core: always convert hostname to IP for UDP remotes

src/mavsdk/core/CMakeLists.txt

@@ -24,6 +24,7 @@ target_sources(mavsdk
     file_cache.cpp
     flight_mode.cpp
     fs_utils.cpp
+    hostname_to_ip.cpp
     inflate_lzma.cpp
     math_conversions.cpp
     mavsdk.cpp
@@ -85,8 +86,9 @@ if (NOT BUILD_WITHOUT_CURL)
     )
 
     list(APPEND UNIT_TEST_SOURCES
-        # TODO: add this again
         ${PROJECT_SOURCE_DIR}/mavsdk/core/curl_test.cpp
+        ${PROJECT_SOURCE_DIR}/mavsdk/core/hostname_to_ip_test.cpp
+        # TODO: add this again
         #${PROJECT_SOURCE_DIR}/mavsdk/core/http_loader_test.cpp
     )
 else()

src/mavsdk/core/hostname_to_ip.cpp

@@ -0,0 +1,60 @@
+#include "hostname_to_ip.h"
+#include "log.h"
+
+#if defined(WINDOWS)
+#include <winsock2.h>
+#include <ws2tcpip.h>
+#pragma comment(lib, "ws2_32.lib")
+#else
+#include <netdb.h>
+#include <arpa/inet.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#endif
+
+namespace mavsdk {
+
+std::optional<std::string> resolve_hostname_to_ip(const std::string& hostname)
+{
+#if defined(WINDOWS)
+    WSADATA wsaData;
+    if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {
+        std::cerr << "WSAStartup failed" << std::endl;
+        return {};
+    }
+#endif
+
+    addrinfo hints{};
+    hints.ai_family = AF_INET; // IPv4
+    hints.ai_socktype = SOCK_STREAM;
+    hints.ai_flags = AI_PASSIVE;
+
+    addrinfo* result = nullptr;
+    int res = getaddrinfo(hostname.c_str(), nullptr, &hints, &result);
+    if (res != 0) {
+#if defined(WINDOWS)
+        LogErr() << "getaddrinfo failed: " << WSAGetLastError();
+        WSACleanup();
+#else
+        LogErr() << "getaddrinfo failed: " << gai_strerror(res);
+#endif
+        return {};
+    }
+
+    std::string ipAddress;
+    for (addrinfo* ptr = result; ptr != nullptr; ptr = ptr->ai_next) {
+        sockaddr_in* sockaddrIpv4 = reinterpret_cast<sockaddr_in*>(ptr->ai_addr);
+        char ipStr[INET_ADDRSTRLEN];
+        inet_ntop(AF_INET, &(sockaddrIpv4->sin_addr), ipStr, INET_ADDRSTRLEN);
+        ipAddress = ipStr;
+        break; // Take the first result
+    }
+
+    freeaddrinfo(result);
+#if defined(WINDOWS)
+    WSACleanup();
+#endif
+    return {ipAddress};
+}
+
+} // namespace mavsdk

src/mavsdk/core/hostname_to_ip.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <string>
+#include <optional>
+
+namespace mavsdk {
+
+std::optional<std::string> resolve_hostname_to_ip(const std::string& hostname);
+
+} // namespace mavsdk

src/mavsdk/core/hostname_to_ip_test.cpp

@@ -0,0 +1,34 @@
+#include "hostname_to_ip.h"
+#include <gtest/gtest.h>
+
+using namespace mavsdk;
+
+TEST(HostnameToIp, Localhost)
+{
+    auto host = "localhost";
+    auto ip = resolve_hostname_to_ip(host);
+    ASSERT_TRUE(ip);
+    EXPECT_EQ(ip.value(), "127.0.0.1");
+}
+
+TEST(HostnameToIp, Ip)
+{
+    auto host = "127.0.0.1";
+    auto ip = resolve_hostname_to_ip(host);
+    ASSERT_TRUE(ip);
+    EXPECT_EQ(ip.value(), host);
+}
+
+TEST(HostnameToIp, Empty)
+{
+    auto host = "";
+    auto ip = resolve_hostname_to_ip(host);
+    EXPECT_FALSE(ip);
+}
+
+TEST(HostnameToIp, Something)
+{
+    auto host = "something";
+    auto ip = resolve_hostname_to_ip(host);
+    EXPECT_FALSE(ip);
+}

src/mavsdk/core/mavsdk_impl.cpp

@@ -16,6 +16,7 @@
 #include "plugin_base.h"
 #include "mavlink_channels.h"
 #include "callback_list.tpp"
+#include "hostname_to_ip.h"
 
 namespace mavsdk {
 
@@ -538,7 +539,15 @@ MavsdkImpl::add_udp_connection(const CliArg::Udp& udp, ForwardingOption forwardi
     auto handle = add_connection(new_conn);
 
     if (udp.mode == CliArg::Udp::Mode::Out) {
-        new_conn->add_remote(udp.host, udp.port);
+        // We need to add the IP rather than a hostname, otherwise we end up with two remotes:
+        // one for the IP, and one for a hostname.
+        auto remote_ip = resolve_hostname_to_ip(udp.host);
+
+        if (!remote_ip) {
+            return {ConnectionResult::DestinationIpUnknown, Mavsdk::ConnectionHandle{}};
+        }
+
+        new_conn->add_remote(remote_ip.value(), udp.port);
         std::lock_guard<std::recursive_mutex> lock(_systems_mutex);
 
         // With a UDP remote, we need to initiate the connection by sending heartbeats.