1 /*++
2 /* NAME
3 /* timed_read 3
4 /* SUMMARY
5 /* read operation with pre-read timeout
6 /* SYNOPSIS
7 /* #include <iostuff.h>
8 /*
9 /* ssize_t timed_read(fd, buf, len, timeout, context)
10 /* int fd;
11 /* void *buf;
12 /* size_t len;
13 /* int timeout;
14 /* void *context;
15 /* DESCRIPTION
16 /* timed_read() performs a read() operation when the specified
17 /* descriptor becomes readable within a user-specified deadline.
18 /*
19 /* Arguments:
20 /* .IP fd
21 /* File descriptor in the range 0..FD_SETSIZE.
22 /* .IP buf
23 /* Read buffer pointer.
24 /* .IP len
25 /* Read buffer size.
26 /* .IP timeout
27 /* The deadline in seconds. If this is <= 0, the deadline feature
28 /* is disabled.
29 /* .IP context
30 /* Application context. This parameter is unused. It exists only
31 /* for the sake of VSTREAM compatibility.
32 /* DIAGNOSTICS
33 /* When the operation does not complete within the deadline, the
34 /* result value is -1, and errno is set to ETIMEDOUT.
35 /* All other returns are identical to those of a read(2) operation.
36 /* LICENSE
37 /* .ad
38 /* .fi
39 /* The Secure Mailer license must be distributed with this software.
40 /* AUTHOR(S)
41 /* Wietse Venema
42 /* IBM T.J. Watson Research
43 /* P.O. Box 704
44 /* Yorktown Heights, NY 10598, USA
45 /*--*/
46
47 /* System library. */
48
49 #include <sys_defs.h>
50 #include <unistd.h>
51 #include <errno.h>
52
53 /* Utility library. */
54
55 #include <msg.h>
56 #include <iostuff.h>
57
58 /* timed_read - read with deadline */
59
timed_read(int fd,void * buf,size_t len,int timeout,void * unused_context)60 ssize_t timed_read(int fd, void *buf, size_t len,
61 int timeout, void *unused_context)
62 {
63 ssize_t ret;
64
65 /*
66 * Wait for a limited amount of time for something to happen. If nothing
67 * happens, report an ETIMEDOUT error.
68 *
69 * XXX Solaris 8 read() fails with EAGAIN after read-select() returns
70 * success.
71 */
72 for (;;) {
73 if (timeout > 0 && read_wait(fd, timeout) < 0)
74 return (-1);
75 if ((ret = read(fd, buf, len)) < 0 && timeout > 0 && errno == EAGAIN) {
76 msg_warn("read() returns EAGAIN on a readable file descriptor!");
77 msg_warn("pausing to avoid going into a tight select/read loop!");
78 sleep(1);
79 continue;
80 } else if (ret < 0 && errno == EINTR) {
81 continue;
82 } else {
83 return (ret);
84 }
85 }
86 }
87