text: // Copyright (c) Microsoft. All rights reserved.
  // Licensed under the MIT license. See LICENSE file in the project root for full license information.
  
  #include <stdlib.h>
  #include <stdint.h>
  #include <stdbool.h>
  #include <string.h>
  #include <inttypes.h>
  #include "azure_macro_utils/macro_utils.h"
  #include "azure_c_shared_utility/gballoc.h"
  #include "azure_c_shared_utility/xlogging.h"
  #include "azure_c_shared_utility/singlylinkedlist.h"
  #include "azure_uamqp_c/frame_codec.h"
  #include "azure_uamqp_c/amqpvalue.h"
  
  #define FRAME_HEADER_SIZE 8
  #define MAX_TYPE_SPECIFIC_SIZE    ((255 * 4) - 6)
  
  typedef enum RECEIVE_FRAME_STATE_TAG
  {
      RECEIVE_FRAME_STATE_FRAME_SIZE,
      RECEIVE_FRAME_STATE_DOFF,
      RECEIVE_FRAME_STATE_FRAME_TYPE,
      RECEIVE_FRAME_STATE_TYPE_SPECIFIC,
      RECEIVE_FRAME_STATE_FRAME_BODY,
      RECEIVE_FRAME_STATE_ERROR
  } RECEIVE_FRAME_STATE;
  
  typedef struct SUBSCRIPTION_TAG
  {
      uint8_t frame_type;
      ON_FRAME_RECEIVED on_frame_received;
      void* callback_context;
  } SUBSCRIPTION;
  
  typedef struct FRAME_CODEC_INSTANCE_TAG
  {
      /* subscriptions */
      SINGLYLINKEDLIST_HANDLE subscription_list;
  
      /* decode frame */
      RECEIVE_FRAME_STATE receive_frame_state;
      size_t receive_frame_pos;
      uint32_t receive_frame_size;
      uint32_t receive_frame_malloc_size;
      uint32_t type_specific_size;
      uint8_t receive_frame_doff;
      uint8_t receive_frame_type;
      SUBSCRIPTION* receive_frame_subscription;
      unsigned char* receive_frame_bytes;
      ON_FRAME_CODEC_ERROR on_frame_codec_error;
      void* on_frame_codec_error_callback_context;
  
      /* configuration */
      uint32_t max_frame_size;
  } FRAME_CODEC_INSTANCE;
  
  static bool find_subscription_by_frame_type(LIST_ITEM_HANDLE list_item, const void* match_context)
  {
      bool result;
      SUBSCRIPTION* subscription = (SUBSCRIPTION*)singlylinkedlist_item_get_value(list_item);
  
      if (subscription == NULL)
      {
          LogError("Could not get subscription information from the list item");
          result = false;
      }
      else
      {
          result = subscription->frame_type == *((uint8_t*)match_context) ? true : false;
      }
  
      return result;
  }
  
  FRAME_CODEC_HANDLE frame_codec_create(ON_FRAME_CODEC_ERROR on_frame_codec_error, void* callback_context)
  {
      FRAME_CODEC_INSTANCE* result;
  
      /* Codes_SRS_FRAME_CODEC_01_020: [If the on_frame_codec_error argument is NULL, frame_codec_create shall return NULL.] */
      /* Codes_SRS_FRAME_CODEC_01_104: [The callback_context shall be allowed to be NULL.] */
      if (on_frame_codec_error == NULL)
      {
          LogError("NULL on_frame_codec_error");
          result = NULL;
      }
      else
      {
          result = (FRAME_CODEC_INSTANCE*)calloc(1, sizeof(FRAME_CODEC_INSTANCE));
          /* Codes_SRS_FRAME_CODEC_01_022: [If allocating memory for the frame_codec instance fails, frame_codec_create shall return NULL.] */
          if (result == NULL)
          {
              LogError("Could not allocate frame codec");
          }
          else
          {
              /* Codes_SRS_FRAME_CODEC_01_021: [frame_codec_create shall create a new instance of frame_codec and return a non-NULL handle to it on success.] */
              result->receive_frame_state = RECEIVE_FRAME_STATE_FRAME_SIZE;
              result->on_frame_codec_error = on_frame_codec_error;
              result->on_frame_codec_error_callback_context = callback_context;
              result->receive_frame_pos = 0;
              result->receive_frame_size = 0;
              result->receive_frame_malloc_size = 0;
              result->receive_frame_bytes = NULL;
              result->subscription_list = singlylinkedlist_create();
  
