Adding upstream version 3.4.23.upstream/3.4.23upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1882 insertions, 0 deletions

diff --git a/src/util/vstream.c b/src/util/vstream.c
new file mode 100644
index 0000000..d63489b
--- /dev/null
+++ b/src/util/vstream.c
@@ -0,0 +1,1882 @@
+/*++
+/* NAME
+/*	vstream 3
+/* SUMMARY
+/*	light-weight buffered I/O package
+/* SYNOPSIS
+/*	#include <vstream.h>
+/*
+/*	VSTREAM	*vstream_fopen(path, flags, mode)
+/*	const char *path;
+/*	int	flags;
+/*	mode_t	mode;
+/*
+/*	VSTREAM	*vstream_fdopen(fd, flags)
+/*	int	fd;
+/*	int	flags;
+/*
+/*	VSTREAM	*vstream_memopen(string, flags)
+/*	VSTRING	*string;
+/*	int	flags;
+/*
+/*	VSTREAM	*vstream_memreopen(stream, string, flags)
+/*	VSTREAM	*stream;
+/*	VSTRING	*string;
+/*	int	flags;
+/*
+/*	int	vstream_fclose(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	vstream_fdclose(stream)
+/*	VSTREAM	*stream;
+/*
+/*	VSTREAM	*vstream_printf(format, ...)
+/*	const char *format;
+/*
+/*	VSTREAM *vstream_fprintf(stream, format, ...)
+/*	VSTREAM	*stream;
+/*	const char *format;
+/*
+/*	int	VSTREAM_GETC(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	VSTREAM_PUTC(ch, stream)
+/*	int	ch;
+/*
+/*	int	VSTREAM_GETCHAR(void)
+/*
+/*	int	VSTREAM_PUTCHAR(ch)
+/*	int	ch;
+/*
+/*	int	vstream_ungetc(stream, ch)
+/*	VSTREAM	*stream;
+/*	int	ch;
+/*
+/*	int	vstream_fputs(str, stream)
+/*	const char *str;
+/*	VSTREAM	*stream;
+/*
+/*	off_t	vstream_ftell(stream)
+/*	VSTREAM	*stream;
+/*
+/*	off_t	vstream_fseek(stream, offset, whence)
+/*	VSTREAM	*stream;
+/*	off_t	offset;
+/*	int	whence;
+/*
+/*	int	vstream_fflush(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	vstream_fpurge(stream, direction)
+/*	VSTREAM	*stream;
+/*	int	direction;
+/*
+/*	ssize_t	vstream_fread(stream, buf, len)
+/*	VSTREAM	*stream;
+/*	void	*buf;
+/*	ssize_t	len;
+/*
+/*	ssize_t	vstream_fwrite(stream, buf, len)
+/*	VSTREAM	*stream;
+/*	void *buf;
+/*	ssize_t	len;
+/*
+/*	ssize_t	vstream_fread_app(stream, buf, len)
+/*	VSTREAM	*stream;
+/*	VSTRING	*buf;
+/*	ssize_t	len;
+/*
+/*	ssize_t	vstream_fread_buf(stream, buf, len)
+/*	VSTREAM	*stream;
+/*	VSTRING	*buf;
+/*	ssize_t	len;
+/*
+/*	void	vstream_control(stream, name, ...)
+/*	VSTREAM	*stream;
+/*	int	name;
+/*
+/*	int	vstream_fileno(stream)
+/*	VSTREAM	*stream;
+/*
+/*	const ssize_t vstream_req_bufsize(stream)
+/*	VSTREAM	*stream;
+/*
+/*	void	*vstream_context(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	vstream_ferror(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	vstream_ftimeout(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	vstream_feof(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	vstream_clearerr(stream)
+/*	VSTREAM	*stream;
+/*
+/*	const char *VSTREAM_PATH(stream)
+/*	VSTREAM	*stream;
+/*
+/*	char	*vstream_vprintf(format, ap)
+/*	const char *format;
+/*	va_list	*ap;
+/*
+/*	char	*vstream_vfprintf(stream, format, ap)
+/*	VSTREAM	*stream;
+/*	const char *format;
+/*	va_list	*ap;
+/*
+/*	ssize_t	vstream_bufstat(stream, command)
+/*	VSTREAM	*stream;
+/*	int	command;
+/*
+/*	ssize_t	vstream_peek(stream)
+/*	VSTREAM	*stream;
+/*
+/*	const char *vstream_peek_data(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	vstream_setjmp(stream)
+/*	VSTREAM	*stream;
+/*
+/*	void	vstream_longjmp(stream, val)
+/*	VSTREAM	*stream;
+/*	int	val;
+/*
+/*	time_t	vstream_ftime(stream)
+/*	VSTREAM	*stream;
+/*
+/*	struct timeval vstream_ftimeval(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	vstream_rd_error(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	vstream_wr_error(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	vstream_rd_timeout(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	vstream_wr_timeout(stream)
+/*	VSTREAM	*stream;
+/*
+/*	int	vstream_fstat(stream, flags)
+/*	VSTREAM	*stream;
+/*	int	flags;
+/* DESCRIPTION
+/*	The \fIvstream\fR module implements light-weight buffered I/O
+/*	similar to the standard I/O routines.
+/*
+/*	The interface is implemented in terms of VSTREAM structure
+/*	pointers, also called streams. For convenience, three streams
+/*	are predefined: VSTREAM_IN, VSTREAM_OUT, and VSTREAM_ERR. These
+/*	streams are connected to the standard input, output and error
+/*	file descriptors, respectively.
+/*
+/*	Although the interface is patterned after the standard I/O
+/*	library, there are some major differences:
+/* .IP \(bu
+/*	File descriptors are not limited to the range 0..255. This
+/*	was reason #1 to write these routines in the first place.
+/* .IP \(bu
+/*	The application can switch between reading and writing on
+/*	the same stream without having to perform a flush or seek
+/*	operation, and can change write position without having to
+/*	flush.  This was reason #2. Upon position or direction change,
+/*	unread input is discarded, and unwritten output is flushed
+/*	automatically. Exception: with double-buffered streams, unread
+/*	input is not discarded upon change of I/O direction, and
+/*	output flushing is delayed until the read buffer must be refilled.
+/* .IP \(bu
+/*	A bidirectional stream can read and write with the same buffer
+/*	and file descriptor, or it can have separate read/write
+/*	buffers and/or file descriptors.
+/* .IP \(bu
+/*	No automatic flushing of VSTREAM_OUT upon program exit, or of
+/*	VSTREAM_ERR at any time. No unbuffered or line buffered modes.
+/*	This functionality may be added when it is really needed.
+/* .PP
+/*	vstream_fopen() opens the named file and associates a buffered
+/*	stream with it.  The \fIpath\fR, \fIflags\fR and \fImode\fR
+/*	arguments are passed on to the open(2) routine. The result is
+/*	a null pointer in case of problems. The \fIpath\fR argument is
+/*	copied and can be looked up with VSTREAM_PATH().
+/*
+/*	vstream_fdopen() takes an open file and associates a buffered
+/*	stream with it. The \fIflags\fR argument specifies how the file
+/*	was opened. vstream_fdopen() either succeeds or never returns.
+/*
+/*	vstream_memopen() opens a VSTRING as a stream. The \fIflags\fR
+/*	argument must specify one of O_RDONLY, O_WRONLY, or O_APPEND.
+/*	vstream_memopen() either succeeds or never returns. Streams
+/*	opened with vstream_memopen() have limitations: they can't
+/*	be opened in read/write mode, they can't seek beyond the
+/*	end of the VSTRING, and they don't support vstream_control()
+/*	methods that manipulate buffers, file descriptors, or I/O
+/*	functions. After a VSTRING is opened for writing, its content
+/*	will be in an indeterminate state while the stream is open,
+/*	and will be null-terminated when the stream is closed.
+/*
+/*	vstream_memreopen() reopens a memory stream. When the
+/*	\fIstream\fR argument is a null pointer, the behavior is that
+/*	of vstream_memopen().
+/*
+/*	vstream_fclose() closes the named buffered stream. The result
+/*	is 0 in case of success, VSTREAM_EOF in case of problems.
+/*	vstream_fclose() reports the same errors as vstream_ferror().
+/*
+/*	vstream_fdclose() leaves the file(s) open but is otherwise
+/*	identical to vstream_fclose().
+/*
+/*	vstream_fprintf() formats its arguments according to the
+/*	\fIformat\fR argument and writes the result to the named stream.
+/*	The result is the stream argument. It understands the s, c, d, u,
+/*	o, x, X, e, f and g format types, the l modifier, field width and
+/*	precision, sign, and padding with zeros or spaces. In addition,
+/*	vstream_fprintf() recognizes the %m format specifier and expands
+/*	it to the error message corresponding to the current value of the
+/*	global \fIerrno\fR variable.
+/*
+/*	vstream_printf() performs formatted output to the standard output
+/*	stream.
+/*
+/*	VSTREAM_GETC() reads the next character from the named stream.
+/*	The result is VSTREAM_EOF when end-of-file is reached or if a read
+/*	error was detected. VSTREAM_GETC() is an unsafe macro that
+/*	evaluates some arguments more than once.
+/*
+/*	VSTREAM_GETCHAR() is an alias for VSTREAM_GETC(VSTREAM_IN).
+/*
+/*	VSTREAM_PUTC() appends the specified character to the specified
+/*	stream. The result is the stored character, or VSTREAM_EOF in
+/*	case of problems. VSTREAM_PUTC() is an unsafe macro that
+/*	evaluates some arguments more than once.
+/*
+/*	VSTREAM_PUTCHAR(c) is an alias for VSTREAM_PUTC(c, VSTREAM_OUT).
+/*
+/*	vstream_ungetc() pushes back a character onto the specified stream
+/*	and returns the character, or VSTREAM_EOF in case of problems.
+/*	It is an error to push back before reading (or immediately after
+/*	changing the stream offset via vstream_fseek()). Upon successful
+/*	return, vstream_ungetc() clears the end-of-file stream flag.
+/*
+/*	vstream_fputs() appends the given null-terminated string to the
+/*	specified buffered stream. The result is 0 in case of success,
+/*	VSTREAM_EOF in case of problems.
