Retry loading uri if it fails with a 5xx error code. (#3980)

* Log read file error * Add changes * Refactor * Retries * Retries * update * Wip * Move chaching cache system to datastore * Append * Remove old test * File not found * Defined errors for fs * Wip * Bump @azure-tools/uri * Real file sytem test * Add remote calls tests * Update changelog
2021-03-15 11:04:39 -07:00 · 2021-03-15 11:04:39 -07:00 · 5a47e7dbc2
--- a/common/changes/@autorest/configuration/feature-log-errors_2021-03-12-15-49.json
+++ b/common/changes/@autorest/configuration/feature-log-errors_2021-03-12-15-49.json
@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "@autorest/configuration",
+      "comment": "Extract CachingFileSystem out into @azure-tools/datastore",
+      "type": "minor"
+    }
+  ],
+  "packageName": "@autorest/configuration",
+  "email": "tiguerin@microsoft.com"
+}
--- a/common/changes/@autorest/core/feature-log-errors_2021-03-11-23-12.json
+++ b/common/changes/@autorest/core/feature-log-errors_2021-03-11-23-12.json
@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "@autorest/core",
+      "comment": "",
+      "type": "none"
+    }
+  ],
+  "packageName": "@autorest/core",
+  "email": "tiguerin@microsoft.com"
+}
--- a/common/changes/@azure-tools/datastore/feature-log-errors_2021-03-11-19-57.json
+++ b/common/changes/@azure-tools/datastore/feature-log-errors_2021-03-11-19-57.json
@ -0,0 +1,16 @@
+{
+  "changes": [
+    {
+      "packageName": "@azure-tools/datastore",
+      "comment": "Added retry logic for loading uris.",
+      "type": "minor"
+    },
+    {
+      "packageName": "@azure-tools/datastore",
+      "comment": "**Refactor** abstract file system. Moved CachingFileSystem from @autorest/configuration.",
+      "type": "minor"
+    }
+  ],
+  "packageName": "@azure-tools/datastore",
+  "email": "tiguerin@microsoft.com"
+}
--- a/common/config/rush/pnpm-lock.yaml
+++ b/common/config/rush/pnpm-lock.yaml
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      '@types/source-map': 0.5.0
      '@types/webpack': 4.41.26
      '@typescript-eslint/eslint-plugin': 4.17.0_3641211d697b4d4d12940eb9cf33dc28
@ -9239,10 +9239,10 @@ packages:
    dependencies:
      '@azure-tools/linq': 3.1.262
      '@azure-tools/tasks': 3.0.253
-      '@azure-tools/uri': 3.0.255
+      '@azure-tools/uri': 3.0.256
      '@types/jest': 26.0.20
      '@types/jsonpath': 0.2.0
-      '@types/node': 14.14.33
+      '@types/node': 14.14.34
      '@types/source-map': 0.5.0
      '@typescript-eslint/eslint-plugin': 4.17.0_3641211d697b4d4d12940eb9cf33dc28
      '@typescript-eslint/parser': 4.17.0_eslint@7.21.0+typescript@4.2.3
@ -9274,7 +9274,7 @@ packages:
      '@azure-tools/object-comparison': 3.0.252
      '@azure-tools/tasks': 3.0.253
      '@types/jest': 26.0.20
-      '@types/node': 14.14.33
+      '@types/node': 14.14.34
      '@typescript-eslint/eslint-plugin': 4.17.0_3641211d697b4d4d12940eb9cf33dc28
      '@typescript-eslint/parser': 4.17.0_eslint@7.21.0+typescript@4.2.3
      compare-versions: 3.6.0
@ -9298,7 +9298,7 @@ packages:
  file:projects/extension-base.tgz_prettier@2.2.1:
    dependencies:
      '@types/js-yaml': 4.0.0
-      '@types/node': 14.14.33
+      '@types/node': 14.14.34
      '@typescript-eslint/eslint-plugin': 4.17.0_3641211d697b4d4d12940eb9cf33dc28
      '@typescript-eslint/parser': 4.17.0_eslint@7.21.0+typescript@4.2.3
      eslint: 7.21.0
@ -9325,7 +9325,7 @@ packages:
      '@azure-tools/tasks': 3.0.253
      '@types/command-exists': 1.2.0
      '@types/jest': 26.0.20
