src/hb-sanitize.hh - third_party/harfbuzz - Git at Google

 /*
  * Copyright © 2007,2008,2009,2010  Red Hat, Inc.
  * Copyright © 2012,2018  Google, Inc.
  *
  *  This is part of HarfBuzz, a text shaping library.
  *
  * Permission is hereby granted, without written agreement and without
  * license or royalty fees, to use, copy, modify, and distribute this
  * software and its documentation for any purpose, provided that the
  * above copyright notice and the following two paragraphs appear in
  * all copies of this software.
  *
  * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
  * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
  * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
  * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
  * DAMAGE.
  *
  * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
  * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
  * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
  * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
  * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
  *
  * Red Hat Author(s): Behdad Esfahbod
  * Google Author(s): Behdad Esfahbod
  */

 #ifndef HB_SANITIZE_HH
 #define HB_SANITIZE_HH

 #include "hb.hh"
 #include "hb-blob.hh"
 #include "hb-dispatch.hh"


 /*
  * Sanitize
  *
  *
  * === Introduction ===
  *
  * The sanitize machinery is at the core of our zero-cost font loading.  We
  * mmap() font file into memory and create a blob out of it.  Font subtables
  * are returned as a readonly sub-blob of the main font blob.  These table
  * blobs are then sanitized before use, to ensure invalid memory access does
  * not happen.  The toplevel sanitize API use is like, eg. to load the 'head'
  * table:
  *
  *   hb_blob_t *head_blob = hb_sanitize_context_t ().reference_table<OT::head> (face);
  *
  * The blob then can be converted to a head table struct with:
  *
  *   const head *head_table = head_blob->as<head> ();
  *
  * What the reference_table does is, to call hb_face_reference_table() to load
  * the table blob, sanitize it and return either the sanitized blob, or empty
  * blob if sanitization failed.  The blob->as() function returns the null
  * object of its template type argument if the blob is empty.  Otherwise, it
  * just casts the blob contents to the desired type.
  *
  * Sanitizing a blob of data with a type T works as follows (with minor
  * simplification):
  *
  *   - Cast blob content to T*, call sanitize() method of it,
  *   - If sanitize succeeded, return blob.
  *   - Otherwise, if blob is not writable, try making it writable,
  *     or copy if cannot be made writable in-place,
  *   - Call sanitize() again.  Return blob if sanitize succeeded.
  *   - Return empty blob otherwise.
  *
  *
  * === The sanitize() contract ===
  *
  * The sanitize() method of each object type shall return true if it's safe to
  * call other methods of the object, and %false otherwise.
  *
  * Note that what sanitize() checks for might align with what the specification
  * describes as valid table data, but does not have to be.  In particular, we
  * do NOT want to be pedantic and concern ourselves with validity checks that
  * are irrelevant to our use of the table.  On the contrary, we want to be
  * lenient with error handling and accept invalid data to the extent that it
  * does not impose extra burden on us.
  *
  * Based on the sanitize contract, one can see that what we check for depends
  * on how we use the data in other table methods.  Ie. if other table methods
  * assume that offsets do NOT point out of the table data block, then that's
  * something sanitize() must check for (GSUB/GPOS/GDEF/etc work this way).  On
  * the other hand, if other methods do such checks themselves, then sanitize()
  * does not have to bother with them (glyf/local work this way).  The choice
  * depends on the table structure and sanitize() performance.  For example, to
  * check glyf/loca offsets in sanitize() would cost O(num-glyphs).  We try hard
  * to avoid such costs during font loading.  By postponing such checks to the
  * actual glyph loading, we reduce the sanitize cost to O(1) and total runtime
  * cost to O(used-glyphs).  As such, this is preferred.
  *
  * The same argument can be made re GSUB/GPOS/GDEF, but there, the table
  * structure is so complicated that by checking all offsets at sanitize() time,
  * we make the code much simpler in other methods, as offsets and referenced
  * objects do not need to be validated at each use site.
  */

