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ihasmail/web/src/lib/__tests__/htmlAlternative.test.ts
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import { describe, expect, it } from "vitest";
import { hasHtmlAlternative } from "../html";
/*
* The rule: `htmlBody` is derived, so its presence proves nothing. Only the
* part's own type says whether there is an HTML alternative to render.
*
* The shapes below are what Stalwart 0.16.21 actually returned for one thread
* on 2026-09-10, read back through `Email/get` with
* `bodyProperties: ["partId", "type"]`. A plain-text message named the *same*
* part in both lists; a message with a real alternative named two.
*
* Getting this wrong is not a rendering nicety. Plain text went to the HTML
* path, which places the body under `white-space: normal`, so every line break
* collapsed: hard-wrapped mail arrived as one paragraph, and the signature and
* the quoted reply ran into the prose.
*/
describe("deciding whether a message has an HTML alternative", () => {
it("says no to a plain-text message, whose htmlBody holds the text part", () => {
// As returned for [email protected]: htmlBody[0] and textBody[0] are the
// same part, typed text/plain.
expect(hasHtmlAlternative({ type: "text/plain" }, "Hey,\n\nmy earlier response was before\n")).toBe(false);
});
it("says yes to a real multipart/alternative", () => {
expect(hasHtmlAlternative({ type: "text/html" }, "<p>Hello</p>")).toBe(true);
});
it("keeps the parameters that follow a media type", () => {
// `type` arrives bare in practice, but a charset must not turn a real HTML
// part into a plain-text one.
expect(hasHtmlAlternative({ type: "text/html; charset=utf-8" }, "<p>Hi</p>")).toBe(true);
});
it("is not fooled by a type that merely starts with the right letters", () => {
expect(hasHtmlAlternative({ type: "text/htmlish" }, "<p>Hi</p>")).toBe(false);
});
it("matches the type case-insensitively, since a header may be capitalized", () => {
expect(hasHtmlAlternative({ type: "TEXT/HTML" }, "<p>Hi</p>")).toBe(true);
});
it("says no when the part is HTML but its value never arrived", () => {
// maxBodyValueBytes can leave a part named with nothing fetched; falling
// through to the text body is the useful answer, not an empty pane.
expect(hasHtmlAlternative({ type: "text/html" }, undefined)).toBe(false);
expect(hasHtmlAlternative({ type: "text/html" }, "")).toBe(false);
});
it("says no when there is no part at all", () => {
expect(hasHtmlAlternative(undefined, undefined)).toBe(false);
expect(hasHtmlAlternative({}, "something")).toBe(false);
});
});