move information to schema

Author: julienledem

format/Message.fbs

@@ -107,6 +107,10 @@ table Field {
   // present only if the field is dictionary encoded
   // will point to a dictionary provided by a DictionaryBatch message
   dictionary: long;
+  /// the buffers produced for this type (as derived from the Type)
+  /// does not include children
+  /// each recordbatch will return instances of those Buffers.
+  buffers: [ VectorType ];
   // children apply only to Nested data types like Struct, List and Union
   children: [Field];
 }
@@ -145,7 +149,7 @@ enum VectorType: short {
 }
 
 /// A Buffer represents a single contiguous memory segment
-table Buffer {
+struct Buffer {
   /// The shared memory page id where this buffer is located. Currently this is
   /// not used
   page: int;
@@ -157,9 +161,6 @@ table Buffer {
   /// The absolute length (in bytes) of the memory buffer. The memory is found
   /// from offset (inclusive) to offset + length (non-inclusive).
   length: long;
-
-  /// the type of the vector to be explicit
-  type: VectorType;
 }
 
 /// Metadata about a field at some level of a nested type tree (but not
@@ -168,7 +169,7 @@ table Buffer {
 /// For example, a List<Int16> with values [[1, 2, 3], null, [4], [5, 6], null]
 /// would have {length: 5, null_count: 2} for its List node, and {length: 6,
 /// null_count: 0} for its Int16 node, as separate FieldNode structs
-table FieldNode {
+struct FieldNode {
   /// The number of value slots in the Arrow array at this level of a nested
   /// tree
   length: int;
@@ -177,30 +178,26 @@ table FieldNode {
   /// to write their physical validity bitmap out as a materialized buffer,
   /// instead setting the length of the bitmap buffer to 0.
   null_count: int;
-
-  /// children according to the schema
-  children: [FieldNode];
-
-  /// Buffers correspond to the pre-ordered flattened buffer tree
-  ///
-  /// The number of buffers appended to this list depends on the field type and length.
-  /// For example, most primitive arrays will have 2 buffers, 1 for the validity
-  /// bitmap and 1 for the values. For struct arrays, there will only be a
-  /// single buffer for the validity (nulls) bitmap
-  vectors: [Buffer];
 }
 
 /// A data header describing the shared memory layout of a "record" or "row"
 /// batch. Some systems call this a "row batch" internally and others a "record
 /// batch".
 table RecordBatch {
-  /// number of records / rows. The root arrays in the batch should all have this
+  /// number of records / rows. The arrays in the batch should all have this
   /// length
   length: int;
 
-  /// Nodes correspond to the first level of the logical schema
+  /// Nodes correspond to the pre-ordered flattened logical schema
   nodes: [FieldNode];
 
+  /// Buffers correspond to the pre-ordered flattened buffer tree
+  ///
+  /// The number of buffers appended to this list depends on the schema. For
+  /// example, most primitive arrays will have 2 buffers, 1 for the validity
+  /// bitmap and 1 for the values. For struct arrays, there will only be a
+  /// single buffer for the validity (nulls) bitmap
+  buffers: [Buffer];
 }
 
 /// ----------------------------------------------------------------------