fix(NODE-4977): load snappy lazily

src/cmap/wire_protocol/compression.ts

@@ -2,7 +2,7 @@ import { promisify } from 'util';
 import * as zlib from 'zlib';
 
 import { LEGACY_HELLO_COMMAND } from '../../constants';
-import { getZstdLibrary, Snappy, type ZStandard } from '../../deps';
+import { getSnappy, getZstdLibrary, type SnappyLib, type ZStandard } from '../../deps';
 import { MongoDecompressionError, MongoInvalidArgumentError } from '../../error';
 
 /** @public */
@@ -38,6 +38,17 @@ const zlibInflate = promisify(zlib.inflate.bind(zlib));
 const zlibDeflate = promisify(zlib.deflate.bind(zlib));
 
 let zstd: typeof ZStandard;
+let Snappy: SnappyLib | null = null;
+async function loadSnappy() {
+  if (Snappy == null) {
+    const snappyImport = await getSnappy();
+    if (snappyImport.status === 'rejected') {
+      throw snappyImport.reason;
+    }
+    Snappy = snappyImport.value;
+  }
+  return Snappy;
+}
 
 // Facilitate compressing a message using an agreed compressor
 export async function compress(
@@ -47,9 +58,7 @@ export async function compress(
   const zlibOptions = {} as zlib.ZlibOptions;
   switch (options.agreedCompressor) {
     case 'snappy': {
-      if ('kModuleError' in Snappy) {
-        throw Snappy['kModuleError'];
-      }
+      Snappy ??= await loadSnappy();
       return Snappy.compress(dataToBeCompressed);
     }
     case 'zstd': {
@@ -88,9 +97,7 @@ export async function decompress(compressorID: number, compressedData: Buffer):
 
   switch (compressorID) {
     case Compressor.snappy: {
-      if ('kModuleError' in Snappy) {
-        throw Snappy['kModuleError'];
-      }
+      Snappy ??= await loadSnappy();
       return Snappy.uncompress(compressedData, { asBuffer: true });
     }
     case Compressor.zstd: {

src/deps.ts

@@ -6,6 +6,11 @@ import { MongoMissingDependencyError } from './error';
 import type { MongoClient } from './mongo_client';
 import type { Callback } from './utils';
 
+/** @internal */
+export type ImportResult<Module> =
+  | { status: 'fulfilled'; value: Module }
+  | { status: 'rejected'; reason: MongoMissingDependencyError };
+
 function makeErrorModule(error: any) {
   const props = error ? { kModuleError: error } : {};
   return new Proxy(props, {
@@ -97,7 +102,8 @@ export function getAwsCredentialProvider():
   }
 }
 
-type SnappyLib = {
+/** @internal */
+export type SnappyLib = {
   /**
    * In order to support both we must check the return value of the function
    * @param buf - Buffer to be compressed
@@ -111,16 +117,18 @@ type SnappyLib = {
   uncompress(buf: Buffer, opt: { asBuffer: true }): Promise<Buffer>;
 };
 
-export let Snappy: SnappyLib | { kModuleError: MongoMissingDependencyError } = makeErrorModule(
-  new MongoMissingDependencyError(
-    'Optional module `snappy` not found. Please install it to enable snappy compression'
-  )
-);
-
-try {
-  // Ensure you always wrap an optional require in the try block NODE-3199
-  Snappy = require('snappy');
-} catch {} // eslint-disable-line
+export async function getSnappy(): Promise<ImportResult<SnappyLib>> {
+  try {
+    const value = require('snappy');
+    return { status: 'fulfilled', value };
+  } catch (cause) {
+    const reason = new MongoMissingDependencyError(
+      'Optional module `snappy` not found. Please install it to enable snappy compression',
+      { cause }
+    );
+    return { status: 'rejected', reason };
+  }
+}
 
 export let saslprep: typeof import('saslprep') | { kModuleError: MongoMissingDependencyError } =
   makeErrorModule(

src/error.ts

@@ -692,8 +692,9 @@ export class MongoMissingCredentialsError extends MongoAPIError {
  * @category Error
  */
 export class MongoMissingDependencyError extends MongoAPIError {
-  constructor(message: string) {
+  constructor(message: string, { cause }: { cause?: Error } = {}) {
     super(message);
+    if (cause) this.cause = cause;
   }
 
   override get name(): string {

test/action/dependency.test.ts

@@ -5,6 +5,7 @@ import * as path from 'node:path';
 import { expect } from 'chai';
 
 import { dependencies, peerDependencies, peerDependenciesMeta } from '../../package.json';
+import { itInNodeProcess } from '../tools/utils';
 
 const EXPECTED_DEPENDENCIES = ['bson', 'mongodb-connection-string-url', 'socks'];
 const EXPECTED_PEER_DEPENDENCIES = [
@@ -65,11 +66,25 @@ describe('package.json', function () {
 
