Improved de/serialise error messages

Fortune for rsh's current commit: Half curse − 半凶

src/message/binary.rs

@@ -9,6 +9,25 @@ use bytes::{
     Buf,
 };
 
+macro_rules! try_from {
+    (ref $into:ty, $from:expr $(; $fmt:literal)?) => {
+	{
+	    let from = &$from;
+	    #[inline] fn _type_name_of_val<T: ?Sized>(_: &T) -> &'static str
+	    {
+		::std::any::type_name::<T>()
+	    }
+	    <$into>::try_from(*from).wrap_err(eyre!("Failed to convert type"))
+		.with_section(|| ::std::any::type_name::<$into>().header("New type"))
+		.with_section(|| _type_name_of_val(from).header("Old type"))
+		.with_section(|| from.to_string().header("Value was"))
+	}
+    };
+}
+
+/// Check bit written/read from binary streams to check basic integrity.
+pub const MESSAGE_HEADER_CHECK: [u8; 4] = (0xc0ffee00u32).to_be_bytes();
+
 impl<V: ?Sized> SerializedMessage<V>
 {
     /// Write this message to a buffer
@@ -41,15 +60,22 @@ impl<V: ?Sized> SerializedMessage<V>
 	    (: $ser:expr) => {
 		{		    
 		    let mut v = StackVec::new();
-		    serde_cbor::to_writer(&mut v, $ser)?;
-		    buffer.put_u64(v.len().try_into()?);
+		    #[inline] fn _type_name_of_val<T: ?Sized>(_: &T) -> &'static str
+		    {
+			::std::any::type_name::<T>()
+		    }
+		    let ser = $ser;
+		    serde_cbor::to_writer(&mut v, $ser)
+			.wrap_err(eyre!("Failed to serialise value to temporary buffer"))
+			.with_section(|| _type_name_of_val(ser).header("Type was"))?;
+		    buffer.put_u64(try_from!(ref u64, v.len())?);
 		    write!(&v[..]);
 		}
 	    };
 	}
-	
+	write!(MESSAGE_HEADER_CHECK);
 	write!(: &self.header);
-	buffer.put_u64(self.data.len().try_into()?);
+	buffer.put_u64(try_from!(ref u64, self.data.len())?);
 	write!(self.data);
 	write!(self.hash);
 	write!(? self.enc_key);
@@ -93,21 +119,21 @@ impl<V: ?Sized + MessageValue> SerializedMessage<V>
 			    Some(def)
 			},
 			x => {
-			    return Err(eyre!("Invalid optional-set bit: {}", x));
+			    return Err(eyre!("Invalid optional-set bit (should be 0 or 1)").with_section(|| x.header("Value was")));
 			}
 		    }
 		}
 	    };
 	    (: $ser:ty) => {
 		{
-		    let len = usize::try_from(bytes.get_u64())?;
+		    let len = try_from!(ref usize, bytes.get_u64())?;
 		    if len > MAX_ALLOC_SIZE {
 			return Err(eyre!("Invalid length read: {}", len)
 				   .with_section(|| format!("Max length read: {}", MAX_ALLOC_SIZE)))
 		    }
 		    alloc_local_bytes(len, |de| {
 			read!(&mut de[..]);
-			serde_cbor::from_slice::<$ser>(&de[..]).wrap_err(eyre!("Failed to deserialise {} from reader", std::any::type_name::<$ser>()))
+			serde_cbor::from_slice::<$ser>(&de[..]).wrap_err(eyre!("Failed to deserialise CBOR from reader")).with_section(|| std::any::type_name::<$ser>().header("Type to deserialise was"))
 		    })?
 			
 		}
@@ -120,13 +146,22 @@ impl<V: ?Sized + MessageValue> SerializedMessage<V>
 		}
 	    }
 	}
-
+	let mut check = [0u8; MESSAGE_HEADER_CHECK.len()];
+	read!(&mut check[..]);
+	if check != MESSAGE_HEADER_CHECK {
+	    return Err(eyre!("Invalid check bit for message header"))
+		.with_section(|| u32::from_be_bytes(check).header("Expected"))
+		.with_section(|| u32::from_be_bytes(MESSAGE_HEADER_CHECK).header("Got"));
+	}
+	
 	let header = read!(: SerHeader);
-	let data_len = usize::try_from(bytes.get_u64())?;
+	let data_len = try_from!(ref usize, bytes.get_u64())?;
 	let mut data = Vec::with_capacity(std::cmp::min(data_len, MAX_ALLOC_SIZE)); //XXX: Redesign so we don't allocate OR try to read massive buffers by accident on corrupted/malformed messages
 	read!(&mut data, data_len);
 	if data.len()!=data_len {
-	    return Err(eyre!("Failed to read {} bytes from buffer (got {})", data_len, data.len()));
+	    return Err(eyre!("Failed to read body bytes from buffer"))
+		.with_section(|| format!("{} bytes", data_len).header("Tried to read"))
+		.with_section(|| format!("{} bytes", data.len()).header("Read only"));
 	}
 	let mut hash = sha256::Sha256Hash::default();
 	read!(&mut hash);