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/* vi: set sw=4 ts=4: */
/*
* Utility routines.
*
* Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
*
* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
*/
#include "libbb.h"
ssize_t safe_read(int fd, void *buf, size_t count)
{
ssize_t n;
do {
n = read(fd, buf, count);
} while (n < 0 && errno == EINTR);
return n;
}
/* Suppose that you are a shell. You start child processes.
* They work and eventually exit. You want to get user input.
* You read stdin. But what happens if last child switched
* its stdin into O_NONBLOCK mode?
*
* *** SURPRISE! It will affect the parent too! ***
* *** BIG SURPRISE! It stays even after child exits! ***
*
* This is a design bug in UNIX API.
* fcntl(0, F_SETFL, fcntl(0, F_GETFL, 0) | O_NONBLOCK);
* will set nonblocking mode not only on _your_ stdin, but
* also on stdin of your parent, etc.
*
* In general,
* fd2 = dup(fd1);
* fcntl(fd2, F_SETFL, fcntl(fd2, F_GETFL, 0) | O_NONBLOCK);
* sets both fd1 and fd2 to O_NONBLOCK. This includes cases
* where duping is done implicitly by fork() etc.
*
* We need
* fcntl(fd2, F_SETFD, fcntl(fd2, F_GETFD, 0) | O_NONBLOCK);
* (note SETFD, not SETFL!) but such thing doesn't exist.
*
* Alternatively, we need nonblocking_read(fd, ...) which doesn't
* require O_NONBLOCK dance at all. Actually, it exists:
* n = recv(fd, buf, len, MSG_DONTWAIT);
* "MSG_DONTWAIT:
* Enables non-blocking operation; if the operation
* would block, EAGAIN is returned."
* but recv() works only for sockets!
*
* So far I don't see any good solution, I can only propose
* that affected readers should be careful and use this routine,
* which detects EAGAIN and uses poll() to wait on the fd.
* Thankfully, poll() doesn't care about O_NONBLOCK flag.
*/
ssize_t nonblock_safe_read(int fd, void *buf, size_t count)
{
struct pollfd pfd[1];
ssize_t n;
while (1) {
n = safe_read(fd, buf, count);
if (n >= 0 || errno != EAGAIN)
return n;
/* fd is in O_NONBLOCK mode. Wait using poll and repeat */
pfd[0].fd = fd;
pfd[0].events = POLLIN;
safe_poll(pfd, 1, -1);
}
}
/*
* Read all of the supplied buffer from a file.
* This does multiple reads as necessary.
* Returns the amount read, or -1 on an error.
* A short read is returned on an end of file.
*/
ssize_t full_read(int fd, void *buf, size_t len)
{
ssize_t cc;
ssize_t total;
total = 0;
while (len) {
cc = safe_read(fd, buf, len);
if (cc < 0)
return cc; /* read() returns -1 on failure. */
if (cc == 0)
break;
buf = ((char *)buf) + cc;
total += cc;
len -= cc;
}
return total;
}
// Die with an error message if we can't read the entire buffer.
void xread(int fd, void *buf, size_t count)
{
if (count) {
ssize_t size = full_read(fd, buf, count);
if (size != count)
bb_error_msg_and_die("short read");
}
}
// Die with an error message if we can't read one character.
unsigned char xread_char(int fd)
{
char tmp;
xread(fd, &tmp, 1);
return tmp;
}
// Read one line a-la fgets. Works only on seekable streams
char *reads(int fd, char *buffer, size_t size)
{
char *p;
if (size < 2)
return NULL;
size = full_read(fd, buffer, size-1);
if ((ssize_t)size <= 0)
return NULL;
buffer[size] = '\0';
p = strchr(buffer, '\n');
if (p) {
off_t offset;
*p++ = '\0';
// avoid incorrect (unsigned) widening
offset = (off_t)(p-buffer) - (off_t)size;
// set fd position right after '\n'
if (offset && lseek(fd, offset, SEEK_CUR) == (off_t)-1)
return NULL;
}
return buffer;
}
// Read one line a-la fgets. Reads byte-by-byte.
// Useful when it is important to not read ahead.
// Bytes are appended to pfx (which must be malloced, or NULL).
char *xmalloc_reads(int fd, char *buf)
{
char *p;
int sz = buf ? strlen(buf) : 0;
goto jump_in;
while (1) {
if (p - buf == sz) {
jump_in:
buf = xrealloc(buf, sz + 128);
p = buf + sz;
sz += 128;
}
/* nonblock_safe_read() because we are used by e.g. shells */
if (nonblock_safe_read(fd, p, 1) != 1) { /* EOF/error */
if (p == buf) {
/* we read nothing [and buf was NULL initially] */
free(buf);
return NULL;
}
break;
}
if (*p == '\n')
break;
p++;
}
*p++ = '\0';
return xrealloc(buf, p - buf);
}
ssize_t read_close(int fd, void *buf, size_t size)
{
/*int e;*/
size = full_read(fd, buf, size);
/*e = errno;*/
close(fd);
/*errno = e;*/
return size;
}
ssize_t open_read_close(const char *filename, void *buf, size_t size)
{
int fd = open(filename, O_RDONLY);
if (fd < 0)
return fd;
return read_close(fd, buf, size);
}
// Read (potentially big) files in one go. File size is estimated by
// lseek to end.
void *xmalloc_open_read_close(const char *filename, size_t *sizep)
{
char *buf;
size_t size = sizep ? *sizep : INT_MAX;
int fd;
off_t len;
fd = xopen(filename, O_RDONLY);
/* /proc/N/stat files report len 0 here */
/* In order to make such files readable, we add small const */
len = xlseek(fd, 0, SEEK_END) | 0x3ff; /* + up to 1k */
xlseek(fd, 0, SEEK_SET);
if (len < size)
size = len;
buf = xmalloc(size + 1);
size = read_close(fd, buf, size);
if ((ssize_t)size < 0)
bb_perror_msg_and_die("'%s'", filename);
xrealloc(buf, size + 1);
buf[size] = '\0';
if (sizep)
*sizep = size;
return buf;
}
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