WIP pipeline post processor checks, but no general make frame yet

disk/src/agg/scalarbinbatch.rs

@@ -1,5 +1,5 @@
 use crate::agg::binnedt::{AggregatableTdim, AggregatorTdim};
-use crate::agg::streams::{Appendable, Bins, StreamItem};
+use crate::agg::streams::{Appendable, Bins, StreamItem, ToJsonBytes};
 use crate::agg::{AggregatableXdim1Bin, Fits, FitsInside};
 use crate::binned::{MakeBytesFrame, RangeCompletableItem, StreamKind};
 use crate::frame::makeframe::make_frame;
@@ -331,3 +331,9 @@ impl Appendable for MinMaxAvgScalarBinBatch {
         self.avgs.extend_from_slice(&src.avgs);
     }
 }
+
+impl ToJsonBytes for MinMaxAvgScalarBinBatch {
+    fn to_json_bytes(&self) -> Result<Vec<u8>, Error> {
+        Ok(serde_json::to_vec(self)?)
+    }
+}

disk/src/agg/streams.rs

@@ -48,9 +48,12 @@ pub trait CollectionSpecMaker2 {
     fn spec(bin_count_exp: u32) -> Box<dyn CollectionSpec2>;
 }
 
+pub trait ToJsonBytes {
+    fn to_json_bytes(&self) -> Result<Vec<u8>, Error>;
+}
+
 pub trait ToJsonResult {
-    type Output;
-    fn to_json_result(&self) -> Result<Self::Output, Error>;
+    fn to_json_result(&self) -> Result<Box<dyn ToJsonBytes>, Error>;
 }
 
 pub trait Appendable: WithLen {