I know this isn't a high priority item, but here's a patch that makes
tracker's thumbnail support follow the fd.o spec.  It uses the
$HOME/.thumbnails directory, so it'll work along side nautilus,
thundar, and konq.  It will not overwrite up-to-date thumbnails, but
the File.SmallThumbnailPath metadata item will be filled in correctly.

Currently, it only works for "normal" size, or 128x128, thumbnails.
This is because tracker defines "large" as 640x640 while fd.o spec
defines it as only 256x256.  Maybe we could create a new directory,
called "preview", for these extra-large thumbnails.

The patch also removes the hard-coded disabling of thumbnails, so
you'll be able to enable it via the EnableThumbnails key in
tracker.cfg.  If everything is working right, nautilus should start
showing thumbnails for your OO.o documents (currently the only
thumbnail generator we have, that nautilus doesn't).

Also, this puts a hard dependancy on libpng.  It's needed because the
file's URI and MTime need to be embeded in the thumbnail file so it
can be tested for validity.  I doubt this should be a problem though.
Index: configure.in
===================================================================
RCS file: /cvs/gnome/tracker/configure.in,v
retrieving revision 1.41
diff -u -p -r1.41 configure.in
--- configure.in	20 Nov 2006 15:12:45 -0000	1.41
+++ configure.in	26 Nov 2006 22:25:00 -0000
@@ -59,6 +59,11 @@ PKG_CHECK_MODULES(DBUS, [dbus-1 >= 0.50 
 AC_SUBST(DBUS_CFLAGS)
 AC_SUBST(DBUS_LIBS)
 
+# Check for libpng 1.2 or higher
+PKG_CHECK_MODULES(LIBPNG, [libpng >= 1.2])
+AC_SUBST(LIBPNG_CFLAGS)
+AC_SUBST(LIBPNG_LIBS)
+
 ####################################################################
 # Compiler warning checks
 ####################################################################
@@ -489,6 +494,7 @@ AC_CONFIG_FILES([
 	src/text-filters/html_converter/Makefile
 	src/text-filters/ooo_converter/Makefile
 	src/tracker-extract/Makefile
+	src/tracker-thumbnailer/Makefile
 	src/trackerd/Makefile
 	src/libtracker/Makefile
 	src/tracker-search-tool/Makefile
Index: src/Makefile.am
===================================================================
RCS file: /cvs/gnome/tracker/src/Makefile.am,v
retrieving revision 1.11
diff -u -p -r1.11 Makefile.am
--- src/Makefile.am	7 Nov 2006 00:38:35 -0000	1.11
+++ src/Makefile.am	26 Nov 2006 22:25:37 -0000
@@ -13,5 +13,5 @@ sqlite_dir = sqlite3
 endif
 
 
-SUBDIRS = libstemmer $(sqlite_dir) text-filters trackerd libtracker tracker-extract $(tracker_gui_dir)
-DIST_SUBDIRS = libstemmer $(sqlite_dir) text-filters trackerd libtracker tracker-extract $(tracker_gui_dir)
+SUBDIRS = libstemmer $(sqlite_dir) text-filters trackerd libtracker tracker-extract tracker-thumbnailer $(tracker_gui_dir)
+DIST_SUBDIRS = libstemmer $(sqlite_dir) text-filters trackerd libtracker tracker-extract tracker-thumbnailer $(tracker_gui_dir)
? src/trackerd/.tracker-db.c.swp
? src/trackerd/.trackerd.c.swp
Index: src/trackerd/tracker-metadata.c
===================================================================
RCS file: /cvs/gnome/tracker/src/trackerd/tracker-metadata.c,v
retrieving revision 1.21
diff -u -p -r1.21 tracker-metadata.c
--- src/trackerd/tracker-metadata.c	19 Nov 2006 23:50:02 -0000	1.21
+++ src/trackerd/tracker-metadata.c	26 Nov 2006 22:26:36 -0000
@@ -331,89 +331,42 @@ tracker_metadata_get_text_file (const ch
 
 
 char *
-tracker_metadata_get_thumbnail (const char *uri, const char *mime, const char *max_size)
+tracker_metadata_get_thumbnail (const char *path, const char *mime, const char *size)
 {
-	char *tmp, *thumbnailer;
+	gchar   *thumbnail;
+	gchar   *argv[5];
+	gint     exit_status;
+
+	argv[0] = g_strdup ("tracker-thumbnailer");
+	argv[1] = g_filename_from_utf8 (path, -1, NULL, NULL, NULL);
+	argv[2] = g_strdup (mime);
+	argv[3] = g_strdup (size);
+	argv[4] = NULL;
+
+	if (!g_spawn_sync (NULL,
+			  argv,
+			  NULL,
+			  G_SPAWN_SEARCH_PATH | G_SPAWN_STDERR_TO_DEV_NULL,
+			  set_child_timeout_cb,
+			  GINT_TO_POINTER (10),
+			  &thumbnail,
+			  NULL,
+			  &exit_status,
+			  NULL)) {
 