 /* This limits sanitizing time on really broken fonts. */
 #ifndef HB_SANITIZE_MAX_EDITS
 #define HB_SANITIZE_MAX_EDITS 32
 #endif
 #ifndef HB_SANITIZE_MAX_OPS_FACTOR
 #define HB_SANITIZE_MAX_OPS_FACTOR 64
 #endif
 #ifndef HB_SANITIZE_MAX_OPS_MIN
 #define HB_SANITIZE_MAX_OPS_MIN 16384
 #endif
 #ifndef HB_SANITIZE_MAX_OPS_MAX
 #define HB_SANITIZE_MAX_OPS_MAX 0x3FFFFFFF
 #endif
 #ifndef HB_SANITIZE_MAX_SUBTABLES
 #define HB_SANITIZE_MAX_SUBTABLES 0x4000
 #endif

 struct hb_sanitize_context_t :
        hb_dispatch_context_t<hb_sanitize_context_t, bool, HB_DEBUG_SANITIZE>
 {
   hb_sanitize_context_t () :
 	start (nullptr), end (nullptr),
 	max_ops (0), max_subtables (0),
 	writable (false), edit_count (0),
 	blob (nullptr),
 	num_glyphs (65536),
 	num_glyphs_set (false) {}

   const char *get_name () { return "SANITIZE"; }
   template <typename T, typename F>
   bool may_dispatch (const T *obj HB_UNUSED, const F *format)
   { return format->sanitize (this); }
   static return_t default_return_value () { return true; }
   static return_t no_dispatch_return_value () { return false; }
   bool stop_sublookup_iteration (const return_t r) const { return !r; }

   bool visit_subtables (unsigned count)
   {
     max_subtables += count;
     return max_subtables < HB_SANITIZE_MAX_SUBTABLES;
   }

   private:
   template <typename T, typename ...Ts> auto
   _dispatch (const T &obj, hb_priority<1>, Ts&&... ds) HB_AUTO_RETURN
   ( obj.sanitize (this, hb_forward<Ts> (ds)...) )
   template <typename T, typename ...Ts> auto
   _dispatch (const T &obj, hb_priority<0>, Ts&&... ds) HB_AUTO_RETURN
   ( obj.dispatch (this, hb_forward<Ts> (ds)...) )
   public:
   template <typename T, typename ...Ts> auto
   dispatch (const T &obj, Ts&&... ds) HB_AUTO_RETURN
   ( _dispatch (obj, hb_prioritize, hb_forward<Ts> (ds)...) )


   void init (hb_blob_t *b)
   {
     this->blob = hb_blob_reference (b);
     this->writable = false;
   }

   void set_num_glyphs (unsigned int num_glyphs_)
   {
     num_glyphs = num_glyphs_;
     num_glyphs_set = true;
   }
   unsigned int get_num_glyphs () { return num_glyphs; }

   void set_max_ops (int max_ops_) { max_ops = max_ops_; }

   template <typename T>
   void set_object (const T *obj)
   {
     reset_object ();

     if (!obj) return;

     const char *obj_start = (const char *) obj;
     if (unlikely (obj_start < this->start || this->end <= obj_start))
       this->start = this->end = nullptr;
     else
     {
       this->start = obj_start;
       this->end   = obj_start + hb_min (size_t (this->end - obj_start), obj->get_size ());
     }
   }

   void reset_object ()
   {
     this->start = this->blob->data;
     this->end = this->start + this->blob->length;
     assert (this->start <= this->end); /* Must not overflow. */
   }

   void start_processing ()
   {
     reset_object ();
     if (unlikely (hb_unsigned_mul_overflows (this->end - this->start, HB_SANITIZE_MAX_OPS_FACTOR)))
       this->max_ops = HB_SANITIZE_MAX_OPS_MAX;
     else
       this->max_ops = hb_clamp ((unsigned) (this->end - this->start) * HB_SANITIZE_MAX_OPS_FACTOR,
 				(unsigned) HB_SANITIZE_MAX_OPS_MIN,
 				(unsigned) HB_SANITIZE_MAX_OPS_MAX);
     this->edit_count = 0;
     this->debug_depth = 0;

     DEBUG_MSG_LEVEL (SANITIZE, start, 0, +1,
 		     "start [%p..%p] (%lu bytes)",
 		     this->start, this->end,
 		     (unsigned long) (this->end - this->start));
   }

   void end_processing ()
   {
     DEBUG_MSG_LEVEL (SANITIZE, this->start, 0, -1,
 		     "end [%p..%p] %u edit requests",
 		     this->start, this->end, this->edit_count);

     hb_blob_destroy (this->blob);
     this->blob = nullptr;
     this->start = this->end = nullptr;
   }

   unsigned get_edit_count () { return edit_count; }

   bool check_range (const void *base,
 		    unsigned int len) const
   {
     const char *p = (const char *) base;
     bool ok = !len ||
 	      (this->start <= p &&
 	       p <= this->end &&
 	       (unsigned int) (this->end - p) >= len &&
 	       (this->max_ops -= len) > 0);

     DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0,
 		     "check_range [%p..%p]"
 		     " (%d bytes) in [%p..%p] -> %s",
 		     p, p + len, len,
 		     this->start, this->end,
 		     ok ? "OK" : "OUT-OF-RANGE");

     return likely (ok);
   }

   template <typename T>
   bool check_range (const T *base,
 		    unsigned int a,
 		    unsigned int b) const
   {
     return !hb_unsigned_mul_overflows (a, b) &&
 	   this->check_range (base, a * b);
   }

   template <typename T>
   bool check_range (const T *base,
 		    unsigned int a,
 		    unsigned int b,
 		    unsigned int c) const
   {
     return !hb_unsigned_mul_overflows (a, b) &&
 	   this->check_range (base, a * b, c);
   }

   template <typename T>
   bool check_array (const T *base, unsigned int len) const
   {
     return this->check_range (base, len, hb_static_size (T));
   }

   template <typename T>
   bool check_array (const T *base,
 		    unsigned int a,
 		    unsigned int b) const
   {
     return this->check_range (base, a, b, hb_static_size (T));
   }

   template <typename Type>
   bool check_struct (const Type *obj) const
   { return likely (this->check_range (obj, obj->min_size)); }

   bool may_edit (const void *base, unsigned int len)
   {
     if (this->edit_count >= HB_SANITIZE_MAX_EDITS)
       return false;

     const char *p = (const char *) base;
     this->edit_count++;

     DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0,
        "may_edit(%u) [%p..%p] (%d bytes) in [%p..%p] -> %s",
        this->edit_count,
        p, p + len, len,
        this->start, this->end,
        this->writable ? "GRANTED" : "DENIED");

     return this->writable;
   }

   template <typename Type, typename ValueType>
   bool try_set (const Type *obj, const ValueType &v)
   {
     if (this->may_edit (obj, hb_static_size (Type)))
     {
       * const_cast<Type *> (obj) = v;
       return true;
     }
     return false;
   }

   template <typename Type>
   hb_blob_t *sanitize_blob (hb_blob_t *blob)
   {
     bool sane;

     init (blob);

   retry:
     DEBUG_MSG_FUNC (SANITIZE, start, "start");

     start_processing ();

     if (unlikely (!start))
     {
       end_processing ();
       return blob;
     }

     Type *t = reinterpret_cast<Type *> (const_cast<char *> (start));

     sane = t->sanitize (this);
     if (sane)
     {
       if (edit_count)
       {
 	DEBUG_MSG_FUNC (SANITIZE, start, "passed first round with %d edits; going for second round", edit_count);

 	/* sanitize again to ensure no toe-stepping */
 	edit_count = 0;
 	sane = t->sanitize (this);
 	if (edit_count) {
 	  DEBUG_MSG_FUNC (SANITIZE, start, "requested %d edits in second round; FAILLING", edit_count);
 	  sane = false;
 	}
       }
     }
     else
     {
       if (edit_count && !writable) {
 	start = hb_blob_get_data_writable (blob, nullptr);
 	end = start + blob->length;

 	if (start)
 	{
 	  writable = true;
 	  /* ok, we made it writable by relocating.  try again */
 	  DEBUG_MSG_FUNC (SANITIZE, start, "retry");
 	  goto retry;
 	}
       }
     }

     end_processing ();

     DEBUG_MSG_FUNC (SANITIZE, start, sane ? "PASSED" : "FAILED");
     if (sane)
     {
       hb_blob_make_immutable (blob);
       return blob;
     }
     else
     {
       hb_blob_destroy (blob);
       return hb_blob_get_empty ();
     }
   }

   template <typename Type>
   hb_blob_t *reference_table (const hb_face_t *face, hb_tag_t tableTag = Type::tableTag)
   {
     if (!num_glyphs_set)
       set_num_glyphs (hb_face_get_glyph_count (face));
     return sanitize_blob<Type> (hb_face_reference_table (face, tableTag));
   }

   const char *start, *end;
   mutable int max_ops, max_subtables;
   private:
   bool writable;
   unsigned int edit_count;
   hb_blob_t *blob;
   unsigned int num_glyphs;
   bool  num_glyphs_set;
 };

 struct hb_sanitize_with_object_t
 {
   template <typename T>
   hb_sanitize_with_object_t (hb_sanitize_context_t *c, const T& obj) : c (c)
   { c->set_object (obj); }
   ~hb_sanitize_with_object_t ()
   { c->reset_object (); }

   private:
   hb_sanitize_context_t *c;
 };


