Add DeltaPatcher module to handle Delta bundles

Reviewed By: jeanlauliac

Differential Revision: D5761096

fbshipit-source-id: 8c8ef5fb720b08e3f4f097c5a76f793dc4f1c1da

packages/metro-bundler/src/DeltaBundler/DeltaPatcher.js

@@ -0,0 +1,89 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ * @format
+ */
+
+'use strict';
+
+import type {DeltaBundle} from './';
+
+/**
+ * This is a reference client for the Delta Bundler: it maintains cached the
+ * last patched bundle delta and it's capable of applying new Deltas received
+ * from the Bundler and stringify them to convert them into a full bundle.
+ */
+class DeltaPatcher {
+  _lastBundle = {
+    pre: '',
+    post: '',
+    modules: {},
+  };
+  _initialized = false;
+
+  /**
+   * Applies a Delta Bundle to the current bundle.
+   */
+  applyDelta(deltaBundle: DeltaBundle) {
+    // Make sure that the first received delta is a fresh one.
+    if (!this._initialized && !deltaBundle.reset) {
+      throw new Error(
+        'DeltaPatcher should receive a fresh Delta when being initialized',
+      );
+    }
+
+    this._initialized = true;
+
+    // Reset the current delta when we receive a fresh delta.
+    if (deltaBundle.reset) {
+      this._lastBundle = {
+        pre: '',
+        post: '',
+        modules: {},
+      };
+    }
+
+    // Override the prepended sources.
+    if (deltaBundle.pre) {
+      this._lastBundle.pre = deltaBundle.pre;
+    }
+
+    // Override the appended sources.
+    if (deltaBundle.post) {
+      this._lastBundle.post = deltaBundle.post;
+    }
+
+    // Patch the received modules.
+    for (const i in deltaBundle.delta) {
+      if (deltaBundle.delta[i] == null) {
+        delete this._lastBundle.modules[i];
+      } else {
+        this._lastBundle.modules[i] = deltaBundle.delta[i];
+      }
+    }
+
+    return this;
+  }
+
+  /**
+   * Converts the current delta bundle to a standard string bundle, ready to
+   * be interpreted by any JS VM.
+   */
+  stringify() {
+    return []
+      .concat(
+        this._lastBundle.pre,
+        Object.values(this._lastBundle.modules),
+        this._lastBundle.post,
+      )
+      .join('\n;');
+  }
+}
+
+module.exports = DeltaPatcher;

packages/metro-bundler/src/DeltaBundler/__tests__/DeltaPatcher-test.js

@@ -0,0 +1,105 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @emails oncall+javascript_tools
+ * @format
+ */
+
+'use strict';
+
+const DeltaPatcher = require('../DeltaPatcher');
+
+describe('DeltaPatcher', () => {
+  let deltaPatcher;
+
+  beforeEach(() => {
+    deltaPatcher = new DeltaPatcher();
+  });
+
+  it('should throw if received a non-reset delta as the initial one', () => {
+    expect(() =>
+      deltaPatcher.applyDelta({
+        pre: 'pre',
+        post: 'post',
+        delta: {},
+      }),
+    ).toThrow();
+  });
+
+  it('should apply an initial delta correctly', () => {
+    const result = deltaPatcher
+      .applyDelta({
+        reset: 1,
+        pre: 'pre',
+        post: 'post',
+        delta: {
+          1: 'middle',
+        },
+      })
+      .stringify();
+
+    expect(result).toMatchSnapshot();
+  });
+
+  it('should apply many different patches correctly', () => {
+    const result = deltaPatcher
+      .applyDelta({
+        reset: 1,
+        pre: 'pre',
+        post: 'post',
+        delta: {
+          1: 'middle',
+        },
+      })
+      .applyDelta({
+        delta: {
+          2: 'another',
+        },
+      })
+      .applyDelta({
+        delta: {
+          2: 'another',
+          87: 'third',
+        },
+      })
+      .stringify();
+
+    expect(result).toMatchSnapshot();
+
+    const anotherResult = deltaPatcher
+      .applyDelta({
+        pre: 'new pre',
+        delta: {
+          2: 'another',
+          1: null,
+        },
+      })
+      .applyDelta({
+        delta: {
+          2: null,
+          12: 'twelve',
+        },
+      })
+      .stringify();
+
+    expect(anotherResult).toMatchSnapshot();
+
+    expect(
+      deltaPatcher
+        .applyDelta({
+          pre: '1',
+          post: '1',
+          delta: {
+            12: 'ten',
+          },
+          reset: true,
+        })
+        .stringify(),
+    ).toMatchSnapshot();
+  });
+});

packages/metro-bundler/src/DeltaBundler/__tests__/__snapshots__/DeltaPatcher-test.js.snap

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+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`DeltaPatcher should apply an initial delta correctly 1`] = `
+"pre
+;middle
+;post"
+`;
+
+exports[`DeltaPatcher should apply many different patches correctly 1`] = `
+"pre
+;middle
+;another
+;third
+;post"
+`;
+
+exports[`DeltaPatcher should apply many different patches correctly 2`] = `
+"new pre
+;twelve
+;third
+;post"
+`;
+
+exports[`DeltaPatcher should apply many different patches correctly 3`] = `
+"1
+;ten
+;1"
+`;