feat(NODE-6325): implement document sequence support

src/cmap/commands.ts

@@ -411,6 +411,17 @@ export interface OpMsgOptions {
   readPreference: ReadPreference;
 }
 
+/** @internal */
+export class DocumentSequence {
+  field: string;
+  documents: Document[];
+
+  constructor(field: string, documents: Document[]) {
+    this.field = field;
+    this.documents = documents;
+  }
+}
+
 /** @internal */
 export class OpMsgRequest {
   requestId: number;
@@ -491,14 +502,48 @@ export class OpMsgRequest {
   }
 
   makeDocumentSegment(buffers: Uint8Array[], document: Document): number {
+    const sequencesBuffer = this.extractDocumentSequences(document);
     const payloadTypeBuffer = Buffer.alloc(1);
     payloadTypeBuffer[0] = 0;
 
     const documentBuffer = this.serializeBson(document);
     buffers.push(payloadTypeBuffer);
     buffers.push(documentBuffer);
+    buffers.push(sequencesBuffer);
 
-    return payloadTypeBuffer.length + documentBuffer.length;
+    return payloadTypeBuffer.length + documentBuffer.length + sequencesBuffer.length;
+  }
+
+  extractDocumentSequences(document: Document): Uint8Array {
+    // Pull out any field in the command document that's value is a document sequence.
+    const chunks = [];
+    for (const [key, value] of Object.entries(document)) {
+      if (value instanceof DocumentSequence) {
+        // Document sequences starts with type 1 at the first byte.
+        const payloadTypeBuffer = Buffer.alloc(1);
+        payloadTypeBuffer[0] = 1;
+        chunks.push(payloadTypeBuffer);
+        // Second part of the sequence is the length;
+        const lengthBuffer = Buffer.alloc(4);
+        chunks.push(lengthBuffer);
+        // Third part is the field name.
+        const fieldBuffer = Buffer.from(key);
+        chunks.push(fieldBuffer);
+        // Fourth part are the documents' bytes.
+        let docsLength = 0;
+        for (const doc of value.documents) {
+          const docBson = this.serializeBson(doc);
+          docsLength += docBson.length;
+          chunks.push(docBson);
+        }
+        lengthBuffer.writeInt32LE(fieldBuffer.length + docsLength);
+        delete document[key];
+      }
+    }
+    if (chunks.length > 0) {
+      return Buffer.concat(chunks);
+    }
+    return Buffer.alloc(0);
   }
 
   serializeBson(document: Document): Uint8Array {