add peek method to read without advancing

src/readstream.rs

@@ -680,6 +680,24 @@ where
         T::read(self, size)
     }
 
+    /// Read a value based on the provided type without advancing the stream
+    #[inline]
+    pub fn peek<T: BitRead<'a, E>>(&mut self) -> Result<T> {
+        let pos = self.pos;
+        let result = T::read(self);
+        self.pos = pos;
+        result
+    }
+
+    /// Read a value based on the provided type and size without advancing the stream
+    #[inline]
+    pub fn peek_sized<T: BitReadSized<'a, E>>(&mut self, size: usize) -> Result<T> {
+        let pos = self.pos;
+        let result = T::read(self, size);
+        self.pos = pos;
+        result
+    }
+
     #[doc(hidden)]
     #[inline]
     pub unsafe fn read_sized_unchecked<T: BitReadSized<'a, E>>(

tests/read_tests.rs

@@ -295,6 +295,20 @@ fn read_trait() {
     assert_eq!(Some(0b0110_1010), f);
 }
 
+#[test]
+fn peek_trait() {
+    let buffer = BitReadBuffer::new(BYTES, BigEndian);
+    let mut stream = BitReadStream::new(buffer);
+    let a: u8 = stream.read().unwrap();
+    assert_eq!(0b1011_0101, a);
+    assert_eq!(8, stream.pos());
+    let b: i8 = stream.peek().unwrap();
+    assert_eq!(8, stream.pos());
+    assert_eq!(0b110_1010, b);
+    let b: i8 = stream.read().unwrap();
+    assert_eq!(0b110_1010, b);
+}
+
 #[test]
 fn read_trait_unchecked() {
     unsafe {
@@ -346,6 +360,15 @@ fn read_sized_trait() {
     assert_eq!(0b10u8, result.read_int::<u8>(2).unwrap());
 }
 
+#[test]
+fn peek_sized_trait() {
+    let buffer = BitReadBuffer::new(BYTES, BigEndian);
+    let mut stream = BitReadStream::new(buffer);
+    let a: u8 = stream.peek_sized(4).unwrap();
+    assert_eq!(0b1011, a);
+    assert_eq!(0, stream.pos());
+}
+
 #[test]
 fn read_sized_trait_unchecked() {
     unsafe {