Combine related getBuffer* functions. Add tests (elastic#82766)

## Summary
Move logic from `getBufferExtractorForContentType` into `getBufferExtractor` & change the interface so one function can be used.

### Diff showing old vs new call
```diff
-  getBufferExtractorForContentType(contentType);
+  getBufferExtractor({ contentType });
```
```diff
-  getBufferExtractor(archivePath);
+  getBufferExtractor({ archivePath });
```

### Checklist

- [x] [Unit or functional tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html) were updated or added to match the most common scenarios

x-pack/plugins/ingest_manager/server/services/epm/archive/index.ts

@@ -18,7 +18,7 @@ import {
 import { PackageInvalidArchiveError, PackageUnsupportedMediaTypeError } from '../../../errors';
 import { pkgToPkgKey } from '../registry';
 import { cacheGet, cacheSet, setArchiveFilelist } from '../registry/cache';
-import { unzipBuffer, untarBuffer, ArchiveEntry } from '../registry/extract';
+import { ArchiveEntry, getBufferExtractor } from '../registry/extract';
 
 export async function loadArchivePackage({
   archiveBuffer,
@@ -37,24 +37,17 @@ export async function loadArchivePackage({
   };
 }
 
-function getBufferExtractorForContentType(contentType: string) {
-  if (contentType === 'application/gzip') {
-    return untarBuffer;
-  } else if (contentType === 'application/zip') {
-    return unzipBuffer;
-  } else {
-    throw new PackageUnsupportedMediaTypeError(
-      `Unsupported media type ${contentType}. Please use 'application/gzip' or 'application/zip'`
-    );
-  }
-}
-
 export async function unpackArchiveToCache(
   archiveBuffer: Buffer,
   contentType: string,
   filter = (entry: ArchiveEntry): boolean => true
 ): Promise<string[]> {
-  const bufferExtractor = getBufferExtractorForContentType(contentType);
+  const bufferExtractor = getBufferExtractor({ contentType });
+  if (!bufferExtractor) {
+    throw new PackageUnsupportedMediaTypeError(
+      `Unsupported media type ${contentType}. Please use 'application/gzip' or 'application/zip'`
+    );
+  }
   const paths: string[] = [];
   try {
     await bufferExtractor(archiveBuffer, filter, (entry: ArchiveEntry) => {

x-pack/plugins/ingest_manager/server/services/epm/registry/extract.ts

@@ -17,7 +17,7 @@ export async function untarBuffer(
   buffer: Buffer,
   filter = (entry: ArchiveEntry): boolean => true,
   onEntry = (entry: ArchiveEntry): void => {}
-): Promise<void> {
+): Promise<unknown> {
   const deflatedStream = bufferToStream(buffer);
   // use tar.list vs .extract to avoid writing to disk
   const inflateStream = tar.list().on('entry', (entry: tar.FileStat) => {
@@ -36,7 +36,7 @@ export async function unzipBuffer(
   buffer: Buffer,
   filter = (entry: ArchiveEntry): boolean => true,
   onEntry = (entry: ArchiveEntry): void => {}
-): Promise<void> {
+): Promise<unknown> {
   const zipfile = await yauzlFromBuffer(buffer, { lazyEntries: true });
   zipfile.readEntry();
   zipfile.on('entry', async (entry: yauzl.Entry) => {
@@ -50,6 +50,26 @@ export async function unzipBuffer(
   return new Promise((resolve, reject) => zipfile.on('end', resolve).on('error', reject));
 }
 
+type BufferExtractor = typeof unzipBuffer | typeof untarBuffer;
+export function getBufferExtractor(
+  args: { contentType: string } | { archivePath: string }
+): BufferExtractor | undefined {
+  if ('contentType' in args) {
+    if (args.contentType === 'application/gzip') {
+      return untarBuffer;
+    } else if (args.contentType === 'application/zip') {
+      return unzipBuffer;
+    }
+  } else if ('archivePath' in args) {
+    if (args.archivePath.endsWith('.zip')) {
+      return unzipBuffer;
+    }
+    if (args.archivePath.endsWith('.gz')) {
+      return untarBuffer;
+    }
+  }
+}
+
 function yauzlFromBuffer(buffer: Buffer, opts: yauzl.Options): Promise<yauzl.ZipFile> {
   return new Promise((resolve, reject) =>
     yauzl.fromBuffer(buffer, opts, (err?: Error, handle?: yauzl.ZipFile) =>

x-pack/plugins/ingest_manager/server/services/epm/registry/index.test.ts

@@ -82,14 +82,38 @@ describe('splitPkgKey tests', () => {
   });
 });
 
