REST endpoint for searching Gerrit documentation.

The documentation of this endpoint is available in
rest-api-docsearch[.txt|.html].

The UI of showing the search result and doing the search will be in a
separate change.

Change-Id: Ifa4f5a7d576ada7f88a4fa1b765a38cba6d7e964

gerrit-httpd/BUCK

@@ -1,11 +1,24 @@
-SRCS = glob(['src/main/java/**/*.java'])
+CONSTANTS_SRC = [
+  'src/main/java/com/google/gerrit/httpd/rpc/doc/Constants.java',
+]
+SRCS = glob(
+  ['src/main/java/**/*.java'],
+  excludes = CONSTANTS_SRC,
+)
 RESOURCES = glob(['src/main/resources/**/*'])
 
+java_library2(
+  name = 'constants',
+  srcs = CONSTANTS_SRC,
+  visibility = ['PUBLIC'],
+)
+
 java_library2(
   name = 'httpd',
   srcs = SRCS,
   resources = RESOURCES,
   deps = [
+    ':constants',
     '//gerrit-antlr:query_exception',
     '//gerrit-common:server',
     '//gerrit-extension-api:api',
@@ -30,6 +43,9 @@ java_library2(
     '//lib/jgit:jgit',
     '//lib/jgit:jgit-servlet',
     '//lib/log:api',
+    '//lib/lucene:analyzers-common',
+    '//lib/lucene:core',
+    '//lib/lucene:query-parser',
   ],
   compile_deps = ['//lib:servlet-api-3_0'],
   visibility = ['PUBLIC'],

gerrit-httpd/src/main/java/com/google/gerrit/httpd/UrlModule.java

@@ -30,6 +30,7 @@ import com.google.gerrit.httpd.rpc.account.AccountsRestApiServlet;
 import com.google.gerrit.httpd.rpc.change.ChangesRestApiServlet;
 import com.google.gerrit.httpd.rpc.change.DeprecatedChangeQueryServlet;
 import com.google.gerrit.httpd.rpc.config.ConfigRestApiServlet;
+import com.google.gerrit.httpd.rpc.doc.QueryDocumentationFilter;
 import com.google.gerrit.httpd.rpc.group.GroupsRestApiServlet;
 import com.google.gerrit.httpd.rpc.project.ProjectsRestApiServlet;
 import com.google.gerrit.reviewdb.client.Change;
@@ -110,6 +111,8 @@ class UrlModule extends ServletModule {
     serveRegex("^/(?:a/)?groups/(.*)?$").with(GroupsRestApiServlet.class);
     serveRegex("^/(?:a/)?projects/(.*)?$").with(ProjectsRestApiServlet.class);
 
+    filter("/Documentation/").through(QueryDocumentationFilter.class);
+
     if (cfg.deprecatedQuery) {
       serve("/query").with(DeprecatedChangeQueryServlet.class);
     }

gerrit-httpd/src/main/java/com/google/gerrit/httpd/restapi/RestApiServlet.java

@@ -607,7 +607,7 @@ public class RestApiServlet extends HttpServlet {
     throw new InstantiationException("Cannot make " + type);
   }
 
-  private static void replyJson(@Nullable HttpServletRequest req,
+  public static void replyJson(@Nullable HttpServletRequest req,
       HttpServletResponse res,
       Multimap<String, String> config,
       Object result)

gerrit-httpd/src/main/java/com/google/gerrit/httpd/rpc/doc/Constants.java

@@ -0,0 +1,24 @@
+// Copyright (C) 2013 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.httpd.rpc.doc;
+
+public class Constants {
+
+  public static final String DOC_FIELD = "doc";
+  public static final String TITLE_FIELD = "title";
+  public static final String URL_FIELD = "url";
+
+  private Constants() {}
+}

gerrit-httpd/src/main/java/com/google/gerrit/httpd/rpc/doc/QueryDocumentationFilter.java

@@ -0,0 +1,191 @@
+// Copyright (C) 2013 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.httpd.rpc.doc;
+
+import com.google.common.base.Strings;
+import com.google.common.collect.LinkedHashMultimap;
+import com.google.common.collect.Lists;
+import com.google.common.collect.Multimap;
+import com.google.gerrit.httpd.restapi.RestApiServlet;
+import com.google.inject.Inject;
+import com.google.inject.Singleton;
+
+import org.apache.lucene.analysis.standard.StandardAnalyzer;
+import org.apache.lucene.document.Document;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.queryparser.classic.ParseException