Support duplicate header keys in session files

[ducaale]

Headers will be saved as key-value pairs, and any session using the old format will be migrated automatically

Before:

{
  "__meta__": { "about": "xh session file", "xh": "0.0.0" },
  "auth": { "type": null, "raw_auth": null },
  "cookies": {},
  "headers": {
    "hello": "world"
  }
}

After:

{
  "__meta__": { "about": "xh session file", "xh": "0.0.0" },
  "auth": { "type": null, "raw_auth": null },
  "cookies": {},
  "headers": [
    { "key": "hello", "value": "world" }
  ]
}

Resolves #245

[blyxxyz]

When the session file has multiple headers only the first one is sent. Replacing headers.entry(key).or_insert_with(|| value.clone()); by headers.append(key, value.clone()); in main.rs fixes it. (Could probably use a test!)

[blyxxyz]

HTTPie calls these name, not key, so they fail to load each other's sessions. Maybe we can copy a file from HTTPie's test suite?

[ducaale]

Yup, that is a good idea 👍

[ducaale]

Update: I haven't used a verbatim test file from HTTPie since we are not yet 100% compatible with the current session format. I am planning to address this in a follow-up PR that adds support for the new style cookies introduced in httpie/cli#1312

[blyxxyz]

not yet 100% compatible

Do you mean that we crash or that we interpret the session files incorrectly?

[ducaale]

We would fail to load a session where cookies are stored as a list. For example:

tests/fixtures/session_data/new/cookies_dict_with_extras.json

{
    "__meta__": {
        "about": "HTTPie session file",
        "help": "https://httpie.io/docs#sessions",
        "httpie": "__version__"
    },
    "auth": {
        "raw_auth": "foo:bar",
        "type": "basic"
    },
    "cookies": [
        {
            "domain": __host__,
            "expires": null,
            "name": "baz",
            "path": "/",
            "secure": false,
            "value": "quux"
        },
        {
            "domain": __host__,
            "expires": null,
            "name": "foo",
            "path": "/",
            "secure": false,
            "value": "bar"
        }
    ],
    "headers": {
        "X-Data": "value",
        "X-Foo": "bar"
    }
}

[ducaale]

Actually, there are test files that mix the new header format with the old cookie format. See https://github.com/httpie/httpie/blob/master/tests/fixtures/session_data/old/cookies_dict_with_extras.json

[ducaale]

Given that this code path will never run, I wonder if we should replace it with unreachable!(). I am doing a similar thing with cookies, and I can't think of a reason to maintain unreachable code.

[blyxxyz]

unreachable!() sounds fine, as long as we have a test that loads the old format to make sure. This code is a bit misleading.

It would be nice to just not have this case at all but none of the solutions I can think of are a net improvement.

[ducaale]

Done

[blyxxyz]

Looks good! I didn't find any differences compared to HTTPie's behavior.