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

src/network.cpp

@@ -206,4 +206,32 @@ namespace net {
 
     return mapped_port;
   }
+
+  /**
+   * @brief Returns a string for use as the instance name for mDNS.
+   * @return Hostname-based instance name or "Sunshine" if hostname is invalid.
+   */
+  std::string
+  mdns_instance_name() {
+    std::string hostname = boost::asio::ip::host_name();
+
+    // Truncate to 63 characters per RFC 6763 section 7.2.
+    if (hostname.size() > 63) {
+      hostname.resize(63);
+    }
+
+    for (auto i = 0; i < hostname.size(); i++) {
+      // Replace any spaces with dashes
+      if (hostname[i] == ' ') {
+        hostname[i] = '-';
+      }
+      else if (!std::isalnum(hostname[i]) && hostname[i] != '-') {
+        // Stop at the first invalid character
+        hostname.resize(i);
+        break;
+      }
+    }
+
+    return !hostname.empty() ? hostname : "Sunshine";
+  }
 }  // namespace net

src/network.h

@@ -105,4 +105,11 @@ namespace net {
    */
   int
   encryption_mode_for_address(boost::asio::ip::address address);
+
+  /**
+   * @brief Returns a string for use as the instance name for mDNS.
+   * @return Hostname-based instance name or "Sunshine" if hostname is invalid.
+   */
+  std::string
+  mdns_instance_name();
 }  // 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();
+    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__
@@ -107,8 +106,8 @@ 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() };
+    std::wstring name = from_utf8(net::mdns_instance_name() + '.') + domain;
 
     auto host = from_utf8(boost::asio::ip::host_name() + ".local");
 

tests/unit/test_network.cpp

@@ -0,0 +1,23 @@
+/**
+ * @file tests/unit/test_network.cpp
+ * @brief Test src/network.*
+ */
+#include <src/network.h>
+
+#include "../tests_common.h"
+
+TEST(MdnsInstanceNameTests, ValidLength) {
+  auto name = net::mdns_instance_name();
+
+  // The instance name must be 63 characters or less
+  EXPECT_LT(name.size(), 64);
+}
+
+TEST(MdnsInstanceNameTests, ValidCharacters) {
+  auto name = net::mdns_instance_name();
+
+  // The string must not contain invalid hostname characters
+  for (const char& c : name) {
+    EXPECT_TRUE(std::isalnum(c) || c == '-');
+  }
+}