feat(resolvers): Implement substitutions for js resolvers (#545)

src/__tests__/js-resolvers.test.ts

@@ -0,0 +1,140 @@
+import { Api } from '../resources/Api';
+import { JsResolver } from '../resources/JsResolver';
+import * as given from './given';
+import fs from 'fs';
+
+const plugin = given.plugin();
+
+describe('Mapping Templates', () => {
+  let mock: jest.SpyInstance;
+  let mockEists: jest.SpyInstance;
+
+  beforeEach(() => {
+    mock = jest
+      .spyOn(fs, 'readFileSync')
+      .mockImplementation(
+        (path) => `Content of ${`${path}`.replace(/\\/g, '/')}`,
+      );
+    mockEists = jest.spyOn(fs, 'existsSync').mockReturnValue(true);
+  });
+
+  afterEach(() => {
+    mock.mockRestore();
+    mockEists.mockRestore();
+  });
+
+  it('should substitute variables', () => {
+    const api = new Api(given.appSyncConfig(), plugin);
+    const mapping = new JsResolver(api, {
+      path: 'foo.vtl',
+      substitutions: {
+        foo: 'bar',
+        var: { Ref: 'MyReference' },
+      },
+    });
+    const template = `const foo = '#foo#';
+       const var = '#var#';
+       const unknonw = '#unknown#'`;
+    expect(mapping.processTemplateSubstitutions(template))
+      .toMatchInlineSnapshot(`
+      Object {
+        "Fn::Join": Array [
+          "",
+          Array [
+            "const foo = '",
+            Object {
+              "Fn::Sub": Array [
+                "\${foo}",
+                Object {
+                  "foo": "bar",
+                },
+              ],
+            },
+            "';
+             const var = '",
+            Object {
+              "Fn::Sub": Array [
+                "\${var}",
+                Object {
+                  "var": Object {
+                    "Ref": "MyReference",
+                  },
+                },
+              ],
+            },
+            "';
+             const unknonw = '#unknown#'",
+          ],
+        ],
+      }
+    `);
+  });
+
+  it('should substitute variables and use defaults', () => {
+    const api = new Api(
+      given.appSyncConfig({
+        substitutions: {
+          foo: 'bar',
+          var: 'bizz',
+        },
+      }),
+      plugin,
+    );
+    const mapping = new JsResolver(api, {
+      path: 'foo.vtl',
+      substitutions: {
+        foo: 'fuzz',
+      },
+    });
+    const template = `const foo = '#foo#';
+    const var = '#var#';`;
+    expect(mapping.processTemplateSubstitutions(template))
+      .toMatchInlineSnapshot(`
+      Object {
+        "Fn::Join": Array [
+          "",
+          Array [
+            "const foo = '",
+            Object {
+              "Fn::Sub": Array [
+                "\${foo}",
+                Object {
+                  "foo": "fuzz",
+                },
+              ],
+            },
+            "';
+          const var = '",
+            Object {
+              "Fn::Sub": Array [
+                "\${var}",
+                Object {
+                  "var": "bizz",
+                },
+              ],
+            },
+            "';",
+          ],
+        ],
+      }
+    `);
+  });
+
+  it('should fail if template is missing', () => {
+    mockEists = jest.spyOn(fs, 'existsSync').mockReturnValue(false);
+    const api = new Api(given.appSyncConfig(), plugin);
+    const mapping = new JsResolver(api, {
+      path: 'foo.vtl',
+      substitutions: {
+        foo: 'bar',
+        var: { Ref: 'MyReference' },
+      },
+    });
+
+    expect(function () {
+      mapping.compile();
+    }).toThrowErrorMatchingInlineSnapshot(
+      `"The resolver handler file 'foo.vtl' does not exist"`,
+    );
+  });
+});

src/__tests__/mapping-templates.test.ts

@@ -23,7 +23,7 @@ describe('Mapping Templates', () => {
     mockEists.mockRestore();
   });
 
-  it('should substritute variables', () => {
+  it('should substitute variables', () => {
     const api = new Api(given.appSyncConfig(), plugin);
     const mapping = new MappingTemplate(api, {
       path: 'foo.vtl',
@@ -67,7 +67,7 @@ describe('Mapping Templates', () => {
     `);
   });
 
