fix: preview .eml attachments that carry attachments of their own

patches/postal-mime+3.0.0.patch

@@ -0,0 +1,82 @@
+diff --git a/node_modules/postal-mime/src/base64-decoder.js b/node_modules/postal-mime/src/base64-decoder.js
+index 93c2aea..ba6e3f1 100644
+--- a/node_modules/postal-mime/src/base64-decoder.js
++++ b/node_modules/postal-mime/src/base64-decoder.js
+@@ -1,4 +1,4 @@
+-import { decodeBase64, blobToArrayBuffer } from './decode-strings.js';
++import { decodeBase64, concatChunks } from './decode-strings.js';
+ 
+ export default class Base64Decoder {
+     constructor(opts) {
+@@ -49,6 +49,6 @@ export default class Base64Decoder {
+     finalize() {
+         this.flushRemainder();
+ 
+-        return blobToArrayBuffer(new Blob(this.chunks, { type: 'application/octet-stream' }));
++        return concatChunks(this.chunks);
+     }
+ }
+diff --git a/node_modules/postal-mime/src/decode-strings.js b/node_modules/postal-mime/src/decode-strings.js
+index a5e058e..f255e8d 100644
+--- a/node_modules/postal-mime/src/decode-strings.js
++++ b/node_modules/postal-mime/src/decode-strings.js
+@@ -145,6 +145,23 @@ export function getDecoder(charset) {
+  * @param {Blob} blob Blob to convert
+  * @returns {ArrayBuffer} Converted value
+  */
++// React Native's Blob cannot be built from ArrayBuffers or typed arrays, so
++// the decoders join their chunks here instead of through a Blob.
++export function concatChunks(chunks) {
++    const parts = chunks.map(chunk => {
++        if (typeof chunk === 'string') return textEncoder.encode(chunk);
++        if (chunk instanceof ArrayBuffer) return new Uint8Array(chunk);
++        return new Uint8Array(chunk.buffer, chunk.byteOffset, chunk.byteLength);
++    });
++    const out = new Uint8Array(parts.reduce((n, part) => n + part.byteLength, 0));
++    let pos = 0;
++    for (const part of parts) {
++        out.set(part, pos);
++        pos += part.byteLength;
++    }
++    return out.buffer;
++}
++
+ export async function blobToArrayBuffer(blob) {
+     if ('arrayBuffer' in blob) {
+         return await blob.arrayBuffer();
+diff --git a/node_modules/postal-mime/src/pass-through-decoder.js b/node_modules/postal-mime/src/pass-through-decoder.js
+index ad1c222..1e1d012 100644
+--- a/node_modules/postal-mime/src/pass-through-decoder.js
++++ b/node_modules/postal-mime/src/pass-through-decoder.js
+@@ -1,4 +1,4 @@
+-import { blobToArrayBuffer } from './decode-strings.js';
++import { concatChunks } from './decode-strings.js';
+ 
+ export default class PassThroughDecoder {
+     constructor() {
+@@ -12,6 +12,6 @@ export default class PassThroughDecoder {
+ 
+     finalize() {
+         // convert an array of arraybuffers into a blob and then back into a single arraybuffer
+-        return blobToArrayBuffer(new Blob(this.chunks, { type: 'application/octet-stream' }));
++        return concatChunks(this.chunks);
+     }
+ }
+diff --git a/node_modules/postal-mime/src/qp-decoder.js b/node_modules/postal-mime/src/qp-decoder.js
+index adee72c..3973673 100644
+--- a/node_modules/postal-mime/src/qp-decoder.js
++++ b/node_modules/postal-mime/src/qp-decoder.js
+@@ -1,4 +1,4 @@
+-import { blobToArrayBuffer, hexNibble } from './decode-strings.js';
++import { concatChunks, hexNibble } from './decode-strings.js';
+ 
+ const CHR_EQUALS = 0x3d;
+ const CHR_LF = 0x0a;
+@@ -83,6 +83,6 @@ export default class QPDecoder {
+         this.flushBuffer();
+ 
+         // convert an array of arraybuffers into a blob and then back into a single arraybuffer
+-        return blobToArrayBuffer(new Blob(this.chunks, { type: 'application/octet-stream' }));
++        return concatChunks(this.chunks);
+     }
+ }

src/lib/__tests__/postal-mime-rn.test.ts

@@ -0,0 +1,54 @@
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+import PostalMime from 'postal-mime';
+
+// React Native's Blob only takes strings and other Blobs; building one from an
+// ArrayBuffer or typed array throws. postal-mime used to join every decoded
+// part through such a Blob, so an .eml with an attachment could not be
+// previewed on the device (patches/postal-mime+3.0.0.patch).
+class ReactNativeBlob {
+  constructor(parts: unknown[] = []) {
+    if (parts.some((p) => p instanceof ArrayBuffer || ArrayBuffer.isView(p))) {
+      throw new Error("Creating blobs from 'ArrayBuffer' and 'ArrayBufferView' are not supported");
+    }
+  }
+}
+
+const MESSAGE = [
+  'From: Carol <carol@example.org>',
+  'Subject: With parts',
+  'MIME-Version: 1.0',
+  'Content-Type: multipart/mixed; boundary="b1"',
+  '',
+  '--b1',
+  'Content-Type: text/plain; charset=utf-8',
+  'Content-Transfer-Encoding: quoted-printable',
+  '',
+  'Gr=C3=BC=C3=9Fe',
+  '--b1',
+  'Content-Type: application/octet-stream; name="a.bin"',
+  'Content-Transfer-Encoding: base64',
+  'Content-Disposition: attachment; filename="a.bin"',
+  '',
+  'AAECAwQF',
+  '--b1',
+  'Content-Type: text/plain; name="inner.txt"',
+  'Content-Disposition: attachment; filename="inner.txt"',
+  '',
+  'Inner text.',
+  '--b1--',
+  '',
+].join('\r\n');
+
+describe('postal-mime under React Native', () => {
+  const realBlob = globalThis.Blob;
+  beforeEach(() => { (globalThis as { Blob: unknown }).Blob = ReactNativeBlob; });
+  afterEach(() => { globalThis.Blob = realBlob; });
+
+  it('decodes base64, quoted-printable and plain parts without a Blob', async () => {
+    const parsed = await PostalMime.parse(new TextEncoder().encode(MESSAGE), { attachmentEncoding: 'arraybuffer' });
+    expect(parsed.text?.trim()).toBe('Grüße');
+    const [bin, txt] = parsed.attachments;
+    expect(Array.from(new Uint8Array(bin.content as ArrayBuffer))).toEqual([0, 1, 2, 3, 4, 5]);
+    expect(new TextDecoder().decode(txt.content as ArrayBuffer).trim()).toBe('Inner text.');
+  });
+});