CODEWITHSUNDEEP
rubysocketstcp
Pankas
Pankas

Reputation: 137

How to wait until TCP socket response is ready

I'm connecting to a TCP server using Ruby's TCPSocket class.

I send some data about an address and I must wait for the server to do some processing to give me the geocoding of said address. Since the process in the server takes some time, I cannot read the response immediately.

When I used socket.readpartial() I got a response of two white spaces.

I temporarily solved this using sleep(5) but I don't like this at all, because it is hackish and clumsy, and I risk that even after 5 seconds the response is not ready and I still get an empty response.

I know that the responses will always be 285 characters long.

Is there a more correct and elegant way of having my TCP socket wait for the full response?

Here's my code:

  def matchgeocode(rua, nro, cidade, uf)
    count   = 0

    begin
      socket  = TCPSocket.new(GEOCODER_URL, GEOCODER_PORT)

      # Needed for authentication
      socket.write("TICKET #{GEOCODER_TICKET}")

      socket.read(2)

      # Here's the message I send to the server
      socket.write("MATCHGEOCODE -Rua:\"#{rua}\" -Nro:#{nro} -Cidade:\"#{cidade}\" -Uf:\"#{uf}\"")

      # My hackish sleep
      sleep(5)

      # Reading the fixed size response
      response = socket.readpartial(285)

      socket.write('QUIT')
      socket.close
    rescue Exception => e
      count += 1
      puts e.message

      if count <= 5 && response.eql?('')
        retry 
      end
    end

    response    
  end

Upvotes: 1

Views: 1684

Answers (1)

Casper
Casper

Reputation: 34328

Since you know the length of the response you should use read, not readpartial.

readpartial returns immediately if ANY data is available, even one byte is enough. That's why you need the sleep call so that the response has time to return to you before readpartial tries to peek at what data is present.

read on the other hand blocks completely until ALL requested data is available. Since you know the length of the result then read is the natural solution here.

Upvotes: 1

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