src/backup/data_blob.rs: move parts into single files

src/backup/checksum_writer.rs

@@ -0,0 +1,48 @@
+use failure::*;
+use std::io::Write;
+
+pub struct ChecksumWriter<'a, W> {
+    writer: W,
+    hasher: crc32fast::Hasher,
+    signer: Option<openssl::sign::Signer<'a>>,
+}
+
+impl <'a, W: Write> ChecksumWriter<'a, W> {
+
+    pub fn new(writer: W, signer: Option<openssl::sign::Signer<'a>>) -> Self {
+        let hasher = crc32fast::Hasher::new();
+        Self { writer, hasher, signer }
+    }
+
+    pub fn finish(mut self) -> Result<(W, u32, Option<[u8; 32]>), Error> {
+        let crc = self.hasher.finalize();
+
+        if let Some(ref mut signer) = self.signer {
+            let mut tag = [0u8; 32];
+            signer.sign(&mut tag)?;
+            Ok((self.writer, crc, Some(tag)))
+        } else {
+            Ok((self.writer, crc, None))
+        }
+    }
+}
+
+impl <'a, W: Write> Write for ChecksumWriter<'a, W> {
+
+    fn write(&mut self, buf: &[u8]) -> Result<usize, std::io::Error> {
+        self.hasher.update(buf);
+        if let Some(ref mut signer) = self.signer {
+            signer.update(buf)
+                .map_err(|err| {
+                    std::io::Error::new(
+                        std::io::ErrorKind::Other,
+                        format!("hmac update failed - {}", err))
+                })?;
+        }
+        self.writer.write(buf)
+    }
+
+    fn flush(&mut self) -> Result<(), std::io::Error> {
+        self.writer.flush()
+    }
+}