feat: initial parser exposing walker/writer

pkg/message/parser/writer_test.go

@@ -0,0 +1,39 @@
+package parser
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestParserWrite(t *testing.T) {
+	p := newTestParser(t, "text_html_octet_attachment.eml")
+
+	w := p.NewWriter()
+
+	buf := new(bytes.Buffer)
+
+	assert.NoError(t, w.Write(buf))
+	assert.Equal(t, s("text_html_octet_attachment.eml"), buf.String())
+}
+
+func TestParserWriteNoAttachments(t *testing.T) {
+	p := newTestParser(t, "text_html_octet_attachment.eml")
+
+	w := p.
+		NewWriter().
+		WithCondition(func(p *Part) bool {
+			// We don't write if the content disposition says it's an attachment.
+			if disp, _, err := p.Header.ContentDisposition(); err == nil && disp == "attachment" {
+				return false
+			}
+
+			return true
+		})
+
+	buf := new(bytes.Buffer)
+
+	assert.NoError(t, w.Write(buf))
+	assert.Equal(t, s("text_html.eml"), buf.String())
+}