[refactor] build host information in the wire library

libs/wire/include/remote_action.h

@@ -10,6 +10,7 @@
 #include <cstddef>
 #include <cstdint>
 #include <string>
+#include <vector>
 
 #include <remote_cursor_shape.h>
 
@@ -179,6 +180,25 @@ struct RemoteAction {
 // Other RemoteAction variants do not own memory and are left unchanged.
 void FreeRemoteAction(RemoteAction& action);
 
+// One display as advertised in host information; bounds are virtual-desktop
+// pixel coordinates.
+struct HostDisplay {
+  std::string name;
+  int left = 0;
+  int top = 0;
+  int right = 0;
+  int bottom = 0;
+};
+
+// Builds the host_infomation message advertised on every new connection.
+// |host_name| is truncated to the wire field size. The display arrays are
+// heap-allocated with the same layout the decoder produces; release the
+// result with FreeRemoteAction. An allocation failure yields an empty display
+// list rather than a partially filled one.
+RemoteAction MakeHostInformation(const std::string& host_name,
+                                 const std::vector<HostDisplay>& displays,
+                                 bool supports_privacy_screen);
+
 }  // namespace crossdesk
 
 #endif

libs/wire/src/remote_action.cpp

@@ -37,8 +37,47 @@ bool AllocateHostDisplays(HostInfo& info, std::size_t count) {
          info.bottom;
 }
 
+char* DuplicateString(const std::string& value) {
+  char* copy = static_cast<char*>(std::malloc(value.size() + 1));
+  if (copy == nullptr) return nullptr;
+  std::memcpy(copy, value.data(), value.size());
+  copy[value.size()] = '\0';
+  return copy;
+}
+
 }  // namespace
 
+RemoteAction MakeHostInformation(const std::string& host_name,
+                                 const std::vector<HostDisplay>& displays,
+                                 bool supports_privacy_screen) {
+  RemoteAction action{};
+  action.type = ControlType::host_infomation;
+  ResetHostInfo(action.i);
+
+  const std::size_t count = displays.size();
+  if (AllocateHostDisplays(action.i, count)) {
+    action.i.display_num = count;
+    for (std::size_t index = 0; index < count; ++index) {
+      const HostDisplay& display = displays[index];
+      action.i.display_list[index] = DuplicateString(display.name);
+      action.i.left[index] = display.left;
+      action.i.top[index] = display.top;
+      action.i.right[index] = display.right;
+      action.i.bottom[index] = display.bottom;
+    }
+  } else {
+    FreeRemoteAction(action);
+  }
+
+  action.i.supports_privacy_screen = supports_privacy_screen;
+  const std::size_t name_size =
+      std::min(host_name.size(), sizeof(action.i.host_name) - 1);
+  std::memcpy(action.i.host_name, host_name.data(), name_size);
+  action.i.host_name[name_size] = '\0';
+  action.i.host_name_size = name_size;
+  return action;
+}
+
 std::string RemoteAction::to_json() const { return ToJson(*this); }
 
 bool RemoteAction::from_json(const std::string& json_string) {