Dremini

Highly concurrent and multi-threaded gemini client and server library for the Drogon web application framework

This library is in early development. API may clange without notice

Dependencies

• Drogon >= 1.7.3 (or 1.7.2 with MIME patch)

Usage

Client

Async-callback API

There's several ways to use the Gemini client. The most general one is by the async-callback API. The supplied callback function will be invoked once the cliend recived a response from the server.

dremini::sendRequest("gemini://gemini.circumlunar.space/"
    , [](ReqResult result, const HttpResponsePtr& resp) {
        if(result != ReqResult::Ok)
        {
            LOG_ERROR << "Failed to send request";
            return;
        }

        LOG_INFO << "Body size: " << resp->body().size();
    });

C++ Coroutines

If C++ coroutines (requires MSVC 19.25, GCC 11 or better) is avaliable to you. You can also use the more stright forward coroutine API.

try
{
    auto resp = co_await dremini::sendRequestCoro("gemini://gemini.circumlunar.space/");
    LOG_INFO << "Body size: " << resp->body().size();
} 
catch(...)
{
    LOG_ERROR << "Failed to send request";
}

Server

The dremini::GeminiServer plugin that parses and forwards Gemini requests as HTTP Get requests.

Thus, first enable the Gemini server plugin. And tell the server to serve gemini files (if you are also using it as a file server):

// config.json
{
    "app":{
        "document_root": "./",
        "file_types": [
            "gmi"
        ],
        "use_implicit_page": true,
        "implicit_page": "index.gmi",
        "home_page": "index.gmi",
        "mime": {
            "text/gemini": ["gmi", "gemini"]
        }
    },
    "plugins": [
        {
            "name": "dremini::GeminiServerPlugin",
            "config": {
                "listeners": [
                    {
                        "key": "key.pem",
                        "cert": "cert.pem",
                        "ip": "127.0.0.1"
                    }
                ],
                "numThread": 3
            }
        }
    ]
}

Then let's code up ca basic request handler:

app().registerHandler("/hi", [](const HttpRequestPtr& req, std::function<void(const HttpResponsePtr&)>&& callback)
{
    auto resp = HttpResponse::newHttpResponse();
    resp->setBody("# Hello Gemini\nHello!\n");
    resp->setContentTypeCodeAndCustomString(CT_CUSTOM, "text/gemini");
    callback(resp);
});

Finally, the handler can be triggered by using a Gemini client

> gmni gemini://localhost/hi -j once
# Hello Gemini
Hello
>

Mapping from Gemini to HTTP

Drogon is a HTTP framework. Dremini reuses a large portion of it's original functionality to provide easy Gemini server programming. We try hard to keep to Gemini sementic in HTTP.

Status codes

Like HTTP, Gemini uses status codes for servers to indicate the status of the response. Gemini status codes must have 2 digits. Thus a range between 0 and 99. Dremini maps common HTTP status codes into Gemini ones automatically. And converts the rest to an apporiprate category. Here's a list of conversions

HTTP	Gemini
200	20
400	59
404	51
429	44
502	43
504	43

If the returned HTTP status is not listed above. The Gemini status is simply the HTTP status divied by 100. Exception being 4 xx and 5xx. They 4xx is mapped as 50 and 5xx is mapped as 40. Since there's no HTTP status code lesser than 100 exists. Any status code in that range is treads as a Gemini native code. Which does not go through any translation.

HttpResponses from a Gemini client automaticallyi have a gemini-status header that stores the Gemini status code before mapping. And a meta header to store the meta.

Serving Gemini files

Drogon by design is a HTTP server. Thus is has no idea about Gemini files and convension. The following config tells Drogon the following things. Which are required to properly serve gemini pages

• Sets the page root folder to /path/to/the/files
• Serve *.gmi files
  • Add more types if needed
• *.gmi and *.gemini files have the MIME type text/gemini
• When asked to serve a directory, Try serving index.gmi
• The homepage is /index.gmi

{
    "app":{
        "document_root": "/path/to/the/files",
        "file_types": [
            "gmi",
            "gemini"
        ],
        "use_implicit_page": true,
        "implicit_page": "index.gmi",
        "home_page": "index.gmi",
        "mime": {
            "text/gemini": ["gmi", "gemini"]
        }
    }
}

Gemini query

Gemini URLs supports a query parameter using the ? symbol. For example, gemini://localhost/search?Hello has a query of "Hello". Dremini adds a query parameter to the HttpRequest when a query is detected.

Detecting Gemini requests

Dremini adds a protocol header to the proxyed HTTP request to singnal it's comming from a Gemini request. Whom's value is always "gemini"

Translating Gemini into HTML for HTTP requests

Dermini supports translating Gemini into HTML automatically! Add "translate_to_html": true into plugin config. This makes Dremini translate text/gemini contents into HTML when a regular browser requests content

Limitations

Dremini library does not verify server and client certificates yet. Nor client certs are supported.