LookupServer: Switch to LibIPC :^)

The ad-hoc IPC we were doing with LookupServer was kinda gross. With this,
LookupServer is a regular IPC server. In the future, we want to add more APIs
for LookupServer to talk to its clients (such as DHCPClient telling LookupServer
about the DNS server discovered via DHCP, and DNS-SD client browsing for
services), which calls for a more expressive IPC format; this is what LibIPC is
perfect for.

While the LookupServer side is using the regular LibIPC mechanics and patterns,
the LibC side has to hand-roll LibIPC format serialization without actually
using LibIPC. We might be able to get rid of this in the future, but for now it
has to be like that. The good news is the format is not that bad at all.

Userland/Libraries/LibC/netdb.cpp

@@ -46,6 +46,7 @@ static in_addr_t* __gethostbyname_address_list_buffer[2];
 
 static hostent __gethostbyaddr_buffer;
 static in_addr_t* __gethostbyaddr_address_list_buffer[2];
+static constexpr i32 lookup_server_endpoint_magic = 9001;
 
 // Get service entry buffers and file information for the getservent() family of functions.
 static FILE* services_file = nullptr;
@@ -123,32 +124,74 @@ hostent* gethostbyname(const char* name)
         close(fd);
     });
 
-    auto line = String::formatted("L{}\n", name);
-    int nsent = write(fd, line.characters(), line.length());
+    size_t name_length = strlen(name);
+
+    struct [[gnu::packed]] {
+        u32 message_size;
+        i32 endpoint_magic;
+        i32 message_id;
+        i32 name_length;
+    } request_header = {
+        sizeof(request_header) - sizeof(request_header.message_size) + name_length,
+        lookup_server_endpoint_magic,
+        1,
+        (i32)name_length,
+    };
+    int nsent = write(fd, &request_header, sizeof(request_header));
     if (nsent < 0) {
         perror("write");
         return nullptr;
     }
+    ASSERT((size_t)nsent == sizeof(request_header));
+    nsent = write(fd, name, name_length);
+    if (nsent < 0) {
+        perror("write");
+        return nullptr;
+    }
+    ASSERT((size_t)nsent == name_length);
 
-    ASSERT((size_t)nsent == line.length());
+    struct [[gnu::packed]] {
+        u32 message_size;
+        i32 endpoint_magic;
+        i32 message_id;
+        i32 code;
+        u64 addresses_count;
+    } response_header;
 
-    char buffer[1024];
-    int nrecv = read(fd, buffer, sizeof(buffer) - 1);
+    int nrecv = read(fd, &response_header, sizeof(response_header));
     if (nrecv < 0) {
         perror("recv");
         return nullptr;
     }
-
-    if (!memcmp(buffer, "Not found.", sizeof("Not found.") - 1))
+    ASSERT((size_t)nrecv == sizeof(response_header));
+    if (response_header.endpoint_magic != lookup_server_endpoint_magic || response_header.message_id != 2) {
+        dbgln("Received an unexpected message");
         return nullptr;
-
-    auto responses = String(buffer, nrecv).split('\n');
-    if (responses.is_empty())
+    }
+    if (response_header.code != 0) {
+        // TODO: return a specific error.
         return nullptr;
+    }
+    ASSERT(response_header.addresses_count > 0);
 
-    auto& response = responses[0];
+    i32 response_length;
+    nrecv = read(fd, &response_length, sizeof(response_length));
+    if (nrecv < 0) {
+        perror("recv");
+        return nullptr;
+    }
+    ASSERT((size_t)nrecv == sizeof(response_length));
 
-    int rc = inet_pton(AF_INET, response.characters(), &__gethostbyname_address);
+    char response[response_length + 1];
+    nrecv = read(fd, response, response_length);
+    if (nrecv < 0) {
+        perror("recv");
+        return nullptr;
+    }
+    ASSERT(nrecv == response_length);
+    response[response_length] = 0;
+
+    int rc = inet_pton(AF_INET, response, &__gethostbyname_address);
     if (rc <= 0)
         return nullptr;
 
@@ -188,36 +231,66 @@ hostent* gethostbyaddr(const void* addr, socklen_t addr_size, int type)
     });
 