+/*
+/*	vstream_ftell() returns the file offset for the specified stream,
+/*	-1 if the stream is connected to a non-seekable file.
+/*
+/*	vstream_fseek() changes the file position for the next read or write
+/*	operation. Unwritten output is flushed. With unidirectional streams,
+/*	unread input is discarded. The \fIoffset\fR argument specifies the file
+/*	position from the beginning of the file (\fIwhence\fR is SEEK_SET),
+/*	from the current file position (\fIwhence\fR is SEEK_CUR), or from
+/*	the file end (SEEK_END). The result value is the file offset
+/*	from the beginning of the file, -1 in case of problems.
+/*
+/*	vstream_fflush() flushes unwritten data to a file that was
+/*	opened in read-write or write-only mode.
+/*	vstream_fflush() returns 0 in case of success, VSTREAM_EOF in
+/*	case of problems. It is an error to flush a read-only stream.
+/*	vstream_fflush() reports the same errors as vstream_ferror().
+/*
+/*	vstream_fpurge() discards the contents of the stream buffer.
+/*	If direction is VSTREAM_PURGE_READ, it discards unread data,
+/*	else if direction is VSTREAM_PURGE_WRITE, it discards unwritten
+/*	data. In the case of a double-buffered stream, if direction is
+/*	VSTREAM_PURGE_BOTH, it discards the content of both the read
+/*	and write buffers. vstream_fpurge() returns 0 in case of success,
+/*	VSTREAM_EOF in case of problems.
+/*
+/*	vstream_fread() and vstream_fwrite() perform unformatted I/O
+/*	on the named stream. The result value is the number of bytes
+/*	transferred. A short count is returned in case of end-of-file
+/*	or error conditions.
+/*
+/*	vstream_fread_buf() resets the buffer write position,
+/*	allocates space for the specified number of bytes in the
+/*	buffer, reads the bytes from the specified VSTREAM, and
+/*	adjusts the buffer write position. The buffer is NOT
+/*	null-terminated. The result value is as with vstream_fread().
+/*      NOTE: do not skip calling vstream_fread_buf() when len == 0.
+/*      This function has side effects including resetting the buffer
+/*      write position, and skipping the call would invalidate the
+/*      buffer state.
+/*
+/*	vstream_fread_app() is like vstream_fread_buf() but appends
+/*	to existing buffer content, instead of writing over it.
+/*
+/*	vstream_control() allows the user to fine tune the behavior of
+/*	the specified stream.  The arguments are a list of macros with
+/*	zero or more arguments, terminated with CA_VSTREAM_CTL_END
+/*	which has none.  The following lists the names and the types
+/*	of the corresponding value arguments.
+/* .IP "CA_VSTREAM_CTL_READ_FN(ssize_t (*)(int, void *, size_t, int, void *))"
+/*	The argument specifies an alternative for the timed_read(3) function,
+/*	for example, a read function that performs decryption.
+/*	This function receives as arguments a file descriptor, buffer pointer,
+/*	buffer length, timeout value, and the VSTREAM's context value.
+/*	A timeout value <= 0 disables the time limit.
+/*	This function should return the positive number of bytes transferred,
+/*	0 upon EOF, and -1 upon error with errno set appropriately.
+/* .IP "CA_VSTREAM_CTL_WRITE_FN(ssize_t (*)(int, void *, size_t, int, void *))"
+/*	The argument specifies an alternative for the timed_write(3) function,
+/*	for example, a write function that performs encryption.
+/*	This function receives as arguments a file descriptor, buffer pointer,
+/*	buffer length, timeout value, and the VSTREAM's context value.
+/*	A timeout value <= 0 disables the time limit.
+/*	This function should return the positive number of bytes transferred,
+/*	and -1 upon error with errno set appropriately. Instead of -1 it may
+/*	also return 0, e.g., upon remote party-initiated protocol shutdown.
+/* .IP "CA_VSTREAM_CTL_CONTEXT(void *)"
+/*	The argument specifies application context that is passed on to
+/*	the application-specified read/write routines. No copy is made.
+/* .IP "CA_VSTREAM_CTL_PATH(const char *)"
+/*	Updates the stored pathname of the specified stream. The pathname
+/*	is copied.
+/* .IP "CA_VSTREAM_CTL_DOUBLE (no arguments)"
+/*	Use separate buffers for reading and for writing.  This prevents
+/*	unread input from being discarded upon change of I/O direction.
+/* .IP "CA_VSTREAM_CTL_READ_FD(int)"
+/*	The argument specifies the file descriptor to be used for reading.
+/*	This feature is limited to double-buffered streams, and makes the
+/*	stream non-seekable.
+/* .IP "CA_VSTREAM_CTL_WRITE_FD(int)"
+/*	The argument specifies the file descriptor to be used for writing.
+/*	This feature is limited to double-buffered streams, and makes the
+/*	stream non-seekable.
+/* .IP "CA_VSTREAM_CTL_SWAP_FD(VSTREAM *)"
+/*	The argument specifies a VSTREAM pointer; the request swaps the
+/*	file descriptor members of the two streams. This feature is limited
+/*	to streams that are both double-buffered or both single-buffered.
+/* .IP "CA_VSTREAM_CTL_DUPFD(int)"
+/*	The argument specifies a minimum file descriptor value. If
+/*	the actual stream's file descriptors are below the minimum,
+/*	reallocate the descriptors to the first free value greater
+/*	than or equal to the minimum. The VSTREAM_CTL_DUPFD macro
+/*	is defined only on systems with fcntl() F_DUPFD support.
+/* .IP "CA_VSTREAM_CTL_WAITPID_FN(int (*)(pid_t, WAIT_STATUS_T *, int))"
+/*	A pointer to function that behaves like waitpid(). This information
+/*	is used by the vstream_pclose() routine.
+/* .IP "CA_VSTREAM_CTL_TIMEOUT(int)"
+/*	The deadline for a descriptor to become readable in case of a read
+/*	request, or writable in case of a write request. Specify a value
+/*	of 0 to disable deadlines.
+/* .IP "CA_VSTREAM_CTL_EXCEPT (no arguments)"
+/*	Enable exception handling with vstream_setjmp() and vstream_longjmp().
+/*	This involves allocation of additional memory that normally isn't
+/*	used.
+/* .IP "CA_VSTREAM_CTL_BUFSIZE(ssize_t)"
+/*	Specify a non-default buffer size for the next read(2) or
+/*	write(2) operation, or zero to implement a no-op. Requests
+/*	to reduce the buffer size are silently ignored (i.e. any
+/*	positive value <= vstream_req_bufsize()). To get a buffer
+/*	size smaller than VSTREAM_BUFSIZE, make the VSTREAM_CTL_BUFSIZE
+/*	request before the first stream read or write operation
+/*	(i.e., vstream_req_bufsize() returns zero).  Requests to
+/*	change a fixed-size buffer (i.e., VSTREAM_ERR) are not
+/*	allowed.
+/*
+/*	NOTE: the vstream_*printf() routines may silently expand a
+/*	buffer, so that the result of some %letter specifiers can
+/*	be written to contiguous memory.
+/* .IP CA_VSTREAM_CTL_START_DEADLINE (no arguments)
+/*	Change the VSTREAM_CTL_TIMEOUT behavior, to limit the total
+/*	time for all subsequent file descriptor read or write
+/*	operations, and recharge the deadline timer.
+/* .IP CA_VSTREAM_CTL_STOP_DEADLINE (no arguments)
+/*	Revert VSTREAM_CTL_TIMEOUT behavior to the default, i.e.
+/*	a time limit for individual file descriptor read or write
+/*	operations.
+/* .PP
+/*	vstream_fileno() gives access to the file handle associated with
+/*	a buffered stream. With streams that have separate read/write
+/*	file descriptors, the result is the current descriptor.
+/*
+/*	vstream_req_bufsize() returns the buffer size that will be
+/*	used for the next read(2) or write(2) operation on the named
+/*	stream. A zero result means that the next read(2) or write(2)
+/*	operation will use the default buffer size (VSTREAM_BUFSIZE).
+/*
+/*	vstream_context() returns the application context that is passed on to
+/*	the application-specified read/write routines.
+/*
+/*	VSTREAM_PATH() is an unsafe macro that returns the name stored
+/*	with vstream_fopen() or with vstream_control(). The macro is
+/*	unsafe because it evaluates some arguments more than once.
+/*
+/*	vstream_feof() returns non-zero when a previous operation on the
+/*	specified stream caused an end-of-file condition.
+/*	Although further read requests after EOF may complete
+/*	successfully, vstream_feof() will keep returning non-zero
+/*	until vstream_clearerr() is called for that stream.
+/*
+/*	vstream_ferror() returns non-zero when a previous operation on the
+/*	specified stream caused a non-EOF error condition, including timeout.
+/*	After a non-EOF error on a stream, no I/O request will
+/*	complete until after vstream_clearerr() is called for that stream.
+/*
+/*	vstream_ftimeout() returns non-zero when a previous operation on the
+/*	specified stream caused a timeout error condition. See
+/*	vstream_ferror() for error persistence details.
+/*
+/*	vstream_clearerr() resets the timeout, error and end-of-file indication
+/*	of the specified stream, and returns no useful result.
+/*
+/*	vstream_vfprintf() provides an alternate interface
+/*	for formatting an argument list according to a format string.
+/*
+/*	vstream_vprintf() provides a similar alternative interface.
+/*
+/*	vstream_bufstat() provides input and output buffer status
+/*	information.  The command is one of the following:
+/* .IP VSTREAM_BST_IN_PEND
+/*	Return the number of characters that can be read without
+/*	refilling the read buffer.
+/* .IP VSTREAM_BST_OUT_PEND
+/*	Return the number of characters that are waiting in the
+/*	write buffer.
+/* .PP
+/*	vstream_peek() returns the number of characters that can be
+/*	read from the named stream without refilling the read buffer.
+/*	This is an alias for vstream_bufstat(stream, VSTREAM_BST_IN_PEND).
