diff --git a/.gitignore b/.gitignore
index c7101f3a..40dc96a5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,3 @@
-.pytest_cache
 compile
 .pytest_cache
 a.out
diff --git a/libvips/include/vips/type.h b/libvips/include/vips/type.h
index 9e578ab3..3bb3e37f 100644
--- a/libvips/include/vips/type.h
+++ b/libvips/include/vips/type.h
@@ -161,6 +161,8 @@ VipsBlob *vips_blob_new( VipsCallbackFn free_fn,
 	const void *data, size_t length );
 VipsBlob *vips_blob_copy( const void *data, size_t length );
 const void *vips_blob_get( VipsBlob *blob, size_t *length );
+void vips_blob_set( VipsBlob *blob, 
+	VipsCallbackFn free_fn, const void *data, size_t length );
 GType vips_blob_get_type(void);
 
 /**
diff --git a/libvips/iofuncs/stream.c b/libvips/iofuncs/stream.c
index 439055a0..007ae7fd 100644
--- a/libvips/iofuncs/stream.c
+++ b/libvips/iofuncs/stream.c
@@ -611,6 +611,10 @@ vips_stream_output_finalize( GObject *gobject )
 	VIPS_DEBUG_MSG( "vips_stream_output_finalize:\n" );
 
 	VIPS_FREEF( g_byte_array_unref, output->memory ); 
+	if( output->blob ) { 
+		vips_area_unref( VIPS_AREA( output->blob ) ); 
+		output->blob = NULL;
+	}
 
 	G_OBJECT_CLASS( vips_stream_output_parent_class )->finalize( gobject );
 }
@@ -639,7 +643,10 @@ vips_stream_output_build( VipsObject *object )
 
 		int fd;
 
-		if( (fd = vips_tracked_open( filename, MODE_WRITE )) == -1 ) {
+		/* 0644 is rw user, r group and other.
+		 */
+		if( (fd = vips_tracked_open( filename, 
+			MODE_WRITE, 0644 )) == -1 ) {
 			vips_error_system( errno, STREAM_NAME( stream ), 
 				"%s", _( "unable to open for write" ) ); 
 			return( -1 ); 
@@ -696,18 +703,22 @@ vips_stream_output_class_init( VipsStreamOutputClass *class )
 
 	class->write = vips_stream_output_write_real;
 
+	/* SET_ALWAYS means that blob is set by C and the obj system is not
+	 * involved in creation or destruction. It can be read at any time.
+	 */
 	VIPS_ARG_BOXED( class, "blob", 1, 
 		_( "Blob" ),
 		_( "Blob to save to" ),
-		VIPS_ARGUMENT_OPTIONAL_OUTPUT, 
+		VIPS_ARGUMENT_SET_ALWAYS, 
 		G_STRUCT_OFFSET( VipsStreamOutput, blob ),
 		VIPS_TYPE_BLOB );
 
 }
 
 static void
-vips_stream_output_init( VipsStreamOutput *stream )
+vips_stream_output_init( VipsStreamOutput *output )
 {
+	output->blob = vips_blob_new( NULL, NULL, 0 );
 }
 
 /**
@@ -849,11 +860,8 @@ vips_stream_output_finish( VipsStreamOutput *output )
 		length = output->memory->len;
 		data = g_byte_array_free( output->memory, FALSE );
 		output->memory = NULL;
-
-		g_object_set( output, 
-			"blob", vips_blob_new( (VipsCallbackFn) g_free, 
-				data, length ),
-			NULL );
+		vips_blob_set( output->blob,
+			(VipsCallbackFn) g_free, data, length );
 	}
 
 	vips_stream_close( VIPS_STREAM( output ) );
diff --git a/libvips/iofuncs/type.c b/libvips/iofuncs/type.c
index d59f4b56..30b0bc5f 100644
--- a/libvips/iofuncs/type.c
+++ b/libvips/iofuncs/type.c
@@ -171,6 +171,18 @@ vips_area_copy( VipsArea *area )
 	return( area );
 }
 
