LibCore: Make UDPServer::receive() return ErrorOr<ByteBuffer>

This is a first step towards handling OOM errors instead of just
crashing the program.

Now UDPServer's method `receive()` return memory allocation
errors explicitly with help of ErrorOr.

This removes one FIXME and make a bunch of new ones. :(

Tests/LibCore/TestLibCoreStream.cpp

@@ -291,7 +291,9 @@ TEST_CASE(udp_socket_read_write)
     usleep(100000);
 
     struct sockaddr_in client_address;
-    auto server_receive_buffer = udp_server->receive(64, client_address);
+    auto server_receive_buffer_or_error = udp_server->receive(64, client_address);
+    EXPECT(!server_receive_buffer_or_error.is_error());
+    auto server_receive_buffer = server_receive_buffer_or_error.release_value();
     EXPECT(!server_receive_buffer.is_empty());
 
     StringView server_received_data { server_receive_buffer.bytes() };

Userland/Libraries/LibCore/UDPServer.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022, Alexander Narsudinov <a.narsudinov@gmail.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -7,6 +8,7 @@
 #include <AK/IPv4Address.h>
 #include <AK/Types.h>
 #include <LibCore/Notifier.h>
+#include <LibCore/System.h>
 #include <LibCore/UDPServer.h>
 #include <errno.h>
 #include <stdio.h>
@@ -61,18 +63,12 @@ bool UDPServer::bind(IPv4Address const& address, u16 port)
     return true;
 }
 
-ByteBuffer UDPServer::receive(size_t size, sockaddr_in& in)
+ErrorOr<ByteBuffer> UDPServer::receive(size_t size, sockaddr_in& in)
 {
-    // FIXME: Handle possible OOM situation.
+    auto buf = TRY(ByteBuffer::create_uninitialized(size));
-    auto buf = ByteBuffer::create_uninitialized(size).release_value_but_fixme_should_propagate_errors();
     socklen_t in_len = sizeof(in);
-    ssize_t rlen = ::recvfrom(m_fd, buf.data(), size, 0, (sockaddr*)&in, &in_len);
+    auto bytes_received = TRY(Core::System::recvfrom(m_fd, buf.data(), size, 0, (sockaddr*)&in, &in_len));
-    if (rlen < 0) {
+    buf.resize(bytes_received);
-        dbgln("recvfrom: {}", strerror(errno));
-        return {};
-    }
-
-    buf.resize(rlen);
     return buf;
 }
 

Userland/Libraries/LibCore/UDPServer.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022, Alexander Narsudinov <a.narsudinov@gmail.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -23,8 +24,8 @@ public:
     bool is_bound() const { return m_bound; }
 
     bool bind(IPv4Address const& address, u16 port);
-    ByteBuffer receive(size_t size, sockaddr_in& from);
+    ErrorOr<ByteBuffer> receive(size_t size, sockaddr_in& from);
-    ByteBuffer receive(size_t size)
+    ErrorOr<ByteBuffer> receive(size_t size)
     {
         struct sockaddr_in saddr;
         return receive(size, saddr);

Userland/Services/DHCPClient/DHCPv4Client.cpp

@@ -122,7 +122,8 @@ DHCPv4Client::DHCPv4Client(Vector<DeprecatedString> interfaces_with_dhcp_enabled
 {
     m_server = Core::UDPServer::construct(this);
     m_server->on_ready_to_receive = [this] {
-        auto buffer = m_server->receive(sizeof(DHCPv4Packet));
+        // TODO: we need to handle possible errors here somehow
+        auto buffer = MUST(m_server->receive(sizeof(DHCPv4Packet)));
         dbgln_if(DHCPV4CLIENT_DEBUG, "Received {} bytes", buffer.size());
         if (buffer.size() < sizeof(DHCPv4Packet) - DHCPV4_OPTION_FIELD_MAX_LENGTH + 1 || buffer.size() > sizeof(DHCPv4Packet)) {
             dbgln("we expected {}-{} bytes, this is a bad packet", sizeof(DHCPv4Packet) - DHCPV4_OPTION_FIELD_MAX_LENGTH + 1, sizeof(DHCPv4Packet));

Userland/Services/LookupServer/DNSServer.cpp

@@ -28,7 +28,7 @@ DNSServer::DNSServer(Object* parent)
 ErrorOr<void> DNSServer::handle_client()
 {
     sockaddr_in client_address;
-    auto buffer = receive(1024, client_address);
+    auto buffer = TRY(receive(1024, client_address));
     auto optional_request = Packet::from_raw_packet(buffer.data(), buffer.size());
     if (!optional_request.has_value()) {
         dbgln("Got an invalid DNS packet");

Userland/Services/LookupServer/MulticastDNS.cpp

@@ -51,7 +51,8 @@ MulticastDNS::MulticastDNS(Object* parent)
 
 void MulticastDNS::handle_packet()
 {
-    auto buffer = receive(1024);
+    // TODO: propagate the error somehow
+    auto buffer = MUST(receive(1024));
     auto optional_packet = Packet::from_raw_packet(buffer.data(), buffer.size());
     if (!optional_packet.has_value()) {
         dbgln("Got an invalid mDNS packet");
@@ -167,7 +168,8 @@ Vector<Answer> MulticastDNS::lookup(Name const& name, RecordType record_type)
             return {};
         }
 
-        auto buffer = receive(1024);
+        // TODO: propagate the error somehow
+        auto buffer = MUST(receive(1024));
         if (buffer.is_empty())
             return {};
         auto optional_packet = Packet::from_raw_packet(buffer.data(), buffer.size());