              /* Codes_SRS_FRAME_CODEC_01_082: [The initial max_frame_size_shall be 512.] */
              result->max_frame_size = 512;
          }
      }
  
      return result;
  }
  
  void frame_codec_destroy(FRAME_CODEC_HANDLE frame_codec)
  {
      /* Codes_SRS_FRAME_CODEC_01_024: [If frame_codec is NULL, frame_codec_destroy shall do nothing.] */
      if (frame_codec == NULL)
      {
          LogError("NULL frame_codec");
      }
      else
      {
          FRAME_CODEC_INSTANCE* frame_codec_data = (FRAME_CODEC_INSTANCE*)frame_codec;
  
          singlylinkedlist_destroy(frame_codec_data->subscription_list);
          if (frame_codec_data->receive_frame_bytes != NULL)
          {
              free(frame_codec_data->receive_frame_bytes);
          }
  
          /* Codes_SRS_FRAME_CODEC_01_023: [frame_codec_destroy shall free all resources associated with a frame_codec instance.] */
          free(frame_codec);
      }
  }
  
  int frame_codec_set_max_frame_size(FRAME_CODEC_HANDLE frame_codec, uint32_t max_frame_size)
  {
      int result;
      FRAME_CODEC_INSTANCE* frame_codec_data = (FRAME_CODEC_INSTANCE*)frame_codec;
  
      /* Codes_SRS_FRAME_CODEC_01_077: [If frame_codec is NULL, frame_codec_set_max_frame_size shall return a non-zero value.] */
      if ((frame_codec == NULL) ||
          /* Codes_SRS_FRAME_CODEC_01_078: [If max_frame_size is invalid according to the AMQP standard, frame_codec_set_max_frame_size shall return a non-zero value.] */
          (max_frame_size < FRAME_HEADER_SIZE) ||
          /* Codes_SRS_FRAME_CODEC_01_081: [If a frame being decoded already has a size bigger than the max_frame_size argument then frame_codec_set_max_frame_size shall return a non-zero value and the previous frame size shall be kept.] */
          ((max_frame_size < frame_codec_data->receive_frame_size) && (frame_codec_data->receive_frame_state != RECEIVE_FRAME_STATE_FRAME_SIZE)))
      {
          LogError("Bad arguments: frame_codec = %p, max_frame_size = %" PRIu32,
              frame_codec,
              max_frame_size);
          result = MU_FAILURE;
      }
      /* Codes_SRS_FRAME_CODEC_01_097: [Setting a frame size on a frame_codec that had a decode error shall fail.] */
      else if (frame_codec_data->receive_frame_state == RECEIVE_FRAME_STATE_ERROR)
      {
          LogError("Frame codec in error state");
          result = MU_FAILURE;
      }
      else
      {
          /* Codes_SRS_FRAME_CODEC_01_075: [frame_codec_set_max_frame_size shall set the maximum frame size for a frame_codec.] */
          /* Codes_SRS_FRAME_CODEC_01_079: [The new frame size shall take effect immediately, even for a frame that is being decoded at the time of the call.] */
          frame_codec_data->max_frame_size = max_frame_size;
  
          /* Codes_SRS_FRAME_CODEC_01_076: [On success, frame_codec_set_max_frame_size shall return 0.] */
          result = 0;
      }
  
      return result;
  }
  
  /* Codes_SRS_FRAME_CODEC_01_001: [Frames are divided into three distinct areas: a fixed width frame header, a variable width extended header, and a variable width frame body.] */
  /* Codes_SRS_FRAME_CODEC_01_002: [frame header The frame header is a fixed size (8 byte) structure that precedes each frame.] */
  /* Codes_SRS_FRAME_CODEC_01_003: [The frame header includes mandatory information necessary to parse the rest of the frame including size and type information.] */
  /* Codes_SRS_FRAME_CODEC_01_004: [extended header The extended header is a variable width area preceding the frame body.] */
  /* Codes_SRS_FRAME_CODEC_01_007: [frame body The frame body is a variable width sequence of bytes the format of which depends on the frame type.] */
  /* Codes_SRS_FRAME_CODEC_01_028: [The sequence of bytes shall be decoded according to the AMQP ISO.] */
  /* Codes_SRS_FRAME_CODEC_01_029: [The sequence of bytes does not have to be a complete frame, frame_codec shall be responsible for maintaining decoding state between frame_codec_receive_bytes calls.] */
  int frame_codec_receive_bytes(FRAME_CODEC_HANDLE frame_codec, const unsigned char* buffer, size_t size)
  {
      int result = MU_FAILURE;
      FRAME_CODEC_INSTANCE* frame_codec_data = (FRAME_CODEC_INSTANCE*)frame_codec;
  
