Move from read_gz to the pipe()+fork() method.

open_transformer(), common code for pipe+fork.
Function pointer for read() no longer needed.
Allow inflate to be initialised with a specified buffer size to avoid
over-reading.
Reset static variables in inflate_get_next_window to fix a bug where
only the first file in a .zip would be be extracted.

archival/libunarchive/open_transformer.c

@@ -0,0 +1,50 @@
+/*
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU Library General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "libbb.h"
+
+/* transformer(), more than meets the eye */
+extern int open_transformer(int src_fd, int (*transformer)(int src_fd, int dst_fd))
+{
+	int fd_pipe[2];
+	int pid;
+
+	if (pipe(fd_pipe) != 0) {
+		bb_perror_msg_and_die("Can't create pipe");
+	}
+
+	pid = fork();
+	if (pid == -1) {
+		bb_perror_msg_and_die("Fork failed");
+	}
+
+	if (pid == 0) {
+		/* child process */
+	    close(fd_pipe[0]); /* We don't wan't to read from the pipe */
+	    transformer(src_fd, fd_pipe[1]);
+	    close(fd_pipe[1]); /* Send EOF */
+	    exit(0);
+	    /* notreached */
+	}
+	/* parent process */
+	close(fd_pipe[1]); /* Don't want to write down the pipe */
+	close(src_fd);
+
+	return(fd_pipe[0]);
+}