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io
simple library for asynchronous io handling.
Rusty Russell <rusty@rustcorp.com.au>
io provides a mechanism to write I/O servers with multiple connections. Each callback indicates what I/O they plan next (eg. read, write). It is also possible to write custom I/O plans.
// Given tr A-Z a-z outputs tr a-z a-z
#include <ccan/io/io.h>
#include <ccan/err/err.h>
#include <assert.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <string.h>
struct buffer {
bool finished;
size_t start, end, rlen, wlen;
char buf[4096];
};
static void finish(struct io_conn *c, struct buffer *b)
{
// Mark us finished.
b->finished = true;
// Wake writer just in case it's asleep.
io_wake(b);
}
static struct io_plan *read_in(struct io_conn *c, struct buffer *b)
{
// Add what we just read.
b->end += b->rlen;
assert(b->end <= sizeof(b->buf));
// If we just read something, wake writer.
if (b->rlen != 0)
io_wake(b);
// If buffer is empty, return to start.
if (b->start == b->end)
b->start = b->end = 0;
// No room? Wait for writer
if (b->end == sizeof(b->buf))
return io_wait(c, b, read_in, b);
return io_read_partial(c, b->buf + b->end, sizeof(b->buf) - b->end,
&b->rlen, read_in, b);
}
static struct io_plan *write_out(struct io_conn *c, struct buffer *b)
{
// Remove what we just wrote.
b->start += b->wlen;
assert(b->start <= sizeof(b->buf));
// If we wrote something, wake writer.
if (b->wlen != 0)
io_wake(b);
// Nothing to write? Wait for reader.
if (b->end == b->start) {
if (b->finished)
return io_close(c);
return io_wait(c, b, write_out, b);
}
return io_write_partial(c, b->buf + b->start, b->end - b->start,
&b->wlen, write_out, b);
}
// Feed a program our stdin, gather its stdout, print that at end.
int main(int argc, char *argv[])
{
int tochild[2], fromchild[2];
struct buffer to, from;
int status;
struct io_conn *reader;
if (argc == 1)
errx(1, "Usage: runner <cmdline>...");
if (pipe(tochild) != 0 || pipe(fromchild) != 0)
err(1, "Creating pipes");
if (!fork()) {
// Child runs command.
close(tochild[1]);
close(fromchild[0]);
dup2(tochild[0], STDIN_FILENO);
dup2(fromchild[1], STDOUT_FILENO);
execvp(argv[1], argv + 1);
exit(127);
}
close(tochild[0]);
close(fromchild[1]);
signal(SIGPIPE, SIG_IGN);
// Read from stdin, write to child.
memset(&to, 0, sizeof(to));
reader = io_new_conn(NULL, STDIN_FILENO, read_in, &to);
io_set_finish(reader, finish, &to);
io_new_conn(NULL, tochild[1], write_out, &to);
// Read from child, write to stdout.
reader = io_new_conn(NULL, fromchild[0], read_in, &from);
io_set_finish(reader, finish, &from);
io_new_conn(NULL, STDOUT_FILENO, write_out, &from);
io_loop(NULL, NULL);
wait(&status);
return WIFEXITED(status) ? WEXITSTATUS(status) : 2;
}
LGPL (v2.1 or any later version)