 #endif /* HB_SANITIZE_HH */
	/*
	* Copyright © 2007,2008,2009,2010 Red Hat, Inc.
	* Copyright © 2012,2018 Google, Inc.
	*
	* This is part of HarfBuzz, a text shaping library.
	*
	* Permission is hereby granted, without written agreement and without
	* license or royalty fees, to use, copy, modify, and distribute this
	* software and its documentation for any purpose, provided that the
	* above copyright notice and the following two paragraphs appear in
	* all copies of this software.
	*
	* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
	* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
	* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
	* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
	* DAMAGE.
	*
	* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
	* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
	* FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
	* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
	* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
	*
	* Red Hat Author(s): Behdad Esfahbod
	* Google Author(s): Behdad Esfahbod
	*/

	#ifndef HB_SANITIZE_HH
	#define HB_SANITIZE_HH

	#include "hb.hh"
	#include "hb-blob.hh"
	#include "hb-dispatch.hh"


	/*
	* Sanitize
	*
	*
	* === Introduction ===
	*
	* The sanitize machinery is at the core of our zero-cost font loading. We
	* mmap() font file into memory and create a blob out of it. Font subtables
	* are returned as a readonly sub-blob of the main font blob. These table
	* blobs are then sanitized before use, to ensure invalid memory access does
	* not happen. The toplevel sanitize API use is like, eg. to load the 'head'
	* table:
	*
	* hb_blob_t *head_blob = hb_sanitize_context_t ().reference_table<OT::head> (face);
	*
	* The blob then can be converted to a head table struct with:
	*
	* const head *head_table = head_blob->as<head> ();
	*
	* What the reference_table does is, to call hb_face_reference_table() to load
	* the table blob, sanitize it and return either the sanitized blob, or empty
	* blob if sanitization failed. The blob->as() function returns the null
	* object of its template type argument if the blob is empty. Otherwise, it
	* just casts the blob contents to the desired type.
	*
	* Sanitizing a blob of data with a type T works as follows (with minor
	* simplification):
	*
	* - Cast blob content to T*, call sanitize() method of it,
	* - If sanitize succeeded, return blob.
	* - Otherwise, if blob is not writable, try making it writable,
	* or copy if cannot be made writable in-place,
	* - Call sanitize() again. Return blob if sanitize succeeded.
	* - Return empty blob otherwise.
	*
	*
	* === The sanitize() contract ===
	*
	* The sanitize() method of each object type shall return true if it's safe to
	* call other methods of the object, and %false otherwise.
	*
	* Note that what sanitize() checks for might align with what the specification
	* describes as valid table data, but does not have to be. In particular, we
	* do NOT want to be pedantic and concern ourselves with validity checks that
	* are irrelevant to our use of the table. On the contrary, we want to be
	* lenient with error handling and accept invalid data to the extent that it
	* does not impose extra burden on us.
	*
	* Based on the sanitize contract, one can see that what we check for depends
	* on how we use the data in other table methods. Ie. if other table methods
	* assume that offsets do NOT point out of the table data block, then that's
	* something sanitize() must check for (GSUB/GPOS/GDEF/etc work this way). On
	* the other hand, if other methods do such checks themselves, then sanitize()
	* does not have to bother with them (glyf/local work this way). The choice
	* depends on the table structure and sanitize() performance. For example, to
	* check glyf/loca offsets in sanitize() would cost O(num-glyphs). We try hard
	* to avoid such costs during font loading. By postponing such checks to the
	* actual glyph loading, we reduce the sanitize cost to O(1) and total runtime
	* cost to O(used-glyphs). As such, this is preferred.
	*
	* The same argument can be made re GSUB/GPOS/GDEF, but there, the table
	* structure is so complicated that by checking all offsets at sanitize() time,
	* we make the code much simpler in other methods, as offsets and referenced
	* objects do not need to be validated at each use site.
	*/

