add network transparent i/o demo

daemons.py

@@ -17,7 +17,7 @@ import signal
 # I get back more and more AI slop every time I look.
 # This trick is not something i see often anymore.
 # Therefore let's recreate a classic.
-# Daemon's Demystified 2.0 starts right now
+
 
 # Sometimes programs need to run unattended, without tying up
 # a terminal session. This is less of a problem now today
@@ -75,6 +75,18 @@ Never gonna tell a lie and hurt you
 
 """
 
+OTHER_RESP = """
+HTTP/1.1 403 Forbidden
+Date: Fri, 01 Jan 1988 12:56:49 GMT
+Content-Type: application/json
+Content-Length: 110
+
+{
+  "error": "TogetherForever",
+  "message": "Together forever and never to part Together forever we two ."
+}
+
+"""
 client_procs = []
 
 svr_proc = None
@@ -108,7 +120,7 @@ def server_handler():
         client, addr = serversock.accept()
         print(addr)
         client_procs.append(gevent.spawn(client_handler, client))
-        gevent.sleep(0)
+        gevent.sleep(0.25)
 
     serversock.close()
     return
@@ -120,14 +132,34 @@ def server_handler():
 #
 # This is somewhat useful in elfing with ai scraper bots.
 # There are better methods if you wanna try that
+
+# this is done with a bit of defensive programing
+# to ensure a client can't cause us not to release control
+# of the greenlet.
+
+# gevent is a cooperative concurrency model.
+# it multiplexs tasks on to one os thread
+# each task is done inside a "greenlet".abs
+# Which is like a thread except that it is
+# the programers responsibility  to handle scheduling
+# By putting the greenlet to sleep when that's possible
+
+
 def client_handler(sock):
     print("Client handler spawn")
+    junk_counter = 0
     while True:
+        if junk_counter > 3:
+            sock.close()
+            return
         data = sock.recv(4096)
         dstring = data.decode("UTF-8")
         if dstring.startswith("GET"):
             break
-        gevent.sleep(0)
+        else:
+            sock.send(OTHER_RESP.encode("utf-8"))
+            junk_counter += 1
+        gevent.sleep(0.25)
 
     sock.send(RICKROLL_LYRICS.encode("utf-8"))
     sock.close()
@@ -163,22 +195,22 @@ else:
     os.setpgrp()
     os.umask(0)
 
-print(os.getpid())  # to aid in stopping the server
+    print(os.getpid())  # to aid in stopping the server
-# We want to close our connection to the controlling terminal
+    # We want to close our connection to the controlling terminal
-# to avoid accedentially spamming the use. And causing interactive processes
+    # to avoid accedentially spamming the use. And causing interactive processes
-# to be SIGSTOP'ed. I do this with a Null Device class.
+    # to be SIGSTOP'ed. I do this with a Null Device class.
-# You could just as easily do some sort of logging thing.
+    # You could just as easily do some sort of logging thing.
-sys.stdin.close()
+    sys.stdin.close()
-sys.stdout = NullDevice()
+    sys.stdout = NullDevice()
-sys.stderr = NullDevice()
+    sys.stderr = NullDevice()
 
-# The last thing we do before handing things off to the daemon's main
+    # The last thing we do before handing things off to the daemon's main
-# function is set up the daemon's signal table how we want it
+    # function is set up the daemon's signal table how we want it
-# fork, may have initialized it with the default handlers
+    # fork, may have initialized it with the default handlers
-# depending on implementation
+    # depending on implementation
-signal.signal(signal.SIGHUP, hup_handle)
+    signal.signal(signal.SIGHUP, hup_handle)
-signal.signal(signal.SIGTERM, hup_handle)
+    signal.signal(signal.SIGTERM, hup_handle)
-daemon_main()
+    daemon_main()
 