+/*
+/*	vstream_peek_data() returns a pointer to the unread bytes
+/*	that exist according to vstream_peek(), or null if no unread
+/*	bytes are available.
+/*
+/*	vstream_setjmp() saves processing context and makes that context
+/*	available for use with vstream_longjmp().  Normally, vstream_setjmp()
+/*	returns zero.  A non-zero result means that vstream_setjmp() returned
+/*	through a vstream_longjmp() call; the result is the \fIval\fR argument
+/*	given to vstream_longjmp().
+/*
+/*	NB: non-local jumps such as vstream_longjmp() are not safe
+/*	for jumping out of any routine that manipulates VSTREAM data.
+/*	longjmp() like calls are best avoided in signal handlers.
+/*
+/*	vstream_ftime() returns the time of initialization, the last buffer
+/*	fill operation, or the last buffer flush operation for the specified
+/*	stream. This information is maintained only when stream timeouts are
+/*	enabled.
+/*
+/*	vstream_ftimeval() is like vstream_ftime() but returns more
+/*	detail.
+/*
+/*	vstream_rd_mumble() and vstream_wr_mumble() report on
+/*	read and write error conditions, respectively.
+/*
+/*	vstream_fstat() queries stream status information about
+/*	user-requested features. The \fIflags\fR argument is the
+/*	bitwise OR of one or more of the following, and the result
+/*	value is the bitwise OR of the features that are activated.
+/* .IP VSTREAM_FLAG_DEADLINE
+/*	The deadline feature is activated.
+/* .IP VSTREAM_FLAG_DOUBLE
+/*	The double-buffering feature is activated.
+/* .IP VSTREAM_FLAG_MEMORY
+/*	The stream is connected to a VSTRING buffer.
+/* DIAGNOSTICS
+/*	Panics: interface violations. Fatal errors: out of memory.
+/* SEE ALSO
+/*	timed_read(3) default read routine
+/*	timed_write(3) default write routine
+/*	vbuf_print(3) formatting engine
+/*	setjmp(3) non-local jumps
+/* BUGS
+/*	Should use mmap() on reasonable systems.
+/* LICENSE
+/* .ad
+/* .fi
+/*	The Secure Mailer license must be distributed with this software.
+/* AUTHOR(S)
+/*	Wietse Venema
+/*	IBM T.J. Watson Research
+/*	P.O. Box 704
+/*	Yorktown Heights, NY 10598, USA
+/*
+/*	Wietse Venema
+/*	Google, Inc.
+/*	111 8th Avenue
+/*	New York, NY 10011, USA
+/*--*/
+
+/* System library. */
+
+#include <sys_defs.h>
+#include <stdlib.h>			/* 44BSD stdarg.h uses abort() */
+#include <stdarg.h>
+#include <stddef.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <time.h>
+#include <errno.h>
+#include <string.h>
+
+/* Utility library. */
+
+#define VSTRING_INTERNAL
+
+#include "mymalloc.h"
+#include "msg.h"
+#include "vbuf_print.h"
+#include "iostuff.h"
+#include "vstring.h"
+#include "vstream.h"
+
+/* Application-specific. */
+
+ /*
+  * Forward declarations.
+  */
+static int vstream_buf_get_ready(VBUF *);
+static int vstream_buf_put_ready(VBUF *);
+static int vstream_buf_space(VBUF *, ssize_t);
+
+ /*
+  * Initialization of the three pre-defined streams. Pre-allocate a static
+  * I/O buffer for the standard error stream, so that the error handler can
+  * produce a diagnostic even when memory allocation fails.
+  */
+static unsigned char vstream_fstd_buf[VSTREAM_BUFSIZE];
+
+VSTREAM vstream_fstd[] = {
+    {{
+	    0,				/* flags */
+	    0, 0, 0, 0,			/* buffer */
+	    vstream_buf_get_ready, vstream_buf_put_ready, vstream_buf_space,
+    }, STDIN_FILENO, (VSTREAM_RW_FN) timed_read, (VSTREAM_RW_FN) timed_write,
+    0,},
+    {{
+	    0,				/* flags */
+	    0, 0, 0, 0,			/* buffer */
+	    vstream_buf_get_ready, vstream_buf_put_ready, vstream_buf_space,
+    }, STDOUT_FILENO, (VSTREAM_RW_FN) timed_read, (VSTREAM_RW_FN) timed_write,
+    0,},
+    {{
+	    VBUF_FLAG_FIXED | VSTREAM_FLAG_WRITE,
+	    vstream_fstd_buf, VSTREAM_BUFSIZE, VSTREAM_BUFSIZE, vstream_fstd_buf,
+	    vstream_buf_get_ready, vstream_buf_put_ready, vstream_buf_space,
+    }, STDERR_FILENO, (VSTREAM_RW_FN) timed_read, (VSTREAM_RW_FN) timed_write,
+    VSTREAM_BUFSIZE,},
+};
+
+#define VSTREAM_STATIC(v) ((v) >= VSTREAM_IN && (v) <= VSTREAM_ERR)
+
+ /*
+  * A bunch of macros to make some expressions more readable. XXX We're
+  * assuming that O_RDONLY == 0, O_WRONLY == 1, O_RDWR == 2.
+  */
+#define VSTREAM_ACC_MASK(f)	((f) & (O_APPEND | O_WRONLY | O_RDWR))
+
+#define VSTREAM_CAN_READ(f)	(VSTREAM_ACC_MASK(f) == O_RDONLY \
+				|| VSTREAM_ACC_MASK(f) == O_RDWR)
+#define VSTREAM_CAN_WRITE(f)	(VSTREAM_ACC_MASK(f) & O_WRONLY \
+				|| VSTREAM_ACC_MASK(f) & O_RDWR \
+				|| VSTREAM_ACC_MASK(f) & O_APPEND)
+
+#define VSTREAM_BUF_COUNT(bp, n) \
+	((bp)->flags & VSTREAM_FLAG_READ ? -(n) : (n))
+
+#define VSTREAM_BUF_AT_START(bp) { \
+	(bp)->cnt = VSTREAM_BUF_COUNT((bp), (bp)->len); \
+	(bp)->ptr = (bp)->data; \
+    }
+
+#define VSTREAM_BUF_AT_OFFSET(bp, offset) { \
+	(bp)->ptr = (bp)->data + (offset); \
+	(bp)->cnt = VSTREAM_BUF_COUNT(bp, (bp)->len - (offset)); \
+    }
+
+#define VSTREAM_BUF_AT_END(bp) { \
+	(bp)->cnt = 0; \
+	(bp)->ptr = (bp)->data + (bp)->len; \
+    }
+
+#define VSTREAM_BUF_ZERO(bp) { \
+	(bp)->flags = 0; \
+	(bp)->data = (bp)->ptr = 0; \
+	(bp)->len = (bp)->cnt = 0; \
+    }
+
+#define VSTREAM_BUF_ACTIONS(bp, get_action, put_action, space_action) { \
+	(bp)->get_ready = (get_action); \
+	(bp)->put_ready = (put_action); \
+	(bp)->space = (space_action); \
+    }
+
+#define VSTREAM_SAVE_STATE(stream, buffer, filedes) { \
+	stream->buffer = stream->buf; \
+	stream->filedes = stream->fd; \
+    }
+
+#define VSTREAM_RESTORE_STATE(stream, buffer, filedes) do { \
+	stream->buffer.flags = stream->buf.flags; \
+	stream->buf = stream->buffer; \
+	stream->fd = stream->filedes; \
+    } while(0)
+
+#define VSTREAM_FORK_STATE(stream, buffer, filedes) { \
+	stream->buffer = stream->buf; \
+	stream->filedes = stream->fd; \
+	stream->buffer.data = stream->buffer.ptr = 0; \
+	stream->buffer.len = stream->buffer.cnt = 0; \
+	stream->buffer.flags &= ~VSTREAM_FLAG_FIXED; \
+    };
+
+#define VSTREAM_FLAG_READ_DOUBLE (VSTREAM_FLAG_READ | VSTREAM_FLAG_DOUBLE)
+#define VSTREAM_FLAG_WRITE_DOUBLE (VSTREAM_FLAG_WRITE | VSTREAM_FLAG_DOUBLE)
+
+#define VSTREAM_FFLUSH_SOME(stream) \
+	vstream_fflush_some((stream), (stream)->buf.len - (stream)->buf.cnt)
+
+/* Note: this does not change a negative result into a zero result. */
+#define VSTREAM_SUB_TIME(x, y, z) \
+    do { \
+	(x).tv_sec = (y).tv_sec - (z).tv_sec; \
+	(x).tv_usec = (y).tv_usec - (z).tv_usec; \
+	while ((x).tv_usec < 0) { \
+	    (x).tv_usec += 1000000; \
+	    (x).tv_sec -= 1; \
+	} \
+	while ((x).tv_usec >= 1000000) { \
+	    (x).tv_usec -= 1000000; \
+	    (x).tv_sec += 1; \
+	} \
+    } while (0)
+
+/* vstream_buf_init - initialize buffer */
+
+static void vstream_buf_init(VBUF *bp, int flags)
+{
+
+    /*
+     * Initialize the buffer such that the first data access triggers a
+     * buffer boundary action.
+     */
+    VSTREAM_BUF_ZERO(bp);
+    VSTREAM_BUF_ACTIONS(bp,
+			VSTREAM_CAN_READ(flags) ? vstream_buf_get_ready : 0,
+			VSTREAM_CAN_WRITE(flags) ? vstream_buf_put_ready : 0,
+			vstream_buf_space);
+}
+
+/* vstream_buf_alloc - allocate buffer memory */
+
+static void vstream_buf_alloc(VBUF *bp, ssize_t len)
+{
+    VSTREAM *stream = VBUF_TO_APPL(bp, VSTREAM, buf);
+    ssize_t used = bp->ptr - bp->data;
+    const char *myname = "vstream_buf_alloc";
+
+    if (len < bp->len)
+	msg_panic("%s: attempt to shrink buffer", myname);
+    if (bp->flags & VSTREAM_FLAG_FIXED)
+	msg_panic("%s: unable to extend fixed-size buffer", myname);
+
+    /*
+     * Late buffer allocation allows the user to override the default policy.
