Add the lengths to the error message when alloc is available

Author: sgued

src/bytearray.rs

@@ -9,7 +9,35 @@ use core::ops::{Deref, DerefMut};
 use serde::de::{Deserialize, Deserializer, Error, SeqAccess, Visitor};
 use serde::ser::{Serialize, Serializer};
 
-const ERROR_STRING: &str = "Expected a fixed amount of bytes, got a different amount";
+#[cfg(any(feature = "alloc", feature = "std"))]
+fn error_string(expected: usize, got: usize) -> impl AsRef<str> {
+    #[cfg(not(feature = "std"))]
+    let res = alloc::format!("Expected {} bytes, got {}", expected, got);
+
+    #[cfg(feature = "std")]
+    let res = format!("Expected {} bytes, got {}", expected, got);
+    res
+}
+
+#[cfg(all(not(feature = "alloc"), not(feature = "std")))]
+fn error_string(_expected: usize, _got: usize) -> impl AsRef<str> {
+    "Expected a fixed amount of bytes, got a different amount"
+}
+
+#[cfg(any(feature = "alloc", feature = "std"))]
+fn error_string_more(expected: usize) -> impl AsRef<str> {
+    #[cfg(not(feature = "std"))]
+    let res = alloc::format!("Got more than the expected {} bytes", expected);
+
+    #[cfg(feature = "std")]
+    let res = format!("Got more than the expected {} bytes", expected);
+    res
+}
+
+#[cfg(all(not(feature = "alloc"), not(feature = "std")))]
+fn error_string_more(_expected: usize) -> impl AsRef<str> {
+    "Got more than the expected number of bytes"
+}
 
 /// Wrapper around `[u8; N]` to serialize and deserialize efficiently.
 ///
@@ -191,15 +219,15 @@ impl<'de, const N: usize> Visitor<'de> for ByteArrayVisitor<N> {
         let mut idx = 0;
         while let Some(b) = visitor.next_element()? {
             if idx >= N {
-                return Err(V::Error::custom(ERROR_STRING));
+                return Err(V::Error::custom(error_string_more(N).as_ref()));
             }
 
             bytes[idx] = b;
             idx += 1;
         }
 
         if idx != N {
-            return Err(V::Error::custom(ERROR_STRING));
+            return Err(V::Error::custom(error_string(N, idx).as_ref()));
         }
 
         Ok(ByteArray::from(bytes))
@@ -210,7 +238,9 @@ impl<'de, const N: usize> Visitor<'de> for ByteArrayVisitor<N> {
         E: Error,
     {
         Ok(ByteArray {
-            bytes: v.try_into().map_err(|_| E::custom(ERROR_STRING))?,
+            bytes: v
+                .try_into()
+                .map_err(|_| E::custom(error_string(N, v.len()).as_ref()))?,
         })
     }
 
@@ -222,7 +252,7 @@ impl<'de, const N: usize> Visitor<'de> for ByteArrayVisitor<N> {
             bytes: v
                 .as_bytes()
                 .try_into()
-                .map_err(|_| E::custom(ERROR_STRING))?,
+                .map_err(|_| E::custom(error_string(N, v.len()).as_ref()))?,
         })
     }
 }