      /* Codes_SRS_FRAME_CODEC_01_026: [If frame_codec or buffer are NULL, frame_codec_receive_bytes shall return a non-zero value.] */
      if ((frame_codec == NULL) ||
          (buffer == NULL) ||
          /* Codes_SRS_FRAME_CODEC_01_027: [If size is zero, frame_codec_receive_bytes shall return a non-zero value.] */
          (size == 0))
      {
          LogError("Bad arguments: frame_codec = %p, buffer = %p, size = %u",
              frame_codec,
              buffer,
              (unsigned int)size);
          result = MU_FAILURE;
      }
      else
      {
          while (size > 0)
          {
              switch (frame_codec_data->receive_frame_state)
              {
              default:
              case RECEIVE_FRAME_STATE_ERROR:
                  /* Codes_SRS_FRAME_CODEC_01_074: [If a decoding error is detected, any subsequent calls on frame_codec_data_receive_bytes shall fail.] */
                  LogError("Frame codec is in error state");
                  result = MU_FAILURE;
                  size = 0;
                  break;
  
                  /* Codes_SRS_FRAME_CODEC_01_008: [SIZE Bytes 0-3 of the frame header contain the frame size.] */
              case RECEIVE_FRAME_STATE_FRAME_SIZE:
                  /* Codes_SRS_FRAME_CODEC_01_009: [This is an unsigned 32-bit integer that MUST contain the total frame size of the frame header, extended header, and frame body.] */
                  frame_codec_data->receive_frame_size += buffer[0] << (24 - frame_codec_data->receive_frame_pos * 8);
                  buffer++;
                  size--;
                  frame_codec_data->receive_frame_pos++;
  
                  if (frame_codec_data->receive_frame_pos == 4)
                  {
                      /* Codes_SRS_FRAME_CODEC_01_010: [The frame is malformed if the size is less than the size of the frame header (8 bytes).] */
                      if ((frame_codec_data->receive_frame_size < FRAME_HEADER_SIZE) ||
                          /* Codes_SRS_FRAME_CODEC_01_096: [If a frame bigger than the current max frame size is received, frame_codec_receive_bytes shall fail and return a non-zero value.] */
                          (frame_codec_data->receive_frame_size > frame_codec_data->max_frame_size))
                      {
                          /* Codes_SRS_FRAME_CODEC_01_074: [If a decoding error is detected, any subsequent calls on frame_codec_data_receive_bytes shall fail.] */
                          frame_codec_data->receive_frame_state = RECEIVE_FRAME_STATE_ERROR;
                          /* Codes_SRS_FRAME_CODEC_01_103: [Upon any decode error, if an error callback has been passed to frame_codec_create, then the error callback shall be called with the context argument being the on_frame_codec_error_callback_context argument passed to frame_codec_create.] */
                          frame_codec_data->on_frame_codec_error(frame_codec_data->on_frame_codec_error_callback_context);
                          LogError("Received frame size is too big");
                          result = MU_FAILURE;
                      }
                      else
                      {
                          frame_codec_data->receive_frame_state = RECEIVE_FRAME_STATE_DOFF;
                          result = 0;
                      }
                  }
                  else
                  {
                      result = 0;
                  }
  
                  break;
  
              case RECEIVE_FRAME_STATE_DOFF:
                  /* Codes_SRS_FRAME_CODEC_01_011: [DOFF Byte 4 of the frame header is the data offset.] */
                  /* Codes_SRS_FRAME_CODEC_01_013: [The value of the data offset is an unsigned, 8-bit integer specifying a count of 4-byte words.] */
                  /* Codes_SRS_FRAME_CODEC_01_012: [This gives the position of the body within the frame.] */
                  frame_codec_data->receive_frame_doff = buffer[0];
                  buffer++;
                  size--;
  
                  /* Codes_SRS_FRAME_CODEC_01_014: [Due to the mandatory 8-byte frame header, the frame is malformed if the value is less than 2.] */
                  if (frame_codec_data->receive_frame_doff < 2)
                  {
                      /* Codes_SRS_FRAME_CODEC_01_074: [If a decoding error is detected, any subsequent calls on frame_codec_data_receive_bytes shall fail.] */
                      frame_codec_data->receive_frame_state = RECEIVE_FRAME_STATE_ERROR;
  
                      /* Codes_SRS_FRAME_CODEC_01_103: [Upon any decode error, if an error callback has been passed to frame_codec_create, then the error callback shall be called with the context argument being the on_frame_codec_error_callback_context argument passed to frame_codec_create.] */
                      frame_codec_data->on_frame_codec_error(frame_codec_data->on_frame_codec_error_callback_context);
  
