Crow Middlewares

A set of useful middlewares for the Crow microframework.

Middlewares

WhitelistIpGuard

Alias of RemoteIpGuard<allowed_ip_list, true>.

A middleware that checks if the IP an incoming request comes from is in a comma-separated whitelist, and returns result code 403 Forbidden if it is not.

Usage

// Comma-separated list must be constant
const char allowed_ips[] = "127.0.0.1,127.0.0.2";

int main()
{
    // Pass the comma-separated list as template argument
    crow::App<crow::WhitelistIpGuard<allowed_ips>> app;

    ...
}

DynamicWhitelistIpGuard

Alias of RemoteIpGuard<nullptr, true>.

Useful if you want an instance of a WhitelistIpGuard middleware that can have IP addresses added/removed in runtime.

Usage

int main()
{
    crow::App<crow::DynamicWhitelistIpGuard> app;
    
    // Get the instance of the DynamicWhitelistIpGuard middleware
    crow::DynamicWhitelistIpGuard& ipGuard = app.get_middleware<crow::DynamicWhitelistIpGuard>();

    // Remove any existing IPs from the whitelist
    ipGuard.clear_ips();

    // Add IPs
    ipGuard.add_ip("127.0.0.1").add_ip("127.0.0.2");
    
    // Check if IP is whitelisted
    if (ipGuard.is_ip_allowed("127.0.0.2")) {
        // Remove IPs
        ipGuard.remove_ip("127.0.0.2");
    }

    // Add a set of ips to the whitelist
    std::vector<std::string> ips = get_ips();
    ipGuard.add_ips(ips);

    // Check if the whitelist is frozen
    if (!ipGuard.is_frozen()) {
        // Freeze the whitelist. Subsequent attempts to modify the whitelist will do nothing
        ipGuard.freeze();
    }

    // Will do nothing (except log with CROW_LOG_WARNING) since the whitelist was frozen above
    ipGuard.add_ip("127.0.0.2");
    
    ...
}

Remarks

add_ip, add_ips, remove_ip and clear_ips invalidate currently held iterators, which are for allowing/denying requests, as such, they shouldn't be used after the Crow webapplication is run.

BlacklistIpGuard

Alias of RemoteIpGuard<forbidden_ip_list, false>.

A middleware that checks if the IP an incoming request comes from is in a comma-separated blacklist, and returns result code 403 Forbidden if it is.

Usage

// Comma-separated list must be constant
const char forbidden_ips[] = "127.0.0.1,127.0.0.2";

int main()
{
    // Pass the comma-separated list as template argument
    crow::App<crow::WhitelistIpGuard<forbidden_ips>> app;

    ...
}

DynamicBlacklistIpGuard

Alias of DynamicBlacklistIpGuard<nullptr, false>.

Useful if you want an instance of a BlacklistIpGuard middleware that can have IP addresses added/removed in runtime.

Usage

int main()
{
    crow::App<crow::DynamicBlacklistIpGuard> app;
    
    // Get the instance of the DynamicBlacklistIpGuard middleware
    crow::DynamicBlacklistIpGuard& ipGuard = app.get_middleware<crow::DynamicBlacklistIpGuard>();

    // Remove any existing IPs from the blacklist
    ipGuard.clear_ips();

    // Add IPs
    ipGuard.add_ip("127.0.0.1").add_ip("127.0.0.2");
    
    // Check if IP is blacklisted
    if (ipGuard.is_ip_forbidden("127.0.0.2")) {
        // Remove IPs
        ipGuard.remove_ip("127.0.0.2");
    }

    // Add a set of ips to the blacklist
    std::vector<std::string> ips = get_ips();
    ipGuard.add_ips(ips);

    // Check if the blacklist is frozen
    if (!ipGuard.is_frozen()) {
        // Freeze the blacklist. Subsequent attempts to modify the blacklist will do nothing
        ipGuard.freeze();
    }

    // Will do nothing (except log with CROW_LOG_WARNING) since the blacklist was frozen above
    ipGuard.add_ip("127.0.0.2");
    
    ...
}

Remarks

add_ip, add_ips, remove_ip and clear_ips invalidate currently held iterators, which are used for allowing/denying requests, as such, they shouldn't be used after the Crow webapplication is run.