stcp: ed25519 pubkey exchange in handshake, fix instance destroy segfault, fix chat_tcp_test

- u_async.c: process immediate_queue BEFORE epoll_wait in uasync_poll
- stcp_link.c: defensive NULL etcp_conn/etcp_link in stcp_link_close
- utun_instance.c: move stcp_server_list_destroy_all to Phase J (before ETCP),
  add deferred drain in both Phase J and L
- stcp.h/c: STCP_HS_ENC_CLIENT 6→38, STCP_HS_ENC_SERVER 7→39,
  exchange ed25519_pubkey in both handshake directions
- etcp_connections.c: copy peer_ed25519 from STCP to ETCP_CONN in
  etcp_link_enter_ready_tcp; guard link->etcp in tcp_link_close_cb
- chat_sync.c: fix lk->conn NULL dereference for TCP links
- test_stcp.c: update stcp_server_create/stcp_client_connect callsites
- tools/chat_tcp_test: change transport udp→tcp

tools/chatgui/zxing-cpp/core/src/BitMatrixIO.cpp

@@ -0,0 +1,101 @@
+/*
+* Copyright 2017 Huy Cuong Nguyen
+* Copyright 2017 Axel Waggershauser
+*/
+// SPDX-License-Identifier: Apache-2.0
+
+#include "BitMatrixIO.h"
+
+#include <array>
+#include <fstream>
+#include <sstream>
+
+namespace ZXing {
+
+std::string ToString(const BitMatrix& matrix, char one, char zero, bool addSpace, bool printAsCString)
+{
+	std::string result;
+	result.reserve((addSpace ? 2 : 1) * (matrix.width() * matrix.height()) + matrix.height());
+	for (int y = 0; y < matrix.height(); ++y) {
+		if (printAsCString)
+			result += '"';
+		for (auto bit : matrix.row(y)) {
+			result += bit ? one : zero;
+			if (addSpace)
+				result += ' ';
+		}
+		if (printAsCString)
+			result += "\\n\"";
+		result += '\n';
+	}
+	return result;
+}
+
+std::string ToString(const BitMatrix& matrix, bool inverted)
+{
+	constexpr auto map = std::array{" ", "▀", "▄", "█"};
+	std::string res;
+
+	for (int y = 0; y < matrix.height(); y += 2) {
+		for (int x = 0; x < matrix.width(); ++x) {
+			int tp = matrix.get(x, y) ^ inverted;
+			int bt = (matrix.height() == 1 && tp) || (y + 1 < matrix.height() && (matrix.get(x, y + 1) ^ inverted));
+			res += map[tp | (bt << 1)];
+		}
+		res.push_back('\n');
+	}
+
+	return res;
+}
+
+std::string ToSVG(const BitMatrix& matrix)
+{
+	// see https://stackoverflow.com/questions/10789059/create-qr-code-in-vector-image/60638350#60638350
+
+	const int width = matrix.width();
+	const int height = matrix.height();
+	std::ostringstream out;
+
+	out << R"(<?xml version="1.0" encoding="UTF-8"?>)" << "\n"
+		<< R"(<svg xmlns="http://www.w3.org/2000/svg" version="1.1" viewBox="0 0 )" << width << ' ' << height << R"(" stroke="none">)"
+		<< "\n<path d=\"";
+
+	for (int y = 0; y < height; ++y)
+		for (int x = 0; x < width; ++x)
+			if (matrix.get(x, y))
+				out << "M" << x << "," << y << "h1v1h-1z";
+
+	out << "\"/>\n</svg>";
+
+	return out.str();
+}
+
+BitMatrix ParseBitMatrix(const std::string& str, char one, bool expectSpace)
+{
+	auto lineLength = str.find('\n');
+	if (lineLength == std::string::npos)
+		return {};
+
+	int strStride = expectSpace ? 2 : 1;
+	int height = narrow_cast<int>(str.length() / (lineLength + 1));
+	int width = narrow_cast<int>(lineLength / strStride);
+	BitMatrix mat(width, height);
+	for (int y = 0; y < height; ++y) {
+		size_t offset = y * (lineLength + 1);
+		for (int x = 0; x < width; ++x, offset += strStride) {
+			if (str[offset] == one)
+				mat.set(x, y);
+		}
+	}
+	return mat;
+}
+
+void SaveAsPBM(const BitMatrix& matrix, const std::string& filename, int quietZone)
+{
+	auto out = ToMatrix<uint8_t>(Inflate(matrix.copy(), 0, 0, quietZone));
+	std::ofstream file(filename);
+	file << "P5\n" << out.width() << ' ' << out.height() << "\n255\n";
+	file.write(reinterpret_cast<const char*>(out.data()), out.size());
+}
+
+} // ZXing