fix(BRIDGE-627): return RFC3501 compliant response for body-fld-enc & body-fld-param

imap/structure.go

@@ -92,13 +92,28 @@ func singlePartStructure(section *rfc822.Section, fields *paramList, writer *dua
 		return err
 	}
 
+	// Per RFC2045, if Content-Transfer-Encoding is missing, then we should assuume
+	// that the content is `7BIT`.
+	contentTransferEncoding := header.Get("Content-Transfer-Encoding")
+	if contentTransferEncoding == "" {
+		contentTransferEncoding = "7BIT"
+	}
+
 	fields.
 		addString(writer, mimeType).
-		addString(writer, mimeSubType).
-		addMap(writer, mimeParams).
+		addString(writer, mimeSubType)
+
+	// Per RFC3501 if `body-field-params` should be NIL if empty
+	if len(mimeParams) == 0 {
+		fields.addString(writer, "NIL")
+	} else {
+		fields.addMap(writer, mimeParams)
+	}
+
+	fields.
 		addString(writer, header.Get("Content-Id")).
 		addString(writer, header.Get("Content-Description")).
-		addString(writer, header.Get("Content-Transfer-Encoding")).
+		addString(writer, contentTransferEncoding).
 		addNumber(writer, len(section.Body()))
 
 	if mimeType == "message" && mimeSubType == "rfc822" {

imap/structure_test.go

@@ -72,7 +72,7 @@ hey there bro
 	require.NoError(t, err)
 	require.NotNil(t, parsed)
 
-	expected := "((\"text\" \"plain\" (\"charset\" \"utf-8\") NIL NIL \"quoted-printable\" 6 2)(\"message\" \"rfc822\" (\"name\" \"ISO-8859-1.eml\") NIL NIL NIL 127 (NIL \"ISO-8859-1\" ((NIL NIL \"random-mail\" \"pm.me\")) ((NIL NIL \"random-mail\" \"pm.me\")) ((NIL NIL \"random-mail\" \"pm.me\")) ((NIL NIL \"random-mail2\" \"pm.me\")) NIL NIL NIL NIL)(\"text\" \"plain\" (\"charset\" \"iso-8859-1\") NIL NIL NIL 14 1) 6) \"mixed\")"
+	expected := "((\"text\" \"plain\" (\"charset\" \"utf-8\") NIL NIL \"quoted-printable\" 6 2)(\"message\" \"rfc822\" (\"name\" \"ISO-8859-1.eml\") NIL NIL \"7BIT\" 127 (NIL \"ISO-8859-1\" ((NIL NIL \"random-mail\" \"pm.me\")) ((NIL NIL \"random-mail\" \"pm.me\")) ((NIL NIL \"random-mail\" \"pm.me\")) ((NIL NIL \"random-mail2\" \"pm.me\")) NIL NIL NIL NIL)(\"text\" \"plain\" (\"charset\" \"iso-8859-1\") NIL NIL \"7BIT\" 14 1) 6) \"mixed\")"
 	require.Equal(t, expected, parsed.Body)
 }
 

tests/helper_test.go

@@ -880,6 +880,17 @@ func newEmptyBodyStructureValidator() *bodyStructureValidator {
 		require.Empty(tb, s)
 	}
 
+	validEncoding := func(tb testing.TB, s string) {
+		validValues := []string{"7BIT", "8BIT", "BINARY", "BASE64", "QUOTED-PRINTABLE", ""}
+		tb.Helper()
+		for _, value := range validValues {
+			if strings.EqualFold(value, s) {
+				return
+			}
+		}
+		require.Failf(tb, "string not in allowed values", "got %q, want one of %v", s, validValues)
+	}
+
 	return &bodyStructureValidator{
 		validateMIMEType:    emptyString,
 		validateMimeSubType: emptyString,
@@ -888,7 +899,7 @@ func newEmptyBodyStructureValidator() *bodyStructureValidator {
 		},
 		validateID:          emptyString,
 		validateDescription: emptyString,
-		validateEncoding:    emptyString,
+		validateEncoding:    validEncoding,
 		validateSize: func(tb testing.TB, u uint32) {
 			require.Zero(tb, u)
 		},