-      '@types/node': 14.14.33
+      '@types/node': 14.14.34
      '@types/npm-package-arg': 6.1.0
      '@types/semver': 5.5.0
      '@typescript-eslint/eslint-plugin': 4.17.0_3641211d697b4d4d12940eb9cf33dc28
@ -9369,7 +9369,7 @@ packages:
      '@types/js-yaml': 4.0.0
      '@types/morgan': 1.9.2
      '@types/mustache': 4.1.1
-      '@types/node': 14.14.33
+      '@types/node': 14.14.34
      '@types/supertest': 2.0.10
      '@types/yargs': 15.0.13
      '@typescript-eslint/eslint-plugin': 4.17.0_3641211d697b4d4d12940eb9cf33dc28
@ -9408,9 +9408,9 @@ packages:
      '@azure-tools/async-io': 3.0.253
      '@azure-tools/linq': 3.1.262
      '@azure-tools/tasks': 3.0.253
-      '@azure-tools/uri': 3.0.255
+      '@azure-tools/uri': 3.0.256
      '@types/jest': 26.0.20
-      '@types/node': 14.14.33
+      '@types/node': 14.14.34
      '@types/webpack': 4.41.26
      '@typescript-eslint/eslint-plugin': 4.17.0_3641211d697b4d4d12940eb9cf33dc28
      '@typescript-eslint/parser': 4.17.0_eslint@7.21.0+typescript@4.2.3
@ -9442,7 +9442,7 @@ packages:
    dependencies:
      '@types/jest': 26.0.20
      '@types/js-yaml': 4.0.0
-      '@types/node': 14.14.33
+      '@types/node': 14.14.34
      '@types/source-map': 0.5.0
      '@typescript-eslint/eslint-plugin': 4.17.0_3641211d697b4d4d12940eb9cf33dc28
      '@typescript-eslint/parser': 4.17.0_eslint@7.21.0+typescript@4.2.3
@ -9469,7 +9469,7 @@ packages:
  file:projects/openapi.tgz_prettier@2.2.1+ts-node@9.1.1:
    dependencies:
      '@types/jest': 26.0.20
-      '@types/node': 14.14.33
+      '@types/node': 14.14.34
      '@typescript-eslint/eslint-plugin': 4.17.0_3641211d697b4d4d12940eb9cf33dc28
      '@typescript-eslint/parser': 4.17.0_eslint@7.21.0+typescript@4.2.3
      eslint: 7.21.0
@ -9498,7 +9498,7 @@ packages:
    version: 0.0.0
  file:projects/test-public-packages.tgz_prettier@2.2.1:
    dependencies:
-      '@types/node': 14.14.33
+      '@types/node': 14.14.34
      '@types/source-map-support': 0.5.3
      eslint: 7.21.0
      eslint-plugin-prettier: 3.2.0_eslint@7.21.0+prettier@2.2.1
--- a/packages/extensions/core/src/language-service/language-service.ts
+++ b/packages/extensions/core/src/language-service/language-service.ts
@ -630,7 +630,7 @@ class OpenApiLanguageService extends TextDocuments implements IFileSystem {
    }
  }
  // IFileSystem Implementation
-  public async EnumerateFileUris(folderUri: string): Promise<Array<string>> {
+  public async list(folderUri: string): Promise<Array<string>> {
    if (folderUri && folderUri.startsWith("file:")) {
      const folderPath = FileUriToPath(folderUri);
      if (await isDirectory(folderPath)) {
@ -648,7 +648,7 @@ class OpenApiLanguageService extends TextDocuments implements IFileSystem {
    return [];
  }

-  public async ReadFile(fileUri: string): Promise<string> {
+  public async read(fileUri: string): Promise<string> {
    const doc = this.get(fileUri) || this.virtualFile.get(fileUri);
    try {
      if (doc) {
@ -662,6 +662,14 @@ class OpenApiLanguageService extends TextDocuments implements IFileSystem {
    throw new Error(`Unable to read ${fileUri}`);
  }

+  public async EnumerateFileUris(folderUri: string): Promise<Array<string>> {
+    return this.list(folderUri);
+  }
+
+  public async ReadFile(fileUri: string): Promise<string> {
+    return this.read(fileUri);
+  }
+
  private async process(configurationUrl: string) {
    const result = this.results.get(configurationUrl) || new Result(this, configurationUrl);
    this.results.set(configurationUrl, result);
