From 04576dc2a3f761eb041b808b56f13a58052e7655 Mon Sep 17 00:00:00 2001
From: Stefan Zabka <zabkaste@hu-berlin.de>
Date: Sun, 24 May 2020 12:19:52 +0200
Subject: Moved back to 02_exercise

---
 02_exercise/beispiele/pipe_bidirect/pingpong.c | 125 +++++++++++++++++++++++++
 1 file changed, 125 insertions(+)
 create mode 100644 02_exercise/beispiele/pipe_bidirect/pingpong.c

(limited to '02_exercise/beispiele/pipe_bidirect/pingpong.c')

diff --git a/02_exercise/beispiele/pipe_bidirect/pingpong.c b/02_exercise/beispiele/pipe_bidirect/pingpong.c
new file mode 100644
index 0000000..f38394f
--- /dev/null
+++ b/02_exercise/beispiele/pipe_bidirect/pingpong.c
@@ -0,0 +1,125 @@
+#include <fcntl.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+static int split(int fd[2]);
+static int redir(int fd, const char *file);
+static void sig_handler(int sig);
+
+static int parent;
+
+int main(void) {
+    ssize_t bytes;
+    char buf[256];
+    int fd[2];
+
+    // disable buffering for stdout
+    setvbuf(stdout, NULL, _IONBF, 0);
+
+    // redirect stdout to write into a file
+    if (redir(1, "log.txt") < 0) {
+        perror("redir()");
+        exit(-1);
+    }
+
+    // install the signal handler for Ctrl+C
+    if (signal(SIGINT, sig_handler) == SIG_ERR) {
+        perror("signal()");
+        exit(-1);
+    }
+
+    // split processes and assign file descriptors for communication
+    switch (split(fd)) {
+    case -1: // error
+        exit(-1);
+
+    case 0: // child
+        while ((bytes = read(fd[0], buf, sizeof(buf))) > 0) {
+            printf("[%u]: %s\n", getpid(), buf);
+            sleep(1);
+            write(fd[1], "pong", 5);
+        }
+        break;
+
+    case 1: // parent
+        parent = 1;
+        write(fd[1], "ping", 5);
+        while ((bytes = read(fd[0], buf, sizeof(buf))) > 0) {
+            printf("[%u]: %s\n", getpid(), buf);
+            sleep(1);
+            write(fd[1], "ping", 5);
+        }
+        break;
+    }
+
+    // close the file descriptors
+    close(fd[0]);
+    close(fd[1]);
+
+    return 0;
+}
+
+int split(int fd[2]) {
+    int pfd[2][2];
+
+    if (pipe(pfd[0]) < 0) {
+        perror("pipe()");
+        goto err_pipe1;
+    }
+
+    if (pipe(pfd[1]) < 0) {
+        perror("pipe()");
+        goto err_pipe2;
+    }
+
+    switch (fork()) {
+    case -1:
+        perror("fork()");
+        goto err_fork;
+
+    case 0:                // child process
+        close(pfd[0][1]);  // close write for child
+        close(pfd[1][0]);  // close read for parent
+        fd[0] = pfd[0][0]; // keep read for child
+        fd[1] = pfd[1][1]; // keep write for parent
+        return 0;
+
+    default:               // parent process
+        close(pfd[1][1]);  // close write for parent
+        close(pfd[0][0]);  // close read for child
+        fd[0] = pfd[1][0]; // keep read for parent
+        fd[1] = pfd[0][1]; // keep write for child
+        return 1;
+    }
+
+err_fork:
+    close(pfd[1][0]);
+    close(pfd[1][1]);
+err_pipe2:
+    close(pfd[0][0]);
+    close(pfd[0][1]);
+err_pipe1:
+    return -1;
+}
+
+int redir(int fd, const char *file) {
+    int fd2 = open(file, O_WRONLY | O_CREAT | O_TRUNC, 0644);
+
+    if (fd2 < 0)
+        return -1;
+
+    dup2(fd2, fd);
+    close(fd2);
+
+    return 0;
+}
+
+void sig_handler(int sig) {
+    if (parent) {
+        const char msg[] = "Programmabbruch durch Nutzer\n";
+        write(1, msg, sizeof(msg) - 1);
+    }
+    exit(0);
+}
-- 
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