 
 # References

lstnr.c

@@ -0,0 +1,171 @@
+/*
+** server.c -- a stream socket server demo
+*/
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netdb.h>
+#include <arpa/inet.h>
+#include <sys/wait.h>
+#include <signal.h>
+
+#define PORT "3490"  // the port users will be connecting to
+
+#define BACKLOG 10   // how many pending connections queue will hold
+char kthanksbye[2] = {EOF, '\0'};
+int proclaunch(char **args, int sockfd)
+{
+  pid_t pid;
+  int status;
+
+  pid = fork();
+  if (pid == 0) {
+      dup2(sockfd, 0);
+      dup2(sockfd, 1);
+      dup2(sockfd, 2);
+
+    // Child process
+    if (execvp(args[0], args) == -1) {
+      perror("EXECERROR");
+    }
+    exit(EXIT_FAILURE);
+  } else if (pid < 0) {
+    // Error forking
+    perror("fork error");
+  } else {
+    // Parent process
+    do {
+     waitpid(pid, &status, WUNTRACED);
+    } while (!WIFEXITED(status) && !WIFSIGNALED(status));
+  }
+
+  return 1;
+}
+
+void sigchld_handler(int s)
+{
+    // waitpid() might overwrite errno, so we save and restore it:
+    int saved_errno = errno;
+
+    while(waitpid(-1, NULL, WNOHANG) > 0);
+
+    errno = saved_errno;
+}
+
+
+// get sockaddr, IPv4 or IPv6:
+void *get_in_addr(struct sockaddr *sa)
+{
+    if (sa->sa_family == AF_INET) {
+        return &(((struct sockaddr_in*)sa)->sin_addr);
+    }
+
+    return &(((struct sockaddr_in6*)sa)->sin6_addr);
+}
+
+int main(int argc, char *argv[])
+{
+    if (argc < 3) {
+        exit(1);
+    }
+    int sockfd, new_fd;  // listen on sock_fd, new connection on new_fd
+    struct addrinfo hints, *servinfo, *p;
+    struct sockaddr_storage their_addr; // connector's address information
+    socklen_t sin_size;
+    struct sigaction sa;
+    int yes=1;
+    char s[INET6_ADDRSTRLEN];
+    int rv;
+
+    memset(&hints, 0, sizeof hints);
+    hints.ai_family = AF_UNSPEC;
+    hints.ai_socktype = SOCK_STREAM;
+    hints.ai_flags = AI_PASSIVE; // use my IP
+
+    if ((rv = getaddrinfo(NULL, argv[1], &hints, &servinfo)) != 0) {
+        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
+        return 1;
+    }
+
+    // loop through all the results and bind to the first we can
+    for (p = servinfo; p != NULL; p = p->ai_next) {
+        if ((sockfd = socket(p->ai_family, p->ai_socktype,
+                p->ai_protocol)) == -1) {
+            perror("server: socket");
+            continue;
+        }
+
+        if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes,
+                sizeof(int)) == -1) {
+            perror("setsockopt");
+            exit(1);
+        }
+
+        if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
+            close(sockfd);
+            perror("server: bind");
+            continue;
+        }
+
+        break;
+    }
+
+    freeaddrinfo(servinfo); // all done with this structure
+
+    if (p == NULL)  {
+        fprintf(stderr, "server: failed to bind\n");
+        exit(1);
+    }
+
+    if (listen(sockfd, BACKLOG) == -1) {
+        perror("listen");
+        exit(1);
+    }
+
+    sa.sa_handler = sigchld_handler; // reap all dead processes
+    sigemptyset(&sa.sa_mask);
+    sa.sa_flags = SA_RESTART;
+    if (sigaction(SIGCHLD, &sa, NULL) == -1) {
+        perror("sigaction");
+        exit(1);
+    }
+
+    printf("lstnr: Using %s\n", argv[2]);
+
+    while(1) {  // main accept() loop
+        sin_size = sizeof their_addr;
+        new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
+        if (new_fd == -1) {
+            perror("accept");
+            continue;
+        }
+
+        inet_ntop(their_addr.ss_family,
+            get_in_addr((struct sockaddr *)&their_addr),
+            s, sizeof s);
+        printf("server: got connection from %s\n", s);
+
+        if (!fork()) { // this is the child process
+            close(sockfd); // child doesn't need the listener
+   	    proclaunch(&argv[2], new_fd);
+            ssize_t w;
+            w = write(new_fd, &kthanksbye, 2);
+            if (w == -1) {
+                if (errno != EINTR) perror("HUPFAIL");
+                close(new_fd);
+                exit(1);
+            }
+	    close(new_fd);
+            exit(0);
+        }
+        close(new_fd);  // parent doesn't need this
+    }
+
+    return 0;
+}