--- a/packages/extensions/core/src/lib/autorest-core.ts
+++ b/packages/extensions/core/src/lib/autorest-core.ts
@ -194,11 +194,11 @@ export class AutoRest extends EventEmitter {
 export async function LiterateToJson(content: string): Promise<string> {
  try {
    const autorest = new AutoRest({
-      async EnumerateFileUris(folderUri: string): Promise<Array<string>> {
-        return [];
-      },
-      ReadFile: async (f: string): Promise<string> =>
-        f == "none:///empty-file.md" ? content || "# empty file" : "# empty file",
+      list: () => Promise.resolve([]),
+      read: (f: string) => Promise.resolve(f == "none:///empty-file.md" ? content || "# empty file" : "# empty file"),
+      EnumerateFileUris: () => Promise.resolve([]),
+      ReadFile: (f: string) =>
+        Promise.resolve(f == "none:///empty-file.md" ? content || "# empty file" : "# empty file"),
    });
    let result = "";
    autorest.AddConfiguration({ "input-file": "none:///empty-file.md", "output-artifact": ["swagger-document"] });
--- a/packages/extensions/core/src/lib/configuration/autorest-context-loader.ts
+++ b/packages/extensions/core/src/lib/configuration/autorest-context-loader.ts
@ -3,7 +3,7 @@
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/
-import { IFileSystem, LazyPromise, RealFileSystem } from "@azure-tools/datastore";
+import { CachingFileSystem, IFileSystem, LazyPromise, RealFileSystem } from "@azure-tools/datastore";
 import { Extension, ExtensionManager } from "@azure-tools/extension";
 import { CreateFolderUri, ResolveUri } from "@azure-tools/uri";
 import { join } from "path";
@ -11,7 +11,6 @@ import { AutoRestExtension } from "../pipeline/plugin-endpoint";
 import {
  AutorestConfiguration,
  AutorestRawConfiguration,
-  CachingFileSystem,
  ConfigurationLoader,
  getNestedConfiguration,
  mergeConfigurations,
--- a/packages/extensions/core/src/lib/configuration/autorest-context.ts
+++ b/packages/extensions/core/src/lib/configuration/autorest-context.ts
@ -1,15 +1,10 @@
-import { DataStore } from "@azure-tools/datastore";
+import { DataStore, CachingFileSystem } from "@azure-tools/datastore";
 import { clone } from "@azure-tools/linq";
 import { From } from "linq-es2015";
 import { basename, dirname } from "path";
 import { CancellationToken, CancellationTokenSource } from "vscode-jsonrpc";
 import { Artifact } from "../artifact";
-import {
-  CachingFileSystem,
-  getNestedConfiguration,
-  ResolvedDirective,
-  resolveDirectives,
-} from "@autorest/configuration";
+import { getNestedConfiguration, ResolvedDirective, resolveDirectives } from "@autorest/configuration";
 import { MessageEmitter } from "./message-emitter";
 import { IEvent } from "../events";
 import {
--- a/packages/extensions/core/test/file-system-testing.test.ts
+++ b/packages/extensions/core/test/file-system-testing.test.ts
@ -1,19 +0,0 @@
-import { MemoryFileSystem } from "@azure-tools/datastore";
-import assert from "assert";
-
-describe("FileSystemTests", () => {
-  it("does async iterable work", async () => {
-    const f = new MemoryFileSystem(
-      new Map<string, string>([
-        ["readme.md", "# this is a test\n see https://aka.ms/autorest"],
-        ["other.md", "#My Doc."],
-      ]),
-    );
-    let n = 0;
-    for (const name of await f.EnumerateFileUris()) {
-      n++;
-    }
-    assert.equal(n, 2);
-    assert.equal(await f.ReadFile(MemoryFileSystem.DefaultVirtualRootUri + "other.md"), "#My Doc.");
-  });
-});
--- a/packages/libs/configuration/src/configuration-loader/configuration-loader.ts
