config-loader: add substitution transform

packages/config-loader/src/lib/transform/index.ts

@@ -16,3 +16,4 @@
 
 export { applyConfigTransforms } from './apply';
 export { createIncludeTransform } from './include';
+export { createSubstitutionTransform } from './substitution';

packages/config-loader/src/lib/transform/substitution.test.ts

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2020 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { createSubstitutionTransform } from './substitution';
+
+const env = jest.fn(async (name: string) => {
+  return ({
+    SECRET: 'my-secret',
+    TOKEN: 'my-token',
+  } as { [name: string]: string })[name];
+});
+
+const substituteTransform = createSubstitutionTransform(env);
+
+describe('substituteTransform', () => {
+  it('should not transform unknown values', async () => {
+    await expect(substituteTransform(false)).resolves.toEqual([
+      false,
+      expect.anything(),
+    ]);
+    await expect(substituteTransform([1])).resolves.toEqual([
+      false,
+      expect.anything(),
+    ]);
+    await expect(substituteTransform(1)).resolves.toEqual([
+      false,
+      expect.anything(),
+    ]);
+    await expect(substituteTransform({ x: 'y' })).resolves.toEqual([
+      false,
+      expect.anything(),
+    ]);
+    await expect(substituteTransform(null)).resolves.toEqual([false, null]);
+  });
+
+  it('should substitute env var', async () => {
+    await expect(substituteTransform('hello ${SECRET}')).resolves.toEqual([
+      true,
+      'hello my-secret',
+    ]);
+    await expect(
+      substituteTransform('${SECRET      } $${} ${TOKEN }'),
+    ).resolves.toEqual([true, 'my-secret $${} my-token']);
+    await expect(substituteTransform('foo ${MISSING}')).resolves.toEqual([
+      true,
+      undefined,
+    ]);
+    await expect(
+      substituteTransform('foo ${MISSING} ${SECRET}'),
+    ).resolves.toEqual([true, undefined]);
+    await expect(
+      substituteTransform('foo ${SECRET} ${SECRET}'),
+    ).resolves.toEqual([true, 'foo my-secret my-secret']);
+  });
+});

packages/config-loader/src/lib/transform/substitution.ts

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2020 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { JsonValue } from '@backstage/config';
+import { TransformFunc, EnvFunc } from './types';
+
+/**
+ * A environment variable substitution transform that transforms e.g. 'token ${MY_TOKEN}'
+ * to 'token abc' if MY_TOKEN is 'abc'. If any of the substituted variables are undefined,
+ * the entire expression ends up undefined.
+ */
+export function createSubstitutionTransform(env: EnvFunc): TransformFunc {
+  return async (input: JsonValue) => {
+    if (typeof input !== 'string') {
+      return [false, input];
+    }
+
+    const parts: (string | undefined)[] = input.split(/(?<!\$)\$\{([^{}]+)\}/);
+    for (let i = 1; i < parts.length; i += 2) {
+      parts[i] = await env(parts[i]!.trim());
+    }
+    if (parts.some(part => part === undefined)) {
+      return [true, undefined];
+    }
+    return [true, parts.join('')];
+  };
+}

packages/config-loader/src/loader.test.ts

@@ -19,6 +19,8 @@ import mockFs from 'mock-fs';
 
 describe('loadConfig', () => {
   beforeAll(() => {
+    process.env.MY_SECRET = 'is-secret';
+
     mockFs({
       '/root/app-config.yaml': `
         app:
@@ -29,8 +31,14 @@ describe('loadConfig', () => {
       '/root/app-config.development.yaml': `
         app:
           sessionKey: development-key
+        backend:
+          $include: ./included.yaml
       `,
       '/root/secrets/session-key.txt': 'abc123',
+      '/root/included.yaml': `
+        foo:
+          bar: token \${MY_SECRET}
+      `,
     });
   });
 
@@ -104,6 +112,11 @@ describe('loadConfig', () => {
           app: {
             sessionKey: 'development-key',
           },
+          backend: {
+            foo: {
+              bar: 'token is-secret',
+            },
+          },
         },
       },
     ]);

packages/config-loader/src/loader.ts

@@ -22,6 +22,7 @@ import {
   applyConfigTransforms,
   readEnvConfig,
   createIncludeTransform,
+  createSubstitutionTransform,
 } from './lib';
 
 export type LoadConfigOptions = {
@@ -78,6 +79,7 @@ export async function loadConfig(
       const input = yaml.parse(await readFile(configPath));
       const data = await applyConfigTransforms(input, [
         createIncludeTransform(env, readFile),
+        createSubstitutionTransform(env),
       ]);
 
       configs.push({ data, context: basename(configPath) });