feat: Replace data fillcontent with custom reader

content.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"errors"
+	"io"
+)
+
+const contentCharset = "-ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+type contentReader struct {
+	size int64
+	cur  int64
+}
+
+// Read implements the io.Read interface.
+func (r *contentReader) Read(p []byte) (int, error) {
+	length := r.size - 1
+
+	if r.cur >= length {
+		return 0, io.EOF
+	}
+	if len(p) == 0 {
+		return 0, nil
+	}
+
+	var n int
+	if r.cur == 0 {
+		p[n] = '|'
+		r.cur++
+		n++
+	}
+
+	for n < len(p) && r.cur <= length {
+		p[n] = contentCharset[int(r.cur)%len(contentCharset)]
+		r.cur++
+		n++
+	}
+
+	if r.cur >= length {
+		p[n-1] = '|'
+	}
+
+	return n, nil
+}
+
+// Seek implements the io.Seek interface.
+func (r *contentReader) Seek(offset int64, whence int) (int64, error) {
+	switch whence {
+	default:
+		return 0, errors.New("seek: invalid whence")
+	case io.SeekStart:
+		offset += 0
+	case io.SeekCurrent:
+		offset += r.cur
+	case io.SeekEnd:
+		offset += r.size - 1
+	}
+
+	if offset < 0 {
+		return 0, errors.New("seek: invalid offset")
+	}
+
+	r.cur = offset
+
+	return offset, nil
+}