@xmtp/content-type-remote-attachment/src/Attachment.ts

An XMTP content type to support sending file attachments that are stored off network

import {
  ContentTypeId,
  type ContentCodec,
  type EncodedContent,
} from "@xmtp/content-type-primitives";

export const ContentTypeAttachment = new ContentTypeId({
  authorityId: "xmtp.org",
  typeId: "attachment",
  versionMajor: 1,
  versionMinor: 0,
});

export type Attachment = {
  filename: string;
  mimeType: string;
  data: Uint8Array;
};

export type AttachmentParameters = {
  filename: string;
  mimeType: string;
};

export class AttachmentCodec
  implements ContentCodec<Attachment, AttachmentParameters>
{
  get contentType(): ContentTypeId {
    return ContentTypeAttachment;
  }

  encode(content: Attachment) {
    return {
      type: ContentTypeAttachment,
      parameters: {
        filename: content.filename,
        mimeType: content.mimeType,
      },
      content: content.data,
    };
  }

  decode(content: EncodedContent<AttachmentParameters>): Attachment {
    return {
      filename: content.parameters.filename,
      mimeType: content.parameters.mimeType,
      data: content.content,
    };
  }

  fallback(content: Attachment): string | undefined {
    return `Can’t display "${content.filename}". This app doesn’t support attachments.`;
  }

  shouldPush() {
    return true;
  }
}