-	tmp = g_strdup (DATADIR "/tracker/thumbnailers/");
-
-	thumbnailer = g_strconcat (tmp, mime, "_thumbnailer", NULL);
-
-	g_free (tmp);
-
-	if (g_file_test (thumbnailer, G_FILE_TEST_EXISTS)) {
-		char *argv[5];
-		char *tmp_file;
-		int  fd;
-
-		tmp = g_build_filename (g_get_home_dir (), ".Tracker", "thumbs", NULL);
-
-		g_mkdir_with_parents (tmp, 0700);
-
-		tmp_file = g_build_filename (tmp, "thumb_XXXXXX", NULL);
-		g_free (tmp);
-
-
-		fd = g_mkstemp (tmp_file);
-
-		if (fd == -1) {
-			g_warning ("make thumb file %s failed", tmp_file);
-			g_free (thumbnailer);
-			g_free (tmp_file);
-			return NULL;
-		} else {
-			close (fd);
-		}
-
-		argv[0] = g_strdup (thumbnailer);
-		argv[1] = g_filename_from_utf8 (uri, -1, NULL, NULL, NULL);
-		argv[2] = g_strdup (tmp_file);
-		argv[3] = g_strdup (max_size);
-		argv[4] = NULL;
-
-		if (!argv[1]) {
-			tracker_log ("******ERROR**** uri could not be converted to locale format");
-			g_free (argv[0]);
-			g_free (argv[2]);
-			g_free (argv[3]);
-			return NULL;
-		}
-
-		g_debug ("Extracting thumbnail for %s using %s", argv[1], argv[0] );
-
-		if (g_spawn_sync (NULL,
-				  argv,
-				  NULL,
-				  G_SPAWN_STDOUT_TO_DEV_NULL | G_SPAWN_STDERR_TO_DEV_NULL,
-				  set_child_timeout_cb,
-				  GINT_TO_POINTER (10),
-				  NULL,
-				  NULL,
-				  NULL,
-				  NULL)) {
-
-			g_free (argv[0]);
-			g_free (argv[1]);
-			g_free (argv[2]);
-			g_free (argv[3]);
-
-			g_free (thumbnailer);
-
-			return tmp_file;
-
-		} else {
-			g_free (tmp_file);
-
-			g_free (argv[0]);
-			g_free (argv[1]);
-			g_free (argv[2]);
-			g_free (argv[3]);
-		}
+		thumbnail = NULL;
 	}
+	if (exit_status != EXIT_SUCCESS)
+		thumbnail = NULL;
+	else
+		tracker_log ("got thumbnail %s", thumbnail);
+
+	g_free (argv[0]);
+	g_free (argv[1]);
+	g_free (argv[2]);
+	g_free (argv[3]);
 
-	g_free (thumbnailer);
-
-	return NULL;
+	return thumbnail;
 }
 
 
Index: src/trackerd/tracker-metadata.h
===================================================================
RCS file: /cvs/gnome/tracker/src/trackerd/tracker-metadata.h,v
retrieving revision 1.5
diff -u -p -r1.5 tracker-metadata.h
--- src/trackerd/tracker-metadata.h	26 Sep 2006 00:52:39 -0000	1.5
+++ src/trackerd/tracker-metadata.h	26 Nov 2006 22:26:36 -0000
@@ -29,7 +29,7 @@
 void			tracker_metadata_get_embedded 	  	(const char *uri, const char *mime, GHashTable *table);
 char *			tracker_metadata_get_text_file 	  	(const char *uri, const char *mime);
 void			tracker_metadata_parse_text_contents 	(const char *file_as_text, unsigned int ID);
-char *			tracker_metadata_get_thumbnail 	  	(const char *uri, const char *mime, const char *max_size);
+char *			tracker_metadata_get_thumbnail 	  	(const char *path, const char *mime, const char *size);
 char *			tracker_get_service_type_for_mime 	(const char *mime);
 
 #endif
Index: src/trackerd/tracker-utils.c
===================================================================
RCS file: /cvs/gnome/tracker/src/trackerd/tracker-utils.c,v
retrieving revision 1.43
diff -u -p -r1.43 tracker-utils.c
--- src/trackerd/tracker-utils.c	20 Nov 2006 19:53:25 -0000	1.43
+++ src/trackerd/tracker-utils.c	26 Nov 2006 22:26:38 -0000
@@ -1876,9 +1876,6 @@ tracker_load_config_file ()
 
 	if (g_key_file_has_key (key_file, "Indexing", "EnableThumbnails", NULL)) {
 		tracker->enable_thumbnails = g_key_file_get_boolean (key_file, "Indexing", "EnableThumbnails", NULL);
-
-		/* temporarily disable thumb generation as it is not compliant with fdo spec */
-		tracker->enable_thumbnails = FALSE;
 	}
 
 	values =  g_key_file_get_string_list (key_file,
Index: src/trackerd/trackerd.c
===================================================================
RCS file: /cvs/gnome/tracker/src/trackerd/trackerd.c,v
retrieving revision 1.57
diff -u -p -r1.57 trackerd.c
--- src/trackerd/trackerd.c	19 Nov 2006 23:50:06 -0000	1.57
+++ src/trackerd/trackerd.c	26 Nov 2006 22:26:45 -0000
@@ -1474,27 +1474,20 @@ extract_metadata_thread (void)
 
 				if (tracker->enable_thumbnails) {
 					char *small_thumb_file;
+					char *large_thumb_file;
 
