Add specific error for Crc errors. (#112)

src/de/flavors.rs

@@ -259,7 +259,7 @@ pub mod crc {
                                         if crc == prev_crc {
                                             Ok(remainder)
                                         } else {
-                                            Err(Error::DeserializeBadEncoding)
+                                            Err(Error::DeserializeBadCrc)
                                         }
                                     }
                                     e @ Err(_) => e,

src/error.rs

@@ -29,6 +29,8 @@ pub enum Error {
     DeserializeBadEnum,
     /// The original data was not well encoded
     DeserializeBadEncoding,
+    /// Bad CRC while deserializing
+    DeserializeBadCrc,
     /// Serde Serialization Error
     SerdeSerCustom,
     /// Serde Deserialization Error
@@ -60,6 +62,7 @@ impl Display for Error {
                 DeserializeBadOption => "Found an Option discriminant that wasn't 0 or 1",
                 DeserializeBadEnum => "Found an enum discriminant that was > u32::max_value()",
                 DeserializeBadEncoding => "The original data was not well encoded",
+                DeserializeBadCrc => "Bad CRC while deserializing",
                 SerdeSerCustom => "Serde Serialization Error",
                 SerdeDeCustom => "Serde Deserialization Error",
                 CollectStrError => "Error while processing `collect_str` during serialization",

tests/crc.rs

@@ -37,3 +37,24 @@ fn test_crc_8() {
     let remaining_bytes = [];
     assert_eq!(res, (expected_bytes, remaining_bytes.as_slice()));
 }
+
+#[test]
+#[cfg(feature = "use-crc")]
+fn test_crc_error() {
+    use crc::{Crc, CRC_32_ISCSI};
+
+    let data: &[u8] = &[0x01, 0x00, 0x20, 0x30];
+    let buffer = &mut [0u8; 32];
+    let crc = Crc::<u32>::new(&CRC_32_ISCSI);
+    let digest = crc.digest();
+    let res = postcard::to_slice_crc32(data, buffer, digest).unwrap();
+
+    // intentionally corrupt the crc
+    let last = res.len() - 1;
+    res[last] = 0;
+
+    let digest = crc.digest();
+    let res = postcard::take_from_bytes_crc32::<[u8; 5]>(&res, digest);
+
+    assert_eq!(res, Err(postcard::Error::DeserializeBadCrc));
+}