fix up vipsheader with complex field types

"-f name" displays a detailed form, "-a" displays a summary of each
field

fix a problem with string fields as well

ChangeLog

@@ -3,6 +3,7 @@
 - added tiff save to buffer
 - added dzsave save to buffer (zip only)
 - revise header get/set functions
+- better vipsheader behaviour with complex field types
 - added vips_image_hasalpha()
 
 18/10/16 started 8.4.3

TODO

@@ -1,9 +1,3 @@
-- look at vips_image_get_as_string() vs. vips_buf_appendgv()
-
-  should Hist and getext be true header fields?
-
-  vipsheader is not displaying filename correctly
-
 - not sure about utf8 error messages on win
 
 - strange: 

libvips/iofuncs/buf.c

@@ -493,10 +493,12 @@ vips_buf_appendd( VipsBuf *buf, int d )
  * @buf: the buffer
  * @value: #GValue to format and append
  *
- * Format and append a #GValue. This doesn't use g_strdup_value_contents():
- * that doesn't do what we want for some types and can change too much between
- * glib versions.
- * 
+ * Format and append a #GValue as a printable thing. We display text line "3144
+ * bytes of binary data" for BLOBs like icc-profile-data.
+ *
+ * Use vips_image_get_as_string() to make a text representation of a field.
+ * That will base64-encode blobs, for example. 
+ *
  * Returns: %FALSE on overflow, %TRUE otherwise.
  */
 gboolean
@@ -513,11 +515,16 @@ vips_buf_appendgv( VipsBuf *buf, GValue *value )
 
 	switch( fundamental ) {
 	case G_TYPE_STRING:
-		/* These are GStrings, vips refstrings are handled by boxed, see 
-		 * below.
+{
+		const char *str;
+
+		/* These are GStrings (gchararray). vips refstrings are 
+		 * handled by boxed, see below.
 		 */
-		result = vips_buf_appends( buf, g_value_get_string( value ) ); 
+		str = g_value_get_string( value );
+		result = vips_buf_appends( buf, str ); 
 		handled = TRUE;
+}
 		break;
 
 	case G_TYPE_OBJECT:
@@ -583,15 +590,26 @@ vips_buf_appendgv( VipsBuf *buf, GValue *value )
 		break;
 
 	case G_TYPE_BOXED:
-		if( type == VIPS_TYPE_REF_STRING ||
-			type == VIPS_TYPE_BLOB ) {
+		if( type == VIPS_TYPE_REF_STRING ) { 
 			const char *str;
 			size_t str_len;
 
+			/* These should be printable.
+			 */
 			str = vips_value_get_ref_string( value, &str_len );
 			result = vips_buf_appends( buf, str ); 
 			handled = TRUE;
 		}
+		else if( type == VIPS_TYPE_BLOB ) {
+			size_t str_len;
+
+			/* Binary data and not printable.
+			 */
+			(void) vips_value_get_ref_string( value, &str_len );
+			result = vips_buf_appendf( buf, 
+				_( "%zd bytes of binary data" ), str_len ); 
+			handled = TRUE;
+		}
 		else if( type == VIPS_TYPE_ARRAY_DOUBLE ) {
 			double *arr;
 			int n;

libvips/iofuncs/header.c

@@ -966,7 +966,7 @@ vips_set_value_from_pointer( GValue *value, void *data )
 	else if( fundamental == G_TYPE_ENUM )
 		g_value_set_enum( value, *((int *) data) ); 
 	else if( fundamental == G_TYPE_STRING ) 
-		g_value_set_string( value, ((char *) data) ); 
+		g_value_set_string( value, *((char **) data) ); 
 	else
 		g_warning( "%s: unimplemented vips_set_value_from_pointer() "
 			"type %s",
@@ -1486,7 +1486,10 @@ vips_image_set_string( VipsImage *image, const char *field, const char *str )
  * This function will read any field, returning it as a printable string.
  * You need to free the string with g_free() when you are done with it.
  *
- * See also: vips_image_get(), vips_image_get_typeof().
+ * This will base64-encode BLOBs, for example. Use vips_buf_appendgv() to 
+ * make a string that's for humans. 
+ *
+ * See also: vips_image_get(), vips_image_get_typeof(), vips_buf_appendgv().
  *
  * Returns: 0 on success, -1 otherwise.
  */

man/vipsheader.1

@@ -5,23 +5,28 @@ vipsheader \- prints information about an image file
 vipsheader [OPTIONS ...] files ...
 .SH DESCRIPTION
 .B vipsheader(1)
-prints image header fields to stdout.
+prints image header fields to stdout. 
 
 .SH OPTIONS
+
+.TP
+.B -a, --all
+Show all fields. Fields are displayed to be convenient for humans to read, so
+binary data, for example, is summarized rather than simply copied.
+
 .TP
 .B -f FIELD, --field=FIELD
 Print value of 
 .B FIELD 
-from image header. The special field name getext prints
-the VIPS extension block: the XML defining the image metadata. You can alter
-this, then reattach with 
-.B vipsedit(1).
+from image header. Fields are printed in a way suitable for programs to
+understand, so, for example, binary data is base64-encoded and printed as a
+stream of characters. 
 
-.TP
-.B -a, --all
-Show all fields. Normally 
-.B vipsheader
-just shows a one-line summary.
+The special field name 
+.B getext
+prints the VIPS extension block: the XML defining the image metadata. You can 
+alter this, then reattach with 
+.B vipsedit(1).
 
 .SH EXAMPLES
  $ vipsheader -f Xsize ~/pics/*.v   

tools/vipsheader.c

@@ -147,14 +147,11 @@ print_header( VipsImage *im, gboolean many )
 	else if( strcmp( main_option_field, "Hist" ) == 0 ) 
 		printf( "%s", vips_image_get_history( im ) );
 	else {
-		GValue value = { 0 }; 
-		char str[256];
-		VipsBuf buf = VIPS_BUF_STATIC( str );
+		char *str;
 
-		vips_image_get( im, main_option_field, &value );
-		vips_buf_appendgv( &buf, &value );
+		vips_image_get_as_string( im, main_option_field, &str );
 		printf( "%s\n", str );
-		g_value_unset( &value );
+		g_free( str );
 	}
 
 	return( 0 );