           expect(result).to.include('import success!');
         });
+
+        if (depName === 'snappy') {
+          itInNodeProcess(
+            'getSnappy returns rejected import',
+            async function ({ expect, mongodb }) {
+              const snappyImport = await mongodb.getSnappy();
+              expect(snappyImport).to.have.property('status', 'rejected');
+              expect(snappyImport).to.have.nested.property(
+                'reason.name',
+                'MongoMissingDependencyError'
+              );
+            }
+          );
+        }
       });
 
       context(`when ${depName} is installed`, () => {
         beforeEach(async () => {
-          execSync(`npm install --no-save "${depName}"@${depMajor}`);
+          execSync(`npm install --no-save "${depName}"@"${depMajor}"`);
         });
 
         it(`driver is importable`, () => {
@@ -81,7 +96,66 @@ describe('package.json', function () {
 
           expect(result).to.include('import success!');
         });
+
+        if (depName === 'snappy') {
+          itInNodeProcess(
+            'getSnappy returns fulfilled import',
+            async function ({ expect, mongodb }) {
+              const snappyImport = await mongodb.getSnappy();
+              expect(snappyImport).to.have.property('status', 'fulfilled');
+              expect(snappyImport).to.have.property('value');
+            }
+          );
+        }
       });
     }
   });
+
+  const EXPECTED_IMPORTS = [
+    'bson',
+    'saslprep',
+    'sparse-bitfield',
+    'memory-pager',
+    'mongodb-connection-string-url',
+    'whatwg-url',
+    'webidl-conversions',
+    'tr46',
+    'socks',
+    'ip',
+    'smart-buffer'
+  ];
+
+  describe('mongodb imports', () => {
+    let imports: string[];
+    beforeEach(async function () {
+      for (const key of Object.keys(require.cache)) delete require.cache[key];
+      require('../../src');
+      imports = Array.from(
+        new Set(
+          Object.entries(require.cache)
+            .filter(([modKey]) => modKey.includes('/node_modules/'))
+            .map(([modKey]) => {
+              const leadingPkgName = modKey.split('/node_modules/')[1];
+              const [orgName, pkgName] = leadingPkgName.split('/');
+              if (orgName.startsWith('@')) {
+                return `${orgName}/${pkgName}`;
+              }
+              return orgName;
+            })
+        )
+      );
+    });
+
+    context('when importing mongodb', () => {
+      it('only contains the expected imports', function () {
+        expect(imports).to.deep.equal(EXPECTED_IMPORTS);
+      });
+
+      it('does not import optional dependencies', () => {
+        for (const peerDependency of EXPECTED_PEER_DEPENDENCIES) {
+          expect(imports).to.not.include(peerDependency);
+        }
+      });
+    });
+  });
 });

test/tools/utils.ts

@@ -1,3 +1,8 @@
+import * as child_process from 'node:child_process';
+import { once } from 'node:events';
+import * as fs from 'node:fs/promises';
+import * as path from 'node:path';
+
 import { EJSON } from 'bson';
 import * as BSON from 'bson';
 import { expect } from 'chai';
@@ -499,3 +504,58 @@ export function topologyWithPlaceholderClient(
     options as TopologyOptions
   );
 }
+
+export async function itInNodeProcess(
+  title: string,
+  fn: (d: { expect: typeof import('chai').expect; mongodb: typeof import('../mongodb') }) => void
+) {
+  it(title, async () => {
+    const script = `
+      import { expect } from 'chai';
+      import * as mongodb from './test/mongodb';
+      const run = ${fn};
+      run({ expect, mongodb }).then(
+        () => process.exit(0),
+        error => {
+          console.error(error)
+          process.exit(1)
+        }
+      );\n`;
+
+    const scriptName = `./testing_${title.split(/\s/).join('_')}_script.cts`;
+    const cwd = path.resolve(__dirname, '..', '..');
+    const tsNode = path.resolve(__dirname, '..', '..', 'node_modules', '.bin', 'ts-node');
+    try {
+      await fs.writeFile(scriptName, script, { encoding: 'utf8' });
+      const scriptInstance = child_process.fork(scriptName, {
+        signal: AbortSignal.timeout(50_000),
+        cwd,
+        stdio: 'pipe',
+        execArgv: [tsNode]
+      });
+
+      scriptInstance.stdout?.setEncoding('utf8');
+      scriptInstance.stderr?.setEncoding('utf8');
+
+      let stdout = '';
+      scriptInstance.stdout?.addListener('data', data => {
+        stdout += data;
+      });
+
+      let stderr = '';
+      scriptInstance.stderr?.addListener('data', (data: string) => {
+        stderr += data
+          .split('\n')
+          .filter(line => !line.startsWith('Debugger') && !line.startsWith('For help'))
+          .join('\n');
+      });
+
+      const [exitCode] = await once(scriptInstance, 'close');
+
+      if (stderr.length) console.log(stderr);
+      expect({ exitCode, stdout, stderr }).to.deep.equal({ exitCode: 0, stdout: '', stderr: '' });
+    } finally {
+      await fs.unlink(scriptName);
+    }
+  });
+}