A quick/crappy sendfile(2) stub example for OpenBSD

sendfile.c

// Copyright 2019 Dave Voutila <[email protected]>
// Under no circumstances should you consider this safe/correct code.
// Use at your own risk.
//
// Consider it under ISC license.

#include <stdio.h>
#include <fcntl.h>
#include <err.h>
#include <netdb.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <sys/socket.h>
#include <sys/types.h>

#define HOST "127.0.0.1"
#define PORT "9999"
#define BUF_SIZE 512

int sendfile (int fd, int s, off_t offset, size_t nbytes, void *hdr, off_t *sbytes, int flags) {
    int cnt = 0;
	ssize_t r = 0;
	off_t pos = offset;

	char buf[BUF_SIZE];
	memset(&buf, 0, BUF_SIZE);

	while ((r = pread(fd, &buf, BUF_SIZE, pos)) != -1) {
		pos += r;

		printf("[[ read %ld bytes from file ]]\n", r);
		if (r == 0) {
			printf("[done reading from file]\n");
			break;
		}

		printf("[[ sending %ld via socket ]]\n", r);
		ssize_t sock_result = send(s, &buf, r, flags);
		if (sock_result == -1) {
			printf("[err sending to socket]\n");
			return -1;
		}

		if (sbytes != NULL) {
			*sbytes += sock_result;
		}

		memset(&buf, 0, BUF_SIZE);
		cnt++;
		printf("[[ iteration %d ]]\n", cnt);
	}
	return 0;
}


int main (int argc, char **argv) {
	int r = 0;
	off_t skip = 0;

	if (argc < 2) {
		printf("Usage: sendfile [file] [skip=0]\n");
		return 0;
	}

	char *file = argv[1];
	if (argc > 2) {
		skip = strtonum(argv[2], 0, INT32_MAX, NULL);
		printf("skipping %lld bytes...", skip);
	}

	printf("opening %s...\n", file);
	int fd = open(file, O_RDONLY);
	if (fd == -1) {
		err(1, "can't open %s", file);
	}

	int s = socket(AF_INET, SOCK_STREAM, 0);
	if (s == -1) {
		close(fd);
		err(2, "can't create socket");
	}

	printf("connecting to %s:%s...\n", HOST, PORT);
	struct addrinfo *addr;
	if ((r = getaddrinfo(HOST, PORT, NULL, &addr)) != 0) {
		close(fd);
		err(3, "getaddrinfo failed for %s:%s", HOST, PORT);
	}

	if ((r = connect(s, addr->ai_addr, addr->ai_addrlen)) == -1) {
		close(fd);
		err(4, "failed to connect to %s:%s", HOST, PORT);
	}
	printf("connected.\n");

	printf("sending file...\n");
	off_t sent = 0;

	if ((r = sendfile(fd, s, skip, 0, NULL, &sent, 0)) == -1) {
		close(s);
		close(fd);
		err(5, "failed to send file");
	} else {
		printf("sent %lld bytes.\n", sent);
	}

	close(s);
	close(fd);
	return 0;
}