-					/* see if there is a thumbnailer script for the file's mime type */
-
-					small_thumb_file = tracker_metadata_get_thumbnail (info->uri, info->mime, THUMB_SMALL);
+					small_thumb_file = tracker_metadata_get_thumbnail (info->uri, info->mime, "normal");
+					large_thumb_file = tracker_metadata_get_thumbnail (info->uri, info->mime, "large");
+					tracker_db_save_thumbs (db_con, small_thumb_file, large_thumb_file, info->file_id);
 
+					/* to do - emit dbus signal ThumbNailChanged */
 					if (small_thumb_file) {
-						char *large_thumb_file;
-
-						large_thumb_file = tracker_metadata_get_thumbnail (info->uri, info->mime, THUMB_LARGE);
-
-						if (large_thumb_file) {
-
-							tracker_db_save_thumbs (db_con, small_thumb_file, large_thumb_file, info->file_id);
+						g_free (small_thumb_file);
+					}
 
-							/* to do - emit dbus signal ThumbNailChanged */
+					if (large_thumb_file) {
 							g_free (large_thumb_file);
-						}
-
-						g_free (small_thumb_file);
 					}
-		
 				}
 
 				file_as_text = tracker_metadata_get_text_file (info->uri, info->mime);
--- /dev/null	2006-10-18 06:41:50.000000000 -0400
+++ src/tracker-thumbnailer/Makefile.am	2006-11-26 16:31:57.000000000 -0500
@@ -0,0 +1,11 @@
+INCLUDES = $(GLIB2_CFLAGS) $(CFLAGS) -g		\
+	$(LIBPNG_CFLAGS)
+
+bin_PROGRAMS = tracker-thumbnailer
+
+tracker_thumbnailer_SOURCES = tracker-thumbnailer.c	\
+	md5.c			\
+	md5.h
+
+tracker_thumbnailer_LDADD = $(GLIB2_LIBS)		\
+	$(LIBPNG_LIBS)
--- /dev/null	2006-10-18 06:41:50.000000000 -0400
+++ src/tracker-thumbnailer/md5.h	2006-11-25 16:37:43.000000000 -0500
@@ -0,0 +1,94 @@
+/*
+  Copyright (C) 1999 Aladdin Enterprises.  All rights reserved.
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+
+  L. Peter Deutsch
+  [EMAIL PROTECTED]
+
+ */
+/*$Id: md5.h $ */
+/*
+  Independent implementation of MD5 (RFC 1321).
+
+  This code implements the MD5 Algorithm defined in RFC 1321.
+  It is derived directly from the text of the RFC and not from the
+  reference implementation.
+
+  The original and principal author of md5.h is L. Peter Deutsch
+  <[EMAIL PROTECTED]>.  Other authors are noted in the change history
+  that follows (in reverse chronological order):
+
+  1999-11-04 lpd Edited comments slightly for automatic TOC extraction.
+  1999-10-18 lpd Fixed typo in header comment (ansi2knr rather than md5);
+	added conditionalization for C++ compilation from Martin
+	Purschke <[EMAIL PROTECTED]>.
+  1999-05-03 lpd Original version.
+ */
+
+#ifndef md5_INCLUDED
+#  define md5_INCLUDED
+
+/*
+ * This code has some adaptations for the Ghostscript environment, but it
+ * will compile and run correctly in any environment with 8-bit chars and
+ * 32-bit ints.  Specifically, it assumes that if the following are
+ * defined, they have the same meaning as in Ghostscript: P1, P2, P3,
+ * ARCH_IS_BIG_ENDIAN.
+ */
+
+typedef unsigned char md5_byte_t; /* 8-bit byte */
+typedef unsigned int md5_word_t; /* 32-bit word */
+
+/* Define the state of the MD5 Algorithm. */
+typedef struct md5_state_s {
+    md5_word_t count[2];	/* message length in bits, lsw first */
+    md5_word_t abcd[4];		/* digest buffer */
+    md5_byte_t buf[64];		/* accumulate block */
+} md5_state_t;
+
+#ifdef __cplusplus
+extern "C" 
+{
+#endif
+
+/* Initialize the algorithm. */
+#ifdef P1
+void md5_init(P1(md5_state_t *pms));
+#else
+void md5_init(md5_state_t *pms);
+#endif
+
+/* Append a string to the message. */
+#ifdef P3
+void md5_append(P3(md5_state_t *pms, const md5_byte_t *data, int nbytes));
+#else
+void md5_append(md5_state_t *pms, const md5_byte_t *data, int nbytes);
+#endif
+
+/* Finish the message and return the digest. */
+#ifdef P2
