fix(mdns): don't hardcode mDNS instance name (#3084)

src/network.cpp

@@ -206,4 +206,34 @@ namespace net {
 
     return mapped_port;
   }
+
+  /**
+   * @brief Returns a string for use as the instance name for mDNS.
+   * @param hostname The hostname to use for instance name generation.
+   * @return Hostname-based instance name or "Sunshine" if hostname is invalid.
+   */
+  std::string
+  mdns_instance_name(const std::string_view &hostname) {
+    // Start with the unmodified hostname
+    std::string instancename { hostname.data(), hostname.size() };
+
+    // Truncate to 63 characters per RFC 6763 section 7.2.
+    if (instancename.size() > 63) {
+      instancename.resize(63);
+    }
+
+    for (auto i = 0; i < instancename.size(); i++) {
+      // Replace any spaces with dashes
+      if (instancename[i] == ' ') {
+        instancename[i] = '-';
+      }
+      else if (!std::isalnum(instancename[i]) && instancename[i] != '-') {
+        // Stop at the first invalid character
+        instancename.resize(i);
+        break;
+      }
+    }
+
+    return !instancename.empty() ? instancename : "Sunshine";
+  }
 }  // namespace net

src/network.h

@@ -105,4 +105,12 @@ namespace net {
    */
   int
   encryption_mode_for_address(boost::asio::ip::address address);
+
+  /**
+   * @brief Returns a string for use as the instance name for mDNS.
+   * @param hostname The hostname to use for instance name generation.
+   * @return Hostname-based instance name or "Sunshine" if hostname is invalid.
+   */
+  std::string
+  mdns_instance_name(const std::string_view &hostname);
 }  // namespace net

src/platform/linux/publish.cpp

@@ -426,7 +426,8 @@ namespace platf::publish {
       return nullptr;
     }
 
-    name.reset(avahi::strdup(SERVICE_NAME));
+    auto instance_name = net::mdns_instance_name(boost::asio::ip::host_name());
+    name.reset(avahi::strdup(instance_name.c_str()));
 
     client.reset(
       avahi::client_new(avahi::simple_poll_get(poll.get()), avahi::ClientFlags(0), client_callback, nullptr, &avhi_error));

src/platform/macos/publish.cpp

@@ -105,7 +105,8 @@ namespace platf::publish {
       &serviceRef,
       0,  // flags
       0,  // interfaceIndex
-      SERVICE_NAME, SERVICE_TYPE,
+      nullptr,  // name
+      SERVICE_TYPE,
       nullptr,  // domain
       nullptr,  // host
       htons(net::map_port(nvhttp::PORT_HTTP)),

src/platform/windows/publish.cpp

@@ -37,7 +37,6 @@ constexpr auto DNS_QUERY_RESULTS_VERSION1 = 0x1;
 
 #define SERVICE_DOMAIN "local"
 
-constexpr auto SERVICE_INSTANCE_NAME = SV(SERVICE_NAME "." SERVICE_TYPE "." SERVICE_DOMAIN);
 constexpr auto SERVICE_TYPE_DOMAIN = SV(SERVICE_TYPE "." SERVICE_DOMAIN);
 
 #ifndef __MINGW32__
@@ -107,10 +106,11 @@ namespace platf::publish {
   service(bool enable, PDNS_SERVICE_INSTANCE &existing_instance) {
     auto alarm = safe::make_alarm<PDNS_SERVICE_INSTANCE>();
 
-    std::wstring name { SERVICE_INSTANCE_NAME.data(), SERVICE_INSTANCE_NAME.size() };
     std::wstring domain { SERVICE_TYPE_DOMAIN.data(), SERVICE_TYPE_DOMAIN.size() };
 
-    auto host = from_utf8(boost::asio::ip::host_name() + ".local");
+    auto hostname = boost::asio::ip::host_name();
+    auto name = from_utf8(net::mdns_instance_name(hostname) + '.') + domain;
+    auto host = from_utf8(hostname + ".local");
 
     DNS_SERVICE_INSTANCE instance {};
     instance.pszInstanceName = name.data();

tests/unit/test_network.cpp

@@ -0,0 +1,26 @@
+/**
+ * @file tests/unit/test_network.cpp
+ * @brief Test src/network.*
+ */
+#include <src/network.h>
+
+#include "../tests_common.h"
+
+struct MdnsInstanceNameTest: testing::TestWithParam<std::tuple<std::string, std::string>> {};
+
+TEST_P(MdnsInstanceNameTest, Run) {
+  auto [input, expected] = GetParam();
+  ASSERT_EQ(net::mdns_instance_name(input), expected);
+}
+
+INSTANTIATE_TEST_SUITE_P(
+  MdnsInstanceNameTests,
+  MdnsInstanceNameTest,
+  testing::Values(
+    std::make_tuple("shortname-123", "shortname-123"),
+    std::make_tuple("space 123", "space-123"),
+    std::make_tuple("hostname.domain.test", "hostname"),
+    std::make_tuple("&", "Sunshine"),
+    std::make_tuple("", "Sunshine"),
+    std::make_tuple("😁", "Sunshine"),
+    std::make_tuple(std::string(128, 'a'), std::string(63, 'a'))));