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+.\" Copyright (c) 2014 Xin LI <delphij@FreeBSD.org>
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.Dd December 6, 2018
+.Dt ZOPEN 3
+.Os
+.Sh NAME
+.Nm zopen
+.Nd open a gzip compressed stream
+.Sh LIBRARY
+.Lb libz
+.Sh SYNOPSIS
+.Ft FILE *
+.Fn zopen "const char *path" "const char *mode"
+.Ft FILE *
+.Fn zdopen "int fd" "const char *mode"
+.Sh DESCRIPTION
+The
+.Fn zopen
+function opens a gzip file whose name is the string pointed to by
+.Fa path
+and returns a stream which can be used to access the uncompressed contents
+of the file.
+The
+.Fn zdopen
+variant takes a gzip file referenced by the file descriptor
+.Fa fd ,
+analogous to
+.Xr fdopen 3 .
+They are wrappers around
+.Xr zlib 3
+and the standard stream I/O APIs.
+.Pp
+The argument
+.Fa mode
+has the same meaning as it does in
+.Xr fopen 3 .
+.Pp
+The
+.Fn zopen
+and
+.Fn zdopen
+functions will associate the read, write, seek and close
+functions of
+.Xr zlib 3
+with the returned stream.
+.Sh RETURN VALUES
+Upon successful completion
+.Fn zopen
+and
+.Fn zdopen
+return a
+.Tn FILE
+pointer.
+Otherwise,
+.Dv NULL
+is returned and the global variable
+.Va errno
+is set to indicate the error.
+.Sh ERRORS
+In addition to the errors documented for
+.Xr fopen 3
+and
+.Xr fdopen 3 ,
+the functions may also fail for:
+.Bl -tag -width Er
+.It Bq Er ENOMEM
+Insufficient memory is available.
+.El
+.Sh COMPATIBILITY
+The implementation of
+.Fn zopen
+function first appeared in
+.Nx 1.6
+and
+.Fx 4.5 .
+.Fn zdopen
+first appeared in
+.Fx 13.0 .
+These functions may not be portable to systems other than
+.Fx .
+.Sh SEE ALSO
+.Xr fdopen 3 ,
+.Xr fopen 3 ,
+.Xr funopen 3 ,
+.Xr zlib 3