implement validations of pagination URLs

java/org/chromium/distiller/QueryParamPagePattern.java

Index: java/org/chromium/distiller/QueryParamPagePattern.java
diff --git a/java/org/chromium/distiller/QueryParamPagePattern.java b/java/org/chromium/distiller/QueryParamPagePattern.java
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+++ b/java/org/chromium/distiller/QueryParamPagePattern.java
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+// Copyright 2015 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.distiller;
+
+import com.google.gwt.regexp.shared.RegExp;
+
+/**
+ * This class detects the page parameter in the query of a potential pagination URL.  If detected,
+ * it replaces the page param value with PageParameterDetector.PAGE_PARAM_PLACEHOLDER, then creates
+ * and returns a new object.  This object can then be called via PageParameterDetector.PagePattern
+ * interface to:
+ * - validate the generated URL page pattern against the document URL
+ * - determine if a URL is a paging URL based on the page pattern.
+ * Example: if the original url is "http://www.foo.com/a/b/?page=2&query=a", the page pattern is
+ * "http://www.foo.com/a/b?page=[*!]&query=a". (See comments at top of PageParameterDetector.java).
+ */
+public class QueryParamPagePattern implements PageParameterDetector.PagePattern {
+    private final ParsedUrl mUrl;
+    private final int mPageNumber;
+    private final int mPlaceholderStart;
+    private final String mUrlStr;
+    private final int mQueryStart;
+    // Start position of query param containing placeholder.
+    private int mPlaceholderSegmentStart;
+    private final String mPrefix;  // The part of the page pattern before the placeholder.
+    private String mSuffix = "";  // The part of the page pattern after the placeholder.
+    // This is not mSuffix.length(), see their initializations in constructor.
+    private final int mSuffixLen;
+
+    /**
+     * Returns a new QueryParamPagePattern if url is valid and page param is in the query.
+     */
+    static PageParameterDetector.PagePattern create(ParsedUrl url, String queryName,
+            String queryValue) {
+        try {
+            return new QueryParamPagePattern(url, queryName, queryValue);
+        } catch (IllegalArgumentException e) {
+            return null;
+        }
+    }
+
+    @Override
+    public String toString() {
+        return mUrlStr;
+    }
+
+    @Override
+    public int getPageNumber() {
+        return mPageNumber;
+    }
+
+    /**
+     * Returns true if page pattern and URL have the same path components.
+     *
+     * @param docUrl the current document URL
+     */
+    @Override
+    public boolean isValidFor(ParsedUrl docUrl) {
+        return docUrl.getTrimmedPath().equalsIgnoreCase(mUrl.getTrimmedPath());
+    }
+
+    private static RegExp sSlashOrHtmExtRegExp = null;  // Match either '/' or ".htm(l)".
+
+    /**
+     * Returns true if a URL matches this page pattern based on a pipeline of rules:
+     * - suffix (part of pattern after page param placeholder) must be same, and
+     * - scheme, host, and path must be same, and
+     * - query params, except that for page number, must be same in order and value, and
+     * - query value must be a plain number.
+     *
+     * @param url the URL to evalutate
+     */
+    @Override
+    public boolean isPagingUrl(String url) {
+        // Both url and pattern must have the same suffix, if available.
+        if (mSuffixLen != 0 && !url.endsWith(mSuffix)) return false;
+
+        final int suffixStart = url.length() - mSuffixLen;
+
+        // The url matches the pattern only when:
+        //   1. has same prefix (scheme, host, path)
+        //   2. has same query params with same value (except page number query) in the same
+        //      order.
+        // Examples:
+        // If page pattern is http://foo.com/a/b?queryA=v1&queryB=[*!]&queryC=v3
+        // Returns true for:
+        //   - http://foo.com/a/b/?queryA=v1&queryC=v3
+        //   - http://foo.com/a/b/?queryA=v1&queyrB=4&queryC=v3
+        // Otherwise, returns false.
