Make ROS1 service type retrieval more robust (#316)

### Changelog
Fix node crashing in some cases when retrieving ROS1 service types

### Docs
None

### Description
In #306, it was reported that foxglove bridge crashed due to [this
assertion](https://github.com/ros/ros_comm/blob/845f74602c7464e08ef5ac6fd9e26c97d0fe42c9/clients/roscpp/src/libros/connection.cpp#L274)
when retrieving ROS1 service types. I believe that the reason for this
assertion was that the header callback was set twice: Once in our code
and once in the
[ServiceServerLink](https://github.com/ros/ros_comm/blob/845f74602c7464e08ef5ac6fd9e26c97d0fe42c9/clients/roscpp/src/libros/service_server_link.cpp#L118).
To avoid this, I have reworked the service retrieval to not create a
`ServiceServerLink` instance but instead work with a raw
`ros::Connection`.

Fixes #306

ros1_foxglove_bridge/src/service_utils.cpp

@@ -2,26 +2,46 @@
 #include <future>
 
 #include <ros/connection.h>
+#include <ros/connection_manager.h>
+#include <ros/poll_manager.h>
 #include <ros/service_manager.h>
-#include <ros/service_server_link.h>
+#include <ros/this_node.h>
+#include <ros/transport/transport_tcp.h>
 
 #include <foxglove_bridge/service_utils.hpp>
 
 namespace foxglove_bridge {
 
+/**
+ * Looks up the service server host & port and opens a TCP connection to it to retrieve the header
+ * which contains the service type.
+ *
+ * The implementation is similar to how ROS does it under the hood when creating a service server
+ * link:
+ * https://github.com/ros/ros_comm/blob/845f74602c7464e08ef5ac6fd9e26c97d0fe42c9/clients/roscpp/src/libros/service_manager.cpp#L246-L261
+ * https://github.com/ros/ros_comm/blob/845f74602c7464e08ef5ac6fd9e26c97d0fe42c9/clients/roscpp/src/libros/service_server_link.cpp#L114-L130
+ */
 std::string retrieveServiceType(const std::string& serviceName, std::chrono::milliseconds timeout) {
-  auto link = ros::ServiceManager::instance()->createServiceServerLink(serviceName, false, "*", "*",
-                                                                       {{"probe", "1"}});
-  if (!link) {
-    throw std::runtime_error("Failed to create service link");
-  } else if (!link->getConnection()) {
-    throw std::runtime_error("Failed to get service link connection");
+  std::string srvHost;
+  uint32_t srvPort;
+  if (!ros::ServiceManager::instance()->lookupService(serviceName, srvHost, srvPort)) {
+    throw std::runtime_error("Failed to lookup service " + serviceName);
+  }
+
+  auto transport =
+    boost::make_shared<ros::TransportTCP>(&ros::PollManager::instance()->getPollSet());
+  auto connection = boost::make_shared<ros::Connection>();
+  ros::ConnectionManager::instance()->addConnection(connection);
+  connection->initialize(transport, false, ros::HeaderReceivedFunc());
+
+  if (!transport->connect(srvHost, srvPort)) {
+    throw std::runtime_error("Failed to connect to service server of service " + serviceName);
   }
 
   std::promise<std::string> promise;
   auto future = promise.get_future();
 
-  link->getConnection()->setHeaderReceivedCallback(
+  connection->setHeaderReceivedCallback(
     [&promise](const ros::ConnectionPtr& conn, const ros::Header& header) {
       std::string serviceType;
       if (header.getValue("type", serviceType)) {
@@ -35,10 +55,18 @@ std::string retrieveServiceType(const std::string& serviceName, std::chrono::mil
       return true;
     });
 
+  ros::M_string header;
+  header["service"] = serviceName;
+  header["md5sum"] = "*";
+  header["callerid"] = ros::this_node::getName();
+  header["persistent"] = "0";
+  header["probe"] = "1";
+  connection->writeHeader(header, [](const ros::ConnectionPtr&) {});
+
   if (future.wait_for(timeout) != std::future_status::ready) {
-    // Drop connection here, removes the link from the service manager instance and avoids
-    // that the header-received callback is called after the promise has already been destroyed.
-    link->getConnection()->drop(ros::Connection::DropReason::Destructing);
+    // Drop the connection here to prevent that the header-received callback is called after the
+    // promise has already been destroyed.
+    connection->drop(ros::Connection::DropReason::Destructing);
     throw std::runtime_error("Timed out when retrieving service type");
   }