+++ b/packages/libs/configuration/src/configuration-loader/configuration-loader.ts
@ -1,9 +1,8 @@
-import { DataStore, IFileSystem, RealFileSystem } from "@azure-tools/datastore";
+import { DataStore, IFileSystem, RealFileSystem, CachingFileSystem } from "@azure-tools/datastore";
 import { Extension, ExtensionManager, LocalExtension } from "@azure-tools/extension";
 import { CreateFileUri, ResolveUri, simplifyUri, FileUriToPath } from "@azure-tools/uri";
 import { AutorestLogger } from "@autorest/common";
 import untildify from "untildify";
-import { CachingFileSystem } from "../caching-file-system";
 import { AutorestConfiguration } from "../autorest-configuration";
 import { detectConfigurationFile } from "../configuration-file-resolver";
 import { ConfigurationManager, readConfigurationFile } from "../configuration-manager";
--- a/packages/libs/configuration/src/index.ts
+++ b/packages/libs/configuration/src/index.ts
@ -1,6 +1,5 @@
 export * from "./autorest-configuration";
 export * from "./autorest-raw-configuration";
-export * from "./caching-file-system";
 export * from "./configuration-manager";
 export * from "./configuration-file-resolver";
 export * from "./configuration-loader";
--- a/packages/libs/datastore/src/data-store/data-store.ts
+++ b/packages/libs/datastore/src/data-store/data-store.ts
@ -145,12 +145,15 @@ class ReadThroughDataSource extends DataSource {
        // populate cache
        let data: string | null = null;
        try {
-          data = (await this.fs.ReadFile(uri)) || (await ReadUri(uri));
+          data = (await this.fs.read(uri)) || (await ReadUri(uri));
          if (data) {
            const parent = ParentFolderUri(uri) || "";
            // hack to let $(this-folder) resolve to the location...
            data = data.replace(/\$\(this-folder\)\/*/g, parent);
          }
+        } catch (e) {
+          // eslint-disable-next-line no-console
+          console.error("Unexpected error trying to read file", e);
        } finally {
          if (!data) {
            // eslint-disable-next-line no-unsafe-finally
--- a/packages/libs/datastore/src/file-system/caching-file-system.ts
+++ b/packages/libs/datastore/src/file-system/caching-file-system.ts
@ -1,14 +1,14 @@
-import { IFileSystem } from "@azure-tools/datastore";
+import { IFileSystem } from "./file-system";

 export class CachingFileSystem implements IFileSystem {
  protected cache = new Map<string, string | Error>();
  constructor(protected actualFileSystem: IFileSystem) {}

-  EnumerateFileUris(folderUri: string): Promise<Array<string>> {
-    return this.actualFileSystem.EnumerateFileUris(folderUri);
+  public list(folderUri: string): Promise<Array<string>> {
+    return this.actualFileSystem.list(folderUri);
  }

-  async ReadFile(uri: string): Promise<string> {
+  public async read(uri: string): Promise<string> {
    const content = this.cache.get(uri);
    if (content !== undefined) {
      if (typeof content === "string") {
@ -17,7 +17,7 @@ export class CachingFileSystem implements IFileSystem {
      throw content;
    }
    try {
-      const data = await this.actualFileSystem.ReadFile(uri);
+      const data = await this.actualFileSystem.read(uri);
      this.cache.set(uri, data);
      return data;
    } catch (E) {
@ -26,4 +26,18 @@ export class CachingFileSystem implements IFileSystem {
      throw E;
    }
  }
+
+  /**
+   * @deprecated
+   */
+  public EnumerateFileUris(folderUri: string): Promise<Array<string>> {
+    return this.list(folderUri);
