feat(util): improve error handling for file reader

Ovidiu Barabula · Ovidiu Barabula · commit aa62b0d82a44 · 2018-03-25T16:56:29.000+03:00
diff --git a/src/util/file-reader.spec.ts b/src/util/file-reader.spec.ts
@@ -1,3 +1,7 @@
+import * as chai from 'chai';
+import * as chaiAsPromised from 'chai-as-promised';
+chai.use(chaiAsPromised);
+
 import { assert, expect } from 'chai';
 import * as fs from 'fs';
 import 'mocha';
@@ -13,6 +17,8 @@ describe('FileReader', () => {
   const validJsonFile = 'valid.json';
 
   beforeEach(() => {
+    mockfs.restore && mockfs.restore();
+
     mockfs({
       [testDir]: {
         [nonJsonFile]: 'not a JSON file',
@@ -40,29 +46,6 @@ describe('FileReader', () => {
   });
 
 
-  it('returns false if it fails to write file', async () => {
-    const fileReader = FileReader(path.join(testDir, readonlyFile));
-    const contents = await fileReader.read();
-    mockfs.restore();
-    const fileWrite = await fileReader.write({ ...contents,  ...{ customKey: 'customValue' }});
-    expect(fileWrite).to.be.false;
-  });
-
-
-  it('returns false if it\'s not given a json-like file', async () => {
-    const fileReader = FileReader(path.join(testDir, nonJsonFile));
-    const contents = await fileReader.read();
-    expect(contents).to.be.false;
-  });
-
-
-  it('returns false if read failed', async () => {
-    const fileReader = FileReader(path.join(testDir, nonReadableFile));
-    const response = await fileReader.read();
-    expect(response).to.be.false;
-  });
-
-
   it('reads json-like file', async () => {
     const fileReader = FileReader(path.join(testDir, validJsonFile));
     const contents = await fileReader.read();
@@ -73,18 +56,41 @@ describe('FileReader', () => {
   it('writes new contents to file', async () => {
     const fileReader = FileReader(path.join(testDir, validJsonFile));
     const contents = await fileReader.read();
-    const fileWrite = await fileReader.write({ ...contents,  ...{ customKey: 'customValue' }});
+    const fileWrite = await fileReader.write({ ...contents, ...{ customKey: 'customValue' }});
     expect(fileWrite).to.be.true;
   });
 
 
   it('reads newly added content', async () => {
     const fileReader = FileReader(path.join(testDir, validJsonFile));
     const oldContent = await fileReader.read();
-    const fileWrite = await fileReader.write({ ...oldContent,  ...{ customKey: 'customValue' }});
+    const fileWrite = await fileReader.write({ ...oldContent, ...{ customKey: 'customValue' }});
     const newContent = await fileReader.read();
     expect(newContent.customKey).to.equal('customValue');
   });
 
-  afterEach(mockfs.restore);
+
+  it('rejects promise if read failed', () => {
+    const fileReader = FileReader(path.join(testDir, nonReadableFile));
+    return expect(fileReader.read()).to.be.rejectedWith(RegExp(ERRORS.READ_ERROR));
+  });
+
+
+  it('rejects promise if write failed', async () => {
+    const fileReader = FileReader(path.join(testDir, readonlyFile));
+    const contents = await fileReader.read();
+    mockfs.restore();
+    const fileWrite = fileReader.write({ ...contents, ...{ customKey: 'customValue' }});
+    return expect(fileWrite).to.be.rejectedWith(RegExp(ERRORS.WRITE_ERROR));
+  });
+
+
+  it('rejects promise if it\'s not given a JSON-like file', done => {
+    const fileReader = FileReader(path.join(testDir, nonJsonFile));
+    expect(fileReader.read()).to.be.rejectedWith(ERRORS.NOT_JSON).notify(done);
+  });
+
+
+  afterEach(() => mockfs.restore && mockfs.restore());
+  after(() => mockfs.restore && mockfs.restore());
 });
diff --git a/src/util/file-reader.ts b/src/util/file-reader.ts
@@ -6,18 +6,20 @@
  */
 
 import * as fs from 'fs';
+import { Config } from '../config-manager/package-json-config-reader';
 
 interface FileReader {
   read(): Promise<any>;
-  write(object: object): Promise<boolean>;
+  write(object: object): Promise<boolean|Error>;
 }
 
 export const ERRORS = {
-  NOT_FOUND: `File not found`,
+  NOT_FOUND: `FileReader> File not found`,
+  NOT_JSON: `FileReader> File is not in a JSON-like format`,
   PATH_NOT_PASSED: `FileReader requires 1 parameter to be string <filepath>`,
   PATH_NOT_STRING: `FileReader requires parameter 1 to be string`,
-  READ_ERROR: `Could not read file`,
-  WRITE_ERROR: `Could not write file`,
+  READ_ERROR: `FileReader> Could not read file`,
+  WRITE_ERROR: `FileReader> Could not write file`,
 };
 
 /**
@@ -39,14 +41,22 @@ function FileReader(filepath: string): FileReader {
   /**
    * Get file contents
    */
-  function read(): Promise<any> {
-    return new Promise(resolve => {
+  function read(): Promise<boolean|Error> {
+    return new Promise((resolve, reject) => {
       fs.readFile(filepath, 'utf-8', (readError, data) => {
+        // Throw back any read errors
+        if (readError) {
+          return reject(new Error(`${ERRORS.READ_ERROR}: ${readError.message}`));
+        }
+
+        let parsedJson;
         try {
-          resolve(JSON.parse(data));
+          parsedJson = JSON.parse(data);
         } catch (parseError) {
-          resolve(false);
+          return reject(new Error(ERRORS.NOT_JSON));
         }
+
+        return resolve(parsedJson);
       });
     });
   }
@@ -56,19 +66,22 @@ function FileReader(filepath: string): FileReader {
    * Write JSON object to file
    * @param object Object literal
    */
-  function write(object: object): Promise<boolean> {
+  function write(object: Config): Promise<boolean|Error> {
     return new Promise((resolve, reject) => {
+      // TODO: replace 2 with 'detect-indent' module's output
       const content = JSON.stringify(object, null, 2);
-      fs.writeFile(filepath, content, error => {
-        if (error) {
-          return resolve(false);
+      // Write the file content with an empty line at the end
+      fs.writeFile(filepath, `${content}\n`, writeError => {
+        if (writeError) {
+          return reject(new Error(`${ERRORS.WRITE_ERROR}: ${writeError.message}`));
         }
 
         return resolve(true);
       });
     });
   }
 
+
   // Return public API
   return Object.freeze({
     read,
