createSerialRequestSource()

fl::function< fl::optional< fl::json >()> fl::createSerialRequestSource ( const char * prefix = "" )

inline

Definition at line 120 of file serial.h.

                                                                {
    return [prefix]() -> fl::optional<fl::json> {
        // Non-blocking check - any data available?
        int avail = fl::available();
        if (avail <= 0) {
            return fl::nullopt;
        }
 
        // Data available - read a complete line.
        // On Arduino platforms, fl::readLine() delegates to Serial.readStringUntil()
        // which uses yield() (immediate context switch) for fast USB CDC multi-packet
        // assembly. On other platforms, falls back to character-by-character reading.
        auto line = fl::readLine('\n', '\r', fl::optional<u32>(1000));
        if (!line.has_value() || line->empty()) {
            return fl::nullopt;
        }
 
        // Use string_view for zero-copy prefix stripping and trimming
        fl::string_view view = *line;
 
        // Strip prefix if present
        if (prefix && prefix[0] != '\0') {
            if (view.starts_with(prefix)) {
                view.remove_prefix(fl::strlen(prefix));
            }
        }
 
        // Trim leading whitespace
        while (!view.empty() && fl::isspace(view.front())) {
            view.remove_prefix(1);
        }
 
        // Trim trailing whitespace
        while (!view.empty() && fl::isspace(view.back())) {
            view.remove_suffix(1);
        }
 
        // Only parse if input starts with '{'
        if (view.empty() || view[0] != '{') {
            // A short line here is ordinary serial noise -- boot banners,
            // stray newlines -- and warning about it would drown the log.
            // A long one is almost certainly a request that arrived damaged,
            // and dropping that silently is expensive to debug: the caller
            // sees no reply and no error, indistinguishable from an idle
            // link, while the device keeps answering everything else. That
            // is exactly how a receive-buffer truncation presented in
            // FastLED#3956 -- 735 bytes transmitted, nothing returned, and
            // no layer saying anything.
            // Measure what arrived, not what survived normalisation: the
            // view above has had its prefix stripped and whitespace trimmed,
            // so a 64-byte line can fall under the threshold and stay silent,
            // and the reported count would understate what was received.
            if (line->size() >= kDroppedRequestWarnBytes) {
                FL_WARN("[RPC] discarded a " << (static_cast<unsigned>(line->size())) << " byte line that does not begin with '{'; a request that arrived truncated looks exactly like this");
            }
            return fl::nullopt;
        }
 
        // Single copy when parsing JSON (unavoidable - JSON needs owned string)
        fl::string input(view);
        return fl::json::parse(input);
    };
}

References available(), fl::string_view::back(), fl::string_view::empty(), FL_NO_EXCEPT, FL_WARN, fl::string_view::front(), isspace(), kDroppedRequestWarnBytes, nullopt, fl::json::parse(), readLine(), fl::string_view::remove_prefix(), fl::string_view::remove_suffix(), fl::string_view::starts_with(), and strlen().

Referenced by createSerialTransport().

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