-  it('should substritute variables and use defaults', () => {
+  it('should substitute variables and use defaults', () => {
     const api = new Api(
       given.appSyncConfig({
         substitutions: {

src/resources/JsResolver.ts

@@ -0,0 +1,85 @@
+import { IntrinsicFunction } from '../types/cloudFormation';
+import fs from 'fs';
+import { Substitutions } from '../types/plugin';
+import { Api } from './Api';
+
+type JsResolverConfig = {
+  path: string;
+  substitutions?: Substitutions;
+};
+
+export class JsResolver {
+  constructor(private api: Api, private config: JsResolverConfig) {}
+
+  compile(): string | IntrinsicFunction {
+    if (!fs.existsSync(this.config.path)) {
+      throw new this.api.plugin.serverless.classes.Error(
+        `The resolver handler file '${this.config.path}' does not exist`,
+      );
+    }
+
+    const requestTemplateContent = fs.readFileSync(this.config.path, 'utf8');
+    return this.processTemplateSubstitutions(requestTemplateContent);
+  }
+
+  processTemplateSubstitutions(template: string): string | IntrinsicFunction {
+    const substitutions = {
+      ...this.api.config.substitutions,
+      ...this.config.substitutions,
+    };
+    const availableVariables = Object.keys(substitutions);
+    const templateVariables: string[] = [];
+    let searchResult;
+    const variableSyntax = RegExp(/#([\w\d-_]+)#/g);
+    while ((searchResult = variableSyntax.exec(template)) !== null) {
+      templateVariables.push(searchResult[1]);
+    }
+
+    const replacements = availableVariables
+      .filter((value) => templateVariables.includes(value))
+      .filter((value, index, array) => array.indexOf(value) === index)
+      .reduce(
+        (accum, value) =>
+          Object.assign(accum, { [value]: substitutions[value] }),
+        {},
+      );
+
+    // if there are substitutions for this template then add fn:sub
+    if (Object.keys(replacements).length > 0) {
+      return this.substituteGlobalTemplateVariables(template, replacements);
+    }
+
+    return template;
+  }
+
+  /**
+   * Creates Fn::Join object from given template where all given substitutions
+   * are wrapped in Fn::Sub objects. This enables template to have also
+   * characters that are not only alphanumeric, underscores, periods, and colons.
+   *
+   * @param {*} template
+   * @param {*} substitutions
+   */
+  substituteGlobalTemplateVariables(
+    template: string,
+    substitutions: Substitutions,
+  ): IntrinsicFunction {
+    const variables = Object.keys(substitutions).join('|');
+    const regex = new RegExp(`\\#(${variables})#`, 'g');
+    const substituteTemplate = template.replace(regex, '|||$1|||');
+
+    const templateJoin = substituteTemplate
+      .split('|||')
+      .filter((part) => part !== '');
+    const parts: (string | IntrinsicFunction)[] = [];
+    for (let i = 0; i < templateJoin.length; i += 1) {
+      if (templateJoin[i] in substitutions) {
+        const subs = { [templateJoin[i]]: substitutions[templateJoin[i]] };
+        parts[i] = { 'Fn::Sub': [`\${${templateJoin[i]}}`, subs] };
+      } else {
+        parts[i] = templateJoin[i];
+      }
+    }
+    return { 'Fn::Join': ['', parts] };
+  }
+}

src/resources/PipelineFunction.ts

@@ -8,7 +8,7 @@ import { Api } from './Api';
 import path from 'path';
 import { MappingTemplate } from './MappingTemplate';
 import { SyncConfig } from './SyncConfig';
-import fs from 'fs';
+import { JsResolver } from './JsResolver';
 
 export class PipelineFunction {
   constructor(private api: Api, private config: PipelineFunctionConfig) {}
@@ -68,19 +68,18 @@ export class PipelineFunction {
     };
   }
 
-  resolveJsCode = (filePath: string): string => {
+  resolveJsCode = (filePath: string): string | IntrinsicFunction => {
     const codePath = path.join(
       this.api.plugin.serverless.config.servicePath,
       filePath,
     );
 
-    if (!fs.existsSync(codePath)) {
-      throw new this.api.plugin.serverless.classes.Error(
-        `The resolver handler file '${codePath}' does not exist`,
-      );
-    }
+    const template = new JsResolver(this.api, {
+      path: codePath,
+      substitutions: this.config.substitutions,
+    });
 
-    return fs.readFileSync(codePath, 'utf8');
+    return template.compile();
   };
 
   resolveMappingTemplate(

src/resources/Resolver.ts

@@ -8,7 +8,7 @@ import { Api } from './Api';
 import path from 'path';
 import { MappingTemplate } from './MappingTemplate';
 import { SyncConfig } from './SyncConfig';
-import fs from 'fs';
+import { JsResolver } from './JsResolver';
 
 // A decent default for pipeline JS resolvers
 const DEFAULT_JS_RESOLVERS = `
@@ -131,19 +131,18 @@ export class Resolver {
     };
   }
 
-  resolveJsCode = (filePath: string): string => {
+  resolveJsCode = (filePath: string): string | IntrinsicFunction => {
     const codePath = path.join(
       this.api.plugin.serverless.config.servicePath,
       filePath,
     );
 
-    if (!fs.existsSync(codePath)) {
-      throw new this.api.plugin.serverless.classes.Error(
-        `The resolver handler file '${codePath}' does not exist`,
-      );
-    }
+    const template = new JsResolver(this.api, {
+      path: codePath,
+      substitutions: this.config.substitutions,
+    });
 
-    return fs.readFileSync(codePath, 'utf8');
+    return template.compile();
   };
 
   resolveMappingTemplate(