+void
+vips_area_free( VipsArea *area )
+{
+	if( area->free_fn && 
+		area->data ) {
+		area->free_fn( area->data, area );
+		area->free_fn = NULL;
+	}
+
+	area->data = NULL;
+}
+
 void
 vips_area_unref( VipsArea *area )
 {
@@ -191,11 +203,7 @@ vips_area_unref( VipsArea *area )
 	}
 
 	if( area->count == 0 ) {
-		if( area->free_fn && area->data ) {
-			area->free_fn( area->data, area );
-			area->data = NULL;
-			area->free_fn = NULL;
-		}
+		vips_area_free( area );
 
 		g_mutex_unlock( area->lock );
 
@@ -671,6 +679,36 @@ vips_blob_get( VipsBlob *blob, size_t *length )
 		length, NULL, NULL, NULL ) ); 
 }
 
+/* vips_blob_set:
+ * @blob: #VipsBlob to set
+ * @free_fn: (scope async) (allow-none): @data will be freed with this function
+ * @data: (array length=length) (element-type guint8) (transfer full): data to store
+ * @length: number of bytes in @data
+ *
+ * Any old data is freed and new data attached.
+ *
+ * It's sometimes useful to be able to create blobs as empty and then fill
+ * them later.
+ *
+ * See also: vips_blob_new().
+ */
+void
+vips_blob_set( VipsBlob *blob, 
+	VipsCallbackFn free_fn, const void *data, size_t length )
+{
+	VipsArea *area = VIPS_AREA( blob );
+
+	g_mutex_lock( area->lock );
+
+	vips_area_free( area );
+
+	area->free_fn = free_fn;
+	area->length = length;
+	area->data = (void *) data;
+
+	g_mutex_unlock( area->lock );
+}
+
 /* Transform a blob to a G_TYPE_STRING.
  */
 static void
diff --git a/libvips/iofuncs/vips.c b/libvips/iofuncs/vips.c
index 5b43f101..f956bea5 100644
--- a/libvips/iofuncs/vips.c
+++ b/libvips/iofuncs/vips.c
@@ -208,7 +208,7 @@ vips__open_image_write( const char *filename, gboolean temp )
 
 		g_info( "vips__open_image_write: opening with O_TMPFILE" );
 		dirname = g_path_get_dirname( filename ); 
-		fd = vips_tracked_open( dirname, O_TMPFILE | O_RDWR , 0666 );
+		fd = vips_tracked_open( dirname, O_TMPFILE | O_RDWR , 0644 );
 		g_free( dirname ); 
 
 		if( fd < 0 ) 
@@ -230,7 +230,7 @@ vips__open_image_write( const char *filename, gboolean temp )
 
 	if( fd < 0 ) {
 		g_info( "vips__open_image_write: simple open" );
-		fd = vips_tracked_open( filename, flags, 0666 );
+		fd = vips_tracked_open( filename, flags, 0644 );
 	}
 
