refactor(filecoin-proofs): add more information to piece size errors

* fix(comment): remove dead comment
* fix(errors): better error message
* feat(errors): add more error messaging
* refactor(errors): alert user to EOF and 0-byte read

Author: laser

filecoin-proofs/src/api/mod.rs

@@ -90,11 +90,17 @@ pub fn generate_piece_commitment<T: std::io::Read>(
     let n = write_padded(source, &temp_piece_file)
         .map_err(|err| format_err!("failed to write and preprocess bytes: {:?}", err))?;
 
+    if n == 0 {
+        return Err(format_err!(
+            "generate_piece_commitment: read 0 bytes from source before EOF"
+        ));
+    }
+
     let n = UnpaddedBytesAmount(n as u64);
 
     if n != piece_size {
         return Err(format_err!(
-            "wrote more bytes ({:?}) than expected ({:?}) when preprocessing",
+            "wrote ({:?}) but expected to write ({:?}) when preprocessing",
             n,
             piece_size
         ));
@@ -177,6 +183,8 @@ where
 
     match (write_rslt, join_rslt) {
         (Ok(n), Ok(Ok(r))) => {
+            ensure!(n != 0, "add_piece: read 0 bytes before EOF from source");
+
             let n = UnpaddedBytesAmount(n as u64);
 
             ensure!(

filecoin-proofs/src/pieces.rs

@@ -52,14 +52,16 @@ pub fn compute_comm_d(sector_size: SectorSize, piece_infos: &[PieceInfo]) -> Res
     let first = piece_infos.first().unwrap().clone();
     ensure!(
         u64::from(PaddedBytesAmount::from(first.size)).is_power_of_two(),
-        "Piece size must be a power of 2."
+        "Piece size ({:?}) must be a power of 2.",
+        PaddedBytesAmount::from(first.size)
     );
     stack.shift(first);
 
     for piece_info in piece_infos.iter().skip(1) {
         ensure!(
             u64::from(PaddedBytesAmount::from(piece_info.size)).is_power_of_two(),
-            "Piece size must be a power of 2."
+            "Piece size ({:?}) must be a power of 2.",
+            PaddedBytesAmount::from(piece_info.size)
         );
 
         while stack.peek().size < piece_info.size {
@@ -661,8 +663,6 @@ mod tests {
         }
         assert_eq!(staged_sector.len(), u64::from(sector_size) as usize);
 
-        // println!("{:?}", &piece_infos);
-
         let data_tree = graph.merkle_tree(&staged_sector)?;
         let comm_d_root: Fr = data_tree.root().into();
         let comm_d = commitment_from_fr::<Bls12>(comm_d_root);