start CFDP source handler

@@ -2,0 +55,4 @@
+  if (step == TransactionStep::CRC_PROCEDURE) {
+    result = checksumGeneration();
+    if (result != OK) {
+      // TODO: Some error handling

@@ -2,0 +62,4 @@
+  if (step == TransactionStep::SENDING_METADATA) {
+    result = prepareAndSendMetadataPdu();
+    if (result != OK) {
+      // TODO: Error handling

@@ -2,0 +78,4 @@
+  if (step == TransactionStep::SENDING_EOF) {
+    result = prepareAndSendEofPdu();
+    if (result != OK) {
+      // TODO: Error handling

@@ -2,0 +139,4 @@
+      params.size = readLen;
+      auto result = sourceParams.user.vfs.readFromFile(params, buf.data(), buf.size());
+      if (result != OK) {
+        // TODO: I think this is a case for a filestore rejection, but it might sense to print