     IPv4Address ipv4_address((const u8*)&((const in_addr*)addr)->s_addr);
+    auto address = ipv4_address.to_string();
 
-    auto line = String::formatted("R{}.{}.{}.{}.in-addr.arpa\n",
-        ipv4_address[3],
-        ipv4_address[2],
-        ipv4_address[1],
-        ipv4_address[0]);
-    int nsent = write(fd, line.characters(), line.length());
+    struct [[gnu::packed]] {
+        u32 message_size;
+        i32 endpoint_magic;
+        i32 message_id;
+        i32 address_length;
+    } request_header = {
+        sizeof(request_header) - sizeof(request_header.message_size) + address.length(),
+        lookup_server_endpoint_magic,
+        3,
+        (i32)address.length(),
+    };
+    int nsent = write(fd, &request_header, sizeof(request_header));
     if (nsent < 0) {
         perror("write");
         return nullptr;
     }
+    ASSERT((size_t)nsent == sizeof(request_header));
+    nsent = write(fd, address.characters(), address.length());
+    if (nsent < 0) {
+        perror("write");
+        return nullptr;
+    }
+    ASSERT((size_t)nsent == address.length());
 
-    ASSERT((size_t)nsent == line.length());
+    struct [[gnu::packed]] {
+        u32 message_size;
+        i32 endpoint_magic;
+        i32 message_id;
+        i32 code;
+        i32 name_length;
+    } response_header;
 
-    char buffer[1024];
-    int nrecv = read(fd, buffer, sizeof(buffer) - 1);
+    int nrecv = read(fd, &response_header, sizeof(response_header));
     if (nrecv < 0) {
         perror("recv");
         return nullptr;
     }
-
-    if (!memcmp(buffer, "Not found.", sizeof("Not found.") - 1))
+    ASSERT((size_t)nrecv == sizeof(response_header));
+    if (response_header.endpoint_magic != lookup_server_endpoint_magic || response_header.message_id != 4) {
+        dbgln("Received an unexpected message");
         return nullptr;
-
-    auto responses = String(buffer, nrecv).split('\n');
-    if (responses.is_empty())
+    }
+    if (response_header.code != 0) {
+        // TODO: return a specific error.
         return nullptr;
+    }
 
-    gethostbyaddr_name_buffer = responses[0];
-    __gethostbyaddr_buffer.h_name = const_cast<char*>(gethostbyaddr_name_buffer.characters());
+    char* buffer;
+    auto string_impl = StringImpl::create_uninitialized(response_header.name_length, buffer);
+    nrecv = read(fd, buffer, response_header.name_length);
+    if (nrecv < 0) {
+        perror("recv");
+        return nullptr;
+    }
+    ASSERT(nrecv == response_header.name_length);
+
+    gethostbyaddr_name_buffer = move(string_impl);
+    __gethostbyaddr_buffer.h_name = buffer;
     __gethostbyaddr_buffer.h_aliases = nullptr;
     __gethostbyaddr_buffer.h_addrtype = AF_INET;
     // FIXME: Should we populate the hostent's address list here with a sockaddr_in for the provided host?

Userland/Services/LookupServer/CMakeLists.txt

@@ -1,10 +1,16 @@
+compile_ipc(LookupServer.ipc LookupServerEndpoint.h)
+compile_ipc(LookupClient.ipc LookupClientEndpoint.h)
+
 set(SOURCES
     DNSAnswer.cpp
     DNSRequest.cpp
     DNSResponse.cpp
     LookupServer.cpp
+    LookupServerEndpoint.h
+    LookupClientEndpoint.h
+    ClientConnection.cpp
     main.cpp
 )
 
 serenity_bin(LookupServer)
-target_link_libraries(LookupServer LibCore)
+target_link_libraries(LookupServer LibCore LibIPC)

