src/backup/index.rs: new ChunkListReader

src/backup/index.rs

@@ -1,4 +1,42 @@
-pub trait IndexFile {
+pub trait IndexFile: Send {
     fn index_count(&self) -> usize;
     fn index_digest(&self, pos: usize) -> Option<&[u8; 32]>;
 }
+
+/// This struct can read the list of chunks from an `IndexFile`
+///
+/// The reader simply returns a birary stream of 32 byte digest values.
+pub struct ChunkListReader {
+    index: Box<dyn IndexFile>,
+    pos: usize,
+    count: usize,
+}
+
+impl ChunkListReader {
+
+    pub fn new(index: Box<dyn IndexFile>) -> Self {
+        let count = index.index_count();
+        Self { index, pos: 0, count }
+    }
+}
+
+impl std::io::Read for ChunkListReader {
+
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, std::io::Error> {
+        if buf.len() < 32 { panic!("read buffer too small"); }
+        if self.pos < self.count {
+            let mut written = 0;
+            loop {
+                let digest = self.index.index_digest(self.pos).unwrap();
+                unsafe { std::ptr::copy_nonoverlapping(digest.as_ptr(), buf.as_mut_ptr().add(written), 32); }
+                self.pos += 1;
+                written += 32;
+                if self.pos >= self.count { break; }
+                if (written + 32) >= buf.len() { break; }
+            }
+            return Ok(written);
+        } else {
+            return Ok(0);
+        }
+    }
+}