Feature Request: (tools/server) Parameter for endpoint to run chat UI on when using --path

[BradHutchings]

Prerequisites

• I am running the latest code. Mention the version if possible as well.
• I carefully followed the README.md.
• I searched using keywords relevant to my issue to make sure that I am creating a new issue that is not already open (or closed).
• I reviewed the Discussions, and have a new and useful enhancement to share.

Feature Description

I would like a parameter for specifying the endpoint to run the default chat style interface for tools./server, e.g.

--default-ui-endpoint "chat"

This would run the default chat UI on /chat and /chat/ endpoints.

Note: I would appreciate help from a collaborator who has successfully created pull requests against this repo in the past. The code below works. I need to submit it the right way. -Brad

Motivation

I use the --path parameter with tools/server to specify a path to my completion UI. I would also like to include an endpoint /chat (or /chat/) to display the default chat UI.

Possible Implementation

These additions work, and are incorporated into my fork: https://github.com/BradHutchings/Mmojo-Server

common/arg.cpp (end of file):

    add_opt(common_arg(
        {"--default-ui-endpoint"}, "STRING",
        "endpoint for accessing the default chat user interface",
        [](common_params & params, const std::string & value) {
            params.default_ui_endpoint = value;
            // LOG_INF("Setting params.default_ui_endpoint: %s\n", params.default_ui_endpoint.c_str());
        }
    ).set_examples({LLAMA_EXAMPLE_SERVER}));

common/common.h (insert before line 280):

std::string default_ui_endpoint   =    ""; // endpoint for chat UI)```

tools/server/server.cpp (insert after line 33):

// pre C++20 helpers.
bool starts_with (std::string const &fullString, std::string const &beginning);
bool ends_with (std::string const &fullString, std::string const &ending);

bool starts_with (std::string const &fullString, std::string const &beginning) {
    if (fullString.length() >= beginning.length()) {
        return (0 == fullString.compare (0, beginning.length(), beginning));
    }
    else {
        return false;
    } 
}

bool ends_with (std::string const &fullString, std::string const &ending) {
    if (fullString.length() >= ending.length()) {
        return (0 == fullString.compare (fullString.length() - ending.length(), ending.length(), ending));
    }
    else {
        return false;
    } 
}

tools/server/server.cpp (insert before // register API routes, ~5238):

    if (params.default_ui_endpoint != "") {
        std::string endpoint = params.default_ui_endpoint;
        // gracefully handle leading and/or trailing /
        if (!starts_with (endpoint, "/")) {
            endpoint = "/" + endpoint;
        }
        while (ends_with(endpoint, "/")) {
            endpoint = endpoint.substr(0, endpoint.length() - 1);
        }
        
        svr->Get(endpoint, [](const httplib::Request & req, httplib::Response & res) {
            if (req.get_header_value("Accept-Encoding").find("gzip") == std::string::npos) {
                res.set_content("Error: gzip is not supported by this browser", "text/plain");
            } else {
                res.set_header("Content-Encoding", "gzip");
                // COEP and COOP headers, required by pyodide (python interpreter)
                res.set_header("Cross-Origin-Embedder-Policy", "require-corp");
                res.set_header("Cross-Origin-Opener-Policy", "same-origin");
                res.set_content(reinterpret_cast<const char*>(index_html_gz), index_html_gz_len, "text/html; charset=utf-8");
            }
            return false;
        });

        svr->Get(endpoint + "/", [](const httplib::Request & req, httplib::Response & res) {
            res.set_redirect(req.path.substr(0, req.path.length() - 1));
            return false;
        });        
    }