+  }
+
+  /**
+   * @deprecated
+   */
+  public async ReadFile(uri: string): Promise<string> {
+    return this.read(uri);
+  }
 }
--- a/packages/libs/datastore/src/file-system/enhanced-file-system.ts
+++ b/packages/libs/datastore/src/file-system/enhanced-file-system.ts
@ -0,0 +1,38 @@
+import { WriteString } from "@azure-tools/uri";
+import { RealFileSystem } from "./real-file-system";
+
+// handles:
+// - GitHub URI adjustment
+// - GitHub auth
+/**
+ *
+ */
+export class EnhancedFileSystem extends RealFileSystem {
+  public constructor(private githubAuthToken?: string) {
+    super();
+  }
+
+  public async read(uri: string): Promise<string> {
+    return super.read(uri, this.getHeaders(uri));
+  }
+
+  public async write(uri: string, content: string): Promise<void> {
+    return WriteString(uri, content);
+  }
+
+  private getHeaders(uri: string) {
+    const headers: { [key: string]: string } = {};
+
+    // check for GitHub OAuth token
+    if (
+      this.githubAuthToken &&
+      (uri.startsWith("https://raw.githubusercontent.com") || uri.startsWith("https://github.com"))
+    ) {
+      // eslint-disable-next-line no-console
+      console.error(`Used GitHub authentication token to request '${uri}'.`);
+      headers.authorization = `Bearer ${this.githubAuthToken}`;
+    }
+
+    return headers;
+  }
+}
--- a/packages/libs/datastore/src/file-system/errors.ts
+++ b/packages/libs/datastore/src/file-system/errors.ts
@ -0,0 +1,10 @@
+export class FileSystemError extends Error {}
+
+/**
+ * Error representing a uri not found.
+ */
+export class UriNotFoundError extends FileSystemError {
+  public constructor(public uri: string, message?: string) {
+    super(message ?? `${uri} not found.`);
+  }
+}
--- a/packages/libs/datastore/src/file-system/file-system.test.ts
+++ b/packages/libs/datastore/src/file-system/file-system.test.ts
@ -1,18 +0,0 @@
-import { MemoryFileSystem } from "./file-system";
-
-describe("Filesystem", () => {
-  it("Simple memory filesystem test", async () => {
-    const f = new MemoryFileSystem(
-      new Map<string, string>([
-        ["readme.md", "# this is a test\n see https://aka.ms/autorest"],
-        ["other.md", "#My Doc."],
-      ]),
-    );
-    let n = 0;
-    for (const name of await f.EnumerateFileUris()) {
-      n++;
-    }
-    expect(n).toEqual(2);
-    expect(await f.ReadFile(MemoryFileSystem.DefaultVirtualRootUri + "other.md")).toEqual("#My Doc.");
-  });
-});
--- a/packages/libs/datastore/src/file-system/file-system.ts
+++ b/packages/libs/datastore/src/file-system/file-system.ts
@ -1,106 +1,29 @@
-/*---------------------------------------------------------------------------------------------
- *  Copyright (c) Microsoft Corporation. All rights reserved.
- *  Licensed under the MIT License. See License.txt in the project root for license information.
- *--------------------------------------------------------------------------------------------*/
-import { EnumerateFiles, ResolveUri, ReadUri, WriteString } from "@azure-tools/uri";
-// import { From } from "linq-es2015";
-import { items, keys } from "@azure-tools/linq";
+/**
+ * Virtual filesystem, to find and read files.
+ */
+export interface IFileSystem extends ILegacyFileSystem {
+  /**
+   * Read the content of the given Uri
+   * @param fileUri Uri of the file.
+   * @throws {FileSystemError}
+   */
+  read(fileUri: string): Promise<string>;

-import * as Constants from "../constants";
+  /**
+   * List the files in the given folder.
+   * @param fileUri Uri of the folder.
