From 5a12f17032033e483b3ac0535c7a96cba1251baf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miguel=20=C3=81ngel=20Ortu=C3=B1o?= <ortuman@gmail.com>
Date: Tue, 3 Jan 2023 09:15:44 +0100
Subject: [PATCH] Added decoder input offset method
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This new method gives the location in the input stream of the most recently read byte.

Signed-off-by: Miguel Ángel Ortuño <ortuman@gmail.com>
---
 decoder.go      |  7 +++++++
 decoder_test.go | 23 +++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/decoder.go b/decoder.go
index 4a6d5ee..71b6133 100644
--- a/decoder.go
+++ b/decoder.go
@@ -17,6 +17,9 @@ type Decoder interface {
 	// and then only read/touch the fields relevant for that kind.
 	NextToken(t *Token) error
 
+	// InputOffset returns the current offset in the input stream.
+	InputOffset() int
+
 	// Reset resets the Decoder to the given io.Reader.
 	Reset(r io.Reader)
 }
@@ -101,6 +104,10 @@ func (thiz *decoder) discard(n int) (int, error) {
 	return n, nil
 }
 
+func (thiz *decoder) InputOffset() int {
+	return thiz.r
+}
+
 func (thiz *decoder) Reset(r io.Reader) {
 	thiz.rd = r
 	thiz.r = 0
diff --git a/decoder_test.go b/decoder_test.go
index d16de14..ec7eba9 100644
--- a/decoder_test.go
+++ b/decoder_test.go
@@ -178,6 +178,29 @@ func TestIgnoreComments(t *testing.T) {
 	assert.Equal(t, io.EOF, err3)
 }
 
+func TestInputOffset(t *testing.T) {
+	// given
+	var tk gosaxml.Token
+
+	doc := "<a>Testing input offset</a>"
+	lastOffset := len(doc)
+
+	dec := gosaxml.NewDecoder(bufio.NewReaderSize(strings.NewReader(doc), 1024))
+
+	// when
+	_ = dec.NextToken(&tk)
+	off1 := dec.InputOffset()
+	_ = dec.NextToken(&tk)
+	off2 := dec.InputOffset()
+	_ = dec.NextToken(&tk)
+	off3 := dec.InputOffset()
+
+	// then
+	assert.Equal(t, 2, off1)
+	assert.Equal(t, 23, off2)
+	assert.Equal(t, lastOffset, off3)
+}
+
 func assertTextElement(t *testing.T, text string, token gosaxml.Token) {
 	assert.Equal(t, uint8(gosaxml.TokenTypeTextElement), token.Kind)
 	assert.Equal(t, []byte(text), token.ByteData)