dwmblocks/main.c

#define _GNU_SOURCE
#include <X11/Xlib.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/epoll.h>
#include <sys/signalfd.h>
#include <time.h>
#include <unistd.h>

#define LEN(arr) (sizeof(arr) / sizeof(arr[0]))
#define MAX(a, b) (a > b ? a : b)
#define BLOCK(cmd, interval, signal) \
	{ "echo \"$(" cmd ")\"", interval, signal }

typedef const struct {
	const char* command;
	const unsigned int interval;
	const unsigned int signal;
} Block;
#include "config.h"

#ifdef CLICKABLE_BLOCKS
#undef CLICKABLE_BLOCKS
#define CLICKABLE_BLOCKS 1
#else
#define CLICKABLE_BLOCKS 0
#endif

#ifdef LEADING_DELIMITER
#undef LEADING_DELIMITER
#define LEADING_DELIMITER 1
#else
#define LEADING_DELIMITER 0
#endif

static Display* dpy;
static int screen;
static Window root;
static unsigned short statusContinue = 1;
static struct epoll_event event;
static int pipes[LEN(blocks)][2];
static int timer = 0, timerTick = 0, maxInterval = 1;
static int signalFD;
static int epollFD;
static int execLock = 0;

// Longest UTF-8 character is 4 bytes long
static char outputs[LEN(blocks)][CMDLENGTH * 4 + 1 + CLICKABLE_BLOCKS];
static char statusBar[2][LEN(blocks) * (LEN(outputs[0]) - 1) + (LEN(blocks) - 1 + LEADING_DELIMITER) * (LEN(DELIMITER) - 1) + 1];

void (*writeStatus)();

int gcd(int a, int b) {
	int temp;
	while (b > 0) {
		temp = a % b;
		a = b;
		b = temp;
	}
	return a;
}

void closePipe(int* pipe) {
	close(pipe[0]);
	close(pipe[1]);
}

void execBlock(int i, const char* button) {
	// Ensure only one child process exists per block at an instance
	if (execLock & 1 << i)
		return;
	// Lock execution of block until current instance finishes execution
	execLock |= 1 << i;

	if (fork() == 0) {
		close(pipes[i][0]);
		dup2(pipes[i][1], STDOUT_FILENO);
		close(pipes[i][1]);

		if (button)
			setenv("BLOCK_BUTTON", button, 1);
		execl("/bin/sh", "sh", "-c", blocks[i].command, (char*)NULL);
		exit(EXIT_FAILURE);
	}
}

void execBlocks(unsigned int time) {
	for (int i = 0; i < LEN(blocks); i++)
		if (time == 0 || (blocks[i].interval != 0 && time % blocks[i].interval == 0))
			execBlock(i, NULL);
}

int getStatus(char* new, char* old) {
	strcpy(old, new);
	new[0] = '\0';

	for (int i = 0; i < LEN(blocks); i++) {
#if LEADING_DELIMITER
		if (strlen(outputs[i]))
#else
		if (strlen(new) && strlen(outputs[i]))
#endif
			strcat(new, DELIMITER);
		strcat(new, outputs[i]);
	}
	return strcmp(new, old);
}

void updateBlock(int i) {
	char* output = outputs[i];
	char buffer[LEN(outputs[0]) - CLICKABLE_BLOCKS];
	int bytesRead = read(pipes[i][0], buffer, LEN(buffer));

	// Trim UTF-8 string to desired length
	int count = 0, j = 0;
	while (buffer[j] != '\n' && count < CMDLENGTH) {
		count++;

		// Skip continuation bytes, if any
		char ch = buffer[j];
		int skip = 1;
		while ((ch & 0xc0) > 0x80)
			ch <<= 1, skip++;
		j += skip;
	}

	// Cache last character and replace it with a trailing space
	char ch = buffer[j];
	buffer[j] = ' ';

	// Trim trailing spaces
	while (j >= 0 && buffer[j] == ' ')
		j--;
	buffer[j + 1] = 0;

	// Clear the pipe
	if (bytesRead == LEN(buffer)) {
		while (ch != '\n' && read(pipes[i][0], &ch, 1) == 1)
			;
	}

#if CLICKABLE_BLOCKS
	if (bytesRead > 1 && blocks[i].signal > 0) {
		output[0] = blocks[i].signal;
		output++;
	}
#endif

	strcpy(output, buffer);