+   * @throws {FileSystemError}
+   */
+  list(folderUri: string): Promise<string[]>;
+}

-export interface IFileSystem {
+export interface ILegacyFileSystem {
+  /**
+   * @deprecated, use @see {IFileSystem.list}
+   */
  EnumerateFileUris(folderUri: string): Promise<Array<string>>;
+  /**
+   * @deprecated, use @see {IFileSystem.read}
+   */
  ReadFile(uri: string): Promise<string>;
 }
-
-export class MemoryFileSystem implements IFileSystem {
-  public static readonly DefaultVirtualRootUri = "file:///";
-  private filesByUri: Map<string, string>;
-
-  public constructor(files: Map<string, string>) {
-    this.filesByUri = new Map<string, string>(
-      items(files).select(
-        (each) => [ResolveUri(MemoryFileSystem.DefaultVirtualRootUri, each.key), each.value] as [string, string],
-      ),
-    );
-    /*
-        this.filesByUri = new Map<string, string>(
-          From(files.entries()).Select(entry => [
-            ResolveUri(MemoryFileSystem.DefaultVirtualRootUri, entry[0]),
-            entry[1]
-          ] as [string, string]));
-          */
-  }
-  public readonly Outputs: Map<string, string> = new Map<string, string>();
-
-  async ReadFile(uri: string): Promise<string> {
-    if (!this.filesByUri.has(uri)) {
-      throw new Error(`File ${uri} is not in the MemoryFileSystem`);
-    }
-    return <string>this.filesByUri.get(uri);
-  }
-
-  async EnumerateFileUris(folderUri: string = MemoryFileSystem.DefaultVirtualRootUri): Promise<Array<string>> {
-    // return await [...From(this.filesByUri.keys()).Where(uri => {
-    return keys(this.filesByUri)
-      .where((uri) => {
-        // in folder?
-        if (!uri.startsWith(folderUri)) {
-          return false;
-        }
-
-        // not in subfolder?
-        // return uri.substr(folderUri.length).indexOf("/") === -1;
-        return uri.substr(folderUri.length).indexOf("/") === -1;
-      })
-      .toArray();
-    //})];
-  }
-
-  async WriteFile(uri: string, content: string): Promise<void> {
-    this.Outputs.set(uri, content);
-  }
-}
-
-export class RealFileSystem implements IFileSystem {
-  public constructor() {}
-
-  EnumerateFileUris(folderUri: string): Promise<Array<string>> {
-    return EnumerateFiles(folderUri, [Constants.DefaultConfiguration]);
-  }
-  async ReadFile(uri: string): Promise<string> {
-    return ReadUri(uri);
-  }
-  async WriteFile(uri: string, content: string): Promise<void> {
-    return WriteString(uri, content);
-  }
-}
-
-// handles:
-// - GitHub URI adjustment
-// - GitHub auth
-export class EnhancedFileSystem implements IFileSystem {
-  public constructor(private githubAuthToken?: string) {}
-
-  EnumerateFileUris(folderUri: string): Promise<Array<string>> {
-    return EnumerateFiles(folderUri, [Constants.DefaultConfiguration]);
-  }
-  async ReadFile(uri: string): Promise<string> {
-    const headers: { [key: string]: string } = {};
-
-    // check for GitHub OAuth token
-    if (
-      this.githubAuthToken &&
-      (uri.startsWith("https://raw.githubusercontent.com") || uri.startsWith("https://github.com"))
-    ) {
-      // eslint-disable-next-line no-console
-      console.error(`Used GitHub authentication token to request '${uri}'.`);
-      headers.authorization = `Bearer ${this.githubAuthToken}`;
-    }
-
-    return ReadUri(uri, headers);
-  }
-  async WriteFile(uri: string, content: string): Promise<void> {
-    return WriteString(uri, content);
-  }
-}
--- a/packages/libs/datastore/src/file-system/index.ts
+++ b/packages/libs/datastore/src/file-system/index.ts
@ -0,0 +1,6 @@
+export * from "./caching-file-system";
+export * from "./enhanced-file-system";
+export * from "./errors";
+export * from "./file-system";
+export * from "./memory-file-system";
+export * from "./real-file-system";
--- a/packages/libs/datastore/src/file-system/memory-file-system.test.ts
+++ b/packages/libs/datastore/src/file-system/memory-file-system.test.ts
@ -0,0 +1,25 @@
+import { UriNotFoundError } from "./errors";
