lib/model: Verify request content against weak (and possibly strong) hash (#4767)

lib/scanner/blocks.go

@@ -7,6 +7,7 @@
 package scanner
 
 import (
+	"bytes"
 	"context"
 	"hash"
 	"io"
@@ -107,6 +108,29 @@ func Blocks(ctx context.Context, r io.Reader, blocksize int, sizehint int64, cou
 	return blocks, nil
 }
 
+func Validate(buf, hash []byte, weakHash uint32) bool {
+	rd := bytes.NewReader(buf)
+	if weakHash != 0 {
+		whf := adler32.New()
+		if _, err := io.Copy(whf, rd); err == nil && whf.Sum32() == weakHash {
+			return true
+		}
+		// Copy error or mismatch, go to next algo.
+		rd.Seek(0, io.SeekStart)
+	}
+
+	if len(hash) > 0 {
+		hf := sha256.New()
+		if _, err := io.Copy(hf, rd); err == nil {
+			// Sum allocates, so let's hope we don't hit this often.
+			return bytes.Equal(hf.Sum(nil), hash)
+		}
+	}
+
+	// Both algos failed or no hashes were specified. Assume it's all good.
+	return true
+}
+
 type noopHash struct{}
 
 func (noopHash) Sum32() uint32             { return 0 }