Add client communication library

This change adds a library to connect to the X52 daemon and send
commands and receive responses. The library is a thin wrapper around the
POSIX sockets API. While a client could implement the functions
themselves, the library makes it a little bit easier, as well as
allowing for third-party clients to connect to and communicate with the
daemon.

.gitignore

@@ -13,7 +13,7 @@ libx52test*
 libx52util/util_char_map.c
 udev/*.rules
 x52d*
-!daemon/x52d_*.*
+!daemon/x52d*.*
 test-*
 libx52-*.tar.gz
 

Doxyfile.in

@@ -861,6 +861,7 @@ FILE_PATTERNS          = \
                          libx52io.h \
                          libx52util.h \
                          x52_cli.c \
+                         x52dcomm.h \
                          *.dox
 
 # The RECURSIVE tag can be used to specify whether or not subdirectories should

daemon/Makefile.am

@@ -46,6 +46,20 @@ x52d_LDFLAGS += @EVDEV_LIBS@
 x52d_LDADD += libx52io.la
 endif
 
+lib_LTLIBRARIES += libx52dcomm.la
+
+# Client library to communicate with X52 daemon
+libx52dcomm_la_SOURCES = \
+	daemon/x52d_comm_client.c
+libx52dcomm_la_CFLAGS = \
+	-I $(top_srcdir) \
+	-DSYSCONFDIR=\"$(sysconfdir)\" \
+	-DLOCALEDIR=\"$(localedir)\" \
+	-DLOGDIR=\"$(localstatedir)/log\" \
+	-DRUNDIR=\"$(localstatedir)/run\" \
+	$(WARN_CFLAGS)
+libx52dcomm_la_LDFLAGS = $(WARN_LDFLAGS)
+
 x52dconfdir = @sysconfdir@/x52d
 x52dconf_DATA = daemon/x52d.conf
 
@@ -63,6 +77,7 @@ EXTRA_DIST += \
 	daemon/x52d_device.h \
 	daemon/x52d_io.h \
 	daemon/x52d_mouse.h \
+	daemon/x52dcomm.h \
 	daemon/x52d.conf
 
 if HAVE_SYSTEMD

daemon/x52d_comm_client.c

@@ -0,0 +1,108 @@
+/*
+ * Saitek X52 Pro MFD & LED driver - Client communication library
+ *
+ * Copyright (C) 2021 Nirenjan Krishnan (nirenjan@nirenjan.org)
+ *
+ * SPDX-License-Identifier: GPL-2.0-only WITH Classpath-exception-2.0
+ */
+
+#include "config.h"
+
+#include <errno.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+#include "x52dcomm.h"
+#include "x52d_const.h"
+
+int x52d_dial_command(const char *sock_path)
+{
+    int sock;
+    socklen_t len;
+    struct sockaddr_un remote;
+    int saved_errno;
+
+    if (sock_path == NULL) {
+        sock_path = X52D_SOCK_COMMAND;
+    }
+
+    len = strlen(sock_path);
+    if (len >= sizeof(remote.sun_path)) {
+        /* Socket path will not fit inside sun_path */
+        errno = E2BIG;
+        return -1;
+    }
+
+    /* Create a socket */
+    sock = socket(AF_UNIX, SOCK_STREAM, 0);
+    if (sock == -1) {
+        /* Failure creating the socket, abort early */
+        return -1;
+    }
+
+    /* Setup the sockaddr structure */
+    memset(&remote, 0, sizeof(remote));
+    remote.sun_family = AF_UNIX;
+    /* We've already verified that sock_path will fit, so we don't need strncpy */
+    strcpy(remote.sun_path, sock_path);
+    len += sizeof(remote.sun_family);
+
+    /* Connect to the socket */
+    if (connect(sock, (struct sockaddr *)&remote, len) == -1) {
+        /* Failure connecting to the socket. Cleanup */
+        saved_errno = errno;
+        /* close may modify errno, so we save it prior to the call */
+        close(sock);
+        sock = -1;
+        errno = saved_errno;
+    }
+
+    return sock;
+}
+
+int x52d_send_command(int sock_fd, char *buffer, size_t buflen)
+{
+    int rc;
+
+    for (;;) {
+        /*
+         * Unix sockets should have sufficient capacity to send the full
+         * datagram in a single message. Assume that is the case.
+         */
+        rc = send(sock_fd, buffer, buflen, 0);
+        if (rc < 0) {
+            // Error
+            if (errno == EINTR) {
+                // System call interrupted due to signal. Try again
+                continue;
+            } else {
+                // Failed. Return early
+                return -1;
+            }
+        }
+
+        break;
+    }
+
+    /* Wait till we get a response */
+    for (;;) {
+        rc = recv(sock_fd, buffer, buflen, 0);
+        if (rc < 0) {
+            // Error
+            if (errno == EINTR) {
+                // System call interrupted due to signal. Try again
+                continue;
+            } else {
+                // Failed. Return early
+                return -1;
+            }
+        }
+
+        break;
+    }
+
+    return rc;
+}

