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sockatmark(3) [osx man page]

SOCKATMARK(3)						   BSD Library Functions Manual 					     SOCKATMARK(3)

sockatmark -- determine whether the read pointer is at the OOB mark LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/socket.h> int sockatmark(int s); DESCRIPTION
To find out if the read pointer is currently pointing at the mark in the data stream, the sockatmark() function is provided. If sockatmark() returns 1, the next read will return data after the mark. Otherwise (assuming out of band data has arrived), the next read will provide data sent by the client prior to transmission of the out of band signal. The routine used in the remote login process to flush output on receipt of an interrupt or quit signal is shown below. It reads the normal data up to the mark (to discard it), then reads the out-of-band byte. #include <sys/socket.h> ... oob() { int out = FWRITE, mark; char waste[BUFSIZ]; /* flush local terminal output */ ioctl(1, TIOCFLUSH, (char *)&out); for (;;) { if ((mark = sockatmark(rem)) < 0) { perror("sockatmark"); break; } if (mark) break; (void) read(rem, waste, sizeof (waste)); } if (recv(rem, &mark, 1, MSG_OOB) < 0) { perror("recv"); ... } ... } RETURN VALUES
Upon successful completion, the sockatmark() function returns the value 1 if the read pointer is pointing at the OOB mark, 0 if it is not. Otherwise, the value -1 is returned and the global variable errno is set to indicate the error. ERRORS
The sockatmark() call fails if: [EBADF] The s argument is not a valid descriptor. [ENOTTY] The s argument is a descriptor for a file, not a socket. SEE ALSO
recv(2), send(2) HISTORY
The sockatmark() function was introduced by IEEE Std 1003.1-2001 (``POSIX.1''), to standardize the historical SIOCATMARK ioctl(2). The ENOTTY error instead of the usual ENOTSOCK is to match the historical behavior of SIOCATMARK. BSD
October 13, 2002 BSD

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SOCKATMARK(3)						     Linux Programmer's Manual						     SOCKATMARK(3)

sockatmark - determine whether socket is at out-of-band mark SYNOPSIS
#include <sys/socket.h> int sockatmark(int sockfd); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): sockatmark(): _POSIX_C_SOURCE >= 200112L DESCRIPTION
sockatmark() returns a value indicating whether or not the socket referred to by the file descriptor sockfd is at the out-of-band mark. If the socket is at the mark, then 1 is returned; if the socket is not at the mark, 0 is returned. This function does not remove the out-of- band mark. RETURN VALUE
A successful call to sockatmark() returns 1 if the socket is at the out-of-band mark, or 0 if it is not. On error, -1 is returned and errno is set to indicate the error. ERRORS
EBADF sockfd is not a valid file descriptor. EINVAL sockfd is not a file descriptor to which sockatmark() can be applied. VERSIONS
sockatmark() was added to glibc in version 2.2.4. ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). +-------------+---------------+---------+ |Interface | Attribute | Value | +-------------+---------------+---------+ |sockatmark() | Thread safety | MT-Safe | +-------------+---------------+---------+ CONFORMING TO
POSIX.1-2001, POSIX.1-2008. NOTES
If sockatmark() returns 1, then the out-of-band data can be read using the MSG_OOB flag of recv(2). Out-of-band data is supported only on some stream socket protocols. sockatmark() can safely be called from a handler for the SIGURG signal. sockatmark() is implemented using the SIOCATMARK ioctl(2) operation. BUGS
Prior to glibc 2.4, sockatmark() did not work. EXAMPLE
The following code can be used after receipt of a SIGURG signal to read (and discard) all data up to the mark, and then read the byte of data at the mark: char buf[BUF_LEN]; char oobdata; int atmark, s; for (;;) { atmark = sockatmark(sockfd); if (atmark == -1) { perror("sockatmark"); break; } if (atmark) break; s = read(sockfd, buf, BUF_LEN); if (s == -1) perror("read"); if (s <= 0) break; } if (atmark == 1) { if (recv(sockfd, &oobdata, 1, MSG_OOB) == -1) { perror("recv"); ... } } SEE ALSO
fcntl(2), recv(2), send(2), tcp(7) COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at Linux 2017-09-15 SOCKATMARK(3)
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