Websocket re-architecture with websocketd and websocat (#89)

- Replaced beast with websocketd and websocat. #79 #83 #84
- Implemented inbound/outbound peer connection merging.
- Added graceful shutdown of hpcore with sigint. #87

src/comm/comm_client.cpp

@@ -0,0 +1,96 @@
+#include "comm_client.hpp"
+#include "comm_session.hpp"
+#include "comm_session_handler.hpp"
+#include "../hplog.hpp"
+#include "../util.hpp"
+
+namespace comm
+{
+
+int comm_client::start(std::string_view host, const uint16_t port, const uint64_t (&metric_thresholds)[4], const uint64_t max_msg_size)
+{
+    return start_websocat_process(host, port);
+}
+
+void comm_client::stop()
+{
+    if (read_fd > 0)
+        close(read_fd);
+    if (write_fd > 0)
+        close(write_fd);
+
+    if (websocat_pid > 0)
+        kill(websocat_pid, SIGINT); // Kill websocat.
+}
+
+int comm_client::start_websocat_process(std::string_view host, const uint16_t port)
+{
+    // setup pipe I/O
+    if (pipe(read_pipe) < 0 || pipe(write_pipe) < 0)
+    {
+        LOG_ERR << errno << ": websocat pipe creation failed.";
+        return -1;
+    }
+
+    const pid_t pid = fork();
+
+    if (pid > 0)
+    {
+        // HotPocket process.
+        websocat_pid = pid;
+
+        read_fd = read_pipe[0];
+        write_fd = write_pipe[1];
+
+        // Close unused fds by us.
+        close(write_pipe[0]);
+        close(read_pipe[1]);
+
+        // Wait for some time and check if websocat is still running properly.
+        util::sleep(20);
+        int pid_status;
+        waitpid(websocat_pid, &pid_status, WNOHANG);
+        if (WIFEXITED(pid_status)) // This means websocat has exited.
+        {
+            close(read_fd);
+            close(write_fd);
+            return -1;
+        }
+    }
+    else if (pid == 0)
+    {
+        // Websocat process.
+        close(write_pipe[1]); //parent write
+        close(read_pipe[0]);  //parent read
+
+        dup2(write_pipe[0], STDIN_FILENO); //child read
+        close(write_pipe[0]);
+        dup2(read_pipe[1], STDOUT_FILENO); //child write
+        close(read_pipe[1]);
+
+        std::string url = std::string("wss://").append(host).append(":").append(std::to_string(port));
+
+        // Fill process args.
+        char *execv_args[] = {
+            conf::ctx.websocat_exe_path.data(),
+            url.data(),
+            (char *)"-k", // Accept invalid certificates
+            (char *)"-b", // Binary mode
+            (char *)"-E", // Close on EOF
+            (char *)"-q", // Quiet mode
+            NULL};
+
+        const int ret = execv(execv_args[0], execv_args);
+        LOG_ERR << errno << ": websocat process execv failed.";
+        exit(1);
+    }
+    else
+    {
+        LOG_ERR << "fork() failed when starting websocat process.";
+        return -1;
+    }
+
+    return 0;
+}
+
+} // namespace comm