Complete rewrite of the puller (fixes #638, fixes #715, fixes #701)

internal/scanner/blocks.go

@@ -7,6 +7,7 @@ package scanner
 import (
 	"bytes"
 	"crypto/sha256"
+	"fmt"
 	"io"
 
 	"github.com/syncthing/syncthing/internal/protocol"
@@ -88,3 +89,32 @@ func BlockDiff(src, tgt []protocol.BlockInfo) (have, need []protocol.BlockInfo)
 
 	return have, need
 }
+
+// Verify returns nil or an error describing the mismatch between the block
+// list and actual reader contents
+func Verify(r io.Reader, blocksize int, blocks []protocol.BlockInfo) error {
+	hf := sha256.New()
+	for i, block := range blocks {
+		lr := &io.LimitedReader{R: r, N: int64(blocksize)}
+		_, err := io.Copy(hf, lr)
+		if err != nil {
+			return err
+		}
+
+		hash := hf.Sum(nil)
+		hf.Reset()
+
+		if bytes.Compare(hash, block.Hash) != 0 {
+			return fmt.Errorf("hash mismatch %x != %x for block %d", hash, block.Hash, i)
+		}
+	}
+
+	// We should have reached the end  now
+	bs := make([]byte, 1)
+	n, err := r.Read(bs)
+	if n != 0 || err != io.EOF {
+		return fmt.Errorf("file continues past end of blocks")
+	}
+
+	return nil
+}