From e8f3f98aa086936e7975443f4f6f37ccd3c32a73 Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Tue, 15 Aug 2023 21:03:57 +0100
Subject: [PATCH] lib/readers: add NoSeeker to adapt io.Reader to io.ReadSeeker

---
 lib/readers/noseeker.go      | 22 ++++++++++++++++++++++
 lib/readers/noseeker_test.go | 31 +++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)
 create mode 100644 lib/readers/noseeker.go
 create mode 100644 lib/readers/noseeker_test.go

diff --git a/lib/readers/noseeker.go b/lib/readers/noseeker.go
new file mode 100644
index 000000000..1cd7e762c
--- /dev/null
+++ b/lib/readers/noseeker.go
@@ -0,0 +1,22 @@
+package readers
+
+import (
+	"errors"
+	"io"
+)
+
+var (
+	errCantSeek = errors.New("can't Seek")
+)
+
+// NoSeeker adapts an io.Reader into an io.ReadSeeker.
+//
+// However if Seek() is called it will return an error.
+type NoSeeker struct {
+	io.Reader
+}
+
+// Seek the stream - returns an error
+func (r NoSeeker) Seek(offset int64, whence int) (abs int64, err error) {
+	return 0, errCantSeek
+}
diff --git a/lib/readers/noseeker_test.go b/lib/readers/noseeker_test.go
new file mode 100644
index 000000000..3f8d88c2f
--- /dev/null
+++ b/lib/readers/noseeker_test.go
@@ -0,0 +1,31 @@
+package readers
+
+import (
+	"bytes"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNoSeeker(t *testing.T) {
+	r := bytes.NewBufferString("hello")
+	rs := NoSeeker{Reader: r}
+
+	// Check read
+	b := make([]byte, 4)
+	n, err := rs.Read(b)
+	assert.NoError(t, err)
+	assert.Equal(t, 4, n)
+	assert.Equal(t, []byte("hell"), b)
+
+	// Check seek
+	_, err = rs.Seek(0, io.SeekCurrent)
+	assert.Equal(t, errCantSeek, err)
+}
+
+// check interfaces
+var (
+	_ io.Reader = NoSeeker{}
+	_ io.Seeker = NoSeeker{}
+)