+        //
+        // If page pattern is http://foo.com/a/b?page=[*!]&query=a
+        // Returns true for:
+        //   - http://foo.com/a/b?query=a
+        //   - http://foo.com/a/b?page=2&query=a
+        // Otherwise, returns false.
+        //
+        // If page pattern is http://foo.com/a/b?page=[*!]
+        // Returns true for:
+        //   - http://foo.com/a/b/
+        //   - http://foo.com/a/b.html
+        //   - http://foo.com/a/b.htm
+        //   - http://foo.com/a/b?page=2
+        // Otherwise, returns false.
+
+        // Both url and pattern must have the same prefix.
+        if (!url.startsWith(mPrefix)) return false;
+
+        // If the url doesn't have page number query, it is fine.
+        if (mPlaceholderSegmentStart == suffixStart) return true;
+
+        // If the only difference in the page param between url and pattern is "/", ".htm" or
+        // ".html", it is fine.
+        String diffPart = url.substring(mPlaceholderSegmentStart, suffixStart).toLowerCase();
+        if (sSlashOrHtmExtRegExp == null) {
+            sSlashOrHtmExtRegExp = RegExp.compile("^\\/|(.html?)$", "i");
+        }
+        if (sSlashOrHtmExtRegExp.test(diffPart)) return true;
+
+        // Both url and pattern must have the same query name.
+        if (!url.regionMatches(mPlaceholderSegmentStart, mUrlStr, mPlaceholderSegmentStart,
+                mPlaceholderStart - mPlaceholderSegmentStart)) {
+            return false;
+        }
+
+        return PageParameterDetector.isPlainNumber(url.substring(mPlaceholderStart, suffixStart));
+    }
+
+    private QueryParamPagePattern(ParsedUrl url, String queryName, String queryValue)
+            throws IllegalArgumentException {
+        if (queryName.isEmpty()) throw new IllegalArgumentException("Empty query name");
+        if (queryValue.isEmpty()) throw new IllegalArgumentException("Empty query value");
+        if (!StringUtil.isStringAllDigits(queryValue)) {
+            throw new IllegalArgumentException("Query value has non-digits: " + queryValue);
+        }
+        if (PageParameterDetector.isPageParamNameBad(queryName)) {
+            throw new IllegalArgumentException("Query name is bad page param name: " + queryName);
+        }
+
+        int value = StringUtil.toNumber(queryValue);
+        if (value < 0) {
+            throw new IllegalArgumentException("Query value is an invalid number: " + queryValue);
+        }
+
+        String pattern = url.replaceQueryValue(queryName, queryValue,
+                PageParameterDetector.PAGE_PARAM_PLACEHOLDER);
+        mUrl = ParsedUrl.create(pattern);
+        if (mUrl == null) throw new IllegalArgumentException("Invalid URL: " + pattern);
+        mUrlStr = pattern;
+        mPageNumber = value;
+        mPlaceholderStart = pattern.indexOf(PageParameterDetector.PAGE_PARAM_PLACEHOLDER);
+        mQueryStart = mUrlStr.lastIndexOf('?', mPlaceholderStart - 1);
+        mPlaceholderSegmentStart = mUrlStr.lastIndexOf('&', mPlaceholderStart - 1);
+        if (mPlaceholderSegmentStart == -1) {  // Page param is the first query.
+            mPlaceholderSegmentStart = mQueryStart;
+        }
+        mPrefix = mUrlStr.substring(0, mPlaceholderSegmentStart);
+        // Determine suffix, if available.
+        final int urlLen = mUrlStr.length();
+        mSuffixLen = urlLen - mPlaceholderStart - PageParameterDetector.PAGE_PARAM_PLACEHOLDER_LEN;
+        if (mSuffixLen != 0) {
+            mSuffix = mUrlStr.substring(urlLen - mSuffixLen + 1); // +1 to exclude '&' or '?'.
+        }
+    }
+
+}