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bashhttpnetcat

ncat: piping multiline request breaks HTTP

I just started using ncat, and playing around with simple HTTP requests, I came across the following:

Starting ncat and typing a two-line get request works fine:

$ ncat 192.168.56.20 80                                                        
GET / HTTP/1.1
Host: 192.168.56.20

HTTP/1.1 200 OK

If however the request gets echoed to ncat, it apparently breaks somewhere:

$ echo 'GET / HTTP/1.1\nHost: 192.168.56.20' | ncat 192.168.56.20 80
HTTP/1.1 400 Bad Request

I don't get it.

Solution

  • The \n in the string is sent literally. Use echo -e to enable interpretation of backslash escapes. Also, the newline sequence for HTTP 1.1 is \r\n (CRLF). And the header section ends with an additional end-of-line.

    Try:

    echo -e 'GET / HTTP/1.1\r\nHost: 192.168.56.20\r\n\r\n' | ncat 192.168.56.20 80

    Alternatively, the ncat has the option to convert new lines to CRLF:

    -C, --crlf                 Use CRLF for EOL sequence

    Hence, you can write:

    echo -e 'GET / HTTP/1.1\nHost: 192.168.56.20\n\n' | ncat -C 192.168.56.20 80

    and you should get the same result.