LibCore+LibIPC+Everywhere: Return Stream::LocalSocket from LocalServer

This change unfortunately cannot be atomically made without a single
commit changing everything.

Most of the important changes are in LibIPC/Connection.cpp,
LibIPC/ServerConnection.cpp and LibCore/LocalServer.cpp.

The notable changes are:
- IPCCompiler now generates the decode and decode_message functions such
  that they take a Core::Stream::LocalSocket instead of the socket fd.
- IPC::Decoder now uses the receive_fd method of LocalSocket instead of
  doing system calls directly on the fd.
- IPC::ConnectionBase and related classes now use the Stream API
  functions.
- IPC::ServerConnection no longer constructs the socket itself; instead,
  a convenience macro, IPC_CLIENT_CONNECTION, is used in place of
  C_OBJECT and will generate a static try_create factory function for
  the ServerConnection subclass. The subclass is now responsible for
  passing the socket constructed in this function to its
  ServerConnection base; the socket is passed as the first argument to
  the constructor (as a NonnullOwnPtr<Core::Stream::LocalServer>) before
  any other arguments.
- The functionality regarding taking over sockets from SystemServer has
  been moved to LibIPC/SystemServerTakeover.cpp. The Core::LocalSocket
  implementation of this functionality hasn't been deleted due to my
  intention of removing this class in the near future and to reduce
  noise on this (already quite noisy) PR.

Userland/Services/InspectorServer/InspectableProcess.cpp

@@ -16,14 +16,17 @@ InspectableProcess* InspectableProcess::from_pid(pid_t pid)
     return g_processes.get(pid).value_or(nullptr);
 }
 
-InspectableProcess::InspectableProcess(pid_t pid, NonnullRefPtr<Core::LocalSocket> socket)
+InspectableProcess::InspectableProcess(pid_t pid, NonnullOwnPtr<Core::Stream::LocalSocket> socket)
     : m_pid(pid)
     , m_socket(move(socket))
 {
-    m_socket->set_blocking(true);
+    // FIXME: Propagate errors
+    MUST(m_socket->set_blocking(true));
+
     m_socket->on_ready_to_read = [this] {
-        [[maybe_unused]] auto buffer = m_socket->read(1);
-        if (m_socket->eof()) {
+        char c;
+        [[maybe_unused]] auto buffer = m_socket->read({ &c, 1 });
+        if (m_socket->is_eof()) {
             g_processes.remove(m_pid);
             return;
         }
@@ -36,46 +39,51 @@ InspectableProcess::~InspectableProcess()
 
 String InspectableProcess::wait_for_response()
 {
-    if (m_socket->eof()) {
+    if (m_socket->is_eof()) {
         dbgln("InspectableProcess disconnected: PID {}", m_pid);
         m_socket->close();
         return {};
     }
 
     u32 length {};
-    auto nread = m_socket->read((u8*)&length, sizeof(length));
+    auto nread = m_socket->read({ (u8*)&length, sizeof(length) }).release_value_but_fixme_should_propagate_errors();
     if (nread != sizeof(length)) {
         dbgln("InspectableProcess got malformed data: PID {}", m_pid);
         m_socket->close();
         return {};
     }
 
-    ByteBuffer data;
-    size_t remaining_bytes = length;
+    auto data_buffer = ByteBuffer::create_uninitialized(length).release_value();
+    auto remaining_data_buffer = data_buffer.bytes();
 
-    while (remaining_bytes) {
-        auto packet = m_socket->read(remaining_bytes);
-        if (packet.size() == 0)
-            break;
-        if (auto result = data.try_append(packet.data(), packet.size()); result.is_error()) {
-            dbgln("Failed to append {} bytes to data buffer: {}", packet.size(), result.error());
+    while (!remaining_data_buffer.is_empty()) {
+        auto maybe_nread = m_socket->read(remaining_data_buffer);
+        if (maybe_nread.is_error()) {
+            dbgln("InspectableProcess::wait_for_response: Failed to read data: {}", maybe_nread.error());
             break;
         }
-        remaining_bytes -= packet.size();
+
+        auto nread = maybe_nread.release_value();
+        if (nread == 0)
+            break;
+
+        remaining_data_buffer = remaining_data_buffer.slice(nread);
     }
 
-    VERIFY(data.size() == length);
+    VERIFY(data_buffer.size() == length);
     dbgln("Got data size {} and read that many bytes", length);
 
-    return String::copy(data);
+    return String::copy(data_buffer);
 }
 
 void InspectableProcess::send_request(JsonObject const& request)
 {
     auto serialized = request.to_string();
     u32 length = serialized.length();
-    m_socket->write((u8 const*)&length, sizeof(length));
-    m_socket->write(serialized);
+
+    // FIXME: Propagate errors
+    MUST(m_socket->write({ (u8 const*)&length, sizeof(length) }));
+    MUST(m_socket->write(serialized.bytes()));
 }
 
 }