                      LogError("Malformed frame received");
                      result = MU_FAILURE;
                  }
                  else
                  {
                      frame_codec_data->receive_frame_state = RECEIVE_FRAME_STATE_FRAME_TYPE;
                      result = 0;
                  }
  
                  break;
  
              case RECEIVE_FRAME_STATE_FRAME_TYPE:
              {
                  LIST_ITEM_HANDLE item_handle;
                  frame_codec_data->type_specific_size = (frame_codec_data->receive_frame_doff * 4) - 6;
  
                  /* Codes_SRS_FRAME_CODEC_01_015: [TYPE Byte 5 of the frame header is a type code.] */
                  frame_codec_data->receive_frame_type = buffer[0];
                  buffer++;
                  size--;
  
                  /* Codes_SRS_FRAME_CODEC_01_035: [After successfully registering a callback for a certain frame type, when subsequently that frame type is received the callbacks shall be invoked, passing to it the received frame and the callback_context value.] */
                  item_handle = singlylinkedlist_find(frame_codec_data->subscription_list, find_subscription_by_frame_type, &frame_codec_data->receive_frame_type);
                  if (item_handle == NULL)
                  {
                      frame_codec_data->receive_frame_subscription = NULL;
                      frame_codec_data->receive_frame_state = RECEIVE_FRAME_STATE_TYPE_SPECIFIC;
                      result = 0;
                      break;
                  }
                  else
                  {
                      frame_codec_data->receive_frame_subscription = (SUBSCRIPTION*)singlylinkedlist_item_get_value(item_handle);
                      if (frame_codec_data->receive_frame_subscription == NULL)
                      {
                          frame_codec_data->receive_frame_state = RECEIVE_FRAME_STATE_TYPE_SPECIFIC;
                          result = 0;
                          break;
                      }
                      else
                      {
                          frame_codec_data->receive_frame_pos = 0;
  
                          /* Codes_SRS_FRAME_CODEC_01_102: [frame_codec_receive_bytes shall allocate memory to hold the frame_body bytes.] */
                          frame_codec_data->receive_frame_malloc_size = frame_codec_data->receive_frame_size - 6;
                          frame_codec_data->receive_frame_bytes = (unsigned char*)malloc(frame_codec_data->receive_frame_malloc_size);
                          if (frame_codec_data->receive_frame_bytes == NULL)
                          {
                              /* Codes_SRS_FRAME_CODEC_01_101: [If the memory for the frame_body bytes cannot be allocated, frame_codec_receive_bytes shall fail and return a non-zero value.] */
                              /* Codes_SRS_FRAME_CODEC_01_030: [If a decoding error occurs, frame_codec_data_receive_bytes shall return a non-zero value.] */
                              /* Codes_SRS_FRAME_CODEC_01_074: [If a decoding error is detected, any subsequent calls on frame_codec_data_receive_bytes shall fail.] */
                              frame_codec_data->receive_frame_state = RECEIVE_FRAME_STATE_ERROR;
  
                              /* Codes_SRS_FRAME_CODEC_01_103: [Upon any decode error, if an error callback has been passed to frame_codec_create, then the error callback shall be called with the context argument being the on_frame_codec_error_callback_context argument passed to frame_codec_create.] */
                              frame_codec_data->on_frame_codec_error(frame_codec_data->on_frame_codec_error_callback_context);
  
                              LogError("Cannot allocate memory for frame bytes");
                              result = MU_FAILURE;
                              break;
                          }
                          else
                          {
                              frame_codec_data->receive_frame_state = RECEIVE_FRAME_STATE_TYPE_SPECIFIC;
                              result = 0;
                              break;
                          }
                      }
                  }
              }
  
              case RECEIVE_FRAME_STATE_TYPE_SPECIFIC:
              {
                  size_t to_copy = frame_codec_data->type_specific_size - frame_codec_data->receive_frame_pos;
                  if (to_copy > size)
                  {
                      to_copy = size;
                  }
  
