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;
@@ -480,7 +491,7 @@ export class OpMsgRequest {
 
     let totalLength = header.length;
     const command = this.command;
-    totalLength += this.makeDocumentSegment(buffers, command);
+    totalLength += this.makeSections(buffers, command);
 
     header.writeInt32LE(totalLength, 0); // messageLength
     header.writeInt32LE(this.requestId, 4); // requestID
@@ -490,15 +501,66 @@ export class OpMsgRequest {
     return buffers;
   }
 
-  makeDocumentSegment(buffers: Uint8Array[], document: Document): number {
+  /**
+   * Add the sections to the OP_MSG request's buffers and returns the length.
+   */
+  makeSections(buffers: Uint8Array[], document: Document): number {
+    const sequencesBuffer = this.extractDocumentSequences(document);
     const payloadTypeBuffer = Buffer.alloc(1);
     payloadTypeBuffer[0] = 0;
 
     const documentBuffer = this.serializeBson(document);
+    // First section, type 0
     buffers.push(payloadTypeBuffer);
     buffers.push(documentBuffer);
+    // Subsequent sections, type 1
+    buffers.push(sequencesBuffer);
 
-    return payloadTypeBuffer.length + documentBuffer.length;
+    return payloadTypeBuffer.length + documentBuffer.length + sequencesBuffer.length;
+  }
+
+  /**
+   * Extracts the document sequences from the command document and returns
+   * a buffer to be added as multiple sections after the initial type 0
+   * section in the message.
+   */
+  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);
+        // Why are we removing the field from the command? This is because it needs to be
+        // removed in the OP_MSG request first section, and DocumentSequence is not a
+        // BSON type and is specific to the MongoDB wire protocol so there's nothing
+        // our BSON serializer can do about this. Since DocumentSequence is not exposed
+        // in the public API and only used internally, we are never mutating an original
+        // command provided by the user, just our own, and it's cheaper to delete from
+        // our own command than copying it.
+        delete document[key];
+      }
+    }
+    if (chunks.length > 0) {
+      return Buffer.concat(chunks);
+    }
+    return Buffer.alloc(0);
   }
 
   serializeBson(document: Document): Uint8Array {

test/unit/cmap/commands.test.js → test/unit/cmap/commands.test.ts

@@ -1,7 +1,92 @@
-const { expect } = require('chai');
-const { OpReply } = require('../../mongodb');
+import { expect } from 'chai';
+
+import { DocumentSequence, OpMsgRequest, OpReply } from '../../mongodb';
 
 describe('commands', function () {
+  describe('OpMsgRequest', function () {
+    describe('#toBin', function () {
+      /**
+       * Note that #toBin returns an array of buffers, in this case we are interested in
+       * the buffer at index 3 of the array, which is a single buffer of all the
+       * document sequence sections.
+       */
+      context('when the command has document sequences', function () {
+        context('when there is one document sequence', function () {
+          const command = {
+            test: 1,
+            field: new DocumentSequence('test', [{ test: 1 }])
+          };
+          const msg = new OpMsgRequest('admin', command, {});
+          const buffers = msg.toBin();
+
+          it('removes the document sequence fields from the command', function () {
+            expect(command).to.not.haveOwnProperty('field');
+          });
+
+          it('sets the document sequence section type to 1', function () {
+            // First byte is a one byte type.
+            expect(buffers[3][0]).to.equal(1);
+          });
+
+          it('sets the length of the document sequence', function () {
+            // Bytes starting at index 1 is a 4 byte length.
+            expect(buffers[3].readInt32LE(1)).to.equal(20);
+          });
+
+          it('sets the name of the first field to be replaced', function () {
+            // Bytes starting at index 5 is the field name.
+            expect(buffers[3].toString('utf8', 5, 10)).to.equal('field');
+          });
+        });
+
+        context('when there are multiple document sequences', function () {
+          const command = {
+            test: 1,
+            fieldOne: new DocumentSequence('test', [{ test: 1 }]),
+            fieldTwo: new DocumentSequence('test', [{ test: 1 }])
+          };
+          const msg = new OpMsgRequest('admin', command, {});
+          const buffers = msg.toBin();
+
+          it('removes the document sequence fields from the command', function () {
+            expect(command).to.not.haveOwnProperty('fieldOne');
+            expect(command).to.not.haveOwnProperty('fieldTwo');
+          });
+
+          it('sets the document sequence sections first type to 1', function () {
+            // First byte is a one byte type.
+            expect(buffers[3][0]).to.equal(1);
+          });
+
+          it('sets the length of the first document sequence', function () {
+            // Bytes starting at index 1 is a 4 byte length.
+            expect(buffers[3].readInt32LE(1)).to.equal(23);
+          });
+
+          it('sets the name of the first field to be replaced', function () {
+            // Bytes starting at index 5 is the field name.
+            expect(buffers[3].toString('utf8', 5, 13)).to.equal('fieldOne');
+          });
+
+          it('sets the document sequence sections second type to 1', function () {
+            // First byte is a one byte type.
+            expect(buffers[3][28]).to.equal(1);
+          });
+
+          it('sets the length of the second document sequence', function () {
+            // Bytes starting at index 1 is a 4 byte length.
+            expect(buffers[3].readInt32LE(29)).to.equal(23);
+          });
+
+          it('sets the name of the second field to be replaced', function () {
+            // Bytes starting at index 33 is the field name.
+            expect(buffers[3].toString('utf8', 33, 41)).to.equal('fieldTwo');
+          });
+        });
+      });
+    });
+  });
+
   describe('Response', function () {
     describe('#parse', function () {
       context('when the message body is invalid', function () {