httpcat is a simple utility for constructing raw HTTP requests on the command line.

Sometimes it is useful to be able to create an actual raw HTTP request on the command line:

• To debug a server issue
• To test the handling of invalid HTTP requests
• To learn how HTTP works under the hood

In such cases, existing CLI HTTP clients—such as httpie, curl, or wget —are too high-level as they provide an abstraction layer and one doesn't have a complete control over the exact raw data that gets written to the HTTP socket connection.

Lower-level tools, such as the popular netcat, are better suited for this job.

However, the syntax of HTTP requires headers to be separated with \r\n which makes it difficult to produce them on the command line. A typical solution involves the use of echo:

$ echo -ne 'POST /post HTTP/1.1\r\nHost: httpbin.org\r\nContent-Length: 5\r\n\r\nHello' | \
    nc localhost 8000

httpcat makes this easier:

1. Reads command arguments as lines and then lines from stdin
2. Auto-completes them, if necessary
3. Writes them to stdout

• Automatic \r\n completion
• Automatic Method completion in Request-Line
• Automatic HTTP-Version completion in Request-Line

Interactively create a request and send it with nc:

$ httpcat -v | nc httpbin.org 80
POST /post HTTP/1.1
> POST /post HTTP/1.1\r\n
Host: httpbin.org
> Host: httpbin.org\r\n
Content-Length: 6
> Content-Length: 6\r\n

> \r\n
Hello
> Hello

Specify the whole request in the arguments. Here '' represents an empty line which will be converted to \r\n\ separating the headers and the body. Note also that the omitted HTTP-Version is auto-completed:

$ httpcat -v 'POST /post' 'Host: httpbin.org' 'Content-Length: 5' '' 'Hello'  | nc httpbin.org 80
> POST /post HTTP/1.1\r\n
> Host: httpbin.org\r\n
> Content-Length: 5\r\n
> \r\n
> Hello

Omitted Method is set to GET and HTTP-Version is auto-completed:

$ httpcat -v / 'Host: example.org' '' | nc example.org 80
> GET / HTTP/1.1\r\n
> Host: example.org\r\n
> \r\n

You can, for example, use stdin for data and arguments for headers:

$ cat file.txt | httpcat -v 'POST /post' 'Host: httpbin.org' 'Content-Length: 16' '' | nc httpbin.org 80
> POST /post HTTP/1.1\r\n
> Host: httpbin.org\r\n
> Content-Length: 16\r\n
> \r\n
> Hello from file

See also httpcat --help:

usage: httpcat [-h] [-V, --version] [-v] [-n] [line [line ...]]

Create raw HTTP requests on the command line.

positional arguments:
  line            input lines read before lines from stdin

optional arguments:
  -h, --help      show this help message and exit
  -V, --version   show program's version number and exit
  -v, --verbose   print info about output lines to stderr
  -n, --no-stdin  disable reading of lines from stdin

• Python 3

pip3 install httpcat

Alternatively, you can just download httpcat.py manually and invoke it as ./httpcat.py instead of httpcat.

python3 setup.py test

HTTPie CLI starting with version 2.0.0 also provides an --offline mode. This makes it a good alternative to httpcat because it provides a convenient mechanism for crafting arbitrary HTTP requests without sending them using the user-friendly HTTPie syntax, for example:

echo -n 'Hello' | http --offline POST httpbin.org/post

The above command generates the following output:

POST /post HTTP/1.1
Accept: application/json, */*;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Content-Length: 5
Content-Type: application/json
Host: httpbin.org
User-Agent: HTTPie/2.2.0

Hello

The output is valid HTTP, so it can simply be sent using nc:

$ echo -n 'Hello' | http --offline POST httpbin.org/post | nc httpbin.org 80

• 0.0.2 (2016-12-13)

  • Added -v, --verbose and the command is more quiet by default.
  • Added -n, --no-stdin
  • Added -h, --help
  • Added -V, --version

• 0.0.1 (2016-12-12)

  • Initial release.

Jakub Roztocil

• https://github.com/jkbrzt
• https://twitter.com/jkbrzt
• http://roztocil.co