+     * If a buffer already exists, allow for the presence of (output) data.
+     */
+    bp->data = (unsigned char *)
+	(bp->data ? myrealloc((void *) bp->data, len) : mymalloc(len));
+    bp->len = len;
+    if (bp->flags & VSTREAM_FLAG_READ) {
+	bp->ptr = bp->data + used;
+	if (bp->flags & VSTREAM_FLAG_DOUBLE)
+	    VSTREAM_SAVE_STATE(stream, read_buf, read_fd);
+    } else {
+	VSTREAM_BUF_AT_OFFSET(bp, used);
+	if (bp->flags & VSTREAM_FLAG_DOUBLE)
+	    VSTREAM_SAVE_STATE(stream, write_buf, write_fd);
+    }
+}
+
+/* vstream_buf_wipe - reset buffer to initial state */
+
+static void vstream_buf_wipe(VBUF *bp)
+{
+    if ((bp->flags & VBUF_FLAG_FIXED) == 0 && bp->data)
+	myfree((void *) bp->data);
+    VSTREAM_BUF_ZERO(bp);
+    VSTREAM_BUF_ACTIONS(bp, 0, 0, 0);
+}
+
+/* vstream_fflush_some - flush some buffered data */
+
+static int vstream_fflush_some(VSTREAM *stream, ssize_t to_flush)
+{
+    const char *myname = "vstream_fflush_some";
+    VBUF   *bp = &stream->buf;
+    ssize_t used;
+    ssize_t left_over;
+    void   *data;
+    ssize_t len;
+    ssize_t n;
+    int     timeout;
+    struct timeval before;
+    struct timeval elapsed;
+
+    /*
+     * Sanity checks. It is illegal to flush a read-only stream. Otherwise,
+     * if there is buffered input, discard the input. If there is buffered
+     * output, require that the amount to flush is larger than the amount to
+     * keep, so that we can memcpy() the residue.
+     */
+    if (bp->put_ready == 0)
+	msg_panic("%s: read-only stream", myname);
+    switch (bp->flags & (VSTREAM_FLAG_WRITE | VSTREAM_FLAG_READ)) {
+    case VSTREAM_FLAG_READ:			/* discard input */
+	VSTREAM_BUF_AT_END(bp);
+	/* FALLTHROUGH */
+    case 0:					/* flush after seek? */
+	return ((bp->flags & VSTREAM_FLAG_ERR) ? VSTREAM_EOF : 0);
+    case VSTREAM_FLAG_WRITE:			/* output buffered */
+	break;
+    case VSTREAM_FLAG_WRITE | VSTREAM_FLAG_READ:
+	msg_panic("%s: read/write stream", myname);
+    }
+    used = bp->len - bp->cnt;
+    left_over = used - to_flush;
+
+    if (msg_verbose > 2 && stream != VSTREAM_ERR)
+	msg_info("%s: fd %d flush %ld", myname, stream->fd, (long) to_flush);
+    if (to_flush < 0 || left_over < 0)
+	msg_panic("%s: bad to_flush %ld", myname, (long) to_flush);
+    if (to_flush < left_over)
+	msg_panic("%s: to_flush < left_over", myname);
+    if (to_flush == 0)
+	return ((bp->flags & VSTREAM_FLAG_ERR) ? VSTREAM_EOF : 0);
+    if (bp->flags & VSTREAM_FLAG_ERR)
+	return (VSTREAM_EOF);
+
+    /*
+     * When flushing a buffer, allow for partial writes. These can happen
+     * while talking to a network. Update the cached file seek position, if
+     * any.
+     * 
+     * When deadlines are enabled, we count the elapsed time for each write
+     * operation instead of simply comparing the time-of-day clock with a
+     * per-stream deadline. The latter could result in anomalies when an
+     * application does lengthy processing between write operations. Keep in
+     * mind that a receiver may not be able to keep up when a sender suddenly
+     * floods it with a lot of data as it tries to catch up with a deadline.
+     */
+    for (data = (void *) bp->data, len = to_flush; len > 0; len -= n, data += n) {
+	if (bp->flags & VSTREAM_FLAG_DEADLINE) {
+	    timeout = stream->time_limit.tv_sec + (stream->time_limit.tv_usec > 0);
+	    if (timeout <= 0) {
+		bp->flags |= (VSTREAM_FLAG_WR_ERR | VSTREAM_FLAG_WR_TIMEOUT);
+		errno = ETIMEDOUT;
+		return (VSTREAM_EOF);
+	    }
+	    if (len == to_flush)
+		GETTIMEOFDAY(&before);
+	    else
+		before = stream->iotime;
+	} else
+	    timeout = stream->timeout;
+	if ((n = stream->write_fn(stream->fd, data, len, timeout, stream->context)) <= 0) {
+	    bp->flags |= VSTREAM_FLAG_WR_ERR;
+	    if (errno == ETIMEDOUT) {
+		bp->flags |= VSTREAM_FLAG_WR_TIMEOUT;
+		stream->time_limit.tv_sec = stream->time_limit.tv_usec = 0;
+	    }
+	    return (VSTREAM_EOF);
+	}
+	if (timeout) {
+	    GETTIMEOFDAY(&stream->iotime);
+	    if (bp->flags & VSTREAM_FLAG_DEADLINE) {
+		VSTREAM_SUB_TIME(elapsed, stream->iotime, before);
+		VSTREAM_SUB_TIME(stream->time_limit, stream->time_limit, elapsed);
+	    }
+	}
+	if (msg_verbose > 2 && stream != VSTREAM_ERR && n != to_flush)
+	    msg_info("%s: %d flushed %ld/%ld", myname, stream->fd,
+		     (long) n, (long) to_flush);
+    }
+    if (bp->flags & VSTREAM_FLAG_SEEK)
+	stream->offset += to_flush;
+
+    /*
+     * Allow for partial buffer flush requests. We use memcpy() for reasons
+     * of portability to pre-ANSI environments (SunOS 4.x or Ultrix 4.x :-).
+     * This is OK because we have already verified that the to_flush count is
+     * larger than the left_over count.
+     */
+    if (left_over > 0)
+	memcpy(bp->data, bp->data + to_flush, left_over);
+    bp->cnt += to_flush;
+    bp->ptr -= to_flush;
+    return ((bp->flags & VSTREAM_FLAG_ERR) ? VSTREAM_EOF : 0);
+}
+
+/* vstream_fflush_delayed - delayed stream flush for double-buffered stream */
+
+static int vstream_fflush_delayed(VSTREAM *stream)
+{
+    int     status;
+
+    /*
+     * Sanity check.
+     */
+    if ((stream->buf.flags & VSTREAM_FLAG_READ_DOUBLE) != VSTREAM_FLAG_READ_DOUBLE)
+	msg_panic("vstream_fflush_delayed: bad flags");
+
+    /*
+     * Temporarily swap buffers and flush unwritten data. This may seem like
+     * a lot of work, but it's peanuts compared to the write(2) call that we
+     * already have avoided. For example, delayed flush is never used on a
+     * non-pipelined SMTP connection.
+     */
+    stream->buf.flags &= ~VSTREAM_FLAG_READ;
+    VSTREAM_SAVE_STATE(stream, read_buf, read_fd);
+    stream->buf.flags |= VSTREAM_FLAG_WRITE;
+    VSTREAM_RESTORE_STATE(stream, write_buf, write_fd);
+
+    status = VSTREAM_FFLUSH_SOME(stream);
+
+    stream->buf.flags &= ~VSTREAM_FLAG_WRITE;
+    VSTREAM_SAVE_STATE(stream, write_buf, write_fd);
+    stream->buf.flags |= VSTREAM_FLAG_READ;
+    VSTREAM_RESTORE_STATE(stream, read_buf, read_fd);
+
+    return (status);
+}
+
+/* vstream_buf_get_ready - vbuf callback to make buffer ready for reading */
+
+static int vstream_buf_get_ready(VBUF *bp)
+{
+    VSTREAM *stream = VBUF_TO_APPL(bp, VSTREAM, buf);
+    const char *myname = "vstream_buf_get_ready";
+    ssize_t n;
+    struct timeval before;
+    struct timeval elapsed;
+    int     timeout;
+
+    /*
+     * Detect a change of I/O direction or position. If so, flush any
+     * unwritten output immediately when the stream is single-buffered, or
+     * when the stream is double-buffered and the read buffer is empty.
+     */
+    switch (bp->flags & (VSTREAM_FLAG_WRITE | VSTREAM_FLAG_READ)) {
+    case VSTREAM_FLAG_WRITE:			/* change direction */
+	if (bp->ptr > bp->data)
+	    if ((bp->flags & VSTREAM_FLAG_DOUBLE) == 0
+		|| stream->read_buf.cnt >= 0)
+		if (VSTREAM_FFLUSH_SOME(stream))
+		    return (VSTREAM_EOF);
+	bp->flags &= ~VSTREAM_FLAG_WRITE;
+	if (bp->flags & VSTREAM_FLAG_DOUBLE)
+	    VSTREAM_SAVE_STATE(stream, write_buf, write_fd);
+	/* FALLTHROUGH */
+    case 0:					/* change position */
+	bp->flags |= VSTREAM_FLAG_READ;
+	if (bp->flags & VSTREAM_FLAG_DOUBLE) {
+	    VSTREAM_RESTORE_STATE(stream, read_buf, read_fd);
+	    if (bp->cnt < 0)
+		return (0);
+	}
+	/* FALLTHROUGH */
+    case VSTREAM_FLAG_READ:			/* no change */
+	break;
+    case VSTREAM_FLAG_WRITE | VSTREAM_FLAG_READ:
+	msg_panic("%s: read/write stream", myname);
+    }
+
+    /*
+     * If this is the first GET operation, allocate a buffer. Late buffer
+     * allocation gives the application a chance to override the default
+     * buffering policy.
+     * 
+     * XXX Subtle code to set the preferred buffer size as late as possible.
