set ContentType and -Encoding on telemetry (#333)

Author: JuergenSchwertl

shared/src/azure_iot_nx_client.c

@@ -37,6 +37,12 @@
 #define TELEMETRY_BUFFER_SIZE  256
 #define PROPERTIES_BUFFER_SIZE 128
 
+// define static strings for content type and -encoding on message property bag 
+static const UCHAR content_type_property[] = "$.ct";
+static const UCHAR content_encoding_property[] = "$.ce";
+static const UCHAR content_type_json[] = "application%2Fjson";
+static const UCHAR content_encoding_utf8[] = "utf-8";
+
 static UCHAR telemetry_buffer[TELEMETRY_BUFFER_SIZE];
 static UCHAR properties_buffer[PROPERTIES_BUFFER_SIZE];
 
@@ -666,6 +672,28 @@ UINT azure_iot_nx_client_publish_telemetry(AZURE_IOT_NX_CONTEXT* context_ptr,
         return status;
     }
 
+    // set the ContentType property on the message to "application/json" (url-encoded)
+    status = nx_azure_iot_hub_client_telemetry_property_add(packet_ptr, content_type_property, sizeof( content_type_property )-1,
+                                                            content_type_json,  sizeof( content_type_json )-1,
+                                                            NX_WAIT_FOREVER);
+    if (status != NX_AZURE_IOT_SUCCESS)
+    {
+        printf("Error:  cannot set ContentType message property (0x%08X)\r\n", status);
+        nx_azure_iot_hub_client_telemetry_message_delete(packet_ptr);
+        return status;
+    }
+        
+    // set the ContentEncoding property on the message to "utf-8"
+    status = nx_azure_iot_hub_client_telemetry_property_add(packet_ptr, content_encoding_property, sizeof( content_encoding_property )-1,
+                                                            content_encoding_utf8, sizeof( content_encoding_utf8 )-1,
+                                                            NX_WAIT_FOREVER);
+    if (status != NX_AZURE_IOT_SUCCESS)
+    {
+        printf("Error: Canot set ContentEncoding message property (0x%08X)\r\n", status);
+        nx_azure_iot_hub_client_telemetry_message_delete(packet_ptr);
+        return status;
+    }
+
     telemetry_length = nx_azure_iot_json_writer_get_bytes_used(&json_writer);
     if ((status = nx_azure_iot_hub_client_telemetry_send(
              &context_ptr->iothub_client, packet_ptr, telemetry_buffer, telemetry_length, NX_WAIT_FOREVER)))