 	if( fd < 0 ) {
diff --git a/test/.gitignore b/test/.gitignore
new file mode 100644
index 00000000..3b5549c9
--- /dev/null
+++ b/test/.gitignore
@@ -0,0 +1 @@
+test_descriptors
diff --git a/test/test_descriptors b/test/test_descriptors
deleted file mode 100755
index 0e0b2c0c..00000000
--- a/test/test_descriptors
+++ /dev/null
@@ -1,210 +0,0 @@
-#! /bin/bash
-
-# test_descriptors - temporary wrapper script for .libs/test_descriptors
-# Generated by libtool (GNU libtool) 2.4.6 Debian-2.4.6-10
-#
-# The test_descriptors program cannot be directly executed until all the libtool
-# libraries that it depends on are installed.
-#
-# This wrapper script should never be moved out of the build directory.
-# If it is, it will not operate correctly.
-
-# Sed substitution that helps us do robust quoting.  It backslashifies
-# metacharacters that are still active within double-quoted strings.
-sed_quote_subst='s|\([`"$\\]\)|\\\1|g'
-
-# Be Bourne compatible
-if test -n "${ZSH_VERSION+set}" && (emulate sh) >/dev/null 2>&1; then
-  emulate sh
-  NULLCMD=:
-  # Zsh 3.x and 4.x performs word splitting on ${1+"$@"}, which
-  # is contrary to our usage.  Disable this feature.
-  alias -g '${1+"$@"}'='"$@"'
-  setopt NO_GLOB_SUBST
-else
-  case `(set -o) 2>/dev/null` in *posix*) set -o posix;; esac
-fi
-BIN_SH=xpg4; export BIN_SH # for Tru64
-DUALCASE=1; export DUALCASE # for MKS sh
-
-# The HP-UX ksh and POSIX shell print the target directory to stdout
-# if CDPATH is set.
-(unset CDPATH) >/dev/null 2>&1 && unset CDPATH
-
-relink_command=""
-
-# This environment variable determines our operation mode.
-if test "$libtool_install_magic" = "%%%MAGIC variable%%%"; then
-  # install mode needs the following variables:
-  generated_by_libtool_version='2.4.6'
-  notinst_deplibs=' ../libvips/libvips.la'
-else
-  # When we are sourced in execute mode, $file and $ECHO are already set.
-  if test "$libtool_execute_magic" != "%%%MAGIC variable%%%"; then
-    file="$0"
-
-# A function that is used when there is no print builtin or printf.
-func_fallback_echo ()
-{
-  eval 'cat <<_LTECHO_EOF
-$1
-_LTECHO_EOF'
-}
-    ECHO="printf %s\\n"
-  fi
-
-# Very basic option parsing. These options are (a) specific to
-# the libtool wrapper, (b) are identical between the wrapper
-# /script/ and the wrapper /executable/ that is used only on
-# windows platforms, and (c) all begin with the string --lt-
-# (application programs are unlikely to have options that match
-# this pattern).
-#
-# There are only two supported options: --lt-debug and
-# --lt-dump-script. There is, deliberately, no --lt-help.
-#
-# The first argument to this parsing function should be the
-# script's ../libtool value, followed by no.
-lt_option_debug=
-func_parse_lt_options ()
-{
-  lt_script_arg0=$0
-  shift
-  for lt_opt
-  do
-    case "$lt_opt" in
-    --lt-debug) lt_option_debug=1 ;;
-    --lt-dump-script)
-        lt_dump_D=`$ECHO "X$lt_script_arg0" | /bin/sed -e 's/^X//' -e 's%/[^/]*$%%'`
-        test "X$lt_dump_D" = "X$lt_script_arg0" && lt_dump_D=.
-        lt_dump_F=`$ECHO "X$lt_script_arg0" | /bin/sed -e 's/^X//' -e 's%^.*/%%'`
-        cat "$lt_dump_D/$lt_dump_F"
-        exit 0
-      ;;
-    --lt-*)
-        $ECHO "Unrecognized --lt- option: '$lt_opt'" 1>&2
-        exit 1
-      ;;
-    esac
-  done
-
-  # Print the debug banner immediately:
-  if test -n "$lt_option_debug"; then
-    echo "test_descriptors:test_descriptors:$LINENO: libtool wrapper (GNU libtool) 2.4.6 Debian-2.4.6-10" 1>&2