+void md5_finish(P2(md5_state_t *pms, md5_byte_t digest[16]));
+#else
+void md5_finish(md5_state_t *pms, md5_byte_t digest[16]);
+#endif
+
+#ifdef __cplusplus
+}  /* end extern "C" */
+#endif
+
+#endif /* md5_INCLUDED */
--- /dev/null	2006-10-18 06:41:50.000000000 -0400
+++ src/tracker-thumbnailer/md5.c	2006-11-25 18:15:22.000000000 -0500
@@ -0,0 +1,393 @@
+/*
+  Copyright (C) 1999 Aladdin Enterprises.  All rights reserved.
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+
+  L. Peter Deutsch
+  [EMAIL PROTECTED]
+
+ */
+/*$Id: md5.c $ */
+/*
+  Independent implementation of MD5 (RFC 1321).
+
+  This code implements the MD5 Algorithm defined in RFC 1321.
+  It is derived directly from the text of the RFC and not from the
+  reference implementation.
+
+  The original and principal author of md5.c is L. Peter Deutsch
+  <[EMAIL PROTECTED]>.  Other authors are noted in the change history
+  that follows (in reverse chronological order):
+
+  1999-11-04 lpd Edited comments slightly for automatic TOC extraction.
+  1999-10-18 lpd Fixed typo in header comment (ansi2knr rather than md5).
+  1999-05-03 lpd Original version.
+ */
+
+#include <string.h>
+#include "md5.h"
+
+#ifdef TEST
+/*
+ * Compile with -DTEST to create a self-contained executable test program.
+ * The test program should print out the same values as given in section
+ * A.5 of RFC 1321, reproduced below.
+ */
+#include <string.h>
+main()
+{
+    static const char *const test[7] = {
+	"", /*d41d8cd98f00b204e9800998ecf8427e*/
+	"a", /*0cc175b9c0f1b6a831c399e269772661*/
+	"abc", /*900150983cd24fb0d6963f7d28e17f72*/
+	"message digest", /*f96b697d7cb7938d525a2f31aaf161d0*/
+	"abcdefghijklmnopqrstuvwxyz", /*c3fcd3d76192e4007dfb496cca67e13b*/
+	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789",
+				/*d174ab98d277d9f5a5611c2c9f419d9f*/
+	"12345678901234567890123456789012345678901234567890123456789012345678901234567890" /*57edf4a22be3c955ac49da2e2107b67a*/
+    };
+    int i;
+
+    for (i = 0; i < 7; ++i) {
+	md5_state_t state;
+	md5_byte_t digest[16];
+	int di;
+
+	md5_init(&state);
+	md5_append(&state, (const md5_byte_t *)test[i], strlen(test[i]));
+	md5_finish(&state, digest);
+	printf("MD5 (\"%s\") = ", test[i]);
+	for (di = 0; di < 16; ++di)
+	    printf("%02x", digest[di]);
+	printf("\n");
+    }
+    return 0;
+}
+#endif /* TEST */
+
+
+/*
+ * For reference, here is the program that computed the T values.
+ */
+#if 0
+#include <math.h>
+main()
+{
+    int i;
+    for (i = 1; i <= 64; ++i) {
+	unsigned long v = (unsigned long)(4294967296.0 * fabs(sin((double)i)));
+	printf("#define T%d 0x%08lx\n", i, v);
+    }
+    return 0;
+}
+#endif
+/*
+ * End of T computation program.
+ */
+#define T1 0xd76aa478
+#define T2 0xe8c7b756
+#define T3 0x242070db
+#define T4 0xc1bdceee
+#define T5 0xf57c0faf
+#define T6 0x4787c62a
+#define T7 0xa8304613
+#define T8 0xfd469501
+#define T9 0x698098d8
+#define T10 0x8b44f7af
+#define T11 0xffff5bb1
+#define T12 0x895cd7be
+#define T13 0x6b901122
+#define T14 0xfd987193
+#define T15 0xa679438e
+#define T16 0x49b40821
+#define T17 0xf61e2562
+#define T18 0xc040b340
+#define T19 0x265e5a51
+#define T20 0xe9b6c7aa
+#define T21 0xd62f105d
+#define T22 0x02441453
+#define T23 0xd8a1e681
+#define T24 0xe7d3fbc8
+#define T25 0x21e1cde6
+#define T26 0xc33707d6
+#define T27 0xf4d50d87
+#define T28 0x455a14ed
+#define T29 0xa9e3e905
+#define T30 0xfcefa3f8
+#define T31 0x676f02d9
+#define T32 0x8d2a4c8a
+#define T33 0xfffa3942
+#define T34 0x8771f681
+#define T35 0x6d9d6122
+#define T36 0xfde5380c
+#define T37 0xa4beea44
+#define T38 0x4bdecfa9
+#define T39 0xf6bb4b60
+#define T40 0xbebfbc70
+#define T41 0x289b7ec6
