xref: /btstack/src/ble/att_db.c (revision c9921182ab4b1f83e3e5c671446dca5ffdf45b90)
1 /*
2  * Copyright (C) 2014 BlueKitchen GmbH
3  *
4  * Redistribution and use in source and binary forms, with or without
5  * modification, are permitted provided that the following conditions
6  * are met:
7  *
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  * 3. Neither the name of the copyright holders nor the names of
14  *    contributors may be used to endorse or promote products derived
15  *    from this software without specific prior written permission.
16  * 4. Any redistribution, use, or modification is done solely for
17  *    personal benefit and not for any commercial purpose or for
18  *    monetary gain.
19  *
20  * THIS SOFTWARE IS PROVIDED BY BLUEKITCHEN GMBH AND CONTRIBUTORS
21  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
22  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
23  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL MATTHIAS
24  * RINGWALD OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
25  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
26  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
27  * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
28  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
29  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
30  * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  *
33  * Please inquire about commercial licensing options at
34  * [email protected]
35  *
36  */
37 
38 #define BTSTACK_FILE__ "att_db.c"
39 
40 #include <string.h>
41 
42 #include "ble/att_db.h"
43 #include "ble/core.h"
44 #include "bluetooth.h"
45 #include "btstack_debug.h"
46 #include "btstack_util.h"
47 
48 // check for ENABLE_ATT_DELAYED_READ_RESPONSE -> ENABLE_ATT_DELAYED_RESPONSE,
49 #ifdef ENABLE_ATT_DELAYED_READ_RESPONSE
50     #error "ENABLE_ATT_DELAYED_READ_RESPONSE was replaced by ENABLE_ATT_DELAYED_RESPONSE. Please update btstack_config.h"
51 #endif
52 
53 typedef enum {
54     ATT_READ,
55     ATT_WRITE,
56 } att_operation_t;
57 
58 
59 static int is_Bluetooth_Base_UUID(uint8_t const *uuid){
60     // Bluetooth Base UUID 00000000-0000-1000-8000-00805F9B34FB in little endian
61     static const uint8_t bluetooth_base_uuid[] = { 0xfb, 0x34, 0x9b, 0x5f, 0x80, 0x00, 0x00, 0x80, 0x00, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
62 
63     if (memcmp(&uuid[0],  &bluetooth_base_uuid[0], 12) != 0) return false;
64     if (memcmp(&uuid[14], &bluetooth_base_uuid[14], 2) != 0) return false;
65     return true;
66 
67 }
68 
69 static uint16_t uuid16_from_uuid(uint16_t uuid_len, uint8_t * uuid){
70     if (uuid_len == 2u) return little_endian_read_16(uuid, 0u);
71     if (!is_Bluetooth_Base_UUID(uuid)) return 0;
72     return little_endian_read_16(uuid, 12);
73 }
74 
75 // ATT Database
76 
77 // new java-style iterator
78 typedef struct att_iterator {
79     // private
80     uint8_t const * att_ptr;
81     // public
82     uint16_t size;
83     uint16_t flags;
84     uint16_t handle;
85     uint8_t  const * uuid;
86     uint16_t value_len;
87     uint8_t  const * value;
88 } att_iterator_t;
89 
90 static void att_persistent_ccc_cache(att_iterator_t * it);
91 
92 static uint8_t const * att_db = NULL;
93 static att_read_callback_t  att_read_callback  = NULL;
94 static att_write_callback_t att_write_callback = NULL;
95 static int      att_prepare_write_error_code   = 0;
96 static uint16_t att_prepare_write_error_handle = 0x0000;
97 
98 // single cache for att_is_persistent_ccc - stores flags before write callback
99 static uint16_t att_persistent_ccc_handle;
100 static uint16_t att_persistent_ccc_uuid16;
101 
102 static void att_iterator_init(att_iterator_t *it){
103     it->att_ptr = att_db;
104 }
105 
106 static bool att_iterator_has_next(att_iterator_t *it){
107     return it->att_ptr != NULL;
108 }
109 
110 static void att_iterator_fetch_next(att_iterator_t *it){
111     it->size   = little_endian_read_16(it->att_ptr, 0);
112     if (it->size == 0u){
113         it->flags = 0;
114         it->handle = 0;
115         it->uuid = NULL;
116         it->value_len = 0;
117         it->value = NULL;
118         it->att_ptr = NULL;
119         return;
120     }
121     it->flags  = little_endian_read_16(it->att_ptr, 2);
122     it->handle = little_endian_read_16(it->att_ptr, 4);
123     it->uuid   = &it->att_ptr[6];
124     // handle 128 bit UUIDs
125     if ((it->flags & ATT_PROPERTY_UUID128) != 0u){
126         it->value_len = it->size - 22u;
127         it->value  = &it->att_ptr[22];
128     } else {
129         it->value_len = it->size - 8u;
130         it->value  = &it->att_ptr[8];
131     }
132     // advance AFTER setting values
133     it->att_ptr += it->size;
134 }
135 
136 static int att_iterator_match_uuid16(att_iterator_t *it, uint16_t uuid){
137     if (it->handle == 0u) return 0u;
138     if (it->flags & ATT_PROPERTY_UUID128){
139         if (!is_Bluetooth_Base_UUID(it->uuid)) return 0;
140         return little_endian_read_16(it->uuid, 12) == uuid;
141     }
142     return little_endian_read_16(it->uuid, 0)  == uuid;
143 }
144 
145 static int att_iterator_match_uuid(att_iterator_t *it, uint8_t *uuid, uint16_t uuid_len){
146     if (it->handle == 0u) return 0u;
147     // input: UUID16
148     if (uuid_len == 2u) {
149         return att_iterator_match_uuid16(it, little_endian_read_16(uuid, 0));
150     }
151     // input and db: UUID128
152     if ((it->flags & ATT_PROPERTY_UUID128) != 0u){
153         return memcmp(it->uuid, uuid, 16) == 0;
154     }
155     // input: UUID128, db: UUID16
156     if (!is_Bluetooth_Base_UUID(uuid)) return 0;
157     return little_endian_read_16(uuid, 12) == little_endian_read_16(it->uuid, 0);
158 }
159 
160 
161 static int att_find_handle(att_iterator_t *it, uint16_t handle){
162     if (handle == 0u) return 0u;
163     att_iterator_init(it);
164     while (att_iterator_has_next(it)){
165         att_iterator_fetch_next(it);
166         if (it->handle != handle) continue;
167         return 1;
168     }
169     return 0;
170 }
171 
172 // experimental client API
173 uint16_t att_uuid_for_handle(uint16_t attribute_handle){
174     att_iterator_t it;
175     int ok = att_find_handle(&it, attribute_handle);
176     if (!ok) return 0;
177     if ((it.flags & ATT_PROPERTY_UUID128) != 0u) return 0u;
178     return little_endian_read_16(it.uuid, 0);
179 }
180 // end of client API
181 
182 static void att_update_value_len(att_iterator_t *it, hci_con_handle_t con_handle){
183     if ((it->flags & ATT_PROPERTY_DYNAMIC) == 0u) return;
184     it->value_len = (*att_read_callback)(con_handle, it->handle, 0, NULL, 0);
185     return;
186 }
187 
188 // copy attribute value from offset into buffer with given size
189 static int att_copy_value(att_iterator_t *it, uint16_t offset, uint8_t * buffer, uint16_t buffer_size, hci_con_handle_t con_handle){
190 
191     // DYNAMIC
192     if ((it->flags & ATT_PROPERTY_DYNAMIC) != 0u){
193         return (*att_read_callback)(con_handle, it->handle, offset, buffer, buffer_size);
194     }
195 
196     // STATIC
197     uint16_t bytes_to_copy = it->value_len - offset;
198     if (bytes_to_copy > buffer_size){
199         bytes_to_copy = buffer_size;
200     }
201     (void)memcpy(buffer, it->value, bytes_to_copy);
202     return bytes_to_copy;
203 }
204 
205 void att_set_db(uint8_t const * db){
206     // validate db version
207     if (db == NULL) return;
208     if (*db++ != ATT_DB_VERSION){
209         log_error("ATT DB version differs, please regenerate .h from .gatt file or update att_db_util.c");
210         return;
211     }
212     att_db = db;
213 }
214 
215 void att_set_read_callback(att_read_callback_t callback){
216     att_read_callback = callback;
217 }
218 
219 void att_set_write_callback(att_write_callback_t callback){
220     att_write_callback = callback;
221 }
222 
223 void att_dump_attributes(void){
224     att_iterator_t it;
225     att_iterator_init(&it);
226     uint8_t uuid128[16];
227     while (att_iterator_has_next(&it)){
228         att_iterator_fetch_next(&it);
229         if (it.handle == 0u) {
230             log_info("Handle: END");
231             return;
232         }
233         log_info("Handle: 0x%04x, flags: 0x%04x, uuid: ", it.handle, it.flags);
234         if ((it.flags & ATT_PROPERTY_UUID128) != 0u){
235             reverse_128(it.uuid, uuid128);
