Dec 12 -- Santa's Postbox

Article:  https://ibr.cs.tu-bs.de/advent/12-postbox/
Workload: ~74 source-code lines

12-postbox/Makefile

+PROG = postbox
+
+DEPS = postbox.c fifo.c domain.c
+
+${PROG}: ${DEPS}
+	gcc ${PROG}.c -o  $@ -Wall -g -lrt
+
+run: ${PROG}
+	./${PROG}
+
+
+
+strace: ${PROG}
+	strace ./${PROG}
+
+clean:
+	rm -f ./${PROG}

12-postbox/domain.c

+int domain_prepare(int epoll_fd) {
+    printf("... by socket: echo 2 | nc -U socket\n");
+    return -1;
+}
+
+
+void domain_accept(int epoll_fd, int sock_fd, int events) {
+}
+
+
+void domain_recv(int epoll_fd, int sock_fd, int events) {
+}

12-postbox/fifo.c

+
+int fifo_prepare(int epoll_fd) {
+    printf("... by fifo:   echo 1 > fifo\n");
+    return -1;
+}
+
+void fifo_handle(int epoll_fd, int fifo_fd, int events) {
+}

12-postbox/postbox.c

+#define _GNU_SOURCE
+#include <stdio.h>
+#include <time.h>
+#include <sys/mman.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <sys/types.h>
+#include <assert.h>
+#include <limits.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/epoll.h>
+#include <fcntl.h>
+#include <stdint.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <signal.h>
+#include <sys/signalfd.h>
+#include <mqueue.h>
+
+#define die(msg) do { perror(msg); exit(EXIT_FAILURE); } while(0)
+
+// Adds a file descriptor to an open epoll instance's list of
+// interesting file descriptors.
+//// events -  For which events are we waiting (usually EPOLLIN)
+//// data   -  The kernel returns this data when an event occurs 
+void epoll_add(int epoll_fd, int fd, int events) {
+    struct epoll_event ev;
+    ev.events   = events;
+    ev.data.fd  = fd;
+
+    if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, fd, &ev) == -1) {
+        die("epoll_ctl: activate");
+    }
+     }
+
+// Remove a file descriptor from the interest list.
+void epoll_del(int epoll_fd, int fd) {
+    if (epoll_ctl(epoll_fd, EPOLL_CTL_DEL, fd, NULL) == -1) {
+        die("epoll_ctl: reset");
+    }
+}
+
+#include "fifo.c"
+#include "domain.c"
+
+
+struct postbox {
+    int fd;
+    int (*prepare)(int epoll_fd);
+    void (*handle)(int epoll_fd, int fd, int events);
+};
+
+struct postbox boxes[] = {
+    {-1, fifo_prepare,     fifo_handle},
+    {-1, domain_prepare,   domain_accept},
+    // This must be the last entry
+    {-1, NULL,             domain_recv}, // Fallback
+};
+
+#define ARRAY_SIZE(arr) (sizeof(arr)/sizeof(*(arr)))
+
+int main() {
+    int epoll_fd = epoll_create1(0);
+	if (epoll_fd == -1)
+        die("epoll_create");
+
+    printf("Santas Postbox is open! Send your requests ...\n");
+    // Initialize all backends by calling the prepare method
+    for (int i = 0; i < ARRAY_SIZE(boxes); i++) {
+        if (boxes[i].prepare) {
+            boxes[i].fd = boxes[i].prepare(epoll_fd);
+        }
+    }
+    while (true) {
+        // We use epoll_wait(2) to wait for at least one event, but we
+        // can receive up to ten events. We do not set a timeout but
+        // wait forever if necessary.
+        struct epoll_event event[10];
+        int nfds = epoll_wait(epoll_fd, event, 10, -1);
+
+        for (int n = 0; n < nfds; n++) {
+            int fd = event[n].data.fd;
+            for (int i = 0; i < ARRAY_SIZE(boxes); i++) {
+                if (boxes[i].fd == fd || boxes[i].fd == -1) {
+                    boxes[i].handle(epoll_fd, fd, event[n].events);
+                    break;
+                }
+            }
+        }
+    }
+
+}