+#define T42 0xeaa127fa
+#define T43 0xd4ef3085
+#define T44 0x04881d05
+#define T45 0xd9d4d039
+#define T46 0xe6db99e5
+#define T47 0x1fa27cf8
+#define T48 0xc4ac5665
+#define T49 0xf4292244
+#define T50 0x432aff97
+#define T51 0xab9423a7
+#define T52 0xfc93a039
+#define T53 0x655b59c3
+#define T54 0x8f0ccc92
+#define T55 0xffeff47d
+#define T56 0x85845dd1
+#define T57 0x6fa87e4f
+#define T58 0xfe2ce6e0
+#define T59 0xa3014314
+#define T60 0x4e0811a1
+#define T61 0xf7537e82
+#define T62 0xbd3af235
+#define T63 0x2ad7d2bb
+#define T64 0xeb86d391
+
+static void
+md5_process(md5_state_t *pms, const md5_byte_t *data /*[64]*/)
+{
+    md5_word_t
+	a = pms->abcd[0], b = pms->abcd[1],
+	c = pms->abcd[2], d = pms->abcd[3];
+    md5_word_t t;
+
+#ifndef ARCH_IS_BIG_ENDIAN
+# define ARCH_IS_BIG_ENDIAN 1	/* slower, default implementation */
+#endif
+#if ARCH_IS_BIG_ENDIAN
+
+    /*
+     * On big-endian machines, we must arrange the bytes in the right
+     * order.  (This also works on machines of unknown byte order.)
+     */
+    md5_word_t X[16];
+    const md5_byte_t *xp = data;
+    int i;
+
+    for (i = 0; i < 16; ++i, xp += 4)
+	X[i] = xp[0] + (xp[1] << 8) + (xp[2] << 16) + (xp[3] << 24);
+
+#else  /* !ARCH_IS_BIG_ENDIAN */
+
+    /*
+     * On little-endian machines, we can process properly aligned data
+     * without copying it.
+     */
+    md5_word_t xbuf[16];
+    const md5_word_t *X;
+
+    if (!((data - (const md5_byte_t *)0) & 3)) {
+	/* data are properly aligned */
+	X = (const md5_word_t *)data;
+    } else {
+	/* not aligned */
+	memcpy(xbuf, data, 64);
+	X = xbuf;
+    }
+#endif
+
+#define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32 - (n))))
+
+    /* Round 1. */
+    /* Let [abcd k s i] denote the operation
+       a = b + ((a + F(b,c,d) + X[k] + T[i]) <<< s). */
+#define F(x, y, z) (((x) & (y)) | (~(x) & (z)))
+#define SET(a, b, c, d, k, s, Ti)\
+  t = a + F(b,c,d) + X[k] + Ti;\
+  a = ROTATE_LEFT(t, s) + b
+    /* Do the following 16 operations. */
+    SET(a, b, c, d,  0,  7,  T1);
+    SET(d, a, b, c,  1, 12,  T2);
+    SET(c, d, a, b,  2, 17,  T3);
+    SET(b, c, d, a,  3, 22,  T4);
+    SET(a, b, c, d,  4,  7,  T5);
+    SET(d, a, b, c,  5, 12,  T6);
+    SET(c, d, a, b,  6, 17,  T7);
+    SET(b, c, d, a,  7, 22,  T8);
+    SET(a, b, c, d,  8,  7,  T9);
+    SET(d, a, b, c,  9, 12, T10);
+    SET(c, d, a, b, 10, 17, T11);
+    SET(b, c, d, a, 11, 22, T12);
+    SET(a, b, c, d, 12,  7, T13);
+    SET(d, a, b, c, 13, 12, T14);
+    SET(c, d, a, b, 14, 17, T15);
+    SET(b, c, d, a, 15, 22, T16);
+#undef SET
+
+     /* Round 2. */
+     /* Let [abcd k s i] denote the operation
+          a = b + ((a + G(b,c,d) + X[k] + T[i]) <<< s). */
+#define G(x, y, z) (((x) & (z)) | ((y) & ~(z)))
+#define SET(a, b, c, d, k, s, Ti)\
+  t = a + G(b,c,d) + X[k] + Ti;\
+  a = ROTATE_LEFT(t, s) + b
+     /* Do the following 16 operations. */
+    SET(a, b, c, d,  1,  5, T17);
+    SET(d, a, b, c,  6,  9, T18);
+    SET(c, d, a, b, 11, 14, T19);
+    SET(b, c, d, a,  0, 20, T20);
+    SET(a, b, c, d,  5,  5, T21);
+    SET(d, a, b, c, 10,  9, T22);
+    SET(c, d, a, b, 15, 14, T23);
+    SET(b, c, d, a,  4, 20, T24);
+    SET(a, b, c, d,  9,  5, T25);
+    SET(d, a, b, c, 14,  9, T26);
+    SET(c, d, a, b,  3, 14, T27);
+    SET(b, c, d, a,  8, 20, T28);
+    SET(a, b, c, d, 13,  5, T29);
+    SET(d, a, b, c,  2,  9, T30);
+    SET(c, d, a, b,  7, 14, T31);
+    SET(b, c, d, a, 12, 20, T32);
+#undef SET
+
+     /* Round 3. */
+     /* Let [abcd k s t] denote the operation
+          a = b + ((a + H(b,c,d) + X[k] + T[i]) <<< s). */
+#define H(x, y, z) ((x) ^ (y) ^ (z))
+#define SET(a, b, c, d, k, s, Ti)\
