✨ Support relationship property for embedded files

The `AFRelationship` key in the PDF file specification dictionary can be
used to indicate the role of an embedded file in the context of the
document. This key is required for PDF/A documents.

This commit adds support for a `relationship` property of an embedded
file to set it.

README.md

@@ -603,14 +603,18 @@ archival purposes. Those files can be added to the document using the
 representing a file with the following properties:
 
 - `content`: The binary content of the file as a `Uint8Array`.
-- `fileName`: The name of the file as it will appear in the
-  list of attachments in the PDF viewer.
+- `fileName`: The name of the file as it will appear in the list of
+  attachments in the PDF viewer.
 - `mimeType`: The MIME type of the file.
 - `description` (optional): A brief description of the file's content or
   purpose. This information can be displayed to the user in the PDF
   viewer.
-- `creationDate` (optional): The date and time when the file was created.
-- `modificationDate` (optional): The date and time when the file was last
+- `creationDate` (optional): The date and time when the file was
+  created.
+- `modificationDate` (optional): The date and time when the file was
+  last modified.
+- `relationship` (optional): A name that specifies the relationship
+  between the file and the document.
 
 ```ts
 const document = {

src/api/document.ts

@@ -101,6 +101,27 @@ export type DocumentDefinition = {
   };
 };
 
+/**
+ * Describes the relationship between the embedded file.
+ * - `Source`: The embedded file is the source material.
+ * - `Data`: The embedded file contains data related to the document.
+ * - `Alternative`: The embedded file is an alternative representation.
+ * - `Supplement`: The embedded file supplements the document.
+ * - `EncryptedPayload`: The embedded file is an encrypted payload.
+ * - `FormData`: The embedded file contains form data.
+ * - `Schema`: The embedded file contains a schema.
+ * - `Unspecified`: No specific relationship.
+ */
+export type FileRelationShip =
+  | 'Source'
+  | 'Data'
+  | 'Alternative'
+  | 'Supplement'
+  | 'EncryptedPayload'
+  | 'FormData'
+  | 'Schema'
+  | 'Unspecified';
+
 export type EmbeddedFile = {
   /**
    * The binary content of the file.
@@ -133,6 +154,11 @@ export type EmbeddedFile = {
    * The date and time when the file was last modified.
    */
   modificationDate?: Date;
+
+  /**
+   * The relationship between the file and the PDF document.
+   */
+  relationship?: FileRelationShip;
 };
 
 /**

src/read-document.ts

@@ -1,5 +1,6 @@
 import type { PDFDocument } from 'pdf-lib';
 
+import type { FileRelationShip } from './api/document.ts';
 import type { BoxEdges, Size } from './box.ts';
 import { parseEdges } from './box.ts';
 import type { FontDef } from './fonts.ts';
@@ -32,6 +33,7 @@ export type DocumentDefinition = {
     description?: string;
     creationDate?: Date;
     modificationDate?: Date;
+    relationship?: FileRelationShip;
   }[];
   onRenderDocument?: (pdfDoc: PDFDocument) => void;
 };
@@ -106,15 +108,33 @@ function readCustomData(input: unknown) {
   );
 }
 
+/**
+ * From the PDF-A3 specification, section **3.1. Requirements -
+ * General**. See:
+ * https://www.pdfa.org/wp-content/uploads/2018/10/PDF20_AN002-AF.pdf
+ */
+const readFileRelationship = types.string({
+  enum: [
+    'Source',
+    'Data',
+    'Alternative',
+    'Supplement',
+    'EncryptedPayload',
+    'FormData',
+    'Schema',
+    'Unspecified',
+  ],
+});
+
 function readEmbeddedFiles(input: unknown) {
   return readObject(input, {
-    url: optional(types.string()),
     content: required(readData),
     fileName: required(types.string()),
     mimeType: required(types.string()),
     description: optional(types.string()),
     creationDate: optional(types.date()),
     modificationDate: optional(types.date()),
+    relationship: optional(readFileRelationship),
   });
 }
 

src/render/render-document.ts

@@ -1,4 +1,4 @@
-import type { PDFDict } from 'pdf-lib';
+import type { AFRelationship, PDFDict } from 'pdf-lib';
 import { PDFDocument, PDFHexString, PDFName } from 'pdf-lib';
 
 import type { Page } from '../page.ts';
@@ -19,6 +19,7 @@ export async function renderDocument(def: DocumentDefinition, pages: Page[]): Pr
       description: file.description,
       creationDate: file.creationDate,
       modificationDate: file.modificationDate,
+      afRelationship: file.relationship as AFRelationship | undefined,
     });
   }