1 files changed, 135 insertions, 0 deletions
diff --git a/proxy.c b/proxy.c
new file mode 100644
index 0000000..04ac9f2
--- /dev/null
+++ b/proxy.c
@@ -0,0 +1,135 @@
+#include <errno.h>
+#include <poll.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <time.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include "proxy.h"
+
+#define BUFFER_SIZE  (1 << 10)
+
+struct list {
+	struct list *next, *prev;
+};
+
+struct packet {
+	struct list        list;
+	unsigned long long recvtime;
+	size_t             length;
+	char               data[BUFFER_SIZE];
+};
+
+static unsigned long long gettime()
+{
+	struct timespec time;
+	clock_gettime(CLOCK_MONOTONIC, &time);
+	return time.tv_sec * 1000000000ULL + time.tv_nsec;
+}
+
+static int read_packet(int fd, struct list *tail, unsigned long long now)
+{
+	struct packet *p = malloc(sizeof *p);
+	if (!p) return -1;
+
+	ssize_t len;
+	while ((len = read(fd, p->data, BUFFER_SIZE)) == -1 && errno == EINTR) ;
+	if (len <= 0) {
+		free(p);
+		return -1;
+	}
+
+	p->list.next = tail;
+	p->list.prev = tail->prev;
+	p->recvtime  = now;
+	p->length    = len;
+	p->list.next->prev = p->list.prev->next = &p->list;
+	return 0;
+}
+
+static int write_packet(int fd, struct packet *p)
+{
+	char  *data = p->data;
+	size_t len  = p->length;
+
+	ssize_t r;
+	while (len && (r = write(fd, data, len)) != -1 && errno != EINTR) {
+		data += r;
+		len  -= r;
+	}
+
+	if (r == -1) return -1;
+	struct list *l = &p->list;
+	l->prev->next = l->next;
+	l->next->prev = l->prev;
+	free(p);
+	return 0;
+}
+
+static void proxy_one(int readfd, int writefd, unsigned long long delayns)
+{
+	struct list head = {0}, tail = {0};
+	head.next = &tail;
+	tail.prev = &head;
+
+	struct pollfd fds = { .fd = readfd, .events = POLLIN };
+	int timeout = -1;
+	for (;;) {
+		while (poll(&fds, 1, timeout) == -1 && errno == EINTR) ;
+		if (fds.revents & (POLLERR | POLLHUP)) return;
+
+		unsigned long long now      = gettime();
+		unsigned long long sendtime = now - delayns;
+		if (fds.revents & POLLIN && read_packet(readfd, &tail, now)) return;
+
+		while (head.next != &tail) {
+			struct packet *p = (struct packet *)head.next;
+			timeout = (p->recvtime - sendtime) / 1000000;
+			if (timeout <= 0) {
+				if (write_packet(writefd, p)) return;
+			} else break;
+		}
+		if (head.next == &tail) timeout = -1;
+	}
+}
+
+static pid_t make_child(int fd0, int fd1, unsigned long long delayns)
+{
+	pid_t child = fork();
+	if (!child) {
+		proxy_one(fd0, fd1, delayns);
+		exit(0);
+	}
+	return child;
+}
+
+static pid_t wait_one(void)
+{
+	pid_t p;
+	while ((p = wait(NULL)) == -1 && errno == EINTR) ;
+	return p;
+}
+
+static void kill_wait(pid_t p)
+{
+	kill(p, SIGINT);
+	wait_one();
+}
+
+void proxy(int fd0, int fd1, unsigned delayms)
+{
+	unsigned long long delayns = delayms * 1000000ULL;
+	pid_t pid0, pid1;
+
+	if ((pid0 = make_child(fd0, fd1, delayns)) < 0) return;
+	if ((pid1 = make_child(fd1, fd0, delayns)) < 0) {
+		kill_wait(pid0);
+		return;
+	}
+
+	pid_t dead = wait_one();
+	kill_wait(dead == pid0 ? pid1 : pid0);
+}
+