Handle an unknown extension

When to reach for this: a user uploaded a file with an extension mime-db doesn’t know (.flv5, .heif, a made-up in-house one) and you still need to send a response header.

#include <polycpp/mime/mime.hpp>

std::string contentTypeOrFallback(const std::string& pathOrExt) {
    using namespace polycpp::mime;
    if (auto ct = contentType(pathOrExt)) return *ct;
    return "application/octet-stream";  // RFC 2046 §4.5.1
}

application/octet-stream is the right default: it tells every client “this is bytes, don’t try to render it inline”. Don’t reach for text/plain — browsers will happily display raw binary content with that type and corrupt the output.

If you routinely see the same unknown extension in production logs, that’s a signal to contribute it upstream to jshttp/mime-db rather than carry a local patch.