Userland/Services/LookupServer/ClientConnection.cpp

@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2021, Sergey Bugaev <bugaevc@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "ClientConnection.h"
+#include "DNSRequest.h"
+#include "LookupServer.h"
+#include <AK/IPv4Address.h>
+
+namespace LookupServer {
+
+static HashMap<int, RefPtr<ClientConnection>> s_connections;
+
+ClientConnection::ClientConnection(AK::NonnullRefPtr<Core::LocalSocket> socket, int client_id)
+    : IPC::ClientConnection<LookupClientEndpoint, LookupServerEndpoint>(*this, move(socket), client_id)
+{
+    s_connections.set(client_id, *this);
+}
+
+ClientConnection::~ClientConnection()
+{
+}
+
+void ClientConnection::die()
+{
+    s_connections.remove(client_id());
+}
+
+OwnPtr<Messages::LookupServer::LookupNameResponse> ClientConnection::handle(const Messages::LookupServer::LookupName& message)
+{
+    auto addresses = LookupServer::the().lookup(message.name(), T_A);
+    if (addresses.is_empty())
+        return make<Messages::LookupServer::LookupNameResponse>(1, Vector<String>());
+    return make<Messages::LookupServer::LookupNameResponse>(0, move(addresses));
+}
+
+OwnPtr<Messages::LookupServer::LookupAddressResponse> ClientConnection::handle(const Messages::LookupServer::LookupAddress& message)
+{
+    auto optional_address = IPv4Address::from_string(message.address());
+    if (!optional_address.has_value())
+        return make<Messages::LookupServer::LookupAddressResponse>(1, String());
+    auto& address = optional_address.value();
+    auto name = String::formatted("{}.{}.{}.{}.in-addr.arpa",
+        address[3],
+        address[2],
+        address[1],
+        address[0]);
+    auto hosts = LookupServer::the().lookup(name, T_PTR);
+    if (hosts.is_empty())
+        return make<Messages::LookupServer::LookupAddressResponse>(1, String());
+    return make<Messages::LookupServer::LookupAddressResponse>(0, hosts[0]);
+}
+}

Userland/Services/LookupServer/ClientConnection.h

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2021, Sergey Bugaev <bugaevc@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/HashMap.h>
+#include <LibIPC/ClientConnection.h>
+#include <LookupServer/LookupClientEndpoint.h>
+#include <LookupServer/LookupServerEndpoint.h>
+
+namespace LookupServer {
+
+class ClientConnection final
+    : public IPC::ClientConnection<LookupClientEndpoint, LookupServerEndpoint>
+    , public LookupServerEndpoint {
+
+    C_OBJECT(ClientConnection);
+
+public:
+    explicit ClientConnection(NonnullRefPtr<Core::LocalSocket>, int client_id);
+    virtual ~ClientConnection() override;
+
+    virtual void die() override;
+
+private:
+    virtual OwnPtr<Messages::LookupServer::LookupNameResponse> handle(const Messages::LookupServer::LookupName&) override;
+    virtual OwnPtr<Messages::LookupServer::LookupAddressResponse> handle(const Messages::LookupServer::LookupAddress&) override;
+};
+
+}

Userland/Services/LookupServer/LookupClient.ipc

@@ -0,0 +1,4 @@
+endpoint LookupClient = 9002
+{
+    Dummy() =|
+}

Userland/Services/LookupServer/LookupServer.cpp

@@ -25,6 +25,7 @@
  */
 
 #include "LookupServer.h"
+#include "ClientConnection.h"
 #include "DNSRequest.h"
 #include "DNSResponse.h"
 #include <AK/ByteBuffer.h>
@@ -43,8 +44,19 @@
 
 namespace LookupServer {
 
+static LookupServer* s_the;
+
+LookupServer& LookupServer::the()
+{
+    ASSERT(s_the);
+    return *s_the;
+}
+
 LookupServer::LookupServer()
 {
+    ASSERT(s_the == nullptr);
+    s_the = this;
+
     auto config = Core::ConfigFile::get_for_system("LookupServer");
     dbgln("Using network config file at {}", config->file_name());
     m_nameservers = config->read_entry("DNS", "Nameservers", "1.1.1.1,1.0.0.1").split(',');
@@ -54,13 +66,13 @@ LookupServer::LookupServer()
     m_local_server = Core::LocalServer::construct(this);
     m_local_server->on_ready_to_accept = [this]() {
         auto socket = m_local_server->accept();
-        if (!socket)
+        if (!socket) {
+            dbgln("Failed to accept a client connection");
             return;
-        socket->on_ready_to_read = [this, socket]() {
-            service_client(*socket);
-            NonnullRefPtr keeper = *socket;
-            const_cast<Core::LocalSocket&>(*socket).on_ready_to_read = [] {};
-        };
+        }
+        static int s_next_client_id = 0;
+        int client_id = ++s_next_client_id;
+        IPC::new_client_connection<ClientConnection>(socket.release_nonnull(), client_id);
     };
     bool ok = m_local_server->take_over_from_system_server();
     ASSERT(ok);
@@ -101,32 +113,17 @@ void LookupServer::load_etc_hosts()
     }
 }
 
