From 7fad5c186fd76904a8a58a9956aecce6d6040e2b Mon Sep 17 00:00:00 2001
From: Sam Gwilym <sam@gwil.garden>
Date: Sun, 14 Jul 2024 11:44:24 +0100
Subject: [PATCH] Implement Error on EncodingConsumerError, DecodeError

---
 data-model/src/encoding/compact_width.rs |  7 ++-
 data-model/src/encoding/error.rs         | 67 ++++++++++++++++++------
 data-model/src/lib.rs                    |  2 +-
 3 files changed, 59 insertions(+), 17 deletions(-)

diff --git a/data-model/src/encoding/compact_width.rs b/data-model/src/encoding/compact_width.rs
index de7e0f2..b768cc3 100644
--- a/data-model/src/encoding/compact_width.rs
+++ b/data-model/src/encoding/compact_width.rs
@@ -1,3 +1,5 @@
+use core::error::Error;
+
 use crate::encoding::error::{DecodeError, EncodingConsumerError};
 use crate::encoding::parameters::Decoder;
 use crate::encoding::unsigned_int::{U16BE, U32BE, U64BE, U8BE};
@@ -92,7 +94,10 @@ impl CompactWidth {
 pub async fn encode_compact_width_be<Consumer: BulkConsumer<Item = u8>>(
     value: u64,
     consumer: &mut Consumer,
-) -> Result<(), EncodingConsumerError<Consumer::Error>> {
+) -> Result<(), EncodingConsumerError<Consumer::Error>>
+where
+    Consumer::Error: Error,
+{
     let width = CompactWidth::from_u64(value).width();
 
     consumer
diff --git a/data-model/src/encoding/error.rs b/data-model/src/encoding/error.rs
index e1b3b3c..e3a0a56 100644
--- a/data-model/src/encoding/error.rs
+++ b/data-model/src/encoding/error.rs
@@ -1,9 +1,7 @@
+use core::error::Error;
+use core::{fmt::Display, fmt::Formatter, num::TryFromIntError};
 use either::Either;
-use std::num::TryFromIntError;
-use ufotofu::{
-    common::errors::{ConsumeFullSliceError, OverwriteFullSliceError},
-    local_nb::producer::PipeIntoSliceError,
-};
+use ufotofu::common::errors::{ConsumeFullSliceError, OverwriteFullSliceError};
 
 /// Returned when a encoding fails to be consumed by a [`ufotofu::local_nb::Consumer`].
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -23,6 +21,25 @@ impl<E> From<ConsumeFullSliceError<E>> for EncodingConsumerError<E> {
     }
 }
 
+impl<E> Error for EncodingConsumerError<E>
+where
+    E: 'static + Error,
+{
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        Some(&self.reason)
+    }
+}
+
+impl<E> Display for EncodingConsumerError<E> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
+        write!(
+            f,
+            "The consumer failed to consume after consuming {} bytes",
+            self.bytes_consumed
+        )
+    }
+}
+
 /// Everything that can go wrong when decoding a value.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum DecodeError<ProducerError> {
@@ -34,8 +51,8 @@ pub enum DecodeError<ProducerError> {
     U64DoesNotFitUsize,
 }
 
-impl<'a, T, F, E> From<PipeIntoSliceError<'a, T, F, E>> for DecodeError<E> {
-    fn from(value: PipeIntoSliceError<'a, T, F, E>) -> Self {
+impl<F, E> From<OverwriteFullSliceError<F, E>> for DecodeError<E> {
+    fn from(value: OverwriteFullSliceError<F, E>) -> Self {
         match value.reason {
             Either::Left(_) => DecodeError::InvalidInput,
             Either::Right(err) => DecodeError::Producer(err),
@@ -43,17 +60,37 @@ impl<'a, T, F, E> From<PipeIntoSliceError<'a, T, F, E>> for DecodeError<E> {
     }
 }
 
-impl<'a, T, F, E> From<OverwriteFullSliceError<'a, T, F, E>> for DecodeError<E> {
-    fn from(value: OverwriteFullSliceError<'a, T, F, E>) -> Self {
-        match value.reason {
-            Either::Left(_) => DecodeError::InvalidInput,
-            Either::Right(err) => DecodeError::Producer(err),
+impl<ProducerError> From<TryFromIntError> for DecodeError<ProducerError> {
+    fn from(_: TryFromIntError) -> Self {
+        DecodeError::U64DoesNotFitUsize
+    }
+}
+
+impl<E> Error for DecodeError<E>
+where
+    E: 'static + Error,
+{
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        match self {
+            DecodeError::Producer(err) => Some(err),
+            DecodeError::InvalidInput => None,
+            DecodeError::U64DoesNotFitUsize => None,
         }
     }
 }
 
-impl<ProducerError> From<TryFromIntError> for DecodeError<ProducerError> {
-    fn from(_: TryFromIntError) -> Self {
-        DecodeError::U64DoesNotFitUsize
+impl<E> Display for DecodeError<E> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
+        match self {
+            DecodeError::Producer(_) => {
+                write!(f, "The underlying producer encountered an error",)
+            }
+            DecodeError::InvalidInput => {
+                write!(f, "Decoding failed due to receiving invalid input",)
+            }
+            DecodeError::U64DoesNotFitUsize => {
+                write!(f, "Tried (and failed) to decode a u64 to a 32-bit usize",)
+            }
+        }
     }
 }
diff --git a/data-model/src/lib.rs b/data-model/src/lib.rs
index 4b3f7b9..40524d6 100644
--- a/data-model/src/lib.rs
+++ b/data-model/src/lib.rs
@@ -1,4 +1,4 @@
-#![feature(new_uninit, async_fn_traits)]
+#![feature(new_uninit, async_fn_traits, error_in_core)]
 
 pub mod encoding;
 pub mod entry;