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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) {
- if (total) {
- /* we already have some! */
- /* user can do another read to know the error code */
- return total;
- }
- 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_t)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;
- }
- // Reads one line a-la fgets (but doesn't save terminating '\n').
- // 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, size_t *maxsz_p)
- {
- char *p;
- size_t sz = buf ? strlen(buf) : 0;
- size_t maxsz = maxsz_p ? *maxsz_p : MAXINT(size_t);
- goto jump_in;
- while (sz < maxsz) {
- if ((size_t)(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 */
- free(buf);
- return NULL;
- }
- break;
- }
- if (*p == '\n')
- break;
- p++;
- }
- *p = '\0';
- if (maxsz_p)
- *maxsz_p = p - buf;
- p++;
- 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 stat.
- void *xmalloc_open_read_close(const char *filename, size_t *sizep)
- {
- char *buf;
- size_t size;
- int fd;
- off_t len;
- struct stat st;
- fd = open(filename, O_RDONLY);
- if (fd < 0)
- return NULL;
- st.st_size = 0; /* in case fstat fail, define to 0 */
- fstat(fd, &st);
- /* /proc/N/stat files report len 0 here */
- /* In order to make such files readable, we add small const */
- len = st.st_size | 0x3ff; /* read only 1k on unseekable files */
- size = sizep ? *sizep : INT_MAX;
- if (len < size)
- size = len;
- buf = xmalloc(size + 1);
- size = read_close(fd, buf, size);
- if ((ssize_t)size < 0) {
- free(buf);
- return NULL;
- }
- xrealloc(buf, size + 1);
- buf[size] = '\0';
- if (sizep)
- *sizep = size;
- return buf;
- }
- #ifdef USING_LSEEK_TO_GET_SIZE
- /* Alternatively, file size can be obtained by lseek to the end.
- * The code is slightly bigger. Retained in case fstat approach
- * will not work for some weird cases (/proc, block devices, etc).
- * (NB: lseek also can fail to work for some weird files) */
- // 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;
- int fd;
- off_t len;
- fd = open(filename, O_RDONLY);
- if (fd < 0)
- return NULL;
- /* /proc/N/stat files report len 0 here */
- /* In order to make such files readable, we add small const */
- size = 0x3ff; /* read only 1k on unseekable files */
- len = lseek(fd, 0, SEEK_END) | 0x3ff; /* + up to 1k */
- if (len != (off_t)-1) {
- xlseek(fd, 0, SEEK_SET);
- size = sizep ? *sizep : INT_MAX;
- if (len < size)
- size = len;
- }
- buf = xmalloc(size + 1);
- size = read_close(fd, buf, size);
- if ((ssize_t)size < 0) {
- free(buf);
- return NULL;
- }
- xrealloc(buf, size + 1);
- buf[size] = '\0';
- if (sizep)
- *sizep = size;
- return buf;
- }
- #endif
- void *xmalloc_xopen_read_close(const char *filename, size_t *sizep)
- {
- void *buf = xmalloc_open_read_close(filename, sizep);
- if (!buf)
- bb_perror_msg_and_die("can't read '%s'", filename);
- return buf;
- }
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