-describe('getBufferExtractor', () => {
-  it('returns unzipBuffer if the archive key ends in .zip', () => {
-    const extractor = getBufferExtractor('.zip');
+describe('getBufferExtractor called with { archivePath }', () => {
+  it('returns unzipBuffer if `archivePath` ends in .zip', () => {
+    const extractor = getBufferExtractor({ archivePath: '.zip' });
     expect(extractor).toBe(unzipBuffer);
   });
 
-  it('returns untarBuffer if the key ends in anything else', () => {
-    const extractor = getBufferExtractor('.xyz');
+  it('returns untarBuffer if `archivePath` ends in .gz', () => {
+    const extractor = getBufferExtractor({ archivePath: '.gz' });
     expect(extractor).toBe(untarBuffer);
+    const extractor2 = getBufferExtractor({ archivePath: '.tar.gz' });
+    expect(extractor2).toBe(untarBuffer);
+  });
+
+  it('returns `undefined` if `archivePath` ends in anything else', () => {
+    const extractor = getBufferExtractor({ archivePath: '.xyz' });
+    expect(extractor).toEqual(undefined);
+  });
+});
+
+describe('getBufferExtractor called with { contentType }', () => {
+  it('returns unzipBuffer if `contentType` is `application/zip`', () => {
+    const extractor = getBufferExtractor({ contentType: 'application/zip' });
+    expect(extractor).toBe(unzipBuffer);
+  });
+
+  it('returns untarBuffer if `contentType` is `application/gzip`', () => {
+    const extractor = getBufferExtractor({ contentType: 'application/gzip' });
+    expect(extractor).toBe(untarBuffer);
+  });
+
+  it('returns `undefined` if `contentType` ends in anything else', () => {
+    const extractor = getBufferExtractor({ contentType: '.xyz' });
+    expect(extractor).toEqual(undefined);
   });
 });

x-pack/plugins/ingest_manager/server/services/epm/registry/index.ts

@@ -26,14 +26,14 @@ import {
   setArchiveFilelist,
   deleteArchiveFilelist,
 } from './cache';
-import { ArchiveEntry, untarBuffer, unzipBuffer } from './extract';
+import { ArchiveEntry, getBufferExtractor } from './extract';
 import { fetchUrl, getResponse, getResponseStream } from './requests';
 import { streamToBuffer } from './streams';
 import { getRegistryUrl } from './registry_url';
 import { appContextService } from '../..';
 import { PackageNotFoundError, PackageCacheError } from '../../../errors';
 
-export { ArchiveEntry } from './extract';
+export { ArchiveEntry, getBufferExtractor } from './extract';
 
 export interface SearchParams {
   category?: CategoryId;
@@ -139,7 +139,10 @@ export async function unpackRegistryPackageToCache(
 ): Promise<string[]> {
   const paths: string[] = [];
   const { archiveBuffer, archivePath } = await fetchArchiveBuffer(pkgName, pkgVersion);
-  const bufferExtractor = getBufferExtractor(archivePath);
+  const bufferExtractor = getBufferExtractor({ archivePath });
+  if (!bufferExtractor) {
+    throw new Error('Unknown compression format. Please use .zip or .gz');
+  }
   await bufferExtractor(archiveBuffer, filter, (entry: ArchiveEntry) => {
     const { path, buffer } = entry;
     const { file } = pathParts(path);
@@ -199,13 +202,6 @@ export function pathParts(path: string): AssetParts {
   } as AssetParts;
 }
 
-export function getBufferExtractor(archivePath: string) {
-  const isZip = archivePath.endsWith('.zip');
-  const bufferExtractor = isZip ? unzipBuffer : untarBuffer;
-
-  return bufferExtractor;
-}
-
 export async function ensureCachedArchiveInfo(
   name: string,
   version: string,