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client.cpp
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client.cpp
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#include <assert.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/ip.h>
static void msg(const char *msg) {
fprintf(stderr, "%s\n", msg);
}
static void die(const char *msg) {
int err = errno;
fprintf(stderr, "[%d] %s\n", err, msg);
abort();
}
static int32_t read_full(int fd, char *buf, size_t n) {
if (buf == NULL) {
return -1;
}
ssize_t rv;
while (n > 0) {
rv = read(fd, buf, n);
if (rv <= 0) {
return -1; // error, or unexpected EOF
}
assert((size_t)rv <= n);
n -= (size_t)rv;
buf += rv;
}
return 0;
}
static int32_t write_all(int fd, const char *buf, size_t n) {
if (buf == NULL) {
return -1;
}
ssize_t rv;
while (n > 0) {
rv = write(fd, buf, n);
if (rv <= 0) {
return -1; // error
}
assert((size_t)rv <= n);
n -= (size_t)rv;
buf += rv;
}
return 0;
}
const size_t k_max_msg = 4096;
static int32_t query(int fd, const char *text) {
uint32_t len = (uint32_t)strlen(text);
if (len > k_max_msg) {
return -1;
}
char wbuf[4 + k_max_msg];
memcpy(wbuf, &len, 4); // assume little endian
memcpy(&wbuf[4], text, len);
if (int32_t err = write_all(fd, wbuf, 4 + len)) {
return err;
}
// 4 bytes header
char rbuf[4 + k_max_msg + 1];
errno = 0;
int32_t err = read_full(fd, rbuf, 4);
if (err) {
if (errno == 0) {
msg("EOF");
} else {
msg("read() error");
}
return err;
}
memcpy(&len, rbuf, 4); // assume little endian
if (len > k_max_msg) {
msg("too long");
return -1;
}
// reply body
err = read_full(fd, &rbuf[4], len);
if (err) {
msg("read() error");
return err;
}
// do something
rbuf[4 + len] = '\0';
printf("server says: %s\n", &rbuf[4]);
return 0;
}
static int32_t send_req(int fd, const std::vector<std::string> &cmd) {
uint32_t len = 4;
for (const std::string &s : cmd) {
len += 4 + s.size();
}
if (len > k_max_msg) {
return -1;
}
char wbuf[4 + k_max_msg];
memcpy(&wbuf[0], &len, 4); // assume little endian
uint32_t n = cmd.size();
memcpy(&wbuf[4], &n, 4);
size_t cur = 8;
for (const std::string &s : cmd) {
uint32_t p = (uint32_t)s.size();
memcpy(&wbuf[cur], &p, 4);
memcpy(&wbuf[cur + 4], s.data(), s.size());
cur += 4 + s.size();
}
return write_all(fd, wbuf, 4 + len);
}
static int32_t read_res(int fd) {
// code omitted...
// print the result
uint32_t rescode = 0;
if (len < 4) {
msg("bad response");
return -1;
}
memcpy(&rescode, &rbuf[4], 4);
printf("server says: [%u] %.*s\n", rescode, len - 4, &rbuf[8]);
return 0;
}
int main(int argc, char **argv) {
int fd = socket(AF_INET, SOCK_STREAM, 0);
if (fd < 0) {
die("socket()");
}
// code omitted...
std::vector<std::string> cmd;
for (int i = 1; i < argc; ++i) {
cmd.push_back(argv[i]);
}
int32_t err = send_req(fd, cmd);
if (err) {
goto L_DONE;
}
err = read_res(fd);
if (err) {
goto L_DONE;
}
L_DONE:
close(fd);
return 0;
}