+  t = a + H(b,c,d) + X[k] + Ti;\
+  a = ROTATE_LEFT(t, s) + b
+     /* Do the following 16 operations. */
+    SET(a, b, c, d,  5,  4, T33);
+    SET(d, a, b, c,  8, 11, T34);
+    SET(c, d, a, b, 11, 16, T35);
+    SET(b, c, d, a, 14, 23, T36);
+    SET(a, b, c, d,  1,  4, T37);
+    SET(d, a, b, c,  4, 11, T38);
+    SET(c, d, a, b,  7, 16, T39);
+    SET(b, c, d, a, 10, 23, T40);
+    SET(a, b, c, d, 13,  4, T41);
+    SET(d, a, b, c,  0, 11, T42);
+    SET(c, d, a, b,  3, 16, T43);
+    SET(b, c, d, a,  6, 23, T44);
+    SET(a, b, c, d,  9,  4, T45);
+    SET(d, a, b, c, 12, 11, T46);
+    SET(c, d, a, b, 15, 16, T47);
+    SET(b, c, d, a,  2, 23, T48);
+#undef SET
+
+     /* Round 4. */
+     /* Let [abcd k s t] denote the operation
+          a = b + ((a + I(b,c,d) + X[k] + T[i]) <<< s). */
+#define I(x, y, z) ((y) ^ ((x) | ~(z)))
+#define SET(a, b, c, d, k, s, Ti)\
+  t = a + I(b,c,d) + X[k] + Ti;\
+  a = ROTATE_LEFT(t, s) + b
+     /* Do the following 16 operations. */
+    SET(a, b, c, d,  0,  6, T49);
+    SET(d, a, b, c,  7, 10, T50);
+    SET(c, d, a, b, 14, 15, T51);
+    SET(b, c, d, a,  5, 21, T52);
+    SET(a, b, c, d, 12,  6, T53);
+    SET(d, a, b, c,  3, 10, T54);
+    SET(c, d, a, b, 10, 15, T55);
+    SET(b, c, d, a,  1, 21, T56);
+    SET(a, b, c, d,  8,  6, T57);
+    SET(d, a, b, c, 15, 10, T58);
+    SET(c, d, a, b,  6, 15, T59);
+    SET(b, c, d, a, 13, 21, T60);
+    SET(a, b, c, d,  4,  6, T61);
+    SET(d, a, b, c, 11, 10, T62);
+    SET(c, d, a, b,  2, 15, T63);
+    SET(b, c, d, a,  9, 21, T64);
+#undef SET
+
+     /* Then perform the following additions. (That is increment each
+        of the four registers by the value it had before this block
+        was started.) */
+    pms->abcd[0] += a;
+    pms->abcd[1] += b;
+    pms->abcd[2] += c;
+    pms->abcd[3] += d;
+}
+
+void
+md5_init(md5_state_t *pms)
+{
+    pms->count[0] = pms->count[1] = 0;
+    pms->abcd[0] = 0x67452301;
+    pms->abcd[1] = 0xefcdab89;
+    pms->abcd[2] = 0x98badcfe;
+    pms->abcd[3] = 0x10325476;
+}
+
+void
+md5_append(md5_state_t *pms, const md5_byte_t *data, int nbytes)
+{
+    const md5_byte_t *p = data;
+    int left = nbytes;
+    int offset = (pms->count[0] >> 3) & 63;
+    md5_word_t nbits = (md5_word_t)(nbytes << 3);
+
+    if (nbytes <= 0)
+	return;
+
+    /* Update the message length. */
+    pms->count[1] += nbytes >> 29;
+    pms->count[0] += nbits;
+    if (pms->count[0] < nbits)
+	pms->count[1]++;
+
+    /* Process an initial partial block. */
+    if (offset) {
+	int copy = (offset + nbytes > 64 ? 64 - offset : nbytes);
+
+	memcpy(pms->buf + offset, p, copy);
+	if (offset + copy < 64)
+	    return;
+	p += copy;
+	left -= copy;
+	md5_process(pms, pms->buf);
+    }
+
+    /* Process full blocks. */
+    for (; left >= 64; p += 64, left -= 64)
+	md5_process(pms, p);
+
+    /* Process a final partial block. */
+    if (left)
+	memcpy(pms->buf, p, left);
+}
+
+void
+md5_finish(md5_state_t *pms, md5_byte_t digest[16])
+{
+    static const md5_byte_t pad[64] = {
+	0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+    };
+    md5_byte_t data[8];
+    int i;
+
+    /* Save the length before padding. */
+    for (i = 0; i < 8; ++i)
+	data[i] = (md5_byte_t)(pms->count[i >> 2] >> ((i & 3) << 3));
+    /* Pad to 56 bytes mod 64. */
+    md5_append(pms, pad, ((55 - (pms->count[0] >> 3)) & 63) + 1);
+    /* Append the length. */
+    md5_append(pms, data, 8);
+    for (i = 0; i < 16; ++i)
+	digest[i] = (md5_byte_t)(pms->abcd[i >> 2] >> ((i & 3) << 3));
+}
--- /dev/null	2006-10-18 06:41:50.000000000 -0400
+++ src/tracker-thumbnailer/tracker-thumbnailer.c	2006-11-26 16:42:32.000000000 -0500
@@ -0,0 +1,233 @@
+