+     */
+    if (stream->req_bufsize == 0)
+	stream->req_bufsize = VSTREAM_BUFSIZE;
+    if (bp->len < stream->req_bufsize)
+	vstream_buf_alloc(bp, stream->req_bufsize);
+
+    /*
+     * If the stream is double-buffered and the write buffer is not empty,
+     * this is the time to flush the write buffer. Delayed flushes reduce
+     * system call overhead, and on TCP sockets, avoid triggering Nagle's
+     * algorithm.
+     */
+    if ((bp->flags & VSTREAM_FLAG_DOUBLE)
+	&& stream->write_buf.len > stream->write_buf.cnt)
+	if (vstream_fflush_delayed(stream))
+	    return (VSTREAM_EOF);
+
+    /*
+     * Did we receive an EOF indication?
+     */
+    if (bp->flags & VSTREAM_FLAG_EOF)
+	return (VSTREAM_EOF);
+
+    /*
+     * Fill the buffer with as much data as we can handle, or with as much
+     * data as is available right now, whichever is less. Update the cached
+     * file seek position, if any.
+     * 
+     * When deadlines are enabled, we count the elapsed time for each read
+     * operation instead of simply comparing the time-of-day clock with a
+     * per-stream deadline. The latter could result in anomalies when an
+     * application does lengthy processing between read operations. Keep in
+     * mind that a sender may get blocked, and may not be able to keep up
+     * when a receiver suddenly wants to read a lot of data as it tries to
+     * catch up with a deadline.
+     */
+    if (bp->flags & VSTREAM_FLAG_DEADLINE) {
+	timeout = stream->time_limit.tv_sec + (stream->time_limit.tv_usec > 0);
+	if (timeout <= 0) {
+	    bp->flags |= (VSTREAM_FLAG_RD_ERR | VSTREAM_FLAG_RD_TIMEOUT);
+	    errno = ETIMEDOUT;
+	    return (VSTREAM_EOF);
+	}
+	GETTIMEOFDAY(&before);
+    } else
+	timeout = stream->timeout;
+    switch (n = stream->read_fn(stream->fd, bp->data, bp->len, timeout, stream->context)) {
+    case -1:
+	bp->flags |= VSTREAM_FLAG_RD_ERR;
+	if (errno == ETIMEDOUT) {
+	    bp->flags |= VSTREAM_FLAG_RD_TIMEOUT;
+	    stream->time_limit.tv_sec = stream->time_limit.tv_usec = 0;
+	}
+	return (VSTREAM_EOF);
+    case 0:
+	bp->flags |= VSTREAM_FLAG_EOF;
+	return (VSTREAM_EOF);
+    default:
+	if (timeout) {
+	    GETTIMEOFDAY(&stream->iotime);
+	    if (bp->flags & VSTREAM_FLAG_DEADLINE) {
+		VSTREAM_SUB_TIME(elapsed, stream->iotime, before);
+		VSTREAM_SUB_TIME(stream->time_limit, stream->time_limit, elapsed);
+	    }
+	}
+	if (msg_verbose > 2)
+	    msg_info("%s: fd %d got %ld", myname, stream->fd, (long) n);
+	bp->cnt = -n;
+	bp->ptr = bp->data;
+	if (bp->flags & VSTREAM_FLAG_SEEK)
+	    stream->offset += n;
+	return (0);
+    }
+}
+
+/* vstream_buf_put_ready - vbuf callback to make buffer ready for writing */
+
+static int vstream_buf_put_ready(VBUF *bp)
+{
+    VSTREAM *stream = VBUF_TO_APPL(bp, VSTREAM, buf);
+    const char *myname = "vstream_buf_put_ready";
+
+    /*
+     * Sanity checks. Detect a change of I/O direction or position. If so,
+     * discard unread input, and reset the buffer to the beginning.
+     */
+    switch (bp->flags & (VSTREAM_FLAG_WRITE | VSTREAM_FLAG_READ)) {
+    case VSTREAM_FLAG_READ:			/* change direction */
+	bp->flags &= ~VSTREAM_FLAG_READ;
+	if (bp->flags & VSTREAM_FLAG_DOUBLE)
+	    VSTREAM_SAVE_STATE(stream, read_buf, read_fd);
+	/* FALLTHROUGH */
+    case 0:					/* change position */
+	bp->flags |= VSTREAM_FLAG_WRITE;
+	if (bp->flags & VSTREAM_FLAG_DOUBLE)
+	    VSTREAM_RESTORE_STATE(stream, write_buf, write_fd);
+	else
+	    VSTREAM_BUF_AT_START(bp);
+	/* FALLTHROUGH */
+    case VSTREAM_FLAG_WRITE:			/* no change */
+	break;
+    case VSTREAM_FLAG_WRITE | VSTREAM_FLAG_READ:
+	msg_panic("%s: read/write stream", myname);
+    }
+
+    /*
+     * Remember the direction. If this is the first PUT operation for this
+     * stream or if the buffer is smaller than the requested size, allocate a
+     * new buffer; obviously there is no data to be flushed yet. Otherwise,
+     * flush the buffer.
+     * 
+     * XXX Subtle code to set the preferred buffer size as late as possible.
+     */
+    if (stream->req_bufsize == 0)
+	stream->req_bufsize = VSTREAM_BUFSIZE;
+    if (bp->len < stream->req_bufsize) {
+	vstream_buf_alloc(bp, stream->req_bufsize);
+    } else if (bp->cnt <= 0) {
+	if (VSTREAM_FFLUSH_SOME(stream))
+	    return (VSTREAM_EOF);
+    }
+    return (0);
+}
+
+/* vstream_buf_space - reserve space ahead of time */
+
+static int vstream_buf_space(VBUF *bp, ssize_t want)
+{
+    VSTREAM *stream = VBUF_TO_APPL(bp, VSTREAM, buf);
+    ssize_t used;
+    ssize_t incr;
+    ssize_t shortage;
+    const char *myname = "vstream_buf_space";
+
+    /*
+     * Sanity checks. Reserving space implies writing. It is illegal to write
+     * to a read-only stream. Detect a change of I/O direction or position.
+     * If so, reset the buffer to the beginning.
+     */
+    if (bp->put_ready == 0)
+	msg_panic("%s: read-only stream", myname);
+    if (want < 0)
+	msg_panic("%s: bad length %ld", myname, (long) want);
+    switch (bp->flags & (VSTREAM_FLAG_READ | VSTREAM_FLAG_WRITE)) {
+    case VSTREAM_FLAG_READ:			/* change direction */
+	bp->flags &= ~VSTREAM_FLAG_READ;
+	if (bp->flags & VSTREAM_FLAG_DOUBLE)
+	    VSTREAM_SAVE_STATE(stream, read_buf, read_fd);
+	/* FALLTHROUGH */
+    case 0:					/* change position */
+	bp->flags |= VSTREAM_FLAG_WRITE;
+	if (bp->flags & VSTREAM_FLAG_DOUBLE)
+	    VSTREAM_RESTORE_STATE(stream, write_buf, write_fd);
+	else
+	    VSTREAM_BUF_AT_START(bp);
+	/* FALLTHROUGH */
+    case VSTREAM_FLAG_WRITE:			/* no change */
+	break;
+    case VSTREAM_FLAG_READ | VSTREAM_FLAG_WRITE:
+	msg_panic("%s: read/write stream", myname);
+    }
+
+    /*
+     * See if enough space is available. If not, flush a multiple of
+     * VSTREAM_BUFSIZE bytes and resize the buffer to a multiple of
+     * VSTREAM_BUFSIZE. We flush multiples of VSTREAM_BUFSIZE in an attempt
+     * to keep file updates block-aligned for better performance.
+     * 
+     * XXX Subtle code to set the preferred buffer size as late as possible.
+     */
+#define VSTREAM_TRUNCATE(count, base)	(((count) / (base)) * (base))
+#define VSTREAM_ROUNDUP(count, base)	VSTREAM_TRUNCATE(count + base - 1, base)
+
+    if (stream->req_bufsize == 0)
+	stream->req_bufsize = VSTREAM_BUFSIZE;
+    if (want > bp->cnt) {
+	if ((used = bp->len - bp->cnt) > stream->req_bufsize)
+	    if (vstream_fflush_some(stream, VSTREAM_TRUNCATE(used, stream->req_bufsize)))
+		return (VSTREAM_EOF);
+	if ((shortage = (want - bp->cnt)) > 0) {
+	    if ((bp->flags & VSTREAM_FLAG_FIXED)
+		|| shortage > __MAXINT__(ssize_t) -bp->len - stream->req_bufsize) {
+		bp->flags |= VSTREAM_FLAG_WR_ERR;
+	    } else {
+		incr = VSTREAM_ROUNDUP(shortage, stream->req_bufsize);
+		vstream_buf_alloc(bp, bp->len + incr);
+	    }
+	}
+    }
+    return (vstream_ferror(stream) ? VSTREAM_EOF : 0);	/* mmap() may fail */
+}
+
+/* vstream_fpurge - discard unread or unwritten content */
+
+int     vstream_fpurge(VSTREAM *stream, int direction)
+{
+    const char *myname = "vstream_fpurge";
+    VBUF   *bp = &stream->buf;
+
+#define VSTREAM_MAYBE_PURGE_WRITE(d, b) if ((d) & VSTREAM_PURGE_WRITE) \
+	VSTREAM_BUF_AT_START((b))
+#define VSTREAM_MAYBE_PURGE_READ(d, b) if ((d) & VSTREAM_PURGE_READ) \
+	VSTREAM_BUF_AT_END((b))
+
+    /*
+     * To discard all unread contents, position the read buffer at its end,
+     * so that we skip over any unread data, and so that the next read
+     * operation will refill the buffer.
+     * 
+     * To discard all unwritten content, position the write buffer at its
+     * beginning, so that the next write operation clobbers any unwritten
+     * data.
