Try get methods for Buf trait (#753)

src/lib.rs

@@ -132,12 +132,47 @@ fn min_u64_usize(a: u64, b: usize) -> usize {
     }
 }
 
+/// Error type for the `try_get_` methods of [`Buf`].
+/// Indicates that there were not enough remaining
+/// bytes in the buffer while attempting
+/// to get a value from a [`Buf`] with one
+/// of the `try_get_` methods.
+#[derive(Debug, PartialEq, Eq)]
+pub struct TryGetError {
+    /// The number of bytes necessary to get the value
+    pub requested: usize,
+
+    /// The number of bytes available in the buffer
+    pub available: usize,
+}
+
+impl core::fmt::Display for TryGetError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> Result<(), core::fmt::Error> {
+        write!(
+            f,
+            "Not enough bytes remaining in buffer to read value (requested {} but only {} available)",
+            self.requested,
+            self.available
+        )
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for TryGetError {}
+
+#[cfg(feature = "std")]
+impl From<TryGetError> for std::io::Error {
+    fn from(error: TryGetError) -> Self {
+        std::io::Error::new(std::io::ErrorKind::Other, error)
+    }
+}
+
 /// Panic with a nice error message.
 #[cold]
-fn panic_advance(idx: usize, len: usize) -> ! {
+fn panic_advance(error_info: &TryGetError) -> ! {
     panic!(
         "advance out of bounds: the len is {} but advancing by {}",
-        len, idx
+        error_info.available, error_info.requested
     );
 }