From ca5036ca5bf80e54da6a0f9cbb5ca3eb5ce1007b Mon Sep 17 00:00:00 2001
From: Cameron Gutman <aicommander@gmail.com>
Date: Sat, 24 Aug 2024 19:38:44 -0500
Subject: [PATCH] fix(mdns): don't hardcode mDNS instance name

---
 src/network.cpp                  | 28 ++++++++++++++++++++++++++++
 src/network.h                    |  7 +++++++
 src/platform/linux/publish.cpp   |  3 ++-
 src/platform/macos/publish.cpp   |  3 ++-
 src/platform/windows/publish.cpp |  3 +--
 tests/unit/test_network.cpp      | 23 +++++++++++++++++++++++
 6 files changed, 63 insertions(+), 4 deletions(-)
 create mode 100644 tests/unit/test_network.cpp

diff --git a/src/network.cpp b/src/network.cpp
index b7b18de88b0..b8628d214fe 100644
--- a/src/network.cpp
+++ b/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
diff --git a/src/network.h b/src/network.h
index ffc0b2d2ff4..875d33665dc 100644
--- a/src/network.h
+++ b/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
diff --git a/src/platform/linux/publish.cpp b/src/platform/linux/publish.cpp
index 29641411e50..7368d36029c 100644
--- a/src/platform/linux/publish.cpp
+++ b/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));
diff --git a/src/platform/macos/publish.cpp b/src/platform/macos/publish.cpp
index ec4f1f452dd..b8c977c0673 100644
--- a/src/platform/macos/publish.cpp
+++ b/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)),
diff --git a/src/platform/windows/publish.cpp b/src/platform/windows/publish.cpp
index fe3352e2309..c6901c8a09b 100644
--- a/src/platform/windows/publish.cpp
+++ b/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");
 
diff --git a/tests/unit/test_network.cpp b/tests/unit/test_network.cpp
new file mode 100644
index 00000000000..13436dd3ce3
--- /dev/null
+++ b/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 == '-');
+  }
+}