NFC Design: Add note about NDEF Message construction.

features/nfc/doc/nfc_design.md

@@ -436,7 +436,15 @@ virtual void on_parsing_terminated();
 
 ### Serialization
 
-**TBD**
+The class `MessageBuilder` is used to map a record into an NDEF message. It
+includes a data buffer that contains the _raw_ message. Client code use the
+functions `append_record` to append a new record into the message being built.
+
+![ndef_message_builder_diagram]
+
+For convenience, serialization functions for common types are provided as well as
+a specialized `MessageBuilder` named `SimpleMessageBuilder` that exposes them
+in an object oriented fashion.
 
 ## HAL APIs
 
@@ -509,3 +517,4 @@ There are currently at least four event queues (Plaftorm, BLE, USB, IP) in mbed
 [ndef_record_parser_diagram]: uml_diagram_ndef_record_parser.png
 [ndef_common_parsers_diagram]: uml_diagram_ndef_common_parsers.png
 [ndef_simple_parser_diagram]: uml_diagram_ndef_simple_parser.png
+[ndef_message_builder_diagram]: uml_diagram_ndef_message_builder_diagram.png

features/nfc/doc/uml_diagram_ndef_message_builder_diagram.txt

@@ -0,0 +1,64 @@
+@startuml
+
+package ndef {
+
+class MessageBuilder { 
+    +MessageBuilder(uint8_t* buffer, size_t capacity)
+    +~MessageBuilder()
+    +bool append_record(const RecordType& type, const RecordPayload* payload, bool is_last_record = false)
+    +bool append_record(const Record& record)
+    +const uint8_t* get_data() const;
+    +size_t get_data_size() const;
+}
+
+class Record { 
+}
+
+class RecordType{ 
+}
+
+class RecordPayload{ 
+}
+
+class RecordID{
+}
+
+Record *-- RecordType
+Record *-- "0..1" RecordPayload
+Record *-- "0..1" RecordID
+
+Record - MessageBuilder: insert >
+
+}
+
+package common { 
+
+class SimpleMessageBuilder { 
+    +SimpleMessageBuilder(uint8_t* buffer, size_t capacity)
+    +~SimpleMessageBuilder()
+    +bool append_uri(const URI&)
+    +bool append_text(const Text&)
+    +bool append_mime(const Mime&)
+} 
+
+class URI { 
++friend bool append_record(ndef::MessageBuilder&, const URI&)
+}
+
+class Text { 
++friend bool append_record(ndef::MessageBuilder&, const Text&)
+}
+
+class Mime { 
++friend bool append_record(ndef::MessageBuilder&, const Mime&)
+}
+
+SimpleMessageBuilder --|> MessageBuilder
+
+URI -- SimpleMessageBuilder: wrap >
+Text -- SimpleMessageBuilder: wrap >
+Mime -- SimpleMessageBuilder: wrap >
+
+}
+
+@enduml