                  if (frame_codec_data->receive_frame_subscription != NULL)
                  {
                      // [bug:8781089] WRITE address points to the zero page - SEGV
                      if (frame_codec_data->receive_frame_bytes == NULL)
                      {
                          LogError("Frame bytes memory was not allocated");
                          result = MU_FAILURE;
                          size = 0;
                          break;
                      }
                      else if (frame_codec_data->receive_frame_pos + to_copy > frame_codec_data->receive_frame_malloc_size)
                      {
                          result = MU_FAILURE;
                          size = 0;
                          break;
                      }                    
                      (void)memcpy(&frame_codec_data->receive_frame_bytes[frame_codec_data->receive_frame_pos], buffer, to_copy);
                      frame_codec_data->receive_frame_pos += to_copy;
                      buffer += to_copy;
                      size -= to_copy;
                  }
                  else
                  {
                      frame_codec_data->receive_frame_pos += to_copy;
                      buffer += to_copy;
                      size -= to_copy;
                  }
  
                  if (frame_codec_data->receive_frame_pos == frame_codec_data->type_specific_size)
                  {
                      if (frame_codec_data->receive_frame_size == FRAME_HEADER_SIZE)
                      {
                          if (frame_codec_data->receive_frame_subscription != NULL)
                          {
                              /* Codes_SRS_FRAME_CODEC_01_031: [When a complete frame is successfully decoded it shall be indicated to the upper layer by invoking the on_frame_received passed to frame_codec_subscribe.] */
                              /* Codes_SRS_FRAME_CODEC_01_032: [Besides passing the frame information, the callback_context value passed to frame_codec_data_subscribe shall be passed to the on_frame_received function.] */
                              /* Codes_SRS_FRAME_CODEC_01_005: [This is an extension point defined for future expansion.] */
                              /* Codes_SRS_FRAME_CODEC_01_006: [The treatment of this area depends on the frame type.] */
                              /* Codes_SRS_FRAME_CODEC_01_100: [If the frame body size is 0, the frame_body pointer passed to on_frame_received shall be NULL.] */
                              frame_codec_data->receive_frame_subscription->on_frame_received(frame_codec_data->receive_frame_subscription->callback_context, frame_codec_data->receive_frame_bytes, frame_codec_data->type_specific_size, NULL, 0);
                              free(frame_codec_data->receive_frame_bytes);
                              frame_codec_data->receive_frame_bytes = NULL;
                          }
  
                          frame_codec_data->receive_frame_state = RECEIVE_FRAME_STATE_FRAME_SIZE;
                          frame_codec_data->receive_frame_size = 0;
                      }
                      else
                      {
                          frame_codec_data->receive_frame_state = RECEIVE_FRAME_STATE_FRAME_BODY;
                      }
  
                      frame_codec_data->receive_frame_pos = 0;
                  }
  
                  result = 0;
                  break;
              }
  
              case RECEIVE_FRAME_STATE_FRAME_BODY:
              {
                  uint32_t frame_body_size = frame_codec_data->receive_frame_size - (frame_codec_data->receive_frame_doff * 4);
                  size_t to_copy = frame_body_size - frame_codec_data->receive_frame_pos;
  
                  if (to_copy > size)
                  {
                      to_copy = size;
                  }
  
                  if (frame_codec_data->receive_frame_bytes == NULL)
                  {
                      result = MU_FAILURE;
                      size = 0;
                      break;
                  }
  
                  (void)memcpy(frame_codec_data->receive_frame_bytes + frame_codec_data->receive_frame_pos + frame_codec_data->type_specific_size, buffer, to_copy);
  
                  buffer += to_copy;
                  size -= to_copy;
                  frame_codec_data->receive_frame_pos += to_copy;
  
                  if (frame_codec_data->receive_frame_pos == frame_body_size)
                  {
                      if (frame_codec_data->receive_frame_subscription != NULL)
                      {
                          /* Codes_SRS_FRAME_CODEC_01_031: [When a complete frame is successfully decoded it shall be indicated to the upper layer by invoking the on_frame_received passed to frame_codec_subscribe.] */
                          /* Codes_SRS_FRAME_CODEC_01_032: [Besides passing the frame information, the callback_context value passed to frame_codec_data_subscribe shall be passed to the on_frame_received function.] */
                          /* Codes_SRS_FRAME_CODEC_01_005: [This is an extension point defined for future expansion.] */
                          /* Codes_SRS_FRAME_CODEC_01_006: [The treatment of this area depends on the frame type.] */
                          /* Codes_SRS_FRAME_CODEC_01_099: [A pointer to the frame_body bytes shall also be passed to the on_frame_received.] */
                          frame_codec_data->receive_frame_subscription->on_frame_received(frame_codec_data->receive_frame_subscription->callback_context, frame_codec_data->receive_frame_bytes, frame_codec_data->type_specific_size, frame_codec_data->receive_frame_bytes + frame_codec_data->type_specific_size, frame_body_size);
                          free(frame_codec_data->receive_frame_bytes);
                          frame_codec_data->receive_frame_bytes = NULL;
                      }
  
