Make PNG format decoder correctly handle cases where nbit is 0

src/decoder.rs

@@ -12,10 +12,7 @@ use crate::{
         complex::ComplexPackingDecodeError,
         png::PngDecodeError,
         run_length::RunLengthEncodingDecodeError,
-        simple::{
-            SimplePackingDecodeError, SimplePackingDecodeIterator,
-            SimplePackingDecodeIteratorWrapper,
-        },
+        simple::{SimplePackingDecodeError, SimplePackingDecodeIteratorWrapper},
     },
     error::*,
     reader::Grib2Read,
@@ -186,7 +183,7 @@ enum Grib2SubmessageDecoderIteratorWrapper<T0, T2, T3, T40, T41> {
     Template40(PhantomData<T40>),
     #[cfg(not(target_arch = "wasm32"))]
     Template40(SimplePackingDecodeIteratorWrapper<T40>),
-    Template41(SimplePackingDecodeIterator<T41>),
+    Template41(SimplePackingDecodeIteratorWrapper<T41>),
     Template200(std::vec::IntoIter<f32>),
 }
 

src/decoder/png.rs

@@ -1,6 +1,8 @@
 use crate::{
     decoder::{
-        param::SimplePackingParam, simple::SimplePackingDecodeIterator, stream::NBitwiseIterator,
+        param::SimplePackingParam,
+        simple::{SimplePackingDecodeIterator, SimplePackingDecodeIteratorWrapper},
+        stream::{FixedValueIterator, NBitwiseIterator},
     },
     DecodeError, Grib2SubmessageDecoder, GribError,
 };
@@ -13,7 +15,7 @@ pub enum PngDecodeError {
 
 pub(crate) fn decode(
     target: &Grib2SubmessageDecoder,
-) -> Result<SimplePackingDecodeIterator<impl Iterator<Item = u32> + '_>, GribError> {
+) -> Result<SimplePackingDecodeIteratorWrapper<impl Iterator<Item = u32> + '_>, GribError> {
     let sect5_data = &target.sect5_payload;
     let param = SimplePackingParam::from_buf(&sect5_data[6..16])?;
 
@@ -23,6 +25,18 @@ pub(crate) fn decode(
         )))
     })?;
 
+    if param.nbit == 0 {
+        eprintln!(
+            "WARNING: nbit = 0 for PNG decoder is not tested.
+            Please report your data and help us develop the library."
+        );
+        let decoder = SimplePackingDecodeIteratorWrapper::FixedValue(FixedValueIterator::new(
+            param.zero_bit_reference_value(),
+            target.num_points_encoded,
+        ));
+        return Ok(decoder);
+    };
+
     if param.nbit != 16 {
         eprintln!(
             "WARNING: nbit != 16 for PNG decoder is not tested.
@@ -32,6 +46,7 @@ pub(crate) fn decode(
 
     let iter = NBitwiseIterator::new(buf, usize::from(param.nbit));
     let iter = SimplePackingDecodeIterator::new(iter, &param);
+    let iter = SimplePackingDecodeIteratorWrapper::SimplePacking(iter);
     Ok(iter)
 }