236             log_info("%s", uuid128_to_str(uuid128));
237         } else {
238             log_info("%04x", little_endian_read_16(it.uuid, 0));
239         }
240         log_info(", value_len: %u, value: ", it.value_len);
241         log_info_hexdump(it.value, it.value_len);
242     }
243 }
244 
245 static void att_prepare_write_reset(void){
246     att_prepare_write_error_code = 0;
247     att_prepare_write_error_handle = 0x0000;
248 }
249 
250 static void att_prepare_write_update_errors(uint8_t error_code, uint16_t handle){
251     // first ATT_ERROR_INVALID_ATTRIBUTE_VALUE_LENGTH has highest priority
252     if ((error_code == ATT_ERROR_INVALID_ATTRIBUTE_VALUE_LENGTH) && (error_code != att_prepare_write_error_code)){
253         att_prepare_write_error_code = error_code;
254         att_prepare_write_error_handle = handle;
255         return;
256     }
257     // first ATT_ERROR_INVALID_OFFSET is next
258     if ((error_code == ATT_ERROR_INVALID_OFFSET) && (att_prepare_write_error_code == 0)){
259         att_prepare_write_error_code = error_code;
260         att_prepare_write_error_handle = handle;
261         return;
262     }
263 }
264 
265 static uint16_t setup_error(uint8_t * response_buffer, uint16_t request, uint16_t handle, uint8_t error_code){
266     response_buffer[0] = ATT_ERROR_RESPONSE;
267     response_buffer[1] = request;
268     little_endian_store_16(response_buffer, 2, handle);
269     response_buffer[4] = error_code;
270     return 5;
271 }
272 
273 static inline uint16_t setup_error_read_not_permitted(uint8_t * response_buffer, uint16_t request, uint16_t start_handle){
274     return setup_error(response_buffer, request, start_handle, ATT_ERROR_READ_NOT_PERMITTED);
275 }
276 
277 static inline uint16_t setup_error_write_not_permitted(uint8_t * response_buffer, uint16_t request, uint16_t start_handle){
278     return setup_error(response_buffer, request, start_handle, ATT_ERROR_WRITE_NOT_PERMITTED);
279 }
280 
281 static inline uint16_t setup_error_atribute_not_found(uint8_t * response_buffer, uint16_t request, uint16_t start_handle){
282     return setup_error(response_buffer, request, start_handle, ATT_ERROR_ATTRIBUTE_NOT_FOUND);
283 }
284 
285 static inline uint16_t setup_error_invalid_handle(uint8_t * response_buffer, uint16_t request, uint16_t handle){
286     return setup_error(response_buffer, request, handle, ATT_ERROR_INVALID_HANDLE);
287 }
288 
289 static inline uint16_t setup_error_invalid_offset(uint8_t * response_buffer, uint16_t request, uint16_t handle){
290     return setup_error(response_buffer, request, handle, ATT_ERROR_INVALID_OFFSET);
291 }
292 
293 static inline uint16_t setup_error_invalid_pdu(uint8_t *response_buffer, uint16_t request) {
294     return setup_error(response_buffer, request, 0, ATT_ERROR_INVALID_PDU);
295 }
296 
297 static uint8_t att_validate_security(att_connection_t * att_connection, att_operation_t operation, att_iterator_t * it){
298     int required_security_level = 0;
299     bool requires_secure_connection = false;
300     switch (operation){
301         case ATT_READ:
302             if ((it->flags & ATT_PROPERTY_READ_PERMISSION_BIT_0) != 0u){
303                 required_security_level |= 1;
304             }
305             if ((it->flags & ATT_PROPERTY_READ_PERMISSION_BIT_1) != 0u){
306                 required_security_level |= 2;
307             }
308             if ((it->flags & ATT_PROPERTY_READ_PERMISSION_SC) != 0u){
309                 requires_secure_connection = true;
310             }
311             break;
312         case ATT_WRITE:
313             if ((it->flags & ATT_PROPERTY_WRITE_PERMISSION_BIT_0) != 0u){
314                 required_security_level |= 1;
315             }
316             if ((it->flags & ATT_PROPERTY_WRITE_PERMISSION_BIT_1) != 0u){
317                 required_security_level |= 2;
318             }
319             if ((it->flags & ATT_PROPERTY_WRITE_PERMISSION_SC) != 0u){
320                 requires_secure_connection = true;
321             }
322             break;
323     }
324 
325     uint8_t required_encryption_size = it->flags >> 12;
326     if (required_encryption_size != 0) required_encryption_size++;   // store -1 to fit into 4 bit
327 
328     log_debug("att_validate_security. flags 0x%04x (=> security level %u, key size %u) authorized %u, authenticated %u, encryption_key_size %u, secure connection %u",
329         it->flags, required_security_level, required_encryption_size, att_connection->authorized, att_connection->authenticated, att_connection->encryption_key_size, att_connection->secure_connection);
330 
331     bool sc_missing = requires_secure_connection && (att_connection->secure_connection == 0u);
332     switch (required_security_level){
333         case ATT_SECURITY_AUTHORIZED:
334             if ((att_connection->authorized == 0u) || sc_missing){
335                 return ATT_ERROR_INSUFFICIENT_AUTHORIZATION;
336             }
337             /* fall through */
338         case ATT_SECURITY_AUTHENTICATED:
339             if ((att_connection->authenticated == 0u) || sc_missing){
340                 return ATT_ERROR_INSUFFICIENT_AUTHENTICATION;
341             }
342             /* fall through */
343         case ATT_SECURITY_ENCRYPTED:
344             if ((required_encryption_size > 0u) && ((att_connection->encryption_key_size == 0u) || sc_missing)){
345                 return ATT_ERROR_INSUFFICIENT_ENCRYPTION;
346             }
347             if (required_encryption_size > att_connection->encryption_key_size){
348                 return ATT_ERROR_INSUFFICIENT_ENCRYPTION_KEY_SIZE;
349             }
350             break;
351         default:
352             break;
353     }
354     return ATT_ERROR_SUCCESS;
355 }
356 
357 //
358 // MARK: ATT_EXCHANGE_MTU_REQUEST
359 //
360 static uint16_t handle_exchange_mtu_request(att_connection_t * att_connection, uint8_t * request_buffer,  uint16_t request_len,
361                                          uint8_t * response_buffer){
362 
363     if (request_len != 3u) return setup_error_invalid_pdu(response_buffer, ATT_EXCHANGE_MTU_REQUEST);
364 
365     uint16_t client_rx_mtu = little_endian_read_16(request_buffer, 1);
366 
367     // find min(local max mtu, remote mtu) >= ATT_DEFAULT_MTU and use as mtu for this connection
368     uint16_t min_mtu = btstack_min(client_rx_mtu, att_connection->max_mtu);
369     uint16_t new_mtu = btstack_max(ATT_DEFAULT_MTU, min_mtu);
370     att_connection->mtu = new_mtu;
371 
372     response_buffer[0] = ATT_EXCHANGE_MTU_RESPONSE;
373     little_endian_store_16(response_buffer, 1, att_connection->mtu);
374     return 3;
375 }
376 
377 
378 //
379 // MARK: ATT_FIND_INFORMATION_REQUEST
380 //
381 // TODO: handle other types then GATT_PRIMARY_SERVICE_UUID and GATT_SECONDARY_SERVICE_UUID
382 //
383 static uint16_t handle_find_information_request2(att_connection_t * att_connection, uint8_t * response_buffer, uint16_t response_buffer_size,
384                                            uint16_t start_handle, uint16_t end_handle){
385 
386     UNUSED(att_connection);
387 
388     log_info("ATT_FIND_INFORMATION_REQUEST: from %04X to %04X", start_handle, end_handle);
389     uint8_t request_type = ATT_FIND_INFORMATION_REQUEST;
390 
391     if ((start_handle > end_handle) || (start_handle == 0u)){
392         return setup_error_invalid_handle(response_buffer, request_type, start_handle);
393     }
394 
395     uint16_t offset   = 1;
396     uint16_t uuid_len = 0;
397 
398     att_iterator_t it;
399     att_iterator_init(&it);
400     while (att_iterator_has_next(&it)){
401         att_iterator_fetch_next(&it);
402         if (!it.handle) break;
403         if (it.handle > end_handle) break;
404         if (it.handle < start_handle) continue;
405 
406         // log_info("Handle 0x%04x", it.handle);
407 
408         uint16_t this_uuid_len = (it.flags & ATT_PROPERTY_UUID128) ? 16 : 2;
409 
410         // check if value has same len as last one if not first result
411         if (offset > 1u){
412             if (this_uuid_len != uuid_len) {
413                 break;
414             }
415         }
416 
417         // first
418         if (offset == 1u) {
419             uuid_len = this_uuid_len;
420             // set format field
421             response_buffer[offset] = (it.flags & ATT_PROPERTY_UUID128) ? 0x02 : 0x01;
422             offset++;
423         }
424 
425         // space?