+import { MemoryFileSystem } from "./memory-file-system";
+
+describe("MemoryFileSystem", () => {
+  const fs = new MemoryFileSystem(
+    new Map<string, string>([
+      ["readme.md", "# this is a test\n see https://aka.ms/autorest"],
+      ["other.md", "#My Doc."],
+    ]),
+  );
+
+  it("should list files", async () => {
+    const files = await fs.list();
+    expect(files).toHaveLength(2);
+  });
+
+  it("should read file content", async () => {
+    expect(await fs.read(MemoryFileSystem.DefaultVirtualRootUri + "other.md")).toEqual("#My Doc.");
+  });
+
+  it("should throw error if the file doesn't exists", async () => {
+    const uri = MemoryFileSystem.DefaultVirtualRootUri + "unkown-file.md";
+    await expect(() => fs.read(uri)).rejects.toThrowError(UriNotFoundError);
+  });
+});
--- a/packages/libs/datastore/src/file-system/memory-file-system.ts
+++ b/packages/libs/datastore/src/file-system/memory-file-system.ts
@ -0,0 +1,52 @@
+import { ResolveUri } from "@azure-tools/uri";
+import { UriNotFoundError } from "./errors";
+import { IFileSystem } from "./file-system";
+
+export class MemoryFileSystem implements IFileSystem {
+  public static readonly DefaultVirtualRootUri = "file:///";
+  private filesByUri: Map<string, string>;
+
+  public constructor(files: Map<string, string>) {
+    this.filesByUri = new Map<string, string>(
+      [...files.entries()].map(([uri, content]) => [ResolveUri(MemoryFileSystem.DefaultVirtualRootUri, uri), content]),
+    );
+  }
+
+  public readonly outputs: Map<string, string> = new Map<string, string>();
+
+  public async read(uri: string): Promise<string> {
+    const content = this.filesByUri.get(uri);
+    if (content === undefined) {
+      throw new UriNotFoundError(uri, `File ${uri} is not in the MemoryFileSystem`);
+    }
+    return content;
+  }
+
+  async list(folderUri: string = MemoryFileSystem.DefaultVirtualRootUri): Promise<Array<string>> {
+    return [...this.filesByUri.keys()].filter((uri) => {
+      // in folder?
+      if (!uri.startsWith(folderUri)) {
+        return false;
+      }
+      return uri.substr(folderUri.length).indexOf("/") === -1;
+    });
+  }
+
+  public async write(uri: string, content: string): Promise<void> {
+    this.outputs.set(uri, content);
+  }
+
+  /**
+   * @deprecated
+   */
+  public async ReadFile(uri: string): Promise<string> {
+    return this.read(uri);
+  }
+
+  /**
+   * @deprecated
+   */
+  public async EnumerateFileUris(folderUri: string = MemoryFileSystem.DefaultVirtualRootUri): Promise<Array<string>> {
+    return this.list(folderUri);
+  }
+}
--- a/packages/libs/datastore/src/file-system/real-file-system.test.ts
+++ b/packages/libs/datastore/src/file-system/real-file-system.test.ts
@ -0,0 +1,44 @@
+import { ResolveUri, CreateFileOrFolderUri } from "@azure-tools/uri";
+import { join } from "path";
+import { UriNotFoundError } from "./errors";
+import { RealFileSystem } from "./real-file-system";
+
+const baseDir = CreateFileOrFolderUri(join(__dirname, "../../test/resources/fake-fs"));
+
+describe("MemoryFileSystem", () => {
+  const fs = new RealFileSystem();
+
+  describe("accessing load files", () => {
+    it("should list files", async () => {
+      const files = await fs.list(baseDir);
+      expect(files).toHaveLength(2);
+    });
+
+    it("should read local file content", async () => {
+      expect(await fs.read(ResolveUri(baseDir + "/", "foo.txt"))).toEqual("bar\n");
+    });
+
+    it("should throw error if the local file doesn't exists", async () => {
+      const uri = ResolveUri(baseDir + "/", "unkown-file.md");
+      await expect(() => fs.read(uri)).rejects.toThrowError(UriNotFoundError);
+    });
+  });
+
+  describe("accessing remote files", () => {
+    it("should looks for readme.md when listing files", async () => {
+      const files = await fs.list("https://github.com/Azure/autorest/blob/master/");
+      expect(files).toHaveLength(1);
+      expect(files[0]).toEqual("https://github.com/Azure/autorest/blob/master/readme.md");