+     */
+    switch (bp->flags & (VSTREAM_FLAG_READ_DOUBLE | VSTREAM_FLAG_WRITE)) {
+    case VSTREAM_FLAG_READ_DOUBLE:
+	VSTREAM_MAYBE_PURGE_WRITE(direction, &stream->write_buf);
+	/* FALLTHROUGH */
+    case VSTREAM_FLAG_READ:
+	VSTREAM_MAYBE_PURGE_READ(direction, bp);
+	break;
+    case VSTREAM_FLAG_DOUBLE:
+	VSTREAM_MAYBE_PURGE_WRITE(direction, &stream->write_buf);
+	VSTREAM_MAYBE_PURGE_READ(direction, &stream->read_buf);
+	break;
+    case VSTREAM_FLAG_WRITE_DOUBLE:
+	VSTREAM_MAYBE_PURGE_READ(direction, &stream->read_buf);
+	/* FALLTHROUGH */
+    case VSTREAM_FLAG_WRITE:
+	VSTREAM_MAYBE_PURGE_WRITE(direction, bp);
+	break;
+    case VSTREAM_FLAG_READ_DOUBLE | VSTREAM_FLAG_WRITE:
+    case VSTREAM_FLAG_READ | VSTREAM_FLAG_WRITE:
+	msg_panic("%s: read/write stream", myname);
+    }
+
+    /*
+     * Invalidate the cached file seek position.
+     */
+    bp->flags &= ~VSTREAM_FLAG_SEEK;
+    stream->offset = 0;
+
+    return (0);
+}
+
+/* vstream_fseek - change I/O position */
+
+off_t   vstream_fseek(VSTREAM *stream, off_t offset, int whence)
+{
+    const char *myname = "vstream_fseek";
+    VBUF   *bp = &stream->buf;
+
+    /*
+     * TODO: support data length (data length != buffer length). Without data
+     * length information, vstream_fseek() would break vstream_fflush() for
+     * memory streams.
+     */
+    if (stream->buf.flags & VSTREAM_FLAG_MEMORY) {
+#ifdef PENDING_VSTREAM_FSEEK_FOR_MEMORY
+	if (whence == SEEK_CUR)
+	    offset += (bp->ptr - bp->data);
+	else if (whence == SEEK_END)
+	    offset += bp->len;
+	if (offset < 0 || offset > bp->data_len) {
+	    errno = EINVAL;
+	    return (-1);
+	}
+	VSTREAM_BUF_AT_OFFSET(bp, offset);
+	return (offset);
+#else
+	errno = EOPNOTSUPP;
+	return (-1);
+#endif
+    }
+
+    /*
+     * Flush any unwritten output. Discard any unread input. Position the
+     * buffer at the end, so that the next GET or PUT operation triggers a
+     * buffer boundary action.
+     */
+    switch (bp->flags & (VSTREAM_FLAG_READ | VSTREAM_FLAG_WRITE)) {
+    case VSTREAM_FLAG_WRITE:
+	if (bp->ptr > bp->data) {
+	    if (whence == SEEK_CUR)
+		offset += (bp->ptr - bp->data);	/* add unwritten data */
+	    else if (whence == SEEK_END)
+		bp->flags &= ~VSTREAM_FLAG_SEEK;
+	    if (VSTREAM_FFLUSH_SOME(stream))
+		return (-1);
+	}
+	VSTREAM_BUF_AT_END(bp);
+	break;
+    case VSTREAM_FLAG_READ:
+	if (whence == SEEK_CUR)
+	    offset += bp->cnt;			/* subtract unread data */
+	else if (whence == SEEK_END)
+	    bp->flags &= ~VSTREAM_FLAG_SEEK;
+	/* FALLTHROUGH */
+    case 0:
+	VSTREAM_BUF_AT_END(bp);
+	break;
+    case VSTREAM_FLAG_READ | VSTREAM_FLAG_WRITE:
+	msg_panic("%s: read/write stream", myname);
+    }
+
+    /*
+     * Clear the read/write flags to inform the buffer boundary action
+     * routines that we may have changed I/O position.
+     */
+    bp->flags &= ~(VSTREAM_FLAG_READ | VSTREAM_FLAG_WRITE);
+
+    /*
+     * Shave an unnecessary system call.
+     */
+    if (bp->flags & VSTREAM_FLAG_NSEEK) {
+	errno = ESPIPE;
+	return (-1);
+    }
+
+    /*
+     * Update the cached file seek position.
+     */
+    if ((stream->offset = lseek(stream->fd, offset, whence)) < 0) {
+	if (errno == ESPIPE)
+	    bp->flags |= VSTREAM_FLAG_NSEEK;
+    } else {
+	bp->flags |= VSTREAM_FLAG_SEEK;
+    }
+    bp->flags &= ~VSTREAM_FLAG_EOF;
+    return (stream->offset);
+}
+
+/* vstream_ftell - return file offset */
+
+off_t   vstream_ftell(VSTREAM *stream)
+{
+    VBUF   *bp = &stream->buf;
+
+    /*
+     * Special case for memory buffer.
+     */
+    if (stream->buf.flags & VSTREAM_FLAG_MEMORY)
+	return (bp->ptr - bp->data);
+
+    /*
+     * Shave an unnecessary syscall.
+     */
+    if (bp->flags & VSTREAM_FLAG_NSEEK) {
+	errno = ESPIPE;
+	return (-1);
+    }
+
+    /*
+     * Use the cached file offset when available. This is the offset after
+     * the last read, write or seek operation.
+     */
+    if ((bp->flags & VSTREAM_FLAG_SEEK) == 0) {
+	if ((stream->offset = lseek(stream->fd, (off_t) 0, SEEK_CUR)) < 0) {
+	    bp->flags |= VSTREAM_FLAG_NSEEK;
+	    return (-1);
+	}
+	bp->flags |= VSTREAM_FLAG_SEEK;
+    }
+
+    /*
+     * If this is a read buffer, subtract the number of unread bytes from the
+     * cached offset. Remember that read counts are negative.
+     */
+    if (bp->flags & VSTREAM_FLAG_READ)
+	return (stream->offset + bp->cnt);
+
+    /*
+     * If this is a write buffer, add the number of unwritten bytes to the
+     * cached offset.
+     */
+    if (bp->flags & VSTREAM_FLAG_WRITE)
+	return (stream->offset + (bp->ptr - bp->data));
+
+    /*
+     * Apparently, this is a new buffer, or a buffer after seek, so there is
+     * no need to account for unread or unwritten data.
+     */
+    return (stream->offset);
+}
+
+/* vstream_subopen - initialize everything except buffers and I/O handlers */
+
+static VSTREAM *vstream_subopen(void)
+{
+    VSTREAM *stream;
+
+    /* Note: memset() is not a portable way to initialize non-integer types. */
+    stream = (VSTREAM *) mymalloc(sizeof(*stream));
+    stream->offset = 0;
+    stream->path = 0;
+    stream->pid = 0;
+    stream->waitpid_fn = 0;
+    stream->timeout = 0;
+    stream->context = 0;
+    stream->jbuf = 0;
+    stream->iotime.tv_sec = stream->iotime.tv_usec = 0;
+    stream->time_limit.tv_sec = stream->time_limit.tv_usec = 0;
+    stream->req_bufsize = 0;
+    stream->vstring = 0;
+    return (stream);
+}
+
+/* vstream_fdopen - add buffering to pre-opened stream */
+
+VSTREAM *vstream_fdopen(int fd, int flags)
+{
+    VSTREAM *stream;
+
+    /*
+     * Sanity check.
+     */
+    if (fd < 0)
+	msg_panic("vstream_fdopen: bad file %d", fd);
+
+    /*
+     * Initialize buffers etc. but do as little as possible. Late buffer
+     * allocation etc. gives the application a chance to override default
+     * policies. Either this, or the vstream*open() routines would have to
+     * have a really ugly interface with lots of mostly-unused arguments (can
+     * you say VMS?).
+     */
+    stream = vstream_subopen();
+    stream->fd = fd;
+    stream->read_fn = VSTREAM_CAN_READ(flags) ? (VSTREAM_RW_FN) timed_read : 0;
+    stream->write_fn = VSTREAM_CAN_WRITE(flags) ? (VSTREAM_RW_FN) timed_write : 0;
+    vstream_buf_init(&stream->buf, flags);
+    return (stream);
+}
+
+/* vstream_fopen - open buffered file stream */
+
+VSTREAM *vstream_fopen(const char *path, int flags, mode_t mode)
+{
+    VSTREAM *stream;
+    int     fd;
+
+    if ((fd = open(path, flags, mode)) < 0) {
+	return (0);
+    } else {
+	stream = vstream_fdopen(fd, flags);
+	stream->path = mystrdup(path);
+	return (stream);
+    }
+}
+
+/* vstream_fflush - flush write buffer */
+
+int     vstream_fflush(VSTREAM *stream)
+{
+
+    /*
+     * With VSTRING, the write pointer must be positioned behind the end of
+     * data. Without knowing the actual data length, VSTREAM can't support
+     * vstream_fseek() for memory streams, because vstream_fflush() would
+     * leave the VSTRING in a broken state.
+     */
+    if (stream->buf.flags & VSTREAM_FLAG_MEMORY) {
+	if (stream->buf.flags & VSTREAM_FLAG_WRITE) {
+	    VSTRING *string = stream->vstring;
+
+#ifdef PENDING_VSTREAM_FSEEK_FOR_MEMORY
+	    VSTREAM_BUF_AT_OFFSET(&stream->buf, stream->buf.data_len);
+#endif
+	    memcpy(&string->vbuf, &stream->buf, sizeof(stream->buf));
+	    VSTRING_TERMINATE(string);
+	}
+	return (0);
+    }
+    if ((stream->buf.flags & VSTREAM_FLAG_READ_DOUBLE)
+	== VSTREAM_FLAG_READ_DOUBLE
+	&& stream->write_buf.len > stream->write_buf.cnt)
+	vstream_fflush_delayed(stream);
+    return (VSTREAM_FFLUSH_SOME(stream));
+}
+
+/* vstream_fclose - close buffered stream */
+
+int     vstream_fclose(VSTREAM *stream)
+{
+    int     err;
+
+    /*
+     * NOTE: Negative file descriptors are not part of the external
+     * interface. They are for internal use only, in order to support
+     * vstream_fdclose() without a lot of code duplication. Applications that
+     * rely on negative VSTREAM file descriptors will break without warning.