daemon/x52d_const.h

@@ -17,6 +17,8 @@
 
 #define X52D_PID_FILE   RUNDIR "/" X52D_APP_NAME ".pid"
 
+#define X52D_SOCK_COMMAND   RUNDIR "/" X52D_APP_NAME ".cmd"
+
 #include "gettext.h"
 #define N_(x) gettext_noop(x)
 #define _(x) gettext(x)

daemon/x52dcomm.h

@@ -0,0 +1,90 @@
+/*
+ * Saitek X52 Pro MFD & LED driver
+ *
+ * Copyright (C) 2021 Nirenjan Krishnan (nirenjan@nirenjan.org)
+ *
+ * SPDX-License-Identifier: GPL-2.0-only WITH Classpath-exception-2.0
+ */
+
+/**
+ * @file x52dcomm.h
+ * @brief Functions, structures and enumerations for the Saitek X52 MFD & LED
+ * daemon communication library.
+ *
+ * This file contains the type, enum and function prototypes for the Saitek X52
+ * daemon communication library. These functions allow a client application to
+ * communicate with a running X52 daemon, execute commands and retrieve data.
+ *
+ * @author Nirenjan Krishnan (nirenjan@nirenjan.org)
+ */
+#ifndef X52DCOMM_H
+#define X52DCOMM_H
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @defgroup x52dcomm Daemon communication
+ *
+ * These functions are used to communicate with the X52 daemon.
+ *
+ * @{
+ */
+
+/**
+ * @brief Open a connection to the daemon.
+ *
+ * This method opens a socket connection to the daemon command socket. This
+ * socket allows the client to issue commands and retrieve data. The \p sock_path
+ * parameter may be NULL, in which case, it will use the default socket path.
+ *
+ * The client will need to use the returned descriptor to communicate with the
+ * daemon using \ref x52d_send_command. Once finished, the client may use the
+ * \c close(2) method to close the file descriptor.
+ *
+ * @param[in]   sock_path   Path to the daemon command socket.
+ *
+ * @returns Non-negative socket file descriptor on success.
+ * @returns -1 on failure, and set \c errno accordingly.
+ *
+ * @exception E2BIG returned if the passed socket path is too big
+ */
+int x52d_dial_command(const char *sock_path);
+
+/**
+ * @brief Send a command to the daemon and retrieve the response.
+ *
+ * The client sends the command and parameters as a single NULL terminated
+ * string, and retrieves the response in the same manner. Depending on the
+ * result, the return status is either a positive integer or -1, and \c errno
+ * is set accordingly.
+ *
+ * \p buffer should contain sufficient space to accomodate the returned
+ * response string.
+ *
+ * This is a blocking function and will not return until either a response is
+ * received from the server, or an exception condition occurs.
+ *
+ * @param[in]       sock_fd Socket descriptor returned from
+ *                          \ref x52d_dial_command
+ *
+ * @param[inout]    buffer  Pointer to the string containing the command and
+ *                          parameters. This is also used to save the returned
+ *                          response.
+ *
+ * @param[in]       buflen  Length of the buffer to hold the returned response.
+ *
+ * @returns number of bytes returned from the server
+ * @returns -1 on an error condition, and \c errno is set accordingly.
+ */
+int x52d_send_command(int sock_fd, char *buffer, size_t buflen);
+
+/** @} */
+#ifdef __cplusplus
+}
+#endif
+#endif // !defined X52DCOMM_H
+