                      frame_codec_data->receive_frame_state = RECEIVE_FRAME_STATE_FRAME_SIZE;
                      frame_codec_data->receive_frame_pos = 0;
                      frame_codec_data->receive_frame_size = 0;
                  }
                  result = 0;
  
                  break;
              }
              }
          }
      }
  
      return result;
  }
  
  /* Codes_SRS_FRAME_CODEC_01_033: [frame_codec_subscribe subscribes for a certain type of frame received by the frame_codec instance identified by frame_codec.] */
  int frame_codec_subscribe(FRAME_CODEC_HANDLE frame_codec, uint8_t type, ON_FRAME_RECEIVED on_frame_received, void* callback_context)
  {
      int result;
  
      /* Codes_SRS_FRAME_CODEC_01_034: [If any of the frame_codec or on_frame_received arguments is NULL, frame_codec_subscribe shall return a non-zero value.] */
      if ((frame_codec == NULL) ||
          (on_frame_received == NULL))
      {
          LogError("Bad arguments: frame_codec = %p, on_frame_received = %p",
              frame_codec, on_frame_received);
          result = MU_FAILURE;
      }
      else
      {
          FRAME_CODEC_INSTANCE* frame_codec_data = (FRAME_CODEC_INSTANCE*)frame_codec;
          SUBSCRIPTION* subscription;
  
          /* Codes_SRS_FRAME_CODEC_01_036: [Only one callback pair shall be allowed to be registered for a given frame type.] */
          /* find the subscription for this frame type */
          LIST_ITEM_HANDLE list_item = singlylinkedlist_find(frame_codec_data->subscription_list, find_subscription_by_frame_type, &type);
          if (list_item != NULL)
          {
              subscription = (SUBSCRIPTION*)singlylinkedlist_item_get_value(list_item);
              if (subscription == NULL)
              {
                  /* Codes_SRS_FRAME_CODEC_01_037: [If any failure occurs while performing the subscribe operation, frame_codec_subscribe shall return a non-zero value.] */
                  LogError("Cannot retrieve subscription information from the list for type %u", (unsigned int)type);
                  result = MU_FAILURE;
              }
              else
              {
                  /* a subscription was found */
                  subscription->on_frame_received = on_frame_received;
                  subscription->callback_context = callback_context;
  
                  /* Codes_SRS_FRAME_CODEC_01_087: [On success, frame_codec_subscribe shall return zero.] */
                  result = 0;
              }
          }
          else
          {
              /* add a new subscription */
              subscription = (SUBSCRIPTION*)calloc(1, sizeof(SUBSCRIPTION));
              /* Codes_SRS_FRAME_CODEC_01_037: [If any failure occurs while performing the subscribe operation, frame_codec_subscribe shall return a non-zero value.] */
              if (subscription == NULL)
              {
                  LogError("Cannot allocate memory for new subscription");
                  result = MU_FAILURE;
              }
              else
              {
                  subscription->on_frame_received = on_frame_received;
                  subscription->callback_context = callback_context;
                  subscription->frame_type = type;
  
                  /* Codes_SRS_FRAME_CODEC_01_037: [If any failure occurs while performing the subscribe operation, frame_codec_subscribe shall return a non-zero value.] */
                  if (singlylinkedlist_add(frame_codec_data->subscription_list, subscription) == NULL)
                  {
                      free(subscription);
                      LogError("Cannot add subscription to list");
                      result = MU_FAILURE;
                  }
                  else
                  {
                      /* Codes_SRS_FRAME_CODEC_01_087: [On success, frame_codec_subscribe shall return zero.] */
                      result = 0;
                  }
              }
          }
      }
  
      return result;
  }
  
  int frame_codec_unsubscribe(FRAME_CODEC_HANDLE frame_codec, uint8_t type)
  {
      int result;
  
      /* Codes_SRS_FRAME_CODEC_01_039: [If frame_codec is NULL, frame_codec_unsubscribe shall return a non-zero value.] */
      if (frame_codec == NULL)
      {
          LogError("NULL frame_codec");
          result = MU_FAILURE;
      }
      else
      {
          FRAME_CODEC_INSTANCE* frame_codec_data = (FRAME_CODEC_INSTANCE*)frame_codec;
          LIST_ITEM_HANDLE list_item = singlylinkedlist_find(frame_codec_data->subscription_list, find_subscription_by_frame_type, &type);
  