	/* This limits sanitizing time on really broken fonts. */
	#ifndef HB_SANITIZE_MAX_EDITS
	#define HB_SANITIZE_MAX_EDITS 32
	#endif
	#ifndef HB_SANITIZE_MAX_OPS_FACTOR
	#define HB_SANITIZE_MAX_OPS_FACTOR 64
	#endif
	#ifndef HB_SANITIZE_MAX_OPS_MIN
	#define HB_SANITIZE_MAX_OPS_MIN 16384
	#endif
	#ifndef HB_SANITIZE_MAX_OPS_MAX
	#define HB_SANITIZE_MAX_OPS_MAX 0x3FFFFFFF
	#endif
	#ifndef HB_SANITIZE_MAX_SUBTABLES
	#define HB_SANITIZE_MAX_SUBTABLES 0x4000
	#endif

	struct hb_sanitize_context_t :
	hb_dispatch_context_t<hb_sanitize_context_t, bool, HB_DEBUG_SANITIZE>
	{
	hb_sanitize_context_t () :
	start (nullptr), end (nullptr),
	max_ops (0), max_subtables (0),
	writable (false), edit_count (0),
	blob (nullptr),
	num_glyphs (65536),
	num_glyphs_set (false) {}

	const char *get_name () { return "SANITIZE"; }
	template <typename T, typename F>
	bool may_dispatch (const T obj HB_UNUSED, const F format)
	{ return format->sanitize (this); }
	static return_t default_return_value () { return true; }
	static return_t no_dispatch_return_value () { return false; }
	bool stop_sublookup_iteration (const return_t r) const { return !r; }

	bool visit_subtables (unsigned count)
	{
	max_subtables += count;
	return max_subtables < HB_SANITIZE_MAX_SUBTABLES;
	}

	private:
	template <typename T, typename ...Ts> auto
	_dispatch (const T &obj, hb_priority<1>, Ts&&... ds) HB_AUTO_RETURN
	( obj.sanitize (this, hb_forward<Ts> (ds)...) )
	template <typename T, typename ...Ts> auto
	_dispatch (const T &obj, hb_priority<0>, Ts&&... ds) HB_AUTO_RETURN
	( obj.dispatch (this, hb_forward<Ts> (ds)...) )
	public:
	template <typename T, typename ...Ts> auto
	dispatch (const T &obj, Ts&&... ds) HB_AUTO_RETURN
	( _dispatch (obj, hb_prioritize, hb_forward<Ts> (ds)...) )


	void init (hb_blob_t *b)
	{
	this->blob = hb_blob_reference (b);
	this->writable = false;
	}

	void set_num_glyphs (unsigned int num_glyphs_)
	{
	num_glyphs = num_glyphs_;
	num_glyphs_set = true;
	}
	unsigned int get_num_glyphs () { return num_glyphs; }

	void set_max_ops (int max_ops_) { max_ops = max_ops_; }

	template <typename T>
	void set_object (const T *obj)
	{
	reset_object ();

	if (!obj) return;

	const char obj_start = (const char ) obj;
	if (unlikely (obj_start < this->start \|\| this->end <= obj_start))
	this->start = this->end = nullptr;
	else
	{
	this->start = obj_start;
	this->end = obj_start + hb_min (size_t (this->end - obj_start), obj->get_size ());
	}
	}

	void reset_object ()
	{
	this->start = this->blob->data;
	this->end = this->start + this->blob->length;
	assert (this->start <= this->end); /* Must not overflow. */
	}

	void start_processing ()
	{
	reset_object ();
	if (unlikely (hb_unsigned_mul_overflows (this->end - this->start, HB_SANITIZE_MAX_OPS_FACTOR)))
	this->max_ops = HB_SANITIZE_MAX_OPS_MAX;
	else
	this->max_ops = hb_clamp ((unsigned) (this->end - this->start) * HB_SANITIZE_MAX_OPS_FACTOR,
	(unsigned) HB_SANITIZE_MAX_OPS_MIN,
	(unsigned) HB_SANITIZE_MAX_OPS_MAX);
	this->edit_count = 0;
	this->debug_depth = 0;

	DEBUG_MSG_LEVEL (SANITIZE, start, 0, +1,
	"start [%p..%p] (%lu bytes)",
	this->start, this->end,
	(unsigned long) (this->end - this->start));
	}

	void end_processing ()
	{
	DEBUG_MSG_LEVEL (SANITIZE, this->start, 0, -1,
	"end [%p..%p] %u edit requests",
	this->start, this->end, this->edit_count);

	hb_blob_destroy (this->blob);
	this->blob = nullptr;
	this->start = this->end = nullptr;
	}

	unsigned get_edit_count () { return edit_count; }

	bool check_range (const void *base,
	unsigned int len) const
	{
	const char p = (const char ) base;
	bool ok = !len \|\|
	(this->start <= p &&
	p <= this->end &&
	(unsigned int) (this->end - p) >= len &&
	(this->max_ops -= len) > 0);

	DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0,
	"check_range [%p..%p]"
	" (%d bytes) in [%p..%p] -> %s",
	p, p + len, len,
	this->start, this->end,
	ok ? "OK" : "OUT-OF-RANGE");

	return likely (ok);
	}

	template <typename T>
	bool check_range (const T *base,
	unsigned int a,
	unsigned int b) const
	{
	return !hb_unsigned_mul_overflows (a, b) &&
	this->check_range (base, a * b);
	}

	template <typename T>
	bool check_range (const T *base,
	unsigned int a,
	unsigned int b,
	unsigned int c) const
	{
	return !hb_unsigned_mul_overflows (a, b) &&
	this->check_range (base, a * b, c);
	}

	template <typename T>
	bool check_array (const T *base, unsigned int len) const
	{
	return this->check_range (base, len, hb_static_size (T));
	}

	template <typename T>
	bool check_array (const T *base,
	unsigned int a,
	unsigned int b) const
	{
	return this->check_range (base, a, b, hb_static_size (T));
	}

	template <typename Type>
	bool check_struct (const Type *obj) const
	{ return likely (this->check_range (obj, obj->min_size)); }

	bool may_edit (const void *base, unsigned int len)
	{
	if (this->edit_count >= HB_SANITIZE_MAX_EDITS)
	return false;

	const char p = (const char ) base;
	this->edit_count++;

	DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0,
	"may_edit(%u) [%p..%p] (%d bytes) in [%p..%p] -> %s",
	this->edit_count,
	p, p + len, len,
	this->start, this->end,
	this->writable ? "GRANTED" : "DENIED");

	return this->writable;
	}

	template <typename Type, typename ValueType>
	bool try_set (const Type *obj, const ValueType &v)
	{
	if (this->may_edit (obj, hb_static_size (Type)))
	{
	* const_cast<Type *> (obj) = v;
	return true;
	}
	return false;
	}

	template <typename Type>
	hb_blob_t sanitize_blob (hb_blob_t blob)
	{
	bool sane;

	init (blob);

	retry:
	DEBUG_MSG_FUNC (SANITIZE, start, "start");

	start_processing ();

	if (unlikely (!start))
	{
	end_processing ();
	return blob;
	}

	Type t = reinterpret_cast<Type > (const_cast<char *> (start));

	sane = t->sanitize (this);
	if (sane)
	{
	if (edit_count)
	{
	DEBUG_MSG_FUNC (SANITIZE, start, "passed first round with %d edits; going for second round", edit_count);

	/* sanitize again to ensure no toe-stepping */
	edit_count = 0;
	sane = t->sanitize (this);
	if (edit_count) {
	DEBUG_MSG_FUNC (SANITIZE, start, "requested %d edits in second round; FAILLING", edit_count);
	sane = false;
	}
	}
	}
	else
	{
	if (edit_count && !writable) {
	start = hb_blob_get_data_writable (blob, nullptr);
	end = start + blob->length;

	if (start)
	{
	writable = true;
	/* ok, we made it writable by relocating. try again */
	DEBUG_MSG_FUNC (SANITIZE, start, "retry");
	goto retry;
	}
	}
	}

	end_processing ();

	DEBUG_MSG_FUNC (SANITIZE, start, sane ? "PASSED" : "FAILED");
	if (sane)
	{
	hb_blob_make_immutable (blob);
	return blob;
	}
	else
	{
	hb_blob_destroy (blob);
	return hb_blob_get_empty ();
	}
	}

	template <typename Type>
	hb_blob_t reference_table (const hb_face_t face, hb_tag_t tableTag = Type::tableTag)
	{
	if (!num_glyphs_set)
	set_num_glyphs (hb_face_get_glyph_count (face));
	return sanitize_blob<Type> (hb_face_reference_table (face, tableTag));
	}

	const char start, end;
	mutable int max_ops, max_subtables;
	private:
	bool writable;
	unsigned int edit_count;
	hb_blob_t *blob;
	unsigned int num_glyphs;
	bool num_glyphs_set;
	};

	struct hb_sanitize_with_object_t
	{
	template <typename T>
	hb_sanitize_with_object_t (hb_sanitize_context_t *c, const T& obj) : c (c)
	{ c->set_object (obj); }
	~hb_sanitize_with_object_t ()
	{ c->reset_object (); }

	private:
	hb_sanitize_context_t *c;
	};


	#endif /* HB_SANITIZE_HH */