+/* tracker-thumbnailer
+ * Copyright (C) 2006, Edward Duffy <[EMAIL PROTECTED]>
+ *
+ * This library 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 library 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 library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ *
+ * This program is based off the freedesktop.org "Thumbnail Managing Standard"
+ * available at: http://jens.triq.net/thumbnail-spec/index.html
+ */
+
+
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <glib.h>
+#include <glib/gstdio.h>
+#include <png.h>
+#include "md5.h"
+
+#ifndef DATADIR
+#define DATADIR "/usr/share"
+#endif
+
+/* argv[1] == full path of file to be nailed
+ * argv[2] == mime type of said file
+ * argv[3] == requested size: "normal", "large", "preview"
+ */
+
+int main (int argc, char *argv[])
+{
+	gchar         *uri;
+	struct stat    stat_info;
+	gchar         *mtime;
+	md5_state_t    hash_state;
+	guchar         hash[16];
+	gchar          uri_hash[20], *p;
+	int            i;
+	gchar         *thumbnail_filename;
+	FILE          *fp;
+	png_structp    png_ptr;
+	png_infop      info_ptr;
+	png_textp      pngtext;
+	int            count, tests_passed;
+	gchar         *thumbnailer;
+	gchar         *args[5];
+	png_uint_32    width, height;
+	int            bit_depth, color_type, interlace_method;
+	int            compression_method, filter_method;
+	png_colorp     palette;
+	int            num_palette;
+	png_bytepp     row_pointers;
+
+	/* only make normal size thumbnails for now */
+	if (strcmp (argv[3], "normal") != 0) {
+		g_printerr ("Only normal sized thumbnails are supported\n");
+		return EXIT_FAILURE;
+	}
+
+	/* make sure the actual file exists */
+	if (!g_file_test (argv[1], G_FILE_TEST_EXISTS)) {
+		g_printerr ("%s does not exist\n", argv[1]);
+		return EXIT_FAILURE;
+	}
+
+	/* convert file name to URI */
+	uri = g_filename_to_uri (argv[1], NULL, NULL);
+
+	/* get stat information on the file */
+	if (g_stat (argv[1], &stat_info) == -1) {
+		g_printerr ("stat () failed for %s\n", argv[1]);
+		return EXIT_FAILURE;
+	}
+	mtime = g_strdup_printf ("%lu", stat_info.st_mtime);
+
+	/* create path to thumbnail */
+	md5_init (&hash_state);
+	md5_append (&hash_state, (guchar *)uri, strlen (uri));
+	md5_finish (&hash_state, hash);
+	p = uri_hash;
+	for (i = 0; i < 16; i++) {
+		g_sprintf (p, "%02x", hash[i]);
+		p += 2;
+	}
+	g_sprintf (p, ".png");
+	thumbnail_filename = g_build_filename (
+		g_get_home_dir (), ".thumbnails", argv[3], uri_hash, NULL);
+
+	/* check to see if the thumbnail already exists */
+	if (g_file_test (thumbnail_filename, G_FILE_TEST_EXISTS)) {
+		g_printerr ("%s exists\n", thumbnail_filename);
+
+		/* thumbnail exists; but is it valid? */
+		g_assert ((fp = g_fopen (thumbnail_filename, "r")));
+		g_assert ((png_ptr = png_create_read_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL)));
+		g_assert ((info_ptr = png_create_info_struct (png_ptr)));
+		png_init_io (png_ptr, fp);
+		png_read_info (png_ptr, info_ptr);
+		i = png_get_text (png_ptr, info_ptr, &pngtext, &count);
+		tests_passed = 0;
+		for (i = 0; i < count; i++) {
+			if (strcmp (pngtext[i].key, "Thumb::URI") == 0 && strcmp (pngtext[i].text, uri) == 0) {
+				++tests_passed;
+			}
+			else if (strcmp (pngtext[i].key, "Thumb::MTime") == 0 && strcmp (pngtext[i].text, mtime) == 0) {
+				++tests_passed;
+			}
+		}
+		fclose (fp);
+		if (tests_passed == 2) {
+			g_printerr ("Thumbnail valid\n");
+			g_print ("%s\n", thumbnail_filename);
+			return EXIT_SUCCESS;
+		}
+		g_printerr ("Not all tests passed.  Recreating thumbnail...\n");
+	}
+	/* thumbnail either doesn't exist or is invalid; contiue... */
+
+	/* do we have a thumbnailer for this mime type? */
