Download web payment manifests.

chrome/android/java/src/org/chromium/chrome/browser/payments/ManifestDownloader.java

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.payments;
+
+import android.os.AsyncTask;
+
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.net.URL;
+import java.util.List;
+import java.util.Map;
+import java.util.Scanner;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * Downloads the payment method manifest based on the payment method name that is a URL with HTTPS
+ * scheme, e.g., https://bobpay.com. The download happens via two consecutive HTTP requests:
+ *
+ * 1) HEAD request for the payment method name. The HTTP response header is parsed for Link header
+ *    that points to the location of the payment method manifest file. Example of a relative
+ *    location:
+ *
+ *        Link: <data/payment-manifest.json>; rel="payment-method-manifest"
+ *
+ *    (This is relative to the payment method URL.) Example of an absolute location:
+ *
+ *        Link: <https://bobpay.com/data/payment-manifest.json>; rel="payment-method-manifest"
+ *
+ *    The absolute location must use HTTPS scheme.
+ *
+ * 2) GET request for the payment method manifest file.
+ */
+public class ManifestDownloader {
+    /** Interface for the callback to invoke when finished downloading. */
+    public interface ManifestDownloadCallback {
+        /**
+         * Called on successful download of a payment method manifest.
+         *
+         * @param contents The successfully downloaded payment method manifest.
+         */
+        void onManifestDownloadSuccess(String contents);
+
+        /** Called on failed download of a payment method manifest. */
+        void onManifestDownloadFailure();
+    }
+
+    /** The prefix of a payment method name for which a manifest can be downloaded. */
+    public static final String MANIFEST_SCHEME = "https://";
+
+    /** HTTP HEAD method name. */
+    private static final String HTTP_METHOD_HEAD = "HEAD";
+
+    /** HTTP Link header name. */
+    private static final String HTTP_HEADER_LINK = "Link";
+
+    /** The regular expression that captures the URL of the payment method manifest. */
+    private static final String PATTERN_LINK = "^<(.*)>; rel=\"payment-method-manifest\"$";
+
+    /** The regular expression capture group for the URL of the payment method manifest. */
+    private static final int GROUP_URL = 1;
+
+    /** The token for requesting the full text of the download stream. */
+    private static final String SCANNER_FULL_TEXT_TOKEN = "\\A";
+
+    /**
+     * Downloads the manifest file asynchronously.
+     *
+     * @param methodName The payment method name that is a URL with HTTPS scheme. Must be a URL and
+     *                   must start with "https://".
+     * @param callback   The callback to invoke when finished downloading.
+     */
+    public static void download(final String methodName, final ManifestDownloadCallback callback) {
+        assert methodName != null;
+        assert callback != null;
+        assert methodName.startsWith(MANIFEST_SCHEME);
+
+        (new AsyncTask<Void, Void, String>() {
+            @Override
+            protected String doInBackground(Void... ignored) {
+                HttpURLConnection httpConnection = null;
+                try {
+                    httpConnection = (HttpURLConnection) new URL(methodName).openConnection();
+                    if (httpConnection == null) return null;
+
+                    httpConnection.setRequestMethod(HTTP_METHOD_HEAD);
+                    int responseCode = httpConnection.getResponseCode();
+                    if (responseCode != 200) {
+                        httpConnection.disconnect();
+                        return null;
+                    }
+
+                    Map<String, List<String>> headers = httpConnection.getHeaderFields();
+                    Pattern pattern = Pattern.compile(PATTERN_LINK);
+                    String manifestUrl = null;
+                    for (Map.Entry<String, List<String>> header : headers.entrySet()) {
+                        if (HTTP_HEADER_LINK.equals(header.getKey())) {
+                            List<String> values = header.getValue();
+                            for (int i = 0; i < values.size(); i++) {
+                                Matcher matcher = pattern.matcher(values.get(i));
+                                if (matcher.matches()) manifestUrl = matcher.group(GROUP_URL);
+                            }
+                        }
+                    }
+
+                    if (manifestUrl == null) {
+                        httpConnection.disconnect();
+                        return null;
+                    }
+
+                    if (!manifestUrl.startsWith(MANIFEST_SCHEME)) {
+                        manifestUrl = methodName + "/" + manifestUrl;
+                    }
+
+                    httpConnection.disconnect();
+                    httpConnection = (HttpURLConnection) new URL(manifestUrl).openConnection();
+                    responseCode = httpConnection.getResponseCode();
+                    if (responseCode != 200) {
+                        httpConnection.disconnect();
+                        return null;
+                    }
+
+                    Scanner scanner = new Scanner(httpConnection.getInputStream())
+                            .useDelimiter(SCANNER_FULL_TEXT_TOKEN);
+                    String result = scanner.hasNext() ? scanner.next() : null;
+                    httpConnection.disconnect();
+                    return result;
+                } catch (SecurityException | IOException e) {
+                    if (httpConnection != null) httpConnection.disconnect();
+                    return null;
+                }
+            }
+
+            @Override
+            protected void onPostExecute(String data) {
+                if (data != null) {
+                    callback.onManifestDownloadSuccess(data);
+                } else {
+                    callback.onManifestDownloadFailure();
+                }
+            }
+        }).execute();
+    }
+
+    private ManifestDownloader() {}
+}