-void LookupServer::service_client(NonnullRefPtr<Core::LocalSocket> socket)
+Vector<String> LookupServer::lookup(const String& name, unsigned short record_type)
 {
-    u8 client_buffer[1024];
-    int nrecv = socket->read(client_buffer, sizeof(client_buffer) - 1);
-    if (nrecv < 0) {
-        perror("read");
-        return;
-    }
-
-    client_buffer[nrecv] = '\0';
-
-    char lookup_type = client_buffer[0];
-    if (lookup_type != 'L' && lookup_type != 'R') {
-        dbgln("Invalid lookup_type '{}'", lookup_type);
-        return;
-    }
-    auto hostname = String((const char*)client_buffer + 1, nrecv - 1, Chomp);
 #if LOOKUPSERVER_DEBUG
-    dbgln("Got request for '{}'", hostname);
+    dbgln("Got request for '{}'", name);
 #endif
 
     Vector<String> responses;
 
-    if (auto known_host = m_etc_hosts.get(hostname); known_host.has_value()) {
+    if (auto known_host = m_etc_hosts.get(name); known_host.has_value()) {
         responses.append(known_host.value());
-    } else if (!hostname.is_empty()) {
+    } else if (!name.is_empty()) {
         for (auto& nameserver : m_nameservers) {
 #if LOOKUPSERVER_DEBUG
             dbgln("Doing lookup using nameserver '{}'", nameserver);
@@ -134,10 +131,7 @@ void LookupServer::service_client(NonnullRefPtr<Core::LocalSocket> socket)
             bool did_get_response = false;
             int retries = 3;
             do {
-                if (lookup_type == 'L')
-                    responses = lookup(hostname, nameserver, did_get_response, T_A);
-                else if (lookup_type == 'R')
-                    responses = lookup(hostname, nameserver, did_get_response, T_PTR);
+                responses = lookup(name, nameserver, did_get_response, record_type);
                 if (did_get_response)
                     break;
             } while (--retries);
@@ -152,24 +146,11 @@ void LookupServer::service_client(NonnullRefPtr<Core::LocalSocket> socket)
         }
         if (responses.is_empty()) {
             fprintf(stderr, "LookupServer: Tried all nameservers but never got a response :(\n");
-            return;
+            return {};
         }
     }
 
-    if (responses.is_empty()) {
-        int nsent = socket->write("Not found.\n");
-        if (nsent < 0)
-            perror("write");
-        return;
-    }
-    for (auto& response : responses) {
-        auto line = String::formatted("{}\n", response);
-        int nsent = socket->write(line);
-        if (nsent < 0) {
-            perror("write");
-            break;
-        }
-    }
+    return move(responses);
 }
 
 Vector<String> LookupServer::lookup(const String& hostname, const String& nameserver, bool& did_get_response, unsigned short record_type, ShouldRandomizeCase should_randomize_case)

Userland/Services/LookupServer/LookupServer.h

@@ -38,11 +38,13 @@ class LookupServer final : public Core::Object {
     C_OBJECT(LookupServer);
 
 public:
+    static LookupServer& the();
+    Vector<String> lookup(const String& name, unsigned short record_type);
+
 private:
     LookupServer();
 
     void load_etc_hosts();
-    void service_client(NonnullRefPtr<Core::LocalSocket>);
     Vector<String> lookup(const String& hostname, const String& nameserver, bool& did_get_response, unsigned short record_type, ShouldRandomizeCase = ShouldRandomizeCase::Yes);
 
     struct CachedLookup {

Userland/Services/LookupServer/LookupServer.ipc

@@ -0,0 +1,5 @@
+endpoint LookupServer = 9001
+{
+    LookupName(String name) => (int code, Vector<String> addresses)
+    LookupAddress(String address) => (int code, String name)
+}