+	thumbnailer = g_strconcat (DATADIR "/tracker/thumbnailers/",
+	                           argv[2], "_thumbnailer", NULL);
+
+	if (!g_file_test (thumbnailer, G_FILE_TEST_EXISTS)) {
+		g_printerr ("%s not found\n", thumbnailer);
+		return EXIT_FAILURE;
+	}
+
+	/* execute the thumbnailer */
+	args[0] = thumbnailer;
+	args[1] = g_filename_from_utf8 (argv[1], -1, NULL, NULL, NULL);
+	args[2] = thumbnail_filename;
+	if (strcmp (argv[3], "normal") == 0)
+		args[3] = g_strdup ("128");
+	args[4] = NULL;
+
+	if (!g_spawn_sync (NULL, args, NULL,
+	                   G_SPAWN_STDOUT_TO_DEV_NULL | G_SPAWN_STDERR_TO_DEV_NULL,
+	                   NULL, NULL, NULL, NULL, NULL, NULL)) {
+
+		g_printerr ("%s failed to create %s\n", thumbnailer, thumbnail_filename);
+		g_remove (thumbnail_filename);
+		return EXIT_FAILURE;
+	}
+
+	/* the fd.o spec requires us to set certain PNG keys.  As far as I can
+	 * see, libpng doesn't allow you to just set metadata, you have to do
+	 * that when you create the file.  Therefore, we need to copy the newly
+	 * created thumbnail into a new one while setting the required attributes
+	 */
+
+	/* read in the thumbnail into a buffer */
+	g_assert ((fp = g_fopen (thumbnail_filename, "r")));
+	g_assert ((png_ptr = png_create_read_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL)));
+	g_assert ((info_ptr = png_create_info_struct (png_ptr)));
+
+	if (setjmp (png_jmpbuf (png_ptr))) {
+		g_printerr ("Error reading thumbnail\n");
+		fclose (fp);
+		g_remove (thumbnail_filename);
+		return EXIT_FAILURE;
+	}
+
+	png_init_io (png_ptr, fp);
+	png_read_info (png_ptr, info_ptr);
+
+	g_assert ((1 == png_get_IHDR (png_ptr, info_ptr, &width, &height, &bit_depth, &color_type, &interlace_method, &compression_method, &filter_method)));
+
+	png_get_PLTE (png_ptr, info_ptr, &palette, &num_palette);
+
+	row_pointers = g_new (png_bytep, height);
+	for (i = 0; i < height; i++) {
+		row_pointers[i] = (png_bytep) malloc (png_get_rowbytes (png_ptr, info_ptr));
+	}
+	png_read_image (png_ptr, row_pointers);
+	png_read_end (png_ptr, NULL);
+	fclose (fp);
+
+	/* write the new thumbnail (overwrites the old) */
+	g_assert ((fp = g_fopen (thumbnail_filename, "w")));
+	g_assert ((png_ptr = png_create_write_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL)));
+	g_assert ((info_ptr = png_create_info_struct (png_ptr)));
+
+	if (setjmp (png_jmpbuf (png_ptr))) {
+		g_printerr ("Error creating thumbnail\n");
+		fclose (fp);
+		g_remove (thumbnail_filename);
+		return EXIT_FAILURE;
+	}
+
+	png_init_io (png_ptr, fp);
+
+	png_set_IHDR (png_ptr, info_ptr, width, height, bit_depth, color_type, interlace_method, compression_method, filter_method);
+
+	if (palette && num_palette > 0)
+		png_set_PLTE (png_ptr, info_ptr, palette, num_palette);
+
+	/* set the required fields */
+	pngtext = g_new0 (png_text, 3);
+	pngtext[0].key = "Thumb::URI";
+	pngtext[0].text = uri;
+	pngtext[0].text_length = strlen (uri);
+	pngtext[0].compression = PNG_TEXT_COMPRESSION_NONE;
+	pngtext[1].key = "Thumb::MTime";
+	pngtext[1].text = mtime;
+	pngtext[1].text_length = strlen (mtime);
+	pngtext[1].compression = PNG_TEXT_COMPRESSION_NONE;
+	/* set some optional fields */
+	pngtext[2].key = "Software";
+	pngtext[2].text = "Tracker thumbnail factory";
+	pngtext[2].compression = PNG_TEXT_COMPRESSION_NONE;
+	png_set_text(png_ptr, info_ptr, pngtext, 3);
+
+	png_write_info (png_ptr, info_ptr);
+	png_write_image (png_ptr, row_pointers);
+	png_write_end (png_ptr, info_ptr);
+	fclose (fp);
+
+	/* if we get here, everything must have succeeded */
+	g_print ("%s\n", thumbnail_filename);
+	return EXIT_SUCCESS;
+}
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