Detect nonstandard hash algo and stop folder (ref #2314)

lib/protocol/hashalgorithm.go

@@ -0,0 +1,54 @@
+// Copyright (C) 2016 The Protocol Authors.
+
+package protocol
+
+import "fmt"
+
+type HashAlgorithm int
+
+const (
+	SHA256 HashAlgorithm = iota
+)
+
+func (h HashAlgorithm) String() string {
+	switch h {
+	case SHA256:
+		return "sha256"
+	default:
+		return "unknown"
+	}
+}
+
+// FlagBits returns the bits that we should or into the folder flag field to
+// indicate the hash algorithm.
+func (h HashAlgorithm) FlagBits() uint32 {
+	switch h {
+	case SHA256:
+		return FolderHashSHA256 << FolderHashShiftBits
+	default:
+		panic("unknown hash algorithm")
+	}
+}
+
+func (h *HashAlgorithm) UnmarshalText(bs []byte) error {
+	switch string(bs) {
+	case "sha256":
+		*h = SHA256
+		return nil
+	}
+	return fmt.Errorf("Unknown hash algorithm %q", string(bs))
+}
+
+func (h *HashAlgorithm) MarshalText() ([]byte, error) {
+	return []byte(h.String()), nil
+}
+
+func HashAlgorithmFromFlagBits(flags uint32) (HashAlgorithm, error) {
+	algo := flags >> FolderHashShiftBits & FolderHashMask
+	switch algo {
+	case FolderHashSHA256:
+		return SHA256, nil
+	default:
+		return 0, fmt.Errorf("Unknown hash algorithm %d", algo)
+	}
+}

lib/protocol/hashalgorithm_test.go

@@ -0,0 +1,35 @@
+// Copyright (C) 2016 The Protocol Authors.
+
+package protocol
+
+import "testing"
+
+/*
+   0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                       Reserved                  | Hash  |D|P|R|
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+*/
+func TestHashAlgorithmFromFlagBits(t *testing.T) {
+	// SHA256 is algorithm zero, shifted three bits to the left (for clarity,
+	// I know it doesn't actually do anything).
+
+	sha256 := uint32(0 << 3)
+
+	h, err := HashAlgorithmFromFlagBits(sha256)
+	if err != nil {
+		t.Error(err)
+	}
+	if h != SHA256 {
+		t.Error("Zero should have unmarshalled as SHA256")
+	}
+
+	// Any other algorithm is unknown
+	unknown := uint32(1 << 3)
+
+	_, err = HashAlgorithmFromFlagBits(unknown)
+	if err == nil {
+		t.Error("Unknown algo should not have unmarshalled")
+	}
+}

lib/protocol/protocol.go

@@ -66,6 +66,13 @@ const (
 	FlagFolderReadOnly     uint32 = 1 << 0
 	FlagFolderIgnorePerms         = 1 << 1
 	FlagFolderIgnoreDelete        = 1 << 2
+
+	// The folder hash algorithm IDs, to be put in the flags field by shifting
+	// left FolderHashShiftBits
+	FolderHashSHA256 = 0
+	// ... 1 through 15 currently reserved
+	FolderHashMask      = 15
+	FolderHashShiftBits = 3
 )
 
 // ClusterConfigMessage.Folders.Devices flags