+     */
+    if (stream->pid != 0)
+	msg_panic("vstream_fclose: stream has process");
+    if ((stream->buf.flags & VSTREAM_FLAG_MEMORY)
+	|| ((stream->buf.flags & VSTREAM_FLAG_WRITE_DOUBLE) != 0
+	    && stream->fd >= 0))
+	vstream_fflush(stream);
+    /* Do not remove: vstream_fdclose() depends on this error test. */
+    err = vstream_ferror(stream);
+    if (stream->buf.flags & VSTREAM_FLAG_DOUBLE) {
+	if (stream->read_fd >= 0)
+	    err |= close(stream->read_fd);
+	if (stream->write_fd != stream->read_fd)
+	    if (stream->write_fd >= 0)
+		err |= close(stream->write_fd);
+	vstream_buf_wipe(&stream->read_buf);
+	vstream_buf_wipe(&stream->write_buf);
+	stream->buf = stream->read_buf;
+    } else {
+	if (stream->fd >= 0)
+	    err |= close(stream->fd);
+	if ((stream->buf.flags & VSTREAM_FLAG_MEMORY) == 0)
+	    vstream_buf_wipe(&stream->buf);
+    }
+    if (stream->path)
+	myfree(stream->path);
+    if (stream->jbuf)
+	myfree((void *) stream->jbuf);
+    if (!VSTREAM_STATIC(stream))
+	myfree((void *) stream);
+    return (err ? VSTREAM_EOF : 0);
+}
+
+/* vstream_fdclose - close stream, leave file(s) open */
+
+int     vstream_fdclose(VSTREAM *stream)
+{
+
+    /*
+     * Flush unwritten output, just like vstream_fclose(). Errors are
+     * reported by vstream_fclose().
+     */
+    if ((stream->buf.flags & VSTREAM_FLAG_WRITE_DOUBLE) != 0)
+	(void) vstream_fflush(stream);
+
+    /*
+     * NOTE: Negative file descriptors are not part of the external
+     * interface. They are for internal use only, in order to support
+     * vstream_fdclose() without a lot of code duplication. Applications that
+     * rely on negative VSTREAM file descriptors will break without warning.
+     */
+    if (stream->buf.flags & VSTREAM_FLAG_DOUBLE) {
+	stream->fd = stream->read_fd = stream->write_fd = -1;
+    } else {
+	stream->fd = -1;
+    }
+    return (vstream_fclose(stream));
+}
+
+/* vstream_printf - formatted print to stdout */
+
+VSTREAM *vstream_printf(const char *fmt,...)
+{
+    VSTREAM *stream = VSTREAM_OUT;
+    va_list ap;
+
+    va_start(ap, fmt);
+    vbuf_print(&stream->buf, fmt, ap);
+    va_end(ap);
+    return (stream);
+}
+
+/* vstream_fprintf - formatted print to buffered stream */
+
+VSTREAM *vstream_fprintf(VSTREAM *stream, const char *fmt,...)
+{
+    va_list ap;
+
+    va_start(ap, fmt);
+    vbuf_print(&stream->buf, fmt, ap);
+    va_end(ap);
+    return (stream);
+}
+
+/* vstream_fputs - write string to stream */
+
+int     vstream_fputs(const char *str, VSTREAM *stream)
+{
+    int     ch;
+
+    while ((ch = *str++) != 0)
+	if (VSTREAM_PUTC(ch, stream) == VSTREAM_EOF)
+	    return (VSTREAM_EOF);
+    return (0);
+}
+
+/* vstream_fread_buf - unformatted read to VSTRING */
+
+ssize_t vstream_fread_buf(VSTREAM *fp, VSTRING *vp, ssize_t len)
+{
+    ssize_t ret;
+
+    VSTRING_RESET(vp);
+    VSTRING_SPACE(vp, len);
+    ret = vstream_fread(fp, vstring_str(vp), len);
+    if (ret > 0)
+	VSTRING_AT_OFFSET(vp, ret);
+    return (ret);
+}
+
+/* vstream_fread_app - unformatted read to VSTRING */
+
+ssize_t vstream_fread_app(VSTREAM *fp, VSTRING *vp, ssize_t len)
+{
+    ssize_t ret;
+
+    VSTRING_SPACE(vp, len);
+    ret = vstream_fread(fp, vstring_end(vp), len);
+    if (ret > 0)
+	VSTRING_AT_OFFSET(vp, VSTRING_LEN(vp) + ret);
+    return (ret);
+}
+
+/* vstream_control - fine control */
+
+void    vstream_control(VSTREAM *stream, int name,...)
+{
+    const char *myname = "vstream_control";
+    va_list ap;
+    int     floor;
+    int     old_fd;
+    ssize_t req_bufsize = 0;
+    VSTREAM *stream2;
+
+#define SWAP(type,a,b) do { type temp = (a); (a) = (b); (b) = (temp); } while (0)
+
+    /*
+     * A crude 'allow' filter for memory streams.
+     */
+    int     memory_ops =
+    ((1 << VSTREAM_CTL_END) | (1 << VSTREAM_CTL_CONTEXT)
+     | (1 << VSTREAM_CTL_PATH) | (1 << VSTREAM_CTL_EXCEPT));
+
+    for (va_start(ap, name); name != VSTREAM_CTL_END; name = va_arg(ap, int)) {
+	if ((stream->buf.flags & VSTREAM_FLAG_MEMORY)
+	    && (memory_ops & (1 << name)) == 0)
+	    msg_panic("%s: memory stream does not support VSTREAM_CTL_%d",
+		      VSTREAM_PATH(stream), name);
+	switch (name) {
+	case VSTREAM_CTL_READ_FN:
+	    stream->read_fn = va_arg(ap, VSTREAM_RW_FN);
+	    break;
+	case VSTREAM_CTL_WRITE_FN:
+	    stream->write_fn = va_arg(ap, VSTREAM_RW_FN);
+	    break;
+	case VSTREAM_CTL_CONTEXT:
+	    stream->context = va_arg(ap, void *);
+	    break;
+	case VSTREAM_CTL_PATH:
+	    if (stream->path)
+		myfree(stream->path);
+	    stream->path = mystrdup(va_arg(ap, char *));
+	    break;
+	case VSTREAM_CTL_DOUBLE:
+	    if ((stream->buf.flags & VSTREAM_FLAG_DOUBLE) == 0) {
+		stream->buf.flags |= VSTREAM_FLAG_DOUBLE;
+		if (stream->buf.flags & VSTREAM_FLAG_READ) {
+		    VSTREAM_SAVE_STATE(stream, read_buf, read_fd);
+		    VSTREAM_FORK_STATE(stream, write_buf, write_fd);
+		} else {
+		    VSTREAM_SAVE_STATE(stream, write_buf, write_fd);
+		    VSTREAM_FORK_STATE(stream, read_buf, read_fd);
+		}
+	    }
+	    break;
+	case VSTREAM_CTL_READ_FD:
+	    if ((stream->buf.flags & VSTREAM_FLAG_DOUBLE) == 0)
+		msg_panic("VSTREAM_CTL_READ_FD requires double buffering");
+	    stream->read_fd = va_arg(ap, int);
+	    stream->buf.flags |= VSTREAM_FLAG_NSEEK;
+	    break;
+	case VSTREAM_CTL_WRITE_FD:
+	    if ((stream->buf.flags & VSTREAM_FLAG_DOUBLE) == 0)
+		msg_panic("VSTREAM_CTL_WRITE_FD requires double buffering");
+	    stream->write_fd = va_arg(ap, int);
+	    stream->buf.flags |= VSTREAM_FLAG_NSEEK;
+	    break;
+	case VSTREAM_CTL_SWAP_FD:
+	    stream2 = va_arg(ap, VSTREAM *);
+	    if ((stream->buf.flags & VSTREAM_FLAG_DOUBLE)
+		!= (stream2->buf.flags & VSTREAM_FLAG_DOUBLE))
+		msg_panic("VSTREAM_CTL_SWAP_FD can't swap descriptors between "
+			  "single-buffered and double-buffered streams");
+	    if (stream->buf.flags & VSTREAM_FLAG_DOUBLE) {
+		SWAP(int, stream->read_fd, stream2->read_fd);
+		SWAP(int, stream->write_fd, stream2->write_fd);
+		stream->fd = ((stream->buf.flags & VSTREAM_FLAG_WRITE) ?
+			      stream->write_fd : stream->read_fd);
+	    } else {
+		SWAP(int, stream->fd, stream2->fd);
+	    }
+	    break;
+	case VSTREAM_CTL_TIMEOUT:
+	    if (stream->timeout == 0)
+		GETTIMEOFDAY(&stream->iotime);
+	    stream->timeout = va_arg(ap, int);
+	    if (stream->timeout < 0)
+		msg_panic("%s: bad timeout %d", myname, stream->timeout);
+	    break;
+	case VSTREAM_CTL_EXCEPT:
+	    if (stream->jbuf == 0)
+		stream->jbuf =
+		    (VSTREAM_JMP_BUF *) mymalloc(sizeof(VSTREAM_JMP_BUF));
+	    break;
+
+#ifdef VSTREAM_CTL_DUPFD
+
+#define VSTREAM_TRY_DUPFD(backup, fd, floor) do { \
+	if (((backup) = (fd)) < floor) { \
+	    if (((fd) = fcntl((backup), F_DUPFD, (floor))) < 0) \
+		msg_fatal("fcntl F_DUPFD %d: %m", (floor)); \
+	    (void) close(backup); \
+	} \
+    } while (0)
+
+	case VSTREAM_CTL_DUPFD:
+	    floor = va_arg(ap, int);
+	    if (stream->buf.flags & VSTREAM_FLAG_DOUBLE) {
+		VSTREAM_TRY_DUPFD(old_fd, stream->read_fd, floor);
+		if (stream->write_fd == old_fd)
+		    stream->write_fd = stream->read_fd;
+		else
+		    VSTREAM_TRY_DUPFD(old_fd, stream->write_fd, floor);
+		stream->fd = (stream->buf.flags & VSTREAM_FLAG_READ) ?
+		    stream->read_fd : stream->write_fd;
+	    } else {
+		VSTREAM_TRY_DUPFD(old_fd, stream->fd, floor);
+	    }
+	    break;
+#endif
+
+	    /*
+	     * Postpone memory (re)allocation until the space is needed.
