removed literate c
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lit/seed.lit
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lit/seed.lit
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@code_type c .c
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@comment_type /* %s */
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@title seed
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@s Introduction
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Using seed is rather straight forward. The syntax is as follows: `seed COMMAND`.
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The program is also simple. Here is an outline.
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--- seed.c
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@{copyright notice}
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@{c headers}
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@{posix headers}
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@{helper function}
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int
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main(int argc, char *argv[])
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{
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@{variables local to main}
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if (argc < 2) {
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die("%s: not enough arguments\n", argv[0]);
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}
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@{open socket}
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@{send message}
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@{receive and print reply}
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@{cleanup}
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}
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---
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As we can already see we will need to include `stdio.h` and `stdlib.h`.
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--- c headers
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#include <stdio.h>
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#include <stdlib.h>
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---
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@s Copyright
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This project is licensed under the Mozilla Public License Version 2.0. Please read LICENSE for more details.
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--- copyright notice
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/* Copyright (c), Niclas Meyer <niclas@countingsort.com>
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*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at https://mozilla.org/MPL/2.0/.
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*/
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---
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@s Creating the socket object
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This is rather straight forward. We setup all the things in our socket object and then connect.
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We're going to store the file descriptor and the `sockaddr` local to main.
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--- variables local to main
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int sock_fd;
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struct sockaddr_un sock_addr;
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---
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This requires including the following headers.
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--- posix headers
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#include <sys/socket.h>
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#include <sys/un.h>
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---
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Now it's finally time to fill stuff into our `sockaddr`.
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--- open socket
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if ((sock_fd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
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die("%s: failed to open socket\n", argv[0]);
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}
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sock_addr.sun_family = AF_UNIX;
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@{get socket path}
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if (connect(sock_fd, (struct sockaddr *)&sock_addr, sizeof(sock_addr)) < 0) {
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die("%s: failed to connect to socket\n", argv[0]);
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}
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---
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@s Get the socket path
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It's important that we open the correct socket.
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This might be set via an environment variable to allow maximum flexibility, while still keeping a trivial interface.
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We're going to store the path in `sock_path`, local to main.
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--- variables local to main +=
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const char *sock_path;
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---
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We check if `KIWMI_SOCKET` is set, and use it, or default to `/tmp/kiwmi.sock`.
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--- get socket path
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sock_path = getenv("KIWMI_SOCKET");
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if (sock_path) {
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strncpy(sock_addr.sun_path, sock_path, sizeof(sock_addr.sun_path));
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} else {
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strncpy(sock_addr.sun_path, "/tmp/kiwmi.sock", sizeof(sock_addr.sun_path));
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}
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---
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For this we need `string.h`.
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--- c headers +=
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#include <string.h>
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---
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@s Send our message
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This actually consists of two steps.
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--- send message
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@{generate message from argv}
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@{send generated message}
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---
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@s Generate message
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Pretty straight forward. We need a buffer and then we just append all arguments, beginning with `argv[1]`, separated by spaces.
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--- variables local to main +=
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char msg[BUFSIZ];
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size_t msg_len;
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---
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--- generate message from argv
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msg_len = 0;
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for (int i = 1; i < argc; i++) {
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msg_len += (size_t)snprintf(msg + msg_len, sizeof(msg), "%s ", argv[i]);
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}
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msg_len -= 1; // Remove trailing space
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---
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@s Actually send the message
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This is straight forward enough. We just `send` the message.
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--- send generated message
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if (send(sock_fd, msg, msg_len, 0) < 0) {
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die("%s: failed to send message\n", argv[0]);
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}
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---
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@s Handling the reply
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Some commands return a string to print. If there's none, we'll just receive a `\0`.
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This is pretty much stolen from baskerville.
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--- receive and print reply
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struct pollfd fds[] = {
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{ sock_fd, POLLIN, 0 },
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{ STDOUT_FILENO, POLLHUP, 0 },
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};
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while (poll(fds, 2, -1) > 0) {
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if (fds[1].revents & (POLLERR | POLLHUP)) {
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break;
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}
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if (fds[0].revents & POLLIN) {
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if ((msg_len = recv(sock_fd, msg, sizeof(msg) - 1, 0)) > 0) {
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msg[msg_len] = '\0';
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if (msg_len == 1) {
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break;
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}
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printf("%s", msg);
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fflush(stdout);
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} else {
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break;
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}
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}
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}
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---
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This requires us to include `poll.h` and `unistd.h`.
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--- posix headers +=
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#include <poll.h>
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#include <unistd.h>
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---
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@s Cleanup
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Not much to do here. Just close the socket.
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--- cleanup
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close(sock_fd);
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---
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@s Helper function
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We used `die` the whole time. Time to make it a thing already.
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--- helper function
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static void
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die(char *fmt, ...)
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{
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va_list ap;
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va_start(ap, fmt);
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vfprintf(stderr, fmt, ap);
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va_end(ap);
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exit(EXIT_FAILURE);
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}
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---
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Note that this requires the `stdarg.h` header.
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--- c headers +=
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#include <stdarg.h>
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---
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