load HTTP Prompt environment from command line

[tardypad]

It would be convenient to be able to load a HTTP Prompt environment from the command line so as to launch http-prompt with a predefined context without requiring any manual input within http-prompt. Currently the only way to fully load such an environment is to execute exec /path/to/project.hp interactively.
Loading an environment in such a way would allow the creation of aliases

I'm thinking of 2 different ways to do this:

• Option 1:
  add a --env cli parameter to would take the environment file to load as parameter
  http-prompt --env /path/to/project.hp
• Option 2:
  support receiving data from stdin
  cat /path/to/project.hp | http-prompt

Each of these option would make it possible to create aliases:

• Option 1
  alias http_project_prod='http-prompt --env /path/to/project_prod.hp
alias http_project_test='http-prompt --env /path/to/project_test.hp
• Option 2
  alias http_project_prod='cat /path/to/project_prod.hp | http-prompt'
alias http_project_test='cat /path/to/project_test.hp | http-prompt'

Please let me know what you think of it
I'm willing to implement it myself if

[tardypad]

I did a bit of research already and the option 2 might turn to be more tricky.

The prompt-toolkit doesn't support piping (see prompt-toolkit/python-prompt-toolkit#502) and will actually "crash" in such a case

We could surely use the snippet mentioned in that previous issue

if not sys.stdin.isatty():
    data = sys.stdin.read()

and load the context from this data but the prompt still exits (from https://github.com/jonathanslenders/python-prompt-toolkit/blob/master/prompt_toolkit/input.py#L67), unless we overwrite stdin afterwards sys.stdin = sys.stdout
It looks hacky and I don't know if that would cause issues...

Probably the other option would be not to use the prompt shortcut but to build our own CommandLineInterface instance (as mentioned in http://python-prompt-toolkit.readthedocs.io/en/master/pages/reference.html#module-prompt_toolkit.shortcuts)

So if you're ok with the option 1 of the --env cli parameter, it should be much easier to implement I believe

[eliangcs]

I tried it before, piping data to from stdin to a prompt-toolkit app is indeed not an easy thing to do. So I think we can add a --env option in the cli. Free feel the implement it. Thanks!