+	     */
+	case VSTREAM_CTL_BUFSIZE:
+	    req_bufsize = va_arg(ap, ssize_t);
+	    /* Heuristic to detect missing (ssize_t) type cast on LP64 hosts. */
+	    if (req_bufsize < 0 || req_bufsize > INT_MAX)
+		msg_panic("unreasonable VSTREAM_CTL_BUFSIZE request: %ld",
+			  (long) req_bufsize);
+	    if ((stream->buf.flags & VSTREAM_FLAG_FIXED) == 0
+		&& req_bufsize > stream->req_bufsize) {
+		if (msg_verbose)
+		    msg_info("fd=%d: stream buffer size old=%ld new=%ld",
+			     vstream_fileno(stream),
+			     (long) stream->req_bufsize,
+			     (long) req_bufsize);
+		stream->req_bufsize = req_bufsize;
+	    }
+	    break;
+
+	    /*
+	     * Make no gettimeofday() etc. system call until we really know
+	     * that we need to do I/O. This avoids a performance hit when
+	     * sending or receiving body content one line at a time.
+	     */
+	case VSTREAM_CTL_STOP_DEADLINE:
+	    stream->buf.flags &= ~VSTREAM_FLAG_DEADLINE;
+	    break;
+	case VSTREAM_CTL_START_DEADLINE:
+	    if (stream->timeout <= 0)
+		msg_panic("%s: bad timeout %d", myname, stream->timeout);
+	    stream->buf.flags |= VSTREAM_FLAG_DEADLINE;
+	    stream->time_limit.tv_sec = stream->timeout;
+	    stream->time_limit.tv_usec = 0;
+	    break;
+	default:
+	    msg_panic("%s: bad name %d", myname, name);
+	}
+    }
+    va_end(ap);
+}
+
+/* vstream_vprintf - formatted print to stdout */
+
+VSTREAM *vstream_vprintf(const char *format, va_list ap)
+{
+    VSTREAM *vp = VSTREAM_OUT;
+
+    vbuf_print(&vp->buf, format, ap);
+    return (vp);
+}
+
+/* vstream_vfprintf - formatted print engine */
+
+VSTREAM *vstream_vfprintf(VSTREAM *vp, const char *format, va_list ap)
+{
+    vbuf_print(&vp->buf, format, ap);
+    return (vp);
+}
+
+/* vstream_bufstat - get stream buffer status */
+
+ssize_t vstream_bufstat(VSTREAM *vp, int command)
+{
+    VBUF   *bp;
+
+    switch (command & VSTREAM_BST_MASK_DIR) {
+    case VSTREAM_BST_FLAG_IN:
+	if (vp->buf.flags & VSTREAM_FLAG_READ) {
+	    bp = &vp->buf;
+	} else if (vp->buf.flags & VSTREAM_FLAG_DOUBLE) {
+	    bp = &vp->read_buf;
+	} else {
+	    bp = 0;
+	}
+	switch (command & ~VSTREAM_BST_MASK_DIR) {
+	case VSTREAM_BST_FLAG_PEND:
+	    return (bp ? -bp->cnt : 0);
+	    /* Add other requests below. */
+	}
+	break;
+    case VSTREAM_BST_FLAG_OUT:
+	if (vp->buf.flags & VSTREAM_FLAG_WRITE) {
+	    bp = &vp->buf;
+	} else if (vp->buf.flags & VSTREAM_FLAG_DOUBLE) {
+	    bp = &vp->write_buf;
+	} else {
+	    bp = 0;
+	}
+	switch (command & ~VSTREAM_BST_MASK_DIR) {
+	case VSTREAM_BST_FLAG_PEND:
+	    return (bp ? bp->len - bp->cnt : 0);
+	    /* Add other requests below. */
+	}
+	break;
+    }
+    msg_panic("vstream_bufstat: unknown command: %d", command);
+}
+
+#undef vstream_peek			/* API binary compatibility. */
+
+/* vstream_peek - peek at a stream */
+
+ssize_t vstream_peek(VSTREAM *vp)
+{
+    if (vp->buf.flags & VSTREAM_FLAG_READ) {
+	return (-vp->buf.cnt);
+    } else if (vp->buf.flags & VSTREAM_FLAG_DOUBLE) {
+	return (-vp->read_buf.cnt);
+    } else {
+	return (0);
+    }
+}
+
+/* vstream_peek_data - peek at unread data */
+
+const char *vstream_peek_data(VSTREAM *vp)
+{
+    if (vp->buf.flags & VSTREAM_FLAG_READ) {
+	return ((const char *) vp->buf.ptr);
+    } else if (vp->buf.flags & VSTREAM_FLAG_DOUBLE) {
+	return ((const char *) vp->read_buf.ptr);
+    } else {
+	return (0);
+    }
+}
+
+/* vstream_memopen - open a VSTRING */
+
+VSTREAM *vstream_memreopen(VSTREAM *stream, VSTRING *string, int flags)
+{
+    if (stream == 0)
+	stream = vstream_subopen();
+    else if ((stream->buf.flags & VSTREAM_FLAG_MEMORY) == 0)
+	msg_panic("vstream_memreopen: cannot reopen non-memory stream");
+    stream->fd = -1;
+    stream->read_fn = 0;
+    stream->write_fn = 0;
+    stream->vstring = string;
+    memcpy(&stream->buf, &stream->vstring->vbuf, sizeof(stream->buf));
+    stream->buf.flags |= VSTREAM_FLAG_MEMORY;
+    switch (VSTREAM_ACC_MASK(flags)) {
+    case O_RDONLY:
+	stream->buf.flags |= VSTREAM_FLAG_READ;
+	stream->buf.len = stream->buf.ptr - stream->buf.data;
+	VSTREAM_BUF_AT_OFFSET(&stream->buf, 0);
+	break;
+    case O_WRONLY:
+	stream->buf.flags |= VSTREAM_FLAG_WRITE;
+	VSTREAM_BUF_AT_OFFSET(&stream->buf, 0);
+	break;
+    case O_APPEND:
+	stream->buf.flags |= VSTREAM_FLAG_WRITE;
+	VSTREAM_BUF_AT_END(&stream->buf);
+	break;
+    default:
+	msg_panic("vstream_memopen: flags must be one of "
+		  "O_RDONLY, O_WRONLY, or O_APPEND");
+    }
+    return (stream);
+}
+
+#ifdef TEST
+
+static void copy_line(ssize_t bufsize)
+{
+    int     c;
+
+    vstream_control(VSTREAM_IN, CA_VSTREAM_CTL_BUFSIZE(bufsize), VSTREAM_CTL_END);
+    vstream_control(VSTREAM_OUT, CA_VSTREAM_CTL_BUFSIZE(bufsize), VSTREAM_CTL_END);
+    while ((c = VSTREAM_GETC(VSTREAM_IN)) != VSTREAM_EOF) {
+	VSTREAM_PUTC(c, VSTREAM_OUT);
+	if (c == '\n')
+	    break;
+    }
+    vstream_fflush(VSTREAM_OUT);
+}
+
+static void printf_number(void)
+{
+    vstream_printf("%d\n", 1234567890);
+    vstream_fflush(VSTREAM_OUT);
+}
+
+static void do_memory_stream(void)
+{
+    VSTRING *buf = vstring_alloc(1);
+    VSTREAM *fp = vstream_memopen(buf, O_WRONLY);
+
+#ifdef PENDING_VSTREAM_FSEEK_FOR_MEMORY
+    off_t   offset;
+
+#endif
+    int     ch;
+
+    vstream_fprintf(fp, "hallo world\n");
+    if (vstream_fflush(fp))
+	msg_fatal("vstream_fflush: %m");
+    vstream_printf("final memory stream write offset: %ld\n",
+		   (long) vstream_ftell(fp));
+#ifdef PENDING_VSTREAM_FSEEK_FOR_MEMORY
+    vstream_fflush(fp);
+    vstream_printf("buffer size: %ld, content: %s",
+		   (long) VSTRING_LEN(buf), vstring_str(buf));
+    if ((offset = vstream_fseek(fp, 1, SEEK_SET)) != 1)
+	msg_panic("unexpected vstream_fseek return: %ld, expected: %ld",
+		  (long) offset, (long) 1);
+    VSTREAM_PUTC('e', fp);
+#endif
+    vstream_fclose(fp);
+
+    vstream_printf("buffer size: %ld, content: %s",
+		   (long) VSTRING_LEN(buf), vstring_str(buf));
+    vstream_fflush(VSTREAM_OUT);
+
+    fp = vstream_memopen(buf, O_RDONLY);
+    vstream_printf("reading memory stream: ");
+    while ((ch = VSTREAM_GETC(fp)) != VSTREAM_EOF)
+	VSTREAM_PUTCHAR(ch);
+#ifdef PENDING_VSTREAM_FSEEK_FOR_MEMORY
+    vstream_printf("reading memory stream from offset 6: ");
+    if ((offset = vstream_fseek(fp, 6, SEEK_SET)) != 6)
+	msg_panic("unexpected vstream_fseek return: %ld, expected: %ld",
+		  (long) offset, (long) 6);
+    while ((ch = VSTREAM_GETC(fp)) != VSTREAM_EOF)
+	VSTREAM_PUTCHAR(ch);
+#endif
+    vstream_printf("final memory stream read offset: %ld\n",
+		   (long) vstream_ftell(fp));
+    vstream_fflush(VSTREAM_OUT);
+    vstream_fclose(fp);
+    vstring_free(buf);
+}
+
+ /*
+  * Exercise some of the features.
+  */
+int     main(int argc, char **argv)
+{
+
+    /*
+     * Test buffer expansion and shrinking. Formatted print may silently
+     * expand the write buffer and cause multiple bytes to be written.
+     */
+    copy_line(1);			/* one-byte read/write */
+    copy_line(2);				/* two-byte read/write */
+    copy_line(1);				/* two-byte read/write */
+    printf_number();				/* multi-byte write */
+    do_memory_stream();
+
+    exit(0);
+}
+
+#endif