Show warnings in GUI (fixes #66)

blocks.go

@@ -0,0 +1,74 @@
+package main
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"io"
+)
+
+type Block struct {
+	Offset int64
+	Size   uint32
+	Hash   []byte
+}
+
+// Blocks returns the blockwise hash of the reader.
+func Blocks(r io.Reader, blocksize int) ([]Block, error) {
+	var blocks []Block
+	var offset int64
+	for {
+		lr := &io.LimitedReader{r, int64(blocksize)}
+		hf := sha256.New()
+		n, err := io.Copy(hf, lr)
+		if err != nil {
+			return nil, err
+		}
+
+		if n == 0 {
+			break
+		}
+
+		b := Block{
+			Offset: offset,
+			Size:   uint32(n),
+			Hash:   hf.Sum(nil),
+		}
+		blocks = append(blocks, b)
+		offset += int64(n)
+	}
+
+	if len(blocks) == 0 {
+		// Empty file
+		blocks = append(blocks, Block{
+			Offset: 0,
+			Size:   0,
+			Hash:   []uint8{0xe3, 0xb0, 0xc4, 0x42, 0x98, 0xfc, 0x1c, 0x14, 0x9a, 0xfb, 0xf4, 0xc8, 0x99, 0x6f, 0xb9, 0x24, 0x27, 0xae, 0x41, 0xe4, 0x64, 0x9b, 0x93, 0x4c, 0xa4, 0x95, 0x99, 0x1b, 0x78, 0x52, 0xb8, 0x55},
+		})
+	}
+
+	return blocks, nil
+}
+
+// BlockDiff returns lists of common and missing (to transform src into tgt)
+// blocks. Both block lists must have been created with the same block size.
+func BlockDiff(src, tgt []Block) (have, need []Block) {
+	if len(tgt) == 0 && len(src) != 0 {
+		return nil, nil
+	}
+
+	if len(tgt) != 0 && len(src) == 0 {
+		// Copy the entire file
+		return nil, tgt
+	}
+
+	for i := range tgt {
+		if i >= len(src) || bytes.Compare(tgt[i].Hash, src[i].Hash) != 0 {
+			// Copy differing block
+			need = append(need, tgt[i])
+		} else {
+			have = append(have, tgt[i])
+		}
+	}
+
+	return have, need
+}