	// Remove execution lock for the current block
	execLock &= ~(1 << i);
}

void debug() {
	// Only write out if text has changed
	if (!getStatus(statusBar[0], statusBar[1]))
		return;

	write(STDOUT_FILENO, statusBar[0], strlen(statusBar[0]));
	write(STDOUT_FILENO, "\n", 1);
}

int setupX() {
	dpy = XOpenDisplay(NULL);
	if (!dpy)
		return 1;

	screen = DefaultScreen(dpy);
	root = RootWindow(dpy, screen);
	return 0;
}

void setRoot() {
	// Only set root if text has changed
	if (!getStatus(statusBar[0], statusBar[1]))
		return;

	XStoreName(dpy, root, statusBar[0]);
	XFlush(dpy);
}

void signalHandler() {
	struct signalfd_siginfo info;
	read(signalFD, &info, sizeof(info));
	unsigned int signal = info.ssi_signo;

	switch (signal) {
	case SIGALRM:
		// Schedule the next timer event and execute blocks
		alarm(timerTick);
		execBlocks(timer);

		// Wrap `timer` to the interval [1, `maxInterval`]
		timer = (timer + timerTick - 1) % maxInterval + 1;
		return;
	case SIGUSR1:
		// Update all blocks on receiving SIGUSR1
		execBlocks(0);
		return;
	}

	for (int j = 0; j < LEN(blocks); j++) {
		if (blocks[j].signal == signal - SIGRTMIN) {
			char button[] = {'0' + info.ssi_int & 0xff, 0};
			execBlock(j, button);
			break;
		}
	}
}

void termHandler() {
	statusContinue = 0;
}

void setupSignals() {
	sigset_t handledSignals;
	sigemptyset(&handledSignals);
	sigaddset(&handledSignals, SIGUSR1);
	sigaddset(&handledSignals, SIGALRM);

	// Append all block signals to `handledSignals`
	for (int i = 0; i < LEN(blocks); i++)
		if (blocks[i].signal > 0)
			sigaddset(&handledSignals, SIGRTMIN + blocks[i].signal);

	// Create a signal file descriptor for epoll to watch
	signalFD = signalfd(-1, &handledSignals, 0);
	event.data.u32 = LEN(blocks);
	epoll_ctl(epollFD, EPOLL_CTL_ADD, signalFD, &event);

	// Block all realtime and handled signals
	for (int i = SIGRTMIN; i <= SIGRTMAX; i++)
		sigaddset(&handledSignals, i);
	sigprocmask(SIG_BLOCK, &handledSignals, NULL);

	// Handle termination signals
	signal(SIGINT, termHandler);
	signal(SIGTERM, termHandler);

	// Avoid zombie subprocesses
	struct sigaction sa;
	sa.sa_handler = SIG_DFL;
	sigemptyset(&sa.sa_mask);
	sa.sa_flags = SA_NOCLDWAIT;
	sigaction(SIGCHLD, &sa, 0);
}

void statusLoop() {
	// Update all blocks initially
	raise(SIGALRM);

	struct epoll_event events[LEN(blocks) + 1];
	while (statusContinue) {
		int eventCount = epoll_wait(epollFD, events, LEN(events), -1);
		for (int i = 0; i < eventCount; i++) {
			unsigned short id = events[i].data.u32;
			if (id < LEN(blocks))
				updateBlock(id);
			else
				signalHandler();
		}

		if (eventCount != -1)
			writeStatus();
	}
}

void init() {
	epollFD = epoll_create(LEN(blocks));
	event.events = EPOLLIN;

	for (int i = 0; i < LEN(blocks); i++) {
		// Append each block's pipe to `epollFD`
		pipe(pipes[i]);
		event.data.u32 = i;
		epoll_ctl(epollFD, EPOLL_CTL_ADD, pipes[i][0], &event);

		// Calculate the max interval and tick size for the timer
		if (blocks[i].interval) {
			maxInterval = MAX(blocks[i].interval, maxInterval);
			timerTick = gcd(blocks[i].interval, timerTick);
		}
	}

	setupSignals();
}

int main(const int argc, const char* argv[]) {
	if (setupX()) {
		fprintf(stderr, "dwmblocks: Failed to open display\n");
		return 1;
	}

	writeStatus = setRoot;
	for (int i = 0; i < argc; i++)
		if (!strcmp("-d", argv[i]))
			writeStatus = debug;

	init();
	statusLoop();

	XCloseDisplay(dpy);
	close(epollFD);
	close(signalFD);
	for (int i = 0; i < LEN(pipes); i++)
		closePipe(pipes[i]);

	return 0;
}