+    });
+
+    it("should read local file content", async () => {
+      expect(await fs.read("https://github.com/Azure/autorest/blob/master/readme.md")).toContain("Autorest");
+    });
+
+    it("should throw error if the local file doesn't exists", async () => {
+      await expect(() =>
+        fs.read("https://github.com/Azure/autorest/blob/master/this-file-doesnot-exists.md"),
+      ).rejects.toThrowError(UriNotFoundError);
+    });
+  });
+});
--- a/packages/libs/datastore/src/file-system/real-file-system.ts
+++ b/packages/libs/datastore/src/file-system/real-file-system.ts
@ -0,0 +1,92 @@
+import { EnumerateFiles, ReadUri, WriteString } from "@azure-tools/uri";
+import { IFileSystem } from "./file-system";
+import * as Constants from "../constants";
+import { UriNotFoundError } from "./errors";
+
+export class RealFileSystem implements IFileSystem {
+  public constructor() {}
+
+  public list(folderUri: string): Promise<Array<string>> {
+    return EnumerateFiles(folderUri, [Constants.DefaultConfiguration]);
+  }
+
+  public async read(uri: string, headers: { [name: string]: string } = {}): Promise<string> {
+    return await readUriWithRetries(uri, headers);
+  }
+
+  public async write(uri: string, content: string): Promise<void> {
+    return WriteString(uri, content);
+  }
+
+  /**
+   * @deprecated
+   */
+  public async ReadFile(uri: string): Promise<string> {
+    return this.read(uri);
+  }
+
+  /**
+   * @deprecated
+   */
+  public async EnumerateFileUris(folderUri: string): Promise<Array<string>> {
+    return this.list(folderUri);
+  }
+}
+
+const MAX_RETRY_COUNT = 3;
+/**
+ * ReadUri with retries in the case of a remote url and retryable http error.
+ * @param uri uri
+ * @param headers optional headers for the request.
+ */
+export async function readUriWithRetries(uri: string, headers: { [name: string]: string } = {}): Promise<string> {
+  let tryed = 1;
+  for (;;) {
+    try {
+      return await ReadUri(uri, headers);
+    } catch (e) {
+      tryed++;
+      if (isRetryableStatusCode(e.statusCode) && tryed <= MAX_RETRY_COUNT) {
+        // eslint-disable-next-line no-console
+        console.error(`Failed to load uri ${uri}, trying again (${tryed}/${MAX_RETRY_COUNT})`, e);
+      } else {
+        throw processError(uri, e);
+      }
+    }
+  }
+}
+
+export const KnownUriErrorCode = {
+  NotFound: "ENOTFOUND",
+};
+
+/**
+ * @param statusCode Error status code.
+ * @returns Boolean if this request should be retried.
+ */
+function isRetryableStatusCode(statusCode: number): boolean {
+  return statusCode >= 500 || statusCode === 0;
+}
+
+/**
+ * Convert external errors into known error types when able.
+ * @param uri Uri that was loaded.
+ * @param error Error.
+ * @returns new error if error is known or the same error otherwise.
+ */
+function processError(uri: string, error: Error) {
+  if (isCodeError(error)) {
+    if (error.code === KnownUriErrorCode.NotFound) {
+      return new UriNotFoundError(uri, `${uri} is not found: ${error.message}`);
+    }
+  }
+  return error;
+}
+
+interface CodeError extends Error {
+  code: string;
+}
+
+function isCodeError(error: unknown): error is CodeError {
+  return typeof error === "object" && error != null && "code" in error && (error as any)["code"] != null;
+}
--- a/packages/libs/datastore/src/main.ts
+++ b/packages/libs/datastore/src/main.ts
@ -3,7 +3,7 @@
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/
 // export * from "./proxy"
-export * from "./file-system/file-system";
+export * from "./file-system";
 export * from "./json-path/json-path";
 export * from "./json-pointer";
 export * from "./graph-builder";
--- a/packages/libs/datastore/test/resources/fake-fs/foo.txt
+++ b/packages/libs/datastore/test/resources/fake-fs/foo.txt
@ -0,0 +1 @@
+bar
--- a/packages/libs/datastore/test/resources/fake-fs/readme.md
+++ b/packages/libs/datastore/test/resources/fake-fs/readme.md
@ -0,0 +1 @@
+# THis is a readme