Implement de::from_slice_count

src/de.rs

@@ -54,6 +54,42 @@ where
     Ok(value)
 }
 
+/// Decodes a value from the first piece of valid CBOR data in a slice,
+/// returning the number of bytes read to produce the value.
+///
+/// # Examples
+///
+/// Deserialize a `String`
+///
+/// ```
+/// # use serde_cbor::de;
+/// let v: Vec<u8> = vec![0x66, 0x66, 0x6f, 0x6f, 0x62, 0x61, 0x72,
+///                       0xde, 0xad, 0xbe, 0xef]; // nonsense trailing data
+/// let (value, len): (String, _) = de::from_slice_count(&v[..]).unwrap();
+/// assert_eq!(value, "foobar");
+/// assert_eq!(len, 7);
+/// ```
+///
+/// Deserialize two consecutive `String`s
+///
+/// ```
+/// # use serde_cbor::de;
+/// let v: Vec<u8> = vec![0x63, 0x66, 0x6F, 0x6F, 0x63, 0x62, 0x61, 0x72];
+/// let (value_1, off): (String, _) = de::from_slice_count(&v[..]).unwrap();
+/// let (value_2, _): (String, _) = de::from_slice_count(&v[off..]).unwrap();
+/// assert_eq!(value_1, "foo");
+/// assert_eq!(value_2, "bar");
+/// ```
+#[cfg(any(feature = "std", feature = "alloc"))]
+pub fn from_slice_count<'a, T>(slice: &'a [u8]) -> Result<(T, usize)>
+where
+    T: de::Deserialize<'a>,
+{
+    let mut deserializer = Deserializer::from_slice(slice);
+    let value = de::Deserialize::deserialize(&mut deserializer)?;
+    Ok((value, deserializer.byte_offset()))
+}
+
 // When the "std" feature is enabled there should be little to no need to ever use this function,
 // as `from_slice` covers all use cases (at the expense of being less efficient).
 /// Decode a value from CBOR data in a mutable slice.