-  fi
-}
-
-# Used when --lt-debug. Prints its arguments to stdout
-# (redirection is the responsibility of the caller)
-func_lt_dump_args ()
-{
-  lt_dump_args_N=1;
-  for lt_arg
-  do
-    $ECHO "test_descriptors:test_descriptors:$LINENO: newargv[$lt_dump_args_N]: $lt_arg"
-    lt_dump_args_N=`expr $lt_dump_args_N + 1`
-  done
-}
-
-# Core function for launching the target application
-func_exec_program_core ()
-{
-
-      if test -n "$lt_option_debug"; then
-        $ECHO "test_descriptors:test_descriptors:$LINENO: newargv[0]: $progdir/$program" 1>&2
-        func_lt_dump_args ${1+"$@"} 1>&2
-      fi
-      exec "$progdir/$program" ${1+"$@"}
-
-      $ECHO "$0: cannot exec $program $*" 1>&2
-      exit 1
-}
-
-# A function to encapsulate launching the target application
-# Strips options in the --lt-* namespace from $@ and
-# launches target application with the remaining arguments.
-func_exec_program ()
-{
-  case " $* " in
-  *\ --lt-*)
-    for lt_wr_arg
-    do
-      case $lt_wr_arg in
-      --lt-*) ;;
-      *) set x "$@" "$lt_wr_arg"; shift;;
-      esac
-      shift
-    done ;;
-  esac
-  func_exec_program_core ${1+"$@"}
-}
-
-  # Parse options
-  func_parse_lt_options "$0" ${1+"$@"}
-
-  # Find the directory that this script lives in.
-  thisdir=`$ECHO "$file" | /bin/sed 's%/[^/]*$%%'`
-  test "x$thisdir" = "x$file" && thisdir=.
-
-  # Follow symbolic links until we get to the real thisdir.
-  file=`ls -ld "$file" | /bin/sed -n 's/.*-> //p'`
-  while test -n "$file"; do
-    destdir=`$ECHO "$file" | /bin/sed 's%/[^/]*$%%'`
-
-    # If there was a directory component, then change thisdir.
-    if test "x$destdir" != "x$file"; then
-      case "$destdir" in
-      [\\/]* | [A-Za-z]:[\\/]*) thisdir="$destdir" ;;
-      *) thisdir="$thisdir/$destdir" ;;
-      esac
-    fi
-
-    file=`$ECHO "$file" | /bin/sed 's%^.*/%%'`
-    file=`ls -ld "$thisdir/$file" | /bin/sed -n 's/.*-> //p'`
-  done
-
-  # Usually 'no', except on cygwin/mingw when embedded into
-  # the cwrapper.
-  WRAPPER_SCRIPT_BELONGS_IN_OBJDIR=no
-  if test "$WRAPPER_SCRIPT_BELONGS_IN_OBJDIR" = "yes"; then
-    # special case for '.'
-    if test "$thisdir" = "."; then
-      thisdir=`pwd`
-    fi
-    # remove .libs from thisdir
-    case "$thisdir" in
-    *[\\/].libs ) thisdir=`$ECHO "$thisdir" | /bin/sed 's%[\\/][^\\/]*$%%'` ;;
-    .libs )   thisdir=. ;;
-    esac
-  fi
-
-  # Try to get the absolute directory name.
-  absdir=`cd "$thisdir" && pwd`
-  test -n "$absdir" && thisdir="$absdir"
-
-  program='test_descriptors'
-  progdir="$thisdir/.libs"
-
-
-  if test -f "$progdir/$program"; then
-    # Add our own library path to LD_LIBRARY_PATH
-    LD_LIBRARY_PATH="/home/john/GIT/libvips/libvips/.libs:/home/john/vips/lib:$LD_LIBRARY_PATH"
-
-    # Some systems cannot cope with colon-terminated LD_LIBRARY_PATH
-    # The second colon is a workaround for a bug in BeOS R4 sed
-    LD_LIBRARY_PATH=`$ECHO "$LD_LIBRARY_PATH" | /bin/sed 's/::*$//'`
-
-    export LD_LIBRARY_PATH
-
-    if test "$libtool_execute_magic" != "%%%MAGIC variable%%%"; then
-      # Run the actual program with our arguments.
-      func_exec_program ${1+"$@"}
-    fi
-  else
-    # The program doesn't exist.
-    $ECHO "$0: error: '$progdir/$program' does not exist" 1>&2
-    $ECHO "This script is just a wrapper for $program." 1>&2
-    $ECHO "See the libtool documentation for more information." 1>&2
-    exit 1
-  fi
-fi