Add process UID parameter

src/h5_zmq_writer.cpp

@@ -3,6 +3,8 @@
 #include <zmq.hpp>
 #include <cstdlib>
 #include <chrono>
+#include <unistd.h>
+#include <stdexcept>
 #include <boost/property_tree/json_parser.hpp>
 #include <boost/thread.hpp>
 
@@ -245,18 +247,35 @@ void run_writer(string connect_address, string output_file, uint64_t n_images, u
 
 int main (int argc, char *argv[])
 {
-    if (argc != 5) {
+    if (argc != 6) {
         cout << endl;
         cout << "Usage: h5_zmq_writer [connection_address] [output_file] [n_images] [rest_port]" << endl;
         cout << "\tconnection_address: Address to connect to the stream (PULL). Example: tcp://127.0.0.1:40000" << endl;
         cout << "\toutput_file: Name of the output file." << endl;
         cout << "\tn_images: Number of images to acquire. 0 for infinity (untill /stop is called)." << endl;
         cout << "\trest_port: Port to start the REST Api on." << endl;
+        cout << "\tuser_id: uid under which to run the writer. -1 to leave it as it is." << endl;
         cout << endl;
 
         exit(-1);
     }
 
+    // This process can be set to run under a different user.
+    auto user_id = atoi(argv[5]);
+    if (user_id != -1) {
+
+        #ifdef DEBUG_OUTPUT
+            cout << "[h5_zmq_writer::main] Setting process uid to " << user_id << endl;
+        #endif
+
+        if (setuid(user_id)) {
+            stringstream error_message;
+            error_message << "[h5_zmq_writer::main] Cannot set user_id to " << user_id << endl;
+
+            throw runtime_error(error_message.str());
+        }
+    }
+
     run_writer(string(argv[1]), string(argv[2]), atoi(argv[3]), atoi(argv[4]));
 
     return 0;