libos: Add a new LocalServer class for local domain sockets

libos/CMakeLists.txt

@@ -14,6 +14,7 @@ set(SOURCES
     src/Mode.cpp
     src/Prompt.cpp
     src/Security.cpp
+    src/LocalServer.cpp
 )
 
 add_library(os ${SOURCES})

libos/include/os/LocalServer.h

@@ -0,0 +1,132 @@
+#pragma once
+#include <luna/Result.h>
+#include <luna/SharedPtr.h>
+#include <luna/StringView.h>
+
+namespace os
+{
+    /**
+     * @brief A local domain server, used to communicate between processes on the same machine.
+     */
+    class LocalServer : public Shareable
+    {
+      public:
+        /**
+         * @brief Create a new server object and bind it to a local address.
+         *
+         * @param path The path to use for the server socket.
+         * @param blocking Whether the server should block if no connections are available when calling accept().
+         * @return Result<SharedPtr<LocalServer>> An error, or a new server object.
+         */
+        static Result<SharedPtr<LocalServer>> create(StringView path, bool blocking);
+
+        /**
+         * @brief Activate the server and start listening for connections.
+         *
+         * @param backlog The number of unaccepted connections to keep.
+         * @return Result<void> Whether the operation succeded.
+         */
+        Result<void> listen(int backlog);
+
+        /**
+         * @brief Return the underlying socket file descriptor used by this object.
+         *
+         * @return int The file descriptor.
+         */
+        int fd() const
+        {
+            return m_fd;
+        }
+
+        /**
+         * @brief An interface to communicate with clients connected to a local server.
+         */
+        class Client : public Shareable
+        {
+          public:
+            /**
+             * @brief Read arbitrary data from the client. The call will block if there is no data and the parent server
+             * object has not been created as non-blocking.
+             *
+             * @param buf The buffer to read data into.
+             * @param length The maximum amount of bytes to read.
+             * @return Result<usize> An error, or the number of bytes read.
+             */
+            Result<usize> recv(u8* buf, usize length);
+
+            /**
+             * @brief Read an object from the client. The call will block if there is no data and the parent server
+             * object has not been created as non-blocking.
+             *
+             * @tparam T The type of the object.
+             * @param out A reference to the object to read data into.
+             * @return Result<void> Whether the operation succeded.
+             */
+            template <typename T> Result<void> recv_typed(T& out)
+            {
+                TRY(recv((u8*)&out, sizeof(T)));
+                return {};
+            }
+
+            /**
+             * @brief Send arbitrary data to the client.
+             *
+             * @param buf The buffer to send data from.
+             * @param length The amount of bytes to send.
+             * @return Result<usize> An error, or the number of bytes actually sent.
+             */
+            Result<usize> send(const u8* buf, usize length);
+
+            /**
+             * @brief Send an object to the client.
+             *
+             * @tparam T The type of the object.
+             * @param out A reference to the object to send data from.
+             * @return Result<void> Whether the operation succeded.
+             */
+            template <typename T> Result<void> send_typed(const T& out)
+            {
+                TRY(send((const u8*)&out, sizeof(T)));
+                return {};
+            }
+
+            /**
+             * @brief Disconnect from the attached client.
+             *
+             * This will make any further reads on the client return ECONNRESET, and will make this object invalid.
+             */
+            void disconnect();
+
+            /**
+             * @brief Return the underlying socket file descriptor used by this object.
+             *
+             * @return int The file descriptor.
+             */
+            int fd() const
+            {
+                return m_fd;
+            }
+
+            Client(int fd);
+            ~Client();
+
+          private:
+            int m_fd;
+        };
+
+        /**
+         * @brief Accept a new incoming connection and return a handle to it. If there are no incoming connections,
+         * accept() either blocks until there is one (if the object was created with blocking=true), or returns EAGAIN
+         * (if the object was created with blocking=false).
+         *
+         * @return Result<SharedPtr<Client>> An error, or a handle to the new connection.
+         */
+        Result<SharedPtr<Client>> accept();
+
+        ~LocalServer();
+
+      private:
+        int m_fd;
+        bool m_blocking;
+    };
+}

libos/src/LocalServer.cpp

@@ -0,0 +1,87 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <os/FileSystem.h>
+#include <os/LocalServer.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+namespace os
+{
+    Result<SharedPtr<LocalServer>> LocalServer::create(StringView path, bool blocking)
+    {
+        auto server = TRY(make_shared<LocalServer>());
+
+        (void)os::FileSystem::remove(path); // We explicitly ignore any error here, either it doesn't exist (which is
+                                            // fine), or it cannot be removed, which will make bind() fail later.
+
+        int sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
+        if (sockfd < 0) return err(errno);
+
+        struct sockaddr_un un;
+        un.sun_family = AF_UNIX;
+        strncpy(un.sun_path, path.chars(), sizeof(un.sun_path));
+
+        if (bind(sockfd, (struct sockaddr*)&un, sizeof(un)) < 0)
+        {
+            close(sockfd);
+            return err(errno);
+        }
+
+        if (!blocking) { fcntl(sockfd, F_SETFL, O_NONBLOCK); }
+        server->m_blocking = blocking;
+
+        fcntl(sockfd, F_SETFD, FD_CLOEXEC);
+
+        server->m_fd = sockfd;
+        return server;
+    }
+
+    Result<void> LocalServer::listen(int backlog)
+    {
+        if (::listen(m_fd, backlog) < 0) return err(errno);
+        return {};
+    }
+
+    Result<SharedPtr<LocalServer::Client>> LocalServer::accept()
+    {
+        int fd = ::accept(m_fd, nullptr, nullptr);
+        if (fd < 0) return err(errno);
+        if (!m_blocking) fcntl(fd, F_SETFL, O_NONBLOCK);
+        return make_shared<Client>(fd);
+    }
+
+    LocalServer::~LocalServer()
+    {
+        close(m_fd);
+    }
+
+    LocalServer::Client::Client(int fd) : m_fd(fd)
+    {
+    }
+
+    LocalServer::Client::~Client()
+    {
+        if (m_fd >= 0) close(m_fd);
+    }
+
+    Result<usize> LocalServer::Client::recv(u8* buf, usize length)
+    {
+        ssize_t nread = read(m_fd, buf, length);
+        if (nread < 0) return err(errno);
+        return nread;
+    }
+
+    Result<usize> LocalServer::Client::send(const u8* buf, usize length)
+    {
+        ssize_t nwrite = write(m_fd, buf, length);
+        if (nwrite < 0) return err(errno);
+        return nwrite;
+    }
+
+    void LocalServer::Client::disconnect()
+    {
+        close(m_fd);
+        m_fd = -1;
+    }
+}