          if (list_item == NULL)
          {
              /* Codes_SRS_FRAME_CODEC_01_040: [If no subscription for the type frame type exists, frame_codec_unsubscribe shall return a non-zero value.] */
              /* Codes_SRS_FRAME_CODEC_01_041: [If any failure occurs while performing the unsubscribe operation, frame_codec_unsubscribe shall return a non-zero value.] */
              LogError("Cannot find subscription for type %u", (unsigned int)type);
              result = MU_FAILURE;
          }
          else
          {
              SUBSCRIPTION* subscription = (SUBSCRIPTION*)singlylinkedlist_item_get_value(list_item);
              if (subscription == NULL)
              {
                  /* Codes_SRS_FRAME_CODEC_01_041: [If any failure occurs while performing the unsubscribe operation, frame_codec_unsubscribe shall return a non-zero value.] */
                  LogError("singlylinkedlist_item_get_value failed when unsubscribing");
                  result = MU_FAILURE;
              }
              else
              {
                  free(subscription);
                  if (singlylinkedlist_remove(frame_codec_data->subscription_list, list_item) != 0)
                  {
                      /* Codes_SRS_FRAME_CODEC_01_041: [If any failure occurs while performing the unsubscribe operation, frame_codec_unsubscribe shall return a non-zero value.] */
                      LogError("Cannot remove subscription from list");
                      result = MU_FAILURE;
                  }
                  else
                  {
                      /* Codes_SRS_FRAME_CODEC_01_038: [frame_codec_unsubscribe removes a previous subscription for frames of type type and on success it shall return 0.] */
                      result = 0;
                  }
              }
          }
      }
  
      return result;
  }
  
  int frame_codec_encode_frame(FRAME_CODEC_HANDLE frame_codec, uint8_t type, PAYLOAD* payloads, const unsigned char* type_specific_bytes, uint32_t type_specific_size, ON_BYTES_ENCODED on_bytes_encoded, void* callback_context)
  {
      int result;
  
      FRAME_CODEC_INSTANCE* frame_codec_data = (FRAME_CODEC_INSTANCE*)frame_codec;
  
      /* Codes_SRS_FRAME_CODEC_01_044: [If any of arguments `frame_codec` or `on_bytes_encoded` is NULL, `frame_codec_encode_frame` shall return a non-zero value.] */
      if ((frame_codec == NULL) ||
          (on_bytes_encoded == NULL) ||
          /* Codes_SRS_FRAME_CODEC_01_091: [If the argument type_specific_size is greater than 0 and type_specific_bytes is NULL, frame_codec_encode_frame shall return a non-zero value.] */
          ((type_specific_size > 0) && (type_specific_bytes == NULL)) ||
          /* Codes_SRS_FRAME_CODEC_01_092: [If type_specific_size is too big to allow encoding the frame according to the AMQP ISO then frame_codec_encode_frame shall return a non-zero value.] */
          (type_specific_size > MAX_TYPE_SPECIFIC_SIZE))
      {
          LogError("Bad arguments: frame_codec = %p, on_bytes_encoded = %p, type_specific_size = %u, type_specific_bytes = %p",
              frame_codec, on_bytes_encoded, (unsigned int)type_specific_size, type_specific_bytes);
          result = MU_FAILURE;
      }
      else if (!payload_is_valid(payloads))
      {
          /* Codes_SRS_FRAME_CODEC_01_107: [If the argument `payloads` is NULL and `payload_count` is non-zero, `frame_codec_encode_frame` shall return a non-zero value.]*/
          LogError("NULL payloads argument with non-zero payload count");
          result = MU_FAILURE;
      }
      else
      {
          /* round up to the 4 bytes for doff */
          /* Codes_SRS_FRAME_CODEC_01_067: [The value of the data offset is an unsigned, 8-bit integer specifying a count of 4-byte words.] */
          /* Codes_SRS_FRAME_CODEC_01_068: [Due to the mandatory 8-byte frame header, the frame is malformed if the value is less than 2.] */
          uint8_t padding_byte_count;
          uint32_t frame_body_offset = type_specific_size + 6;
          uint8_t doff = (uint8_t)((frame_body_offset + 3) / 4);
          size_t frame_size;
          size_t frame_body_size = 0;
          frame_body_offset = doff * 4;
          padding_byte_count = (uint8_t)(frame_body_offset - type_specific_size - 6);
  
          frame_body_size = payload_get_length(payloads);
  
