Support attachments in your app built with XMTP

Use the remote attachment or attachment content type to support attachments in your app.

Use the remote attachment content type to send attachments of any size.
Use the attachment content type to send attachments smaller than 1MB.

Support remote attachments of any size

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.

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:

//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:

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

Use RemoteAttachmentCodec.encodeEncrypted to encrypt an attachment:

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:

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:

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:

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:

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.

Support attachments smaller than 1MB

Attachments smaller than 1MB can be sent using the AttachmentCodec. The codec will automatically encrypt the attachment and upload it to the XMTP network.

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:

Import and register

Browser

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

Load local file

// Read local file and extract its details
const file = fs.readFileSync("xmtp.png");
const filename = path.basename("xmtp.png");
const extname = path.extname("xmtp.png");
console.log(`Filename: ${filename}`);
console.log(`File Type: ${extname}`);

Send encrypted file

// Convert the file to a Uint8Array
const blob = new Blob([file], { type: extname });
let imgArray = new Uint8Array(await blob.arrayBuffer());
 
const attachment = {
  filename: filename,
  mimeType: extname, //image, video or audio
  data: imgArray,
};
 
console.log("Attachment created", attachment);
await conversation.send(attachment, { contentType: ContentTypeAttachment });

Receive encrypted file

if (message.contentType.sameAs(ContentTypeAttachment)) {
  const blobdecoded = new Blob([message.content.data], {
    type: message.content.mimeType,
  });
  const url = URL.createObjectURL(blobdecoded);
}