.poll({[cfd] = unix.POLLOUT}) or {})[cfd] or 0
      if re & (unix.POLLHUP + unix.POLLERR) > 0 then break end

      -- check if the process took too long to respond
      if not isactive then break end

      local data, errno
      if se & unix.POLLIN > 0 then data, errno = unix.read(rfd1) end
      -- check for end of file or any descriptor errors
      if data == "" or errno and errno:errno() == unix.EBADF then break end

      if data then
        if header then
          local pos = 1
          while true do
            -- allow both CRLF and LF to be handled
            local spos, epos = data:find("\r?\n", pos, false)
            if not spos then break end
            -- found an empty string, which signals the end of headers
            if spos == pos then header = false; pos = epos + 1; break end
            local status, reason
            if pos == 1 then
              status, reason = data:sub(pos, spos-1):match("^HTTP/%d%.%d%s+(%d%d%d)%s+(.+)")
            end
            if status then
              -- found the status line
              SetStatus(status, reason)
            else
              -- found something that may be a header
              local name, value = data:sub(pos, spos-1):match("^(%a[%w_-]+):%s*(.+)")
              -- check if the header has a valid syntax
              -- if not, skip it and handle it as part of the data;
              -- this may happen if an error is thrown instead of a valid context
              local ok, err = pcall(SetHeader, name, value)
              if not name or not value or not ok then
                header = false
                break
              end
            end
            pos = epos + 1
          end
          -- finished parsing headers, so remove them from data
          if not header and pos > 1 then data = data:sub(pos) end
        end
        -- if the headers are set, write the response
        if not header then
          Write(data)
          if nph then coroutine.yield() end
        end
      -- check if reading was interrupted or wasn't done
      elseif not data and (not errno or errno:errno() == unix.EINTR) then
        -- closing connection will fail on send
        -- if it doesn't fail, then redo the interrupted read
      else  -- report an error and stop
        -- TODO: log error
        break
      end
      -- stop reading if the process is already done
      done = not unix.wait(pid, unix.WNOHANG)
      if done then break end
    end
    unix.close(rfd1)
    unix.close(wfd1)
    unix.close(rfd2)
    unix.close(wfd2)
    -- kill launched process if it's still running, as it's been running for too long
    if not done then assert(unix.kill(pid, unix.SIGTERM)) end
  end
end
OnHttpRequest = function()
  cgi({'./redbean.com',
    '-e', [[print('HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\n\r\nEnvironment:') for _,v in ipairs(unix.environ()) do Sleep(0.1) print(_, v) end]], '-e', 'unix.exit()'},
    {nph = true, env = {HTTP_DNT = false}})
end