          {
              /* Codes_SRS_FRAME_CODEC_01_063: [This is an unsigned 32-bit integer that MUST contain the total frame size of the frame header, extended header, and frame body.] */
              frame_size = frame_body_size + frame_body_offset;
  
              if (frame_size > frame_codec_data->max_frame_size)
              {
                  /* Codes_SRS_FRAME_CODEC_01_095: [If the frame_size needed for the frame is bigger than the maximum frame size, frame_codec_encode_frame shall fail and return a non-zero value.] */
                  LogError("Encoded frame size exceeds the maximum allowed frame size");
                  result = MU_FAILURE;
              }
              else
              {
                  /* Codes_SRS_FRAME_CODEC_01_108: [ Memory shall be allocated to hold the entire frame. ]*/
                  PAYLOAD* encoded_frame_payload = payload_create();
                  if (encoded_frame_payload == NULL)
                  {
                      /* Codes_SRS_FRAME_CODEC_01_109: [ If allocating memory fails, `frame_codec_encode_frame` shall fail and return a non-zero value. ]*/
                      LogError("Cannot allocate memory for frame");
                      result = MU_FAILURE;
                  }
                  else
                  {
                      /* Codes_SRS_FRAME_CODEC_01_042: [frame_codec_encode_frame encodes the header, type specific bytes and frame payload of a frame that has frame_payload_size bytes.]*/
                      /* Codes_SRS_FRAME_CODEC_01_055: [Frames are divided into three distinct areas: a fixed width frame header, a variable width extended header, and a variable width frame body.] */
                      /* Codes_SRS_FRAME_CODEC_01_056: [frame header The frame header is a fixed size (8 byte) structure that precedes each frame.] */
                      /* Codes_SRS_FRAME_CODEC_01_057: [The frame header includes mandatory information necessary to parse the rest of the frame including size and type information.] */
                      /* Codes_SRS_FRAME_CODEC_01_058: [extended header The extended header is a variable width area preceding the frame body.] */
                      /* Codes_SRS_FRAME_CODEC_01_059: [This is an extension point defined for future expansion.] */
                      /* Codes_SRS_FRAME_CODEC_01_060: [The treatment of this area depends on the frame type.]*/
                      /* Codes_SRS_FRAME_CODEC_01_062: [SIZE Bytes 0-3 of the frame header contain the frame size.] */
                      /* Codes_SRS_FRAME_CODEC_01_063: [This is an unsigned 32-bit integer that MUST contain the total frame size of the frame header, extended header, and frame body.] */
                      /* Codes_SRS_FRAME_CODEC_01_064: [The frame is malformed if the size is less than the size of the frame header (8 bytes).] */
                      unsigned char frame_header[6];
                      /* Codes_SRS_FRAME_CODEC_01_090: [If the type_specific_size - 2 does not divide by 4, frame_codec_encode_frame shall pad the type_specific bytes with zeroes so that type specific data is according to the AMQP ISO.] */
                      unsigned char padding_bytes[] = { 0x00, 0x00, 0x00 };
  
                      frame_header[0] = (frame_size >> 24) & 0xFF;
                      frame_header[1] = (frame_size >> 16) & 0xFF;
                      frame_header[2] = (frame_size >> 8) & 0xFF;
                      frame_header[3] = frame_size & 0xFF;
                      /* Codes_SRS_FRAME_CODEC_01_065: [DOFF Byte 4 of the frame header is the data offset.] */
                      frame_header[4] = doff;
                      /* Codes_SRS_FRAME_CODEC_01_069: [TYPE Byte 5 of the frame header is a type code.] */
                      frame_header[5] = type;
  
                      payload_reserve_data(encoded_frame_payload, frame_body_offset);
                      payload_append_data(encoded_frame_payload, frame_header, sizeof(frame_header));
  
                      if (type_specific_size > 0)
                      {
                         payload_append_data(encoded_frame_payload, type_specific_bytes, type_specific_size);
                      }
  
                      if (padding_byte_count > 0)
                      {
                         payload_append_data(encoded_frame_payload, padding_bytes, padding_byte_count);
                      }
  
                      /* Codes_SRS_FRAME_CODEC_01_106: [All payloads shall be encoded in order as part of the frame.] */
                      payload_append_payload_as_copy(encoded_frame_payload, payloads);
  
                      /* Codes_SRS_FRAME_CODEC_01_088: [Encoded bytes shall be passed to the `on_bytes_encoded` callback in a single call, while setting the `encode complete` argument to true.] */
                      on_bytes_encoded(callback_context, encoded_frame_payload, true);
  
                      payload_destroy(&encoded_frame_payload);
  
                      /* Codes_SRS_FRAME_CODEC_01_043: [On success it shall return 0.] */
                      result = 0;
                  }
              }
          }
      }
  
      return result;
  }
  