Add StrealReader to allow stream download/unpack in client

Author: Alenar

mithril-client/src/utils/mod.rs

@@ -2,7 +2,9 @@
 //! This module contains tools needed mostly in services layers.
 
 mod progress_reporter;
+mod stream_reader;
 mod unpacker;
 
 pub use progress_reporter::*;
+pub use stream_reader::*;
 pub use unpacker::*;

mithril-client/src/utils/stream_reader.rs

@@ -0,0 +1,35 @@
+use flume::Receiver;
+use std::io;
+
+// Credits and many thanks to https://stackoverflow.com/a/69967522 for most of this code
+
+/// A channel receiver that implement [io::Read].
+pub struct StreamReader {
+    receiver: Receiver<Vec<u8>>,
+    current: io::Cursor<Vec<u8>>,
+}
+
+impl StreamReader {
+    /// [StreamReader] factory
+    pub fn new(receiver: Receiver<Vec<u8>>) -> Self {
+        Self {
+            receiver,
+            current: io::Cursor::new(vec![]),
+        }
+    }
+}
+
+impl io::Read for StreamReader {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        if self.current.position() == self.current.get_ref().len() as u64 {
+            // We've exhausted the previous chunk, get a new one.
+            if let Ok(vec) = self.receiver.recv() {
+                self.current = io::Cursor::new(vec);
+            }
+            // If recv() "fails", it means the sender closed its part of
+            // the channel, which means EOF. Propagate EOF by allowing
+            // a read from the exhausted cursor.
+        }
+        self.current.read(buf)
+    }
+}