Python TCP socket send String

Question

When sending get in putty the server response with HTTP/1.1 400 Bad Request
this is perfectly fine as i am only checking if the server is up and running.

Now i am trying to automate the process in python, but s.send("get".encode()) seems to do nothing, how do I use s.send()?

the s.recv(1024).decode("utf-8") works fine tho

I am also using the same program to check other ports as well.

import socket

host = "webmail"
port = 80

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((host, port))

s.send("get".encode())
print(s.recv(1024).decode("utf-8"))

basically I am establishing a TCP connection via a third party program called putty to manually send / receive strings (in console) — 0brine
– 0brine, Commented Oct 16, 2020 at 14:35

Community · Accepted Answer · 2021-10-07 12:12:37Z

1

When you send requests via socket you need to ensure to carefully follow the protocol in which the server is expecting. It seems that in this case the server expects valid HTTP/1.1 messages, and so you must strictly follow the protocol. In this case, a simple GET call would need to look something like so:

GET / HTTP/1.1
Host: example.com
Connection: close
Accept: */*

However, note that each line must be escaped properly with what is defined in RFC7230, section 3, Message Format as CRLF, which is simply \r\n, and one extra one at the end of your message. Therefore, the above message would actually look like so:

GET / HTTP/1.1\r\nHost: example.com\r\nConnection: keep-alive\r\nAccept: */*\r\n\r\n

If you are wanting to send raw messages like the above, I recommend checking out two possible modules that can make your life a little bit easier:

httpsuite: (disclaimer: I am the author) allows easy manipulation of HTTP/1.1 requests for socket purposes.
h11: Similar to the above, but I have personally not used it (found it after writing my module above).

You can make your life a little bit easier by abstracting away from socket, and instead using something like requests, which will allow you to more easily send a GET requests:

import requests

requests.get("http://example.com")

If you are interacting with different protocols (like SFTP, SSH, etc.) I would recommend finding modules that abstract away from the raw socket requests, and use them in conjunction. Messing with raw HTTP requests (and/or other protocol) requires a certain level of "confidence" in regards to how the server is bound to reply, and usually these modules will abstract a lot of the backend heavy work (e.g. in the case of HTTP/1.1 200-299 and 300-399 response codes).

edited Oct 7, 2021 at 12:12

CommunityBot

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answered Oct 16, 2020 at 9:38

felipe

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4 Comments

0brine Over a year ago

no, i want to use a TCP connection because i also want to check other services like, smtp, imap, pop, ssh, ...

President James K. Polk Over a year ago

@0brine: This answer shows a minimal correct string to send, however, each "newline" needs to be a carriage-return linefeed pair, e.g. b'\r\n'. Thus s.sendall(b'GET / HTTP/1.1\r\nHost: example.com\r\nConnection: close\r\nAccept: */*\r\n') should suffice.

President James K. Polk Over a year ago

Many http servers will accept invalid HTTP, so for example something as simple as s.send(b'GET\r\n') may work.

felipe Over a year ago

@PresidentJamesK.Polk You are completely right. I originally wrote the answer with the intention to redirect OP towards abstracting out of sockets - not very good in my part. I've expanded my answer to include the CRLF. A quick note on your response, your request is missing the ending CRLF that most server would require to conclude the message is valid - minor, I know, but worth noting in case OP has some fickly servers never responding.

0brine · Accepted Answer · 2020-10-16 14:48:36Z

0

President James K. Polk:

@0brine: This answer shows a minimal correct string to send, however, each "newline" needs to be a carriage-return linefeed pair, e.g. b'\r\n'. Thus s.sendall(b'GET / HTTP/1.1\r\nHost: example.com\r\nConnection: close\r\nAccept: /\r\n') should suffice. –

answered Oct 16, 2020 at 14:48

0brine

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