From 829e0e1a206763af3e0985d77a0747465e4f3857 Mon Sep 17 00:00:00 2001
From: Steven Allen <steven@stebalien.com>
Date: Thu, 13 Aug 2020 16:53:13 -0700
Subject: [PATCH] Add a validate function.

This function is equivalent to Deferred.UnmarshalCBOR, just more efficient
because it doesn't copy.
---
 validate.go      | 59 ++++++++++++++++++++++++++++++++++++++++++++++++
 validate_test.go | 42 ++++++++++++++++++++++++++++++++++
 2 files changed, 101 insertions(+)
 create mode 100644 validate.go
 create mode 100644 validate_test.go

diff --git a/validate.go b/validate.go
new file mode 100644
index 0000000..04a5e26
--- /dev/null
+++ b/validate.go
@@ -0,0 +1,59 @@
+package typegen
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+)
+
+// ValidateCBOR validates that a byte array is a single valid CBOR object.
+func ValidateCBOR(b []byte) error {
+	// The code here is basically identical to the previous function, it
+	// just doesn't copy.
+
+	br := bytes.NewReader(b)
+
+	// Allocate some scratch space.
+	scratch := make([]byte, maxHeaderSize)
+
+	for remaining := uint64(1); remaining > 0; remaining-- {
+		maj, extra, err := CborReadHeaderBuf(br, scratch)
+		if err != nil {
+			return err
+		}
+
+		switch maj {
+		case MajUnsignedInt, MajNegativeInt, MajOther:
+			// nothing fancy to do
+		case MajByteString, MajTextString:
+			if extra > ByteArrayMaxLen {
+				return maxLengthError
+			}
+			if uint64(br.Len()) < extra {
+				return io.ErrUnexpectedEOF
+			}
+
+			if _, err := br.Seek(int64(extra), io.SeekCurrent); err != nil {
+				return err
+			}
+		case MajTag:
+			remaining++
+		case MajArray:
+			if extra > MaxLength {
+				return maxLengthError
+			}
+			remaining += extra
+		case MajMap:
+			if extra > MaxLength {
+				return maxLengthError
+			}
+			remaining += extra * 2
+		default:
+			return fmt.Errorf("unhandled deferred cbor type: %d", maj)
+		}
+	}
+	if br.Len() > 0 {
+		return fmt.Errorf("unexpected %d unread bytes", br.Len())
+	}
+	return nil
+}
diff --git a/validate_test.go b/validate_test.go
new file mode 100644
index 0000000..6bf0f9e
--- /dev/null
+++ b/validate_test.go
@@ -0,0 +1,42 @@
+package typegen
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestValidateShort(t *testing.T) {
+	var buf bytes.Buffer
+	if err := WriteMajorTypeHeader(&buf, MajByteString, 100); err != nil {
+		t.Fatal("failed to write header")
+	}
+
+	if err := ValidateCBOR(buf.Bytes()); err == nil {
+		t.Fatal("expected an error checking truncated cbor")
+	}
+}
+
+func TestValidateDouble(t *testing.T) {
+	var buf bytes.Buffer
+	if err := WriteBool(&buf, false); err != nil {
+		t.Fatal(err)
+	}
+	if err := WriteBool(&buf, false); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := ValidateCBOR(buf.Bytes()); err == nil {
+		t.Fatal("expected an error checking cbor with two objects")
+	}
+}
+
+func TestValidate(t *testing.T) {
+	var buf bytes.Buffer
+	if err := WriteBool(&buf, false); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := ValidateCBOR(buf.Bytes()); err != nil {
+		t.Fatal(err)
+	}
+}
-- 
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