Add deku_input example

CHANGELOG.md

@@ -25,7 +25,9 @@ let ec = EcHdr::from_reader((&mut file, 0)).unwrap();
 ```
 
 - The more internal (with context) `read(..)` was replaced with `from_reader_with_ctx(..)`.
-Now unused variables `deku::input`, `deku::input_bits`, and `deku::rest` were removed. `deku::reader` is the replacement.
+With the switch to internal streaming, the variables `deku::input`, `deku::input_bits`, and `deku::rest` are now not possible and were removed.
+`deku::reader` is a replacement for some of the functionality.
+See [examples/deku_input.rs](examples/deku_input.rs) for a new example of caching all reads.
 
 old:
 ```rust

examples/deku_input.rs

@@ -0,0 +1,43 @@
+//! Example of a close replacement for deku::input
+use deku::prelude::*;
+use std::io::{self, Cursor, Read};
+
+/// Every read to this struct will be saved into an internal cache. This is to keep the cache
+/// around for the crc without reading from the buffer twice
+struct ReaderCrc<R: Read> {
+    reader: R,
+    pub cache: Vec<u8>,
+}
+
+impl<R: Read> ReaderCrc<R> {
+    pub fn new(reader: R) -> Self {
+        Self {
+            reader,
+            cache: vec![],
+        }
+    }
+}
+
+impl<R: Read> Read for ReaderCrc<R> {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        let n = self.reader.read(buf);
+        self.cache.extend_from_slice(buf);
+        n
+    }
+}
+
+#[derive(Debug, DekuRead)]
+pub struct DekuStruct {
+    pub a: u8,
+    pub b: u8,
+}
+
+fn main() {
+    let data = vec![0x01, 0x02];
+    let input = Cursor::new(&data);
+    let mut reader = ReaderCrc::new(input);
+    let (_, s) = DekuStruct::from_reader((&mut reader, 0)).unwrap();
+    assert_eq!(reader.cache, data);
+    assert_eq!(s.a, 1);
+    assert_eq!(s.b, 2);
+}