Support attachments in your app built with XMTP

Use the attachment and remote attachment content types to support attachments in your app. Remote attachments of any size can be sent using the RemoteAttachmentCodec and a storage provider.

Install the package

npm i @xmtp/content-type-remote-attachment

In some SDKs, the AttachmentCodec is already included in the SDK. If not, you can install the package using the following command:

Configure the content type

After importing the package, you can register the codec.

JavaScript

import {
  ContentTypeAttachment,
  AttachmentCodec,
  RemoteAttachmentCodec,
  ContentTypeRemoteAttachment,
} from "@xmtp/content-type-remote-attachment";
// Create the XMTP client
const xmtp = await Client.create(signer, { env: "dev" });
xmtp.registerCodec(new AttachmentCodec());
xmtp.registerCodec(new RemoteAttachmentCodec());

Send a remote attachment

Load the file. This example uses a web browser to load the file:

JavaScript

//image is the uploaded event.target.files[0];
const data = await new Promise((resolve, reject) => {
  const reader = new FileReader();
  reader.onload = () => {
    if (reader.result instanceof ArrayBuffer) {
      resolve(reader.result);
    } else {
      reject(new Error("Not an ArrayBuffer"));
    }
  };
  reader.readAsArrayBuffer(image);
});

Create an attachment object:

TypeScript

// Local file details
const attachment = {
  filename: image?.name,
  mimeType: image?.type,
  data: new Uint8Array(data),
};

Use RemoteAttachmentCodec.encodeEncrypted to encrypt an attachment:

TypeScript

const encryptedEncoded = await RemoteAttachmentCodec.encodeEncrypted(
  attachment,
  new AttachmentCodec()
);

Upload an encrypted attachment to a location where it will be accessible via an HTTPS GET request. This location will depend on which storage provider you use based on your needs. For example, the xmtp.chat example app uses web3.storage. (This information is shared for educational purposes only and is not an endorsement.)

Now that you have a url, you can create a RemoteAttachment:

JavaScript

const remoteAttachment = {
  url: url,
  contentDigest: encryptedEncoded.digest,
  salt: encryptedEncoded.salt,
  nonce: encryptedEncoded.nonce,
  secret: encryptedEncoded.secret,
  scheme: "https://",
  filename: attachment.filename,
  contentLength: attachment.data.byteLength,
};

Now that you have a remote attachment, you can send it:

TypeScript

await conversation.send(remoteAttachment, {
  contentType: ContentTypeRemoteAttachment,
});

Receive, decode, and decrypt a remote attachment

Now that you can receive a remote attachment, you need a way to receive a remote attachment. For example:

TypeScript

import { ContentTypeRemoteAttachment } from "@xmtp/content-type-remote-attachment";
 
if (message.contentType.sameAs(RemoteAttachmentContentType)) {
  const attachment = await RemoteAttachmentCodec.load(message.content, client);
}

You now have the original attachment:

Bash

attachment.filename // => "screenshot.png"
attachment.mimeType // => "image/png",
attachment.data // => [the PNG data]

Once you've created the attachment object, you can create a preview to show in the message input field before sending:

TypeScript

const objectURL = URL.createObjectURL(
  new Blob([Buffer.from(attachment.data)], {
    type: attachment.mimeType,
  })
);
 
const img = document.createElement("img");
img.src = objectURL;
img.title = attachment.filename;

To handle unsupported content types, refer to the fallback section.