feat: add new methods to FairPlayUtils (shaka-project#4029)

This adds 3 new methods to FairPlayUtils:

- isFairPlaySupported --> Closes PR shaka-project#3562
- spcFairPlayRequest --> This method adds basic spc FairPlay request filter
- commonFairPlayResponse --> This method adds a basic FairPlay response filter that supports a lot of DRM providers.

lib/util/fairplay_utils.js

@@ -8,16 +8,41 @@ goog.provide('shaka.util.FairPlayUtils');
 
 goog.require('goog.Uri');
 goog.require('goog.asserts');
+goog.require('shaka.net.NetworkingEngine');
 goog.require('shaka.util.BufferUtils');
 goog.require('shaka.util.Error');
 goog.require('shaka.util.StringUtils');
+goog.require('shaka.util.Uint8ArrayUtils');
 
 
 /**
  * @summary A set of FairPlay utility functions.
  * @export
  */
 shaka.util.FairPlayUtils = class {
+  /**
+   * Check if FairPlay is supported.
+   *
+   * @return {!Promise.<boolean>}
+   * @export
+   */
+  static async isFairPlaySupported() {
+    const config = {
+      initDataTypes: ['cenc', 'sinf', 'skd'],
+      videoCapabilities: [
+        {
+          contentType: 'video/mp4; codecs="avc1.42E01E"',
+        },
+      ],
+    };
+    try {
+      await navigator.requestMediaKeySystemAccess('com.apple.fps', [config]);
+      return true;
+    } catch (err) {
+      return false;
+    }
+  }
+
   /**
    * Using the default method, extract a content ID from the init data.  This is
    * based on the FairPlay example documentation.
@@ -106,4 +131,88 @@ shaka.util.FairPlayUtils = class {
         offset == rebuiltInitData.length, 'Inconsistent init data length');
     return rebuiltInitData;
   }
+
+  /**
+   * SPC FairPlay request.
+   *
+   * @param {shaka.net.NetworkingEngine.RequestType} type
+   * @param {shaka.extern.Request} request
+   * @export
+   */
+  static spcFairPlayRequest(type, request) {
+    if (type !== shaka.net.NetworkingEngine.RequestType.LICENSE) {
+      return;
+    }
+    const body = /** @type {!(ArrayBuffer|ArrayBufferView)} */(request.body);
+    const originalPayload = shaka.util.BufferUtils.toUint8(body);
+    const base64Payload = shaka.util.Uint8ArrayUtils.toBase64(originalPayload);
+    request.headers['Content-Type'] = 'application/x-www-form-urlencoded';
+    request.body = shaka.util.StringUtils.toUTF8('spc=' + base64Payload);
+  }
+
+  /**
+   * Common FairPlay response transform for some DRMs providers.
+   *
+   * @param {shaka.net.NetworkingEngine.RequestType} type
+   * @param {shaka.extern.Response} response
+   * @export
+   */
+  static commonFairPlayResponse(type, response) {
+    if (type !== shaka.net.NetworkingEngine.RequestType.LICENSE) {
+      return;
+    }
+
+    // In Apple's docs, responses can be of the form:
+    //   '\n<ckc>base64encoded</ckc>\n' or 'base64encoded'
+    // We have also seen responses in JSON format from some of our partners.
+    // In all of these text-based formats, the CKC data is base64-encoded.
+
+    let responseText;
+    try {
+      // Convert it to text for further processing.
+      responseText = shaka.util.StringUtils.fromUTF8(response.data);
+    } catch (error) {
+      // Assume it's not a text format of any kind and leave it alone.
+      return;
+    }
+
+    let licenseProcessing = false;
+
+    // Trim whitespace.
+    responseText = responseText.trim();
+
+    // Look for <ckc> wrapper and remove it.
+    if (responseText.substr(0, 5) === '<ckc>' &&
+        responseText.substr(-6) === '</ckc>') {
+      responseText = responseText.slice(5, -6);
+      licenseProcessing = true;
+    }
+
+    // Look for a JSON wrapper and remove it.
+    try {
+      const responseObject = /** @type {!Object} */(JSON.parse(responseText));
+      if (responseObject['ckc']) {
+        responseText = responseObject['ckc'];
+        licenseProcessing = true;
+      }
+      if (responseObject['CkcMessage']) {
+        responseText = responseObject['CkcMessage'];
+        licenseProcessing = true;
+      }
+      if (responseObject['License']) {
+        responseText = responseObject['License'];
+        licenseProcessing = true;
+      }
+    } catch (err) {
+      // It wasn't JSON.  Fall through with other transformations.
+    }
+
+    if (licenseProcessing) {
+      // Decode the base64-encoded data into the format the browser expects.
+      // It's not clear why FairPlay license servers don't just serve this
+      // directly.
+      response.data = shaka.util.BufferUtils.toArrayBuffer(
+          shaka.util.Uint8ArrayUtils.fromBase64(responseText));
+    }
+  }
 };