rename logshipper -> logtap

- it matches the executable name
- it doesn't ship anything anyway, it's just plumbing

pkgs/logtap/Makefile

@@ -0,0 +1,5 @@
+TARGETS=logtap
+default: $(TARGETS)
+
+install: $(TARGETS)
+	install -Dt $(PREFIX)/bin/ logtap

pkgs/logtap/default.nix

@@ -0,0 +1,8 @@
+{
+  stdenv,
+}:
+stdenv.mkDerivation {
+  name = "logtap";
+  makeFlags = [ "PREFIX=${placeholder "out"}" ];
+  src = ./.;
+}

pkgs/logtap/logtap.c

@@ -0,0 +1,142 @@
+#include <poll.h>
+#include <sys/timerfd.h>
+#include <time.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <errno.h>
+
+#define PROGRAM_NAME "logtap"
+
+#ifdef _GNU_SOURCE
+#include <error.h>
+#else
+#include <stdarg.h>
+static void error(int status, int errnum, const char * fmt, ...) {
+    va_list ap;
+    va_start(ap, fmt);
+
+    fprintf(stderr, PROGRAM_NAME  ": ");
+    vfprintf(stderr, fmt, ap);
+    if(errnum) fprintf(stderr, ": %s", strerror(errnum));
+    fprintf(stderr, "\n");
+    if(status) exit(status);
+}
+#endif
+
+
+int open_shipper_socket(char *pathname) {
+    int fd;
+    static int fail_count = 0;
+
+    struct sockaddr_un sa = {
+        .sun_family = AF_LOCAL
+    };
+    strncpy(sa.sun_path, pathname, sizeof(sa.sun_path) - 1);
+
+    fd = socket(AF_LOCAL, SOCK_STREAM, 0);
+    if(fd >= 0) {
+        if(connect(fd, (struct sockaddr *) &sa, sizeof sa)) {
+            if((fail_count % 30) == 0) {
+                printf(PROGRAM_NAME ": cannot connect socket \"%s\": %s\n",
+                       pathname,
+                       strerror(errno));
+	    }
+            fail_count++;
+            close(fd);
+            return -1;
+        }
+        int flags = fcntl(fd, F_GETFL);
+        fcntl(fd, F_SETFL, flags | O_NONBLOCK);
+    }
+    return fd;
+}
+
+struct pollfd fds[] = {
+    { .fd = 0, .events = POLLIN },
+    { .fd = 1, .events = POLLERR },
+    { .fd = -1, .events = POLLERR },
+};
+
+int is_connected(void) {
+    return (fds[2].fd >= 0);
+}
+
+
+int main(int argc, char * argv[]) {
+
+    char * buf = malloc(8192);
+    int out_bytes = 0;
+    int tee_bytes = 0;
+
+    if(argc != 3) {
+        error(1, 0, "usage: " PROGRAM_NAME " /path/to/socket cookie-text");
+    }
+    char * socket_pathname = argv[1];
+    char * cookie = argv[2];
+    char * start_cookie = malloc(strlen(cookie) + 8);
+    char * stop_cookie = malloc(strlen(cookie) + 7);
+
+    if(strlen(socket_pathname) > 108) {
+        error(1, 0, "socket pathname \"%s\" is too long, max 108 bytes",
+              socket_pathname);
+    };
+
+    strcpy(start_cookie, cookie); strcat(start_cookie, " START\n");
+    strcpy(stop_cookie, cookie); strcat(stop_cookie, " STOP\n");
+
+    signal(SIGPIPE, SIG_IGN);
+
+    int flags = fcntl(STDOUT_FILENO, F_GETFL);
+    fcntl(STDOUT_FILENO, F_SETFL, flags | O_NONBLOCK);
+
+    int quitting = 0;
+    while(! quitting) {
+        int nfds = poll(fds, 3, 2000);
+        if(nfds > 0) {
+            if((fds[0].revents & (POLLIN|POLLHUP)) &&
+               (out_bytes == 0) &&
+               (tee_bytes == 0)) {
+                out_bytes = read(fds[0].fd, buf, 8192);
+                if(out_bytes == 0) {
+                    quitting = 1;
+                    buf = PROGRAM_NAME " detected eof of file on stdin, exiting\n";
+                    out_bytes = strlen(buf);
+                };
+                if(is_connected()) tee_bytes = out_bytes;
+            };
+
+            if(out_bytes) {
+                out_bytes -= write(fds[1].fd, buf, out_bytes);
+            };
+            if(fds[1].revents & (POLLERR|POLLHUP)) {
+                exit(1); // can't even log an error if the logging stream fails
+            };
+            if(is_connected()) {
+                if(tee_bytes) {
+                    tee_bytes -= write(fds[2].fd, buf, tee_bytes);
+                };
+                if(fds[2].revents & (POLLERR|POLLHUP)) {
+                    close(fds[2].fd);
+                    fds[2].fd = -1;
+                    (void) write(1, stop_cookie, strlen(stop_cookie));
+                };
+            };
+        } else {
+            if(! is_connected()) {
+                fds[2].fd = open_shipper_socket(argv[1]);
+                if(is_connected()) {
+                    /* write cookie to stdout so that the backfill
+                     * process knows we are now logging realtime
+                     */
+                    write(fds[1].fd, start_cookie, strlen(start_cookie));
+                }
+            }
+        };
+    };
+}