Added protocol buffers support using nanopb. (#2217)

.gitmodules

@@ -227,6 +227,10 @@
 	path = Sming/Libraries/MultipartParser/multipart-parser
 	url = https://github.com/iafonov/multipart-parser-c.git
 	ignore = dirty
+[submodule "Libraries.nanopb"]
+	path = Sming/Libraries/nanopb/nanopb
+	url = https://github.com/nanopb/nanopb.git
+	ignore = dirty
 [submodule "Libraries.RapidXML"]
 	path = Sming/Libraries/RapidXML
 	url = https://github.com/mikee47/Sming-RapidXML

Sming/Libraries/nanopb/README.rst

@@ -0,0 +1,56 @@
+Nano Protocol-Buffer
+====================
+
+Introduction
+------------
+
+This component adds support for `Nano Protocol-Buffer <https://github.com/nanopb/nanopb/>`_ implementation.
+
+   Nanopb is a small code-size `Protocol Buffers <https://developers.google.com/protocol-buffers>`_ implementation in ansi C. It is especially suitable for use in microcontrollers, but fits any memory restricted system.
+
+
+C file generation from Proto files
+----------------------------------
+
+Once this component is installed you can use it to add Nano Protocol-Buffer support to your project and generate C and header files from Proto files.
+One possible way to call the generator is to go to the directory where the proto file is located and run the generator. As shown below::
+
+   make -C $SMING_HOME fetch nano-pb
+   cd <folder-with-proto-file>
+   python $SMING_HOME/Libraries/nanopb/nanopb/generator/nanopb_generator.py <desired-proto-file>.proto
+
+After the generator tool is run you will have newly generated C and header files that can be used in your Sming application.
+
+Using
+-----
+
+1. Add ``COMPONENT_DEPENDS += nanopb`` to your application componenent.mk file.
+2. Add these lines to your application::
+
+      #include <PbUtils.h>
+      // The line below should be replaced with the generated header file
+      #include "cast_channel.pb.h"
+
+3. Example::
+
+      #include <PbUtils.h>
+      #include "cast_channel.pb.h"
+
+      void doSomething(const uint8_t* data, size_t length)
+      {
+         // ...
+
+         extensions_api_cast_channel_CastMessage message = extensions_api_cast_channel_CastMessage_init_default;
+
+         message.protocol_version = extensions_api_cast_channel_CastMessage_ProtocolVersion_CASTV2_1_0;
+         message.source_id.funcs.encode = &pbEncodeData;
+         message.source_id.arg = new PbData(sourceId);
+         message.destination_id.funcs.encode = &pbEncodeData;
+         message.destination_id.arg = new PbData(destinationId);
+         message.nameSpace.funcs.encode = &pbEncodeData;
+         message.nameSpace.arg = new PbData(ns);
+         message.payload_type = extensions_api_cast_channel_CastMessage_PayloadType_STRING;
+         message.payload_utf8.funcs.encode = &pbEncodeData;
+         message.payload_utf8.arg = new PbData((uint8_t*)data, length);
+         // ...
+      }

Sming/Libraries/nanopb/component.mk

@@ -0,0 +1,4 @@
+COMPONENT_SRCDIRS := nanopb src
+COMPONENT_INCDIRS := $(COMPONENT_SRCDIRS)
+
+COMPONENT_SUBMODULES += nanopb

Sming/Libraries/nanopb/src/PbUtils.cpp

@@ -0,0 +1,41 @@
+#include "PbUtils.h"
+
+// See: https://iam777.tistory.com/538
+
+bool pbEncodeData(pb_ostream_t *stream, const pb_field_t *field, void * const *arg)
+{
+  PbData *data = (PbData*) *arg;
+  if(data == nullptr) {
+	  return false;
+  }
+
+  if (!pb_encode_tag_for_field(stream, field)) {
+    return false;
+  }
+
+  return pb_encode_string(stream, (uint8_t*)data->value, data->length);
+}
+
+bool pbDecodeData(pb_istream_t *stream, const pb_field_t *field, void **arg)
+{
+  uint8_t buffer[1024] = {0};
+
+  /* We could read block-by-block to avoid the large buffer... */
+  if (stream->bytes_left > sizeof(buffer) - 1) {
+    return false;
+  }
+
+  size_t available = stream->bytes_left;
+  if (!pb_read(stream, buffer, stream->bytes_left)) {
+    return false;
+  }
+
+
+  MemoryDataStream* data = (MemoryDataStream*) *arg;
+  if(data == nullptr) {
+	  data = new MemoryDataStream();
+	  *arg = (void*)data;
+  }
+  data->write(buffer, available);
+  return true;
+}

Sming/Libraries/nanopb/src/PbUtils.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <SmingCore.h>
+#include <Data/Stream/MemoryDataStream.h>
+#include <pb_encode.h>
+#include <pb_decode.h>
+
+class PbData
+{
+public:
+	uint8_t* value = nullptr;
+	size_t length = 0;
+
+	PbData(const String& text)
+	{
+		PbData((uint8_t *)text.c_str(), text.length());
+	}
+
+	PbData(uint8_t*  data, size_t length)
+	{
+		value = data;
+		this->length = length;
+	}
+};
+
+bool pbEncodeData(pb_ostream_t *stream, const pb_field_t *field, void * const *arg);
+bool pbDecodeData(pb_istream_t *stream, const pb_field_t *field, void **arg);