add MultiReader and TeeReader

Author: yuk1ty

chapter3/Cargo.toml

@@ -32,3 +32,6 @@ path = "src/3_9_5/main.rs"
 [[bin]]
 name = "3_6_1"
 path = "src/3_6_1/main.rs"
+[[bin]]
+name = "3_7"
+path = "src/3_7/main.rs"

chapter3/src/3_7/main.rs

@@ -0,0 +1,51 @@
+use std::io::{Read, Write};
+
+struct MultiReader(Vec<Box<dyn Read>>);
+
+impl MultiReader {
+    pub fn new(readers: Vec<Box<dyn Read>>) -> Self {
+        Self(readers)
+    }
+}
+
+impl Read for MultiReader {
+    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+        for r in &mut self.0 {
+            r.read_exact(buf)?;
+        }
+        Ok(buf.len())
+    }
+}
+
+struct TeeReader<R, W>
+where
+    R: Read,
+    W: Write,
+{
+    reader: R,
+    writer: W,
+}
+
+impl<R, W> TeeReader<R, W>
+where
+    R: Read,
+    W: Write,
+{
+    pub fn new(reader: R, writer: W) -> Self {
+        Self { reader, writer }
+    }
+}
+
+impl<R, W> Read for TeeReader<R, W>
+where
+    R: Read,
+    W: Write,
+{
+    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+        let n = self.reader.read(buf)?;
+        self.writer.write_all(&buf[..n])?;
+        Ok(n)
+    }
+}
+
+fn main() {}