426         if ((offset + 2u + uuid_len) > response_buffer_size) break;
427 
428         // store
429         little_endian_store_16(response_buffer, offset, it.handle);
430         offset += 2u;
431 
432         (void)memcpy(response_buffer + offset, it.uuid, uuid_len);
433         offset += uuid_len;
434     }
435 
436     if (offset == 1u){
437         return setup_error_atribute_not_found(response_buffer, request_type, start_handle);
438     }
439 
440     response_buffer[0] = ATT_FIND_INFORMATION_REPLY;
441     return offset;
442 }
443 
444 static uint16_t handle_find_information_request(att_connection_t * att_connection, uint8_t * request_buffer,  uint16_t request_len,
445                                          uint8_t * response_buffer, uint16_t response_buffer_size){
446 
447     if (request_len != 5u) return setup_error_invalid_pdu(response_buffer, ATT_FIND_INFORMATION_REQUEST);
448 
449     uint16_t start_handle = little_endian_read_16(request_buffer, 1);
450     uint16_t end_handle = little_endian_read_16(request_buffer, 3);
451     return handle_find_information_request2(att_connection, response_buffer, response_buffer_size, start_handle, end_handle);
452 }
453 
454 //
455 // MARK: ATT_FIND_BY_TYPE_VALUE
456 //
457 // "Only attributes with attribute handles between and including the Starting Handle parameter
458 // and the Ending Handle parameter that match the requested attri- bute type and the attribute
459 // value that have sufficient permissions to allow reading will be returned" -> (1)
460 //
461 // TODO: handle other types then GATT_PRIMARY_SERVICE_UUID and GATT_SECONDARY_SERVICE_UUID
462 //
463 // NOTE: doesn't handle DYNAMIC values
464 // NOTE: only supports 16 bit UUIDs
465 //
466 static uint16_t handle_find_by_type_value_request(att_connection_t * att_connection, uint8_t * request_buffer,  uint16_t request_len,
467                                            uint8_t * response_buffer, uint16_t response_buffer_size){
468     UNUSED(att_connection);
469 
470     if (request_len < 7u) return setup_error_invalid_pdu(response_buffer, ATT_FIND_BY_TYPE_VALUE_REQUEST);
471 
472     // parse request
473     uint16_t start_handle = little_endian_read_16(request_buffer, 1);
474     uint16_t end_handle = little_endian_read_16(request_buffer, 3);
475     uint16_t attribute_type = little_endian_read_16(request_buffer, 5);
476     const uint8_t *attribute_value = &request_buffer[7];
477     uint16_t attribute_len = request_len - 7u;
478 
479     log_info("ATT_FIND_BY_TYPE_VALUE_REQUEST: from %04X to %04X, type %04X, value: ", start_handle, end_handle, attribute_type);
480     log_info_hexdump(attribute_value, attribute_len);
481     uint8_t request_type = ATT_FIND_BY_TYPE_VALUE_REQUEST;
482 
483     if ((start_handle > end_handle) || (start_handle == 0u)){
484         return setup_error_invalid_handle(response_buffer, request_type, start_handle);
485     }
486 
487     uint16_t offset      = 1;
488     uint16_t in_group    = 0;
489     uint16_t prev_handle = 0;
490 
491     att_iterator_t it;
492     att_iterator_init(&it);
493     while (att_iterator_has_next(&it)){
494         att_iterator_fetch_next(&it);
495 
496         if (it.handle && (it.handle < start_handle)) continue;
497         if (it.handle > end_handle) break;  // (1)
498 
499         // close current tag, if within a group and a new service definition starts or we reach end of att db
500         if (in_group &&
501             ((it.handle == 0u) || att_iterator_match_uuid16(&it, GATT_PRIMARY_SERVICE_UUID) || att_iterator_match_uuid16(&it, GATT_SECONDARY_SERVICE_UUID))){
502 
503             log_info("End of group, handle 0x%04x", prev_handle);
504             little_endian_store_16(response_buffer, offset, prev_handle);
505             offset += 2u;
506             in_group = 0;
507 
508             // check if space for another handle pair available
509             if ((offset + 4u) > response_buffer_size){
510                 break;
511             }
512         }
513 
514         // keep track of previous handle
515         prev_handle = it.handle;
516 
517         // does current attribute match
518         if (it.handle && att_iterator_match_uuid16(&it, attribute_type) && (attribute_len == it.value_len) && (memcmp(attribute_value, it.value, it.value_len) == 0)){
519             log_info("Begin of group, handle 0x%04x", it.handle);
520             little_endian_store_16(response_buffer, offset, it.handle);
521             offset += 2u;
522             in_group = 1;
523         }
524     }
525 
526     if (offset == 1u){
527         return setup_error_atribute_not_found(response_buffer, request_type, start_handle);
528     }
529 
530     response_buffer[0] = ATT_FIND_BY_TYPE_VALUE_RESPONSE;
531     return offset;
532 }
533 
534 //
535 // MARK: ATT_READ_BY_TYPE_REQUEST
536 //
537 static uint16_t handle_read_by_type_request2(att_connection_t * att_connection, uint8_t * response_buffer, uint16_t response_buffer_size,
538                                       uint16_t start_handle, uint16_t end_handle,
539                                       uint16_t attribute_type_len, uint8_t * attribute_type){
540 
541     log_info("ATT_READ_BY_TYPE_REQUEST: from %04X to %04X, type: ", start_handle, end_handle);
542     log_info_hexdump(attribute_type, attribute_type_len);
543     uint8_t request_type = ATT_READ_BY_TYPE_REQUEST;
544 
545     if ((start_handle > end_handle) || (start_handle == 0u)){
546         return setup_error_invalid_handle(response_buffer, request_type, start_handle);
547     }
548 
549     uint16_t offset   = 1;
550     uint16_t pair_len = 0;
551 
552     att_iterator_t it;
553     att_iterator_init(&it);
554     uint8_t error_code = 0;
555     uint16_t first_matching_but_unreadable_handle = 0;
556 
557     while (att_iterator_has_next(&it)){
558         att_iterator_fetch_next(&it);
559 
560         if ((it.handle == 0u ) || (it.handle > end_handle)) break;
561 
562         if (it.handle < start_handle) continue;
563 
564         // does current attribute match
565         if (!att_iterator_match_uuid(&it, attribute_type, attribute_type_len)) continue;
566 
567         // skip handles that cannot be read but remember that there has been at least one
568         if ((it.flags & ATT_PROPERTY_READ) == 0u) {
569             if (first_matching_but_unreadable_handle == 0u) {
570                 first_matching_but_unreadable_handle = it.handle;
571             }
572             continue;
573         }
574 
575         // check security requirements
576         error_code = att_validate_security(att_connection, ATT_READ, &it);
577         if (error_code != 0u) break;
578 
579         att_update_value_len(&it, att_connection->con_handle);
580 
581 #ifdef ENABLE_ATT_DELAYED_RESPONSE
582         if (it.value_len == ATT_READ_RESPONSE_PENDING){
583             return ATT_READ_RESPONSE_PENDING;
584         }
585 #endif
586 
587         // check if value has same len as last one
588         uint16_t this_pair_len = 2u + it.value_len;
589         if ((offset > 1u) && (pair_len != this_pair_len)) {
590             break;
591         }
592 
593         // first
594         if (offset == 1u) {
595             pair_len = this_pair_len;
596             response_buffer[offset] = pair_len;
597             offset++;
598         }
599 
600         // space?
601         if ((offset + pair_len) > response_buffer_size) {
602             if (offset > 2u) break;
603             it.value_len = response_buffer_size - 4u;
604             response_buffer[1u] = 2u + it.value_len;
605         }
606 
607         // store
608         little_endian_store_16(response_buffer, offset, it.handle);
609         offset += 2u;
610         uint16_t bytes_copied = att_copy_value(&it, 0, response_buffer + offset, it.value_len, att_connection->con_handle);
611         offset += bytes_copied;
612     }
613 
614     // at least one attribute could be read
615     if (offset > 1u){
616         response_buffer[0] = ATT_READ_BY_TYPE_RESPONSE;
617         return offset;
618     }
619 
620     // first attribute had an error
621     if (error_code != 0u){
622         return setup_error(response_buffer, request_type, start_handle, error_code);
623     }
624 
625     // no other errors, but all found attributes had been non-readable
626     if (first_matching_but_unreadable_handle != 0u){
627         return setup_error_read_not_permitted(response_buffer, request_type, first_matching_but_unreadable_handle);
628     }
629 
630     // attribute not found
631     return setup_error_atribute_not_found(response_buffer, request_type, start_handle);
632 }
633 
634 static uint16_t handle_read_by_type_request(att_connection_t * att_connection, uint8_t * request_buffer,  uint16_t request_len,
635                                      uint8_t * response_buffer, uint16_t response_buffer_size){
636 
637     uint16_t attribute_type_len;
638     switch (request_len){
639         case 7:
640             attribute_type_len = 2;
641             break;
642         case 21:
643             attribute_type_len = 16;
644             break;
645         default:
646             return setup_error_invalid_pdu(response_buffer, ATT_READ_BY_TYPE_REQUEST);
647     }
648 
649     uint16_t start_handle = little_endian_read_16(request_buffer, 1);
650     uint16_t end_handle = little_endian_read_16(request_buffer, 3);
651     return handle_read_by_type_request2(att_connection, response_buffer, response_buffer_size, start_handle, end_handle, attribute_type_len, &request_buffer[5]);
652 }
653 
654 //
655 // MARK: ATT_READ_BY_TYPE_REQUEST
656 //
657 static uint16_t handle_read_request2(att_connection_t * att_connection, uint8_t * response_buffer, uint16_t response_buffer_size, uint16_t handle){
658 
659     log_info("ATT_READ_REQUEST: handle %04x", handle);
660     uint8_t request_type = ATT_READ_REQUEST;
661 
662     att_iterator_t it;
663     int ok = att_find_handle(&it, handle);
664     if (!ok){
665         return setup_error_invalid_handle(response_buffer, request_type, handle);
666     }
667 
668     // check if handle can be read
669     if ((it.flags & ATT_PROPERTY_READ) == 0u) {
670         return setup_error_read_not_permitted(response_buffer, request_type, handle);
671     }
672 
673     // check security requirements
674     uint8_t error_code = att_validate_security(att_connection, ATT_READ, &it);
675     if (error_code) {
676         return setup_error(response_buffer, request_type, handle, error_code);
677     }
678 
679     att_update_value_len(&it, att_connection->con_handle);
680 
681 #ifdef ENABLE_ATT_DELAYED_RESPONSE
682     if (it.value_len == ATT_READ_RESPONSE_PENDING) return ATT_READ_RESPONSE_PENDING;
683 #endif
684 
685     // store
686     uint16_t offset   = 1;
687     uint16_t bytes_copied = att_copy_value(&it, 0, response_buffer + offset, response_buffer_size - offset, att_connection->con_handle);
688     offset += bytes_copied;
689 
690     response_buffer[0] = ATT_READ_RESPONSE;
691     return offset;
692 }
693 
694 static uint16_t handle_read_request(att_connection_t * att_connection, uint8_t * request_buffer,  uint16_t request_len,
695                              uint8_t * response_buffer, uint16_t response_buffer_size){
696 
697     if (request_len != 3u) return setup_error_invalid_pdu(response_buffer, ATT_READ_REQUEST);
698 
699     uint16_t handle = little_endian_read_16(request_buffer, 1);
700     return handle_read_request2(att_connection, response_buffer, response_buffer_size, handle);
701 }
702 
703 //s
704 // MARK: ATT_READ_BLOB_REQUEST 0x0c
705 //
706 static uint16_t handle_read_blob_request2(att_connection_t * att_connection, uint8_t * response_buffer, uint16_t response_buffer_size, uint16_t handle, uint16_t value_offset){
707     log_info("ATT_READ_BLOB_REQUEST: handle %04x, offset %u", handle, value_offset);
708     uint8_t request_type = ATT_READ_BLOB_REQUEST;
709 
710     att_iterator_t it;
711     int ok = att_find_handle(&it, handle);
712     if (!ok){
713         return setup_error_invalid_handle(response_buffer, request_type, handle);
714     }
715 
716     // check if handle can be read
717     if ((it.flags & ATT_PROPERTY_READ) == 0u) {
718         return setup_error_read_not_permitted(response_buffer, request_type, handle);
719     }
720 
721     // check security requirements
722     uint8_t error_code = att_validate_security(att_connection, ATT_READ, &it);
723     if (error_code) {
724         return setup_error(response_buffer, request_type, handle, error_code);
725     }
726 
727     att_update_value_len(&it, att_connection->con_handle);
728 
729 #ifdef ENABLE_ATT_DELAYED_RESPONSE
730     if (it.value_len == ATT_READ_RESPONSE_PENDING) return ATT_READ_RESPONSE_PENDING;
731 #endif
732 
733     if (value_offset > it.value_len){
734         return setup_error_invalid_offset(response_buffer, request_type, handle);
735     }
736 
737     // prepare response
738     response_buffer[0] = ATT_READ_BLOB_RESPONSE;
739     uint16_t offset   = 1;
740 
741     // fetch more data if available
742     if (value_offset < it.value_len){
743         uint16_t bytes_copied = att_copy_value(&it, value_offset, &response_buffer[offset], response_buffer_size - offset, att_connection->con_handle);
744         offset += bytes_copied;
745     }
746     return offset;
747 }
748 
749 static uint16_t handle_read_blob_request(att_connection_t * att_connection, uint8_t * request_buffer,  uint16_t request_len,
750                                   uint8_t * response_buffer, uint16_t response_buffer_size){
751 
752     if (request_len != 5u) return setup_error_invalid_pdu(response_buffer, ATT_READ_BLOB_REQUEST);
753 
754     uint16_t handle = little_endian_read_16(request_buffer, 1);
755     uint16_t value_offset = little_endian_read_16(request_buffer, 3);
756     return handle_read_blob_request2(att_connection, response_buffer, response_buffer_size, handle, value_offset);
757 }
758 
759 //
760 // MARK: ATT_READ_MULTIPLE_REQUEST 0x0e
761 //
762 static uint16_t handle_read_multiple_request2(att_connection_t * att_connection, uint8_t * response_buffer, uint16_t response_buffer_size, uint16_t num_handles, uint8_t * handles){
763     log_info("ATT_READ_MULTIPLE_REQUEST: num handles %u", num_handles);
764     uint8_t request_type = ATT_READ_MULTIPLE_REQUEST;
765 
766     // TODO: figure out which error to respond with
767     // if (num_handles < 2){
768     //     return setup_error(response_buffer, ATT_READ_MULTIPLE_REQUEST, handle, ???);
769     // }
770 
771     uint16_t offset   = 1;
772 
773     int i;
774     uint8_t error_code = 0;
775     uint16_t handle = 0;
776 
777 #ifdef ENABLE_ATT_DELAYED_RESPONSE
778     bool read_request_pending = false;
779 #endif
780 
781     for (i=0;i<num_handles;i++){
782         handle = little_endian_read_16(handles, i << 1);
783 
784         if (handle == 0u){
785             return setup_error_invalid_handle(response_buffer, request_type, handle);
786         }
787 
788         att_iterator_t it;
789 
790         int ok = att_find_handle(&it, handle);
791         if (!ok){
792             return setup_error_invalid_handle(response_buffer, request_type, handle);
793         }
794 
795         // check if handle can be read
796         if ((it.flags & ATT_PROPERTY_READ) == 0u) {
797             error_code = ATT_ERROR_READ_NOT_PERMITTED;
798             break;
799         }
800 
801         // check security requirements
802         error_code = att_validate_security(att_connection, ATT_READ, &it);
803         if (error_code) break;
804 
805         att_update_value_len(&it, att_connection->con_handle);
806 
807 #ifdef ENABLE_ATT_DELAYED_RESPONSE
808         if (it.value_len == ATT_READ_RESPONSE_PENDING) {
809             read_request_pending = true;
810         }
811         if (read_request_pending) continue;
812 #endif
813 
814         // store
815         uint16_t bytes_copied = att_copy_value(&it, 0, response_buffer + offset, response_buffer_size - offset, att_connection->con_handle);
816         offset += bytes_copied;
817     }
818 
819     if (error_code){
820         return setup_error(response_buffer, request_type, handle, error_code);
821     }
822 
823     response_buffer[0] = ATT_READ_MULTIPLE_RESPONSE;
824     return offset;
825 }
826 static uint16_t handle_read_multiple_request(att_connection_t * att_connection, uint8_t * request_buffer,  uint16_t request_len,
827                                       uint8_t * response_buffer, uint16_t response_buffer_size){
828 
829     // 1 byte opcode + two or more attribute handles (2 bytes each)
830     if ( (request_len < 5u) || ((request_len & 1u) == 0u) ) return setup_error_invalid_pdu(response_buffer,
831                                                                                         ATT_READ_MULTIPLE_REQUEST);
832 
833     int num_handles = (request_len - 1u) >> 1u;
834     return handle_read_multiple_request2(att_connection, response_buffer, response_buffer_size, num_handles, &request_buffer[1]);
835 }
836 
837 //
838 // MARK: ATT_READ_BY_GROUP_TYPE_REQUEST 0x10
839 //
840 // Only handles GATT_PRIMARY_SERVICE_UUID and GATT_SECONDARY_SERVICE_UUID
841 // Core v4.0, vol 3, part g, 2.5.3
842 // "The «Primary Service» and «Secondary Service» grouping types may be used in the Read By Group Type Request.
843 //  The «Characteristic» grouping type shall not be used in the ATT Read By Group Type Request."
844 //
845 // NOTE: doesn't handle DYNAMIC values
846 //
847 // NOTE: we don't check for security as PRIMARY and SECONDAY SERVICE definition shouldn't be protected
848 // Core 4.0, vol 3, part g, 8.1
849 // "The list of services and characteristics that a device supports is not considered private or
850 //  confidential information, and therefore the Service and Characteristic Discovery procedures
851 //  shall always be permitted. "
852 //
853 static uint16_t handle_read_by_group_type_request2(att_connection_t * att_connection, uint8_t * response_buffer, uint16_t response_buffer_size,
854                                             uint16_t start_handle, uint16_t end_handle,
855                                             uint16_t attribute_type_len, uint8_t * attribute_type){
856 
857     UNUSED(att_connection);
858 
859     log_info("ATT_READ_BY_GROUP_TYPE_REQUEST: from %04X to %04X, buffer size %u, type: ", start_handle, end_handle, response_buffer_size);
860     log_info_hexdump(attribute_type, attribute_type_len);
861     uint8_t request_type = ATT_READ_BY_GROUP_TYPE_REQUEST;
862 
863     if ((start_handle > end_handle) || (start_handle == 0u)){
864         return setup_error_invalid_handle(response_buffer, request_type, start_handle);
865     }
866 
867     // assert UUID is primary or secondary service uuid
868     uint16_t uuid16 = uuid16_from_uuid(attribute_type_len, attribute_type);
869     if ((uuid16 != GATT_PRIMARY_SERVICE_UUID) && (uuid16 != GATT_SECONDARY_SERVICE_UUID)){
870         return setup_error(response_buffer, request_type, start_handle, ATT_ERROR_UNSUPPORTED_GROUP_TYPE);
871     }
872 
873     uint16_t offset   = 1;
874     uint16_t pair_len = 0;
875     uint16_t in_group = 0;
876     uint16_t group_start_handle = 0;
877     uint8_t const * group_start_value = NULL;
878     uint16_t prev_handle = 0;
879 
880     att_iterator_t it;
881     att_iterator_init(&it);
882     while (att_iterator_has_next(&it)){
883         att_iterator_fetch_next(&it);
884 
885         if (it.handle && (it.handle < start_handle)) continue;
886         if (it.handle > end_handle) break;  // (1)
887 
888         // log_info("Handle 0x%04x", it.handle);
889 
890         // close current tag, if within a group and a new service definition starts or we reach end of att db
891         if (in_group &&
892             ((it.handle == 0u) || att_iterator_match_uuid16(&it, GATT_PRIMARY_SERVICE_UUID) || att_iterator_match_uuid16(&it, GATT_SECONDARY_SERVICE_UUID))){
893             // log_info("End of group, handle 0x%04x, val_len: %u", prev_handle, pair_len - 4);
894 
895             little_endian_store_16(response_buffer, offset, group_start_handle);
896             offset += 2u;
897             little_endian_store_16(response_buffer, offset, prev_handle);
898             offset += 2u;
899             (void)memcpy(response_buffer + offset, group_start_value,
900                          pair_len - 4u);
901             offset += pair_len - 4u;
902             in_group = 0;
903 
904             // check if space for another handle pair available
905             if ((offset + pair_len) > response_buffer_size){
906                 break;
907             }
908         }
909 
910         // keep track of previous handle
911         prev_handle = it.handle;
912 
913         // does current attribute match
914         // log_info("compare: %04x == %04x", *(uint16_t*) context->attribute_type, *(uint16_t*) uuid);
915         if (it.handle && att_iterator_match_uuid(&it, attribute_type, attribute_type_len)) {
916 
917             // check if value has same len as last one
918             uint16_t this_pair_len = 4u + it.value_len;
919             if (offset > 1u){
920                 if (this_pair_len != pair_len) {
921                     break;
922                 }
923             }
924 
925             // log_info("Begin of group, handle 0x%04x", it.handle);
926 
927             // first
928             if (offset == 1u) {
929                 pair_len = this_pair_len;
930                 response_buffer[offset] = this_pair_len;
931                 offset++;
932             }
933 
934             group_start_handle = it.handle;
935             group_start_value  = it.value;
936             in_group = 1;
937         }
938     }
939 
940     if (offset == 1u){
941         return setup_error_atribute_not_found(response_buffer, request_type, start_handle);
942     }
943 
944     response_buffer[0] = ATT_READ_BY_GROUP_TYPE_RESPONSE;
945     return offset;
946 }
947 static uint16_t handle_read_by_group_type_request(att_connection_t * att_connection, uint8_t * request_buffer,  uint16_t request_len,
948                                            uint8_t * response_buffer, uint16_t response_buffer_size){
949     uint16_t attribute_type_len;
950     switch (request_len){
951         case 7:
952             attribute_type_len = 2;
953             break;
954         case 21:
955             attribute_type_len = 16;
956             break;
957         default:
958             return setup_error_invalid_pdu(response_buffer, ATT_READ_BY_GROUP_TYPE_REQUEST);
959     }
960 
961     uint16_t start_handle = little_endian_read_16(request_buffer, 1);
962     uint16_t end_handle = little_endian_read_16(request_buffer, 3);
963     return handle_read_by_group_type_request2(att_connection, response_buffer, response_buffer_size, start_handle, end_handle, attribute_type_len, &request_buffer[5]);
964 }
965 
966 //
967 // MARK: ATT_WRITE_REQUEST 0x12
968 static uint16_t handle_write_request(att_connection_t * att_connection, uint8_t * request_buffer,  uint16_t request_len,
969                               uint8_t * response_buffer, uint16_t response_buffer_size){
970 
971     UNUSED(response_buffer_size);
972 
973     if (request_len < 3u) return setup_error_invalid_pdu(response_buffer, ATT_WRITE_REQUEST);
974 
975     uint8_t request_type = ATT_WRITE_REQUEST;
976 
977     uint16_t handle = little_endian_read_16(request_buffer, 1);
978     att_iterator_t it;
979     int ok = att_find_handle(&it, handle);
980     if (!ok) {
981         return setup_error_invalid_handle(response_buffer, request_type, handle);
982     }
983     if (att_write_callback == NULL) {
984         return setup_error_write_not_permitted(response_buffer, request_type, handle);
985     }
986     if ((it.flags & ATT_PROPERTY_WRITE) == 0u) {
987         return setup_error_write_not_permitted(response_buffer, request_type, handle);
988     }
989     if ((it.flags & ATT_PROPERTY_DYNAMIC) == 0u) {
990         return setup_error_write_not_permitted(response_buffer, request_type, handle);
991     }
992     // check security requirements
993     int error_code = att_validate_security(att_connection, ATT_WRITE, &it);
994     if (error_code) {
995         return setup_error(response_buffer, request_type, handle, error_code);
996     }
997     att_persistent_ccc_cache(&it);
998     error_code = (*att_write_callback)(att_connection->con_handle, handle, ATT_TRANSACTION_MODE_NONE, 0u, request_buffer + 3u, request_len - 3u);
999 
1000 #ifdef ENABLE_ATT_DELAYED_RESPONSE
1001     if (error_code == ATT_ERROR_WRITE_RESPONSE_PENDING) return ATT_INTERNAL_WRITE_RESPONSE_PENDING;
1002 #endif
1003 
1004     if (error_code) {
1005         return setup_error(response_buffer, request_type, handle, error_code);
1006     }
1007     response_buffer[0] = ATT_WRITE_RESPONSE;
1008     return 1;
1009 }
1010 
1011 //
1012 // MARK: ATT_PREPARE_WRITE_REQUEST 0x16
1013 static uint16_t handle_prepare_write_request(att_connection_t * att_connection, uint8_t * request_buffer,  uint16_t request_len,
1014                                       uint8_t * response_buffer, uint16_t response_buffer_size){
1015 
1016     uint8_t request_type = ATT_PREPARE_WRITE_REQUEST;
1017 
1018     if (request_len < 5u) return setup_error_invalid_pdu(response_buffer, request_type);
1019 
1020     uint16_t handle = little_endian_read_16(request_buffer, 1);
1021     uint16_t offset = little_endian_read_16(request_buffer, 3);
1022     if (att_write_callback == NULL) {
1023         return setup_error_write_not_permitted(response_buffer, request_type, handle);
1024     }
1025     att_iterator_t it;
1026     if (att_find_handle(&it, handle) == 0) {
1027         return setup_error_invalid_handle(response_buffer, request_type, handle);
1028     }
1029     if ((it.flags & ATT_PROPERTY_WRITE) == 0u) {
1030         return setup_error_write_not_permitted(response_buffer, request_type, handle);
1031     }
1032     if ((it.flags & ATT_PROPERTY_DYNAMIC) == 0u) {
1033         return setup_error_write_not_permitted(response_buffer, request_type, handle);
1034     }
1035     // check security requirements
1036     int error_code = att_validate_security(att_connection, ATT_WRITE, &it);
1037     if (error_code) {
1038         return setup_error(response_buffer, request_type, handle, error_code);
1039     }
1040 
1041     error_code = (*att_write_callback)(att_connection->con_handle, handle, ATT_TRANSACTION_MODE_ACTIVE, offset, request_buffer + 5u, request_len - 5u);
1042     switch (error_code){
1043         case 0:
1044             break;
1045         case ATT_ERROR_INVALID_OFFSET:
1046         case ATT_ERROR_INVALID_ATTRIBUTE_VALUE_LENGTH:
1047             // postpone to execute write request
1048             att_prepare_write_update_errors(error_code, handle);
1049             break;
1050 #ifdef ENABLE_ATT_DELAYED_RESPONSE
1051         case ATT_ERROR_WRITE_RESPONSE_PENDING:
1052             return ATT_INTERNAL_WRITE_RESPONSE_PENDING;
1053 #endif
1054         default:
1055             return setup_error(response_buffer, request_type, handle, error_code);
1056     }
1057 
1058     // response: echo request
1059     uint16_t bytes_to_echo = btstack_min(request_len, response_buffer_size);
1060     (void)memcpy(response_buffer, request_buffer, bytes_to_echo);
1061     response_buffer[0] = ATT_PREPARE_WRITE_RESPONSE;
1062     return request_len;
1063 }
1064 
1065 /*
1066  * @brief transcation queue of prepared writes, e.g., after disconnect
1067  */
1068 void att_clear_transaction_queue(att_connection_t * att_connection){
1069     (*att_write_callback)(att_connection->con_handle, 0, ATT_TRANSACTION_MODE_CANCEL, 0, NULL, 0);
1070 }
1071 
1072 // MARK: ATT_EXECUTE_WRITE_REQUEST 0x18
1073 // NOTE: security has been verified by handle_prepare_write_request
1074 static uint16_t handle_execute_write_request(att_connection_t * att_connection, uint8_t * request_buffer,  uint16_t request_len,
1075                                       uint8_t * response_buffer, uint16_t response_buffer_size){
1076 
1077     UNUSED(response_buffer_size);
1078 
1079     uint8_t request_type = ATT_EXECUTE_WRITE_REQUEST;
1080 
1081     if (request_len < 2u) return setup_error_invalid_pdu(response_buffer, request_type);
1082 
1083     if (att_write_callback == NULL) {
1084         return setup_error_write_not_permitted(response_buffer, request_type, 0);
1085     }
1086 
1087     if (request_buffer[1]) {
1088         // validate queued write
1089         if (att_prepare_write_error_code == 0){
1090             att_prepare_write_error_code = (*att_write_callback)(att_connection->con_handle, 0, ATT_TRANSACTION_MODE_VALIDATE, 0, NULL, 0);
1091         }
1092 #ifdef ENABLE_ATT_DELAYED_RESPONSE
1093         if (att_prepare_write_error_code == ATT_ERROR_WRITE_RESPONSE_PENDING) return ATT_INTERNAL_WRITE_RESPONSE_PENDING;
1094 #endif
1095         // deliver queued errors
1096         if (att_prepare_write_error_code){
1097             att_clear_transaction_queue(att_connection);
1098             uint8_t  error_code = att_prepare_write_error_code;
1099             uint16_t handle     = att_prepare_write_error_handle;
1100             att_prepare_write_reset();
1101             return setup_error(response_buffer, request_type, handle, error_code);
1102         }
1103         att_write_callback(att_connection->con_handle, 0, ATT_TRANSACTION_MODE_EXECUTE, 0, NULL, 0);
1104     } else {
1105         att_clear_transaction_queue(att_connection);
1106     }
1107     response_buffer[0] = ATT_EXECUTE_WRITE_RESPONSE;
1108     return 1;
1109 }
1110 
1111 // MARK: ATT_WRITE_COMMAND 0x52
1112 // Core 4.0, vol 3, part F, 3.4.5.3
1113 // "No Error Response or Write Response shall be sent in response to this command"
1114 static void handle_write_command(att_connection_t * att_connection, uint8_t * request_buffer,  uint16_t request_len, uint16_t required_flags){
1115 
1116     if (request_len < 3u) return;
1117 
1118     uint16_t handle = little_endian_read_16(request_buffer, 1);
1119     if (att_write_callback == NULL) return;
1120 
1121     att_iterator_t it;
1122     int ok = att_find_handle(&it, handle);
1123     if (!ok) return;
1124     if ((it.flags & ATT_PROPERTY_DYNAMIC) == 0u) return;
1125     if ((it.flags & required_flags) == 0u) return;
1126     if (att_validate_security(att_connection, ATT_WRITE, &it)) return;
1127     att_persistent_ccc_cache(&it);
1128     (*att_write_callback)(att_connection->con_handle, handle, ATT_TRANSACTION_MODE_NONE, 0u, request_buffer + 3u, request_len - 3u);
1129 }
1130 
1131 // MARK: helper for ATT_HANDLE_VALUE_NOTIFICATION and ATT_HANDLE_VALUE_INDICATION
1132 static uint16_t prepare_handle_value(att_connection_t * att_connection,
1133                                      uint16_t handle,
1134                                      const uint8_t *value,
1135                                      uint16_t value_len,
1136                                      uint8_t * response_buffer){
1137     little_endian_store_16(response_buffer, 1, handle);
1138     if (value_len > (att_connection->mtu - 3u)){
1139         value_len = att_connection->mtu - 3u;
1140     }
1141     (void)memcpy(&response_buffer[3], value, value_len);
1142     return value_len + 3u;
1143 }
1144 
1145 // MARK: ATT_HANDLE_VALUE_NOTIFICATION 0x1b
1146 uint16_t att_prepare_handle_value_notification(att_connection_t * att_connection,
1147                                                uint16_t handle,
1148                                                const uint8_t *value,
1149                                                uint16_t value_len,
1150                                                uint8_t * response_buffer){
1151 
1152     response_buffer[0] = ATT_HANDLE_VALUE_NOTIFICATION;
1153     return prepare_handle_value(att_connection, handle, value, value_len, response_buffer);
1154 }
1155 
1156 // MARK: ATT_HANDLE_VALUE_INDICATION 0x1d
1157 uint16_t att_prepare_handle_value_indication(att_connection_t * att_connection,
1158                                              uint16_t handle,
1159                                              const uint8_t *value,
1160                                              uint16_t value_len,
1161                                              uint8_t * response_buffer){
1162 
1163     response_buffer[0] = ATT_HANDLE_VALUE_INDICATION;
1164     return prepare_handle_value(att_connection, handle, value, value_len, response_buffer);
1165 }
1166 
1167 // MARK: Dispatcher
1168 uint16_t att_handle_request(att_connection_t * att_connection,
1169                             uint8_t * request_buffer,
1170                             uint16_t request_len,
1171                             uint8_t * response_buffer){
1172     uint16_t response_len = 0;
1173     uint16_t response_buffer_size = att_connection->mtu;
1174 
1175     switch (request_buffer[0]){
1176         case ATT_EXCHANGE_MTU_REQUEST:
1177             response_len = handle_exchange_mtu_request(att_connection, request_buffer, request_len, response_buffer);
1178             break;
1179         case ATT_FIND_INFORMATION_REQUEST:
1180             response_len = handle_find_information_request(att_connection, request_buffer, request_len,response_buffer, response_buffer_size);
1181             break;
1182         case ATT_FIND_BY_TYPE_VALUE_REQUEST:
1183             response_len = handle_find_by_type_value_request(att_connection, request_buffer, request_len, response_buffer, response_buffer_size);
1184             break;
1185         case ATT_READ_BY_TYPE_REQUEST:
1186             response_len = handle_read_by_type_request(att_connection, request_buffer, request_len, response_buffer, response_buffer_size);
1187             break;
1188         case ATT_READ_REQUEST:
1189             response_len = handle_read_request(att_connection, request_buffer, request_len, response_buffer, response_buffer_size);
1190             break;
1191         case ATT_READ_BLOB_REQUEST:
1192             response_len = handle_read_blob_request(att_connection, request_buffer, request_len, response_buffer, response_buffer_size);
1193             break;
1194         case ATT_READ_MULTIPLE_REQUEST:
1195             response_len = handle_read_multiple_request(att_connection, request_buffer, request_len, response_buffer, response_buffer_size);
1196             break;
1197         case ATT_READ_BY_GROUP_TYPE_REQUEST:
1198             response_len = handle_read_by_group_type_request(att_connection, request_buffer, request_len, response_buffer, response_buffer_size);
1199             break;
1200         case ATT_WRITE_REQUEST:
1201             response_len = handle_write_request(att_connection, request_buffer, request_len, response_buffer, response_buffer_size);
1202             break;
1203         case ATT_PREPARE_WRITE_REQUEST:
1204             response_len = handle_prepare_write_request(att_connection, request_buffer, request_len, response_buffer, response_buffer_size);
1205             break;
1206         case ATT_EXECUTE_WRITE_REQUEST:
1207             response_len = handle_execute_write_request(att_connection, request_buffer, request_len, response_buffer, response_buffer_size);
1208             break;
1209         case ATT_WRITE_COMMAND:
1210             handle_write_command(att_connection, request_buffer, request_len, ATT_PROPERTY_WRITE_WITHOUT_RESPONSE);
1211             break;
1212 #ifdef ENABLE_LE_SIGNED_WRITE
1213         case ATT_SIGNED_WRITE_COMMAND:
1214             handle_write_command(att_connection, request_buffer, request_len, ATT_PROPERTY_AUTHENTICATED_SIGNED_WRITE);
1215             break;
1216 #endif
1217         default:
1218             log_info("Unhandled ATT Command: %02X, DATA: ", request_buffer[0]);
1219             log_info_hexdump(&request_buffer[9u], request_len-9u);
1220             break;
1221     }
1222     return response_len;
1223 }
1224 
1225 // returns 1 if service found. only primary service.
1226 bool gatt_server_get_get_handle_range_for_service_with_uuid16(uint16_t uuid16, uint16_t * start_handle, uint16_t * end_handle){
1227     uint16_t in_group    = 0;
1228     uint16_t prev_handle = 0;
1229 
1230     uint8_t attribute_value[2];
1231     int attribute_len = sizeof(attribute_value);
1232     little_endian_store_16(attribute_value, 0, uuid16);
1233 
1234     att_iterator_t it;
1235     att_iterator_init(&it);
1236     while (att_iterator_has_next(&it)){
1237         att_iterator_fetch_next(&it);
1238         int new_service_started = att_iterator_match_uuid16(&it, GATT_PRIMARY_SERVICE_UUID) || att_iterator_match_uuid16(&it, GATT_SECONDARY_SERVICE_UUID);
1239 
1240         // close current tag, if within a group and a new service definition starts or we reach end of att db
1241         if (in_group &&
1242             ((it.handle == 0u) || new_service_started)){
1243             *end_handle = prev_handle;
1244             return true;
1245         }
1246 
1247         // keep track of previous handle
1248         prev_handle = it.handle;
1249 
1250         // check if found
1251         if (it.handle && new_service_started && (attribute_len == it.value_len) && (memcmp(attribute_value, it.value, it.value_len) == 0)){
1252             *start_handle = it.handle;
1253             in_group = true;
1254         }
1255     }
1256     return false;
1257 }
1258 
1259 // returns false if not found
1260 uint16_t gatt_server_get_value_handle_for_characteristic_with_uuid16(uint16_t start_handle, uint16_t end_handle, uint16_t uuid16){
1261     att_iterator_t it;
1262     att_iterator_init(&it);
1263     while (att_iterator_has_next(&it)){
1264         att_iterator_fetch_next(&it);
1265         if (it.handle && (it.handle < start_handle)) continue;
1266         if (it.handle > end_handle) break;  // (1)
1267         if (it.handle == 0u) break;
1268         if (att_iterator_match_uuid16(&it, uuid16)) return it.handle;
1269     }
1270     return 0;
1271 }
1272 
1273 uint16_t gatt_server_get_descriptor_handle_for_characteristic_with_uuid16(uint16_t start_handle, uint16_t end_handle, uint16_t characteristic_uuid16, uint16_t descriptor_uuid16){
1274     att_iterator_t it;
1275     att_iterator_init(&it);
1276     int characteristic_found = 0;
1277     while (att_iterator_has_next(&it)){
1278         att_iterator_fetch_next(&it);
1279         if (it.handle && (it.handle < start_handle)) continue;
1280         if (it.handle > end_handle) break;  // (1)
1281         if (it.handle == 0u) break;
1282         if (att_iterator_match_uuid16(&it, characteristic_uuid16)){
1283             characteristic_found = 1;
1284             continue;
1285         }
1286         if (att_iterator_match_uuid16(&it, GATT_PRIMARY_SERVICE_UUID)
1287          || att_iterator_match_uuid16(&it, GATT_SECONDARY_SERVICE_UUID)
1288          || att_iterator_match_uuid16(&it, GATT_CHARACTERISTICS_UUID)){
1289             if (characteristic_found) break;
1290             continue;
1291         }
1292         if (characteristic_found && att_iterator_match_uuid16(&it, descriptor_uuid16)){
1293             return it.handle;
1294         }
1295     }
1296     return 0;
1297 }
1298 
1299 // returns 0 if not found
1300 uint16_t gatt_server_get_client_configuration_handle_for_characteristic_with_uuid16(uint16_t start_handle, uint16_t end_handle, uint16_t characteristic_uuid16){
1301     return gatt_server_get_descriptor_handle_for_characteristic_with_uuid16(start_handle, end_handle, characteristic_uuid16, GATT_CLIENT_CHARACTERISTICS_CONFIGURATION);
1302 }
1303 // returns 0 if not found
1304 
1305 uint16_t gatt_server_get_server_configuration_handle_for_characteristic_with_uuid16(uint16_t start_handle, uint16_t end_handle, uint16_t characteristic_uuid16){
1306     return gatt_server_get_descriptor_handle_for_characteristic_with_uuid16(start_handle, end_handle, characteristic_uuid16, GATT_SERVER_CHARACTERISTICS_CONFIGURATION);
1307 }
1308 
1309 // returns 1 if service found. only primary service.
1310 int gatt_server_get_get_handle_range_for_service_with_uuid128(const uint8_t * uuid128, uint16_t * start_handle, uint16_t * end_handle){
1311     uint16_t in_group    = 0;
1312     uint16_t prev_handle = 0;
1313 
1314     uint8_t attribute_value[16];
1315     int attribute_len = sizeof(attribute_value);
1316     reverse_128(uuid128, attribute_value);
1317 
1318     att_iterator_t it;
1319     att_iterator_init(&it);
1320     while (att_iterator_has_next(&it)){
1321         att_iterator_fetch_next(&it);
1322         int new_service_started = att_iterator_match_uuid16(&it, GATT_PRIMARY_SERVICE_UUID) || att_iterator_match_uuid16(&it, GATT_SECONDARY_SERVICE_UUID);
1323 
1324         // close current tag, if within a group and a new service definition starts or we reach end of att db
1325         if (in_group &&
1326             ((it.handle == 0u) || new_service_started)){
1327             *end_handle = prev_handle;
1328             return 1;
1329         }
1330 
1331         // keep track of previous handle
1332         prev_handle = it.handle;
1333 
1334         // check if found
1335         if (it.handle && new_service_started && (attribute_len == it.value_len) && (memcmp(attribute_value, it.value, it.value_len) == 0)){
1336             *start_handle = it.handle;
1337             in_group = 1;
1338         }
1339     }
1340     return 0;
1341 }
1342 
1343 // returns 0 if not found
1344 uint16_t gatt_server_get_value_handle_for_characteristic_with_uuid128(uint16_t start_handle, uint16_t end_handle, const uint8_t * uuid128){
1345     uint8_t attribute_value[16];
1346     reverse_128(uuid128, attribute_value);
1347     att_iterator_t it;
1348     att_iterator_init(&it);
1349     while (att_iterator_has_next(&it)){
1350         att_iterator_fetch_next(&it);
1351         if (it.handle && (it.handle < start_handle)) continue;
1352         if (it.handle > end_handle) break;  // (1)
1353         if (it.handle == 0u) break;
1354         if (att_iterator_match_uuid(&it, attribute_value, 16)) return it.handle;
1355     }
1356     return 0;
1357 }
1358 
1359 // returns 0 if not found
1360 uint16_t gatt_server_get_client_configuration_handle_for_characteristic_with_uuid128(uint16_t start_handle, uint16_t end_handle, const uint8_t * uuid128){
1361     uint8_t attribute_value[16];
1362     reverse_128(uuid128, attribute_value);
1363     att_iterator_t it;
1364     att_iterator_init(&it);
1365     int characteristic_found = 0;
1366     while (att_iterator_has_next(&it)){
1367         att_iterator_fetch_next(&it);
1368         if (it.handle && (it.handle < start_handle)) continue;
1369         if (it.handle > end_handle) break;  // (1)
1370         if (it.handle == 0u) break;
1371         if (att_iterator_match_uuid(&it, attribute_value, 16)){
1372             characteristic_found = 1;
1373             continue;
1374         }
1375         if (att_iterator_match_uuid16(&it, GATT_PRIMARY_SERVICE_UUID)
1376          || att_iterator_match_uuid16(&it, GATT_SECONDARY_SERVICE_UUID)
1377          || att_iterator_match_uuid16(&it, GATT_CHARACTERISTICS_UUID)){
1378             if (characteristic_found) break;
1379             continue;
1380         }
1381         if (characteristic_found && att_iterator_match_uuid16(&it, GATT_CLIENT_CHARACTERISTICS_CONFIGURATION)){
1382             return it.handle;
1383         }
1384     }
1385     return 0;
1386 }
1387 
1388 
1389 // 1-item cache to optimize query during write_callback
1390 static void att_persistent_ccc_cache(att_iterator_t * it){
1391     att_persistent_ccc_handle = it->handle;
1392     if (it->flags & ATT_PROPERTY_UUID128){
1393         att_persistent_ccc_uuid16 = 0;
1394     } else {
1395         att_persistent_ccc_uuid16 = little_endian_read_16(it->uuid, 0);
1396     }
1397 }
1398 
1399 bool att_is_persistent_ccc(uint16_t handle){
1400     if (handle != att_persistent_ccc_handle){
1401         att_iterator_t it;
1402         int ok = att_find_handle(&it, handle);
1403         if (!ok) return false;
1404         att_persistent_ccc_cache(&it);
1405     }
1406     return att_persistent_ccc_uuid16 == GATT_CLIENT_CHARACTERISTICS_CONFIGURATION;
1407 }
1408 
1409 // att_read_callback helpers
1410 uint16_t att_read_callback_handle_blob(const uint8_t * blob, uint16_t blob_size, uint16_t offset, uint8_t * buffer, uint16_t buffer_size){
1411     if (buffer){
1412         uint16_t bytes_to_copy = btstack_min(blob_size - offset, buffer_size);
1413         (void)memcpy(buffer, &blob[offset], bytes_to_copy);
1414         return bytes_to_copy;
1415     } else {
1416         return blob_size;
1417     }
1418 }
1419 
1420 uint16_t att_read_callback_handle_little_endian_32(uint32_t value, uint16_t offset, uint8_t * buffer, uint16_t buffer_size){
1421     uint8_t value_buffer[4];
1422     little_endian_store_32(value_buffer, 0, value);
1423     return att_read_callback_handle_blob(value_buffer, sizeof(value_buffer), offset, buffer, buffer_size);
1424 }
1425 
1426 uint16_t att_read_callback_handle_little_endian_16(uint16_t value, uint16_t offset, uint8_t * buffer, uint16_t buffer_size){
1427     uint8_t value_buffer[2];
1428     little_endian_store_16(value_buffer, 0, value);
1429     return att_read_callback_handle_blob(value_buffer, sizeof(value_buffer), offset, buffer, buffer_size);
1430 }
1431 
1432 uint16_t att_read_callback_handle_byte(uint8_t value, uint16_t offset, uint8_t * buffer, uint16_t buffer_size){
1433     uint8_t value_buffer[1];
1434     value_buffer[0] = value;
1435     return att_read_callback_handle_blob(value_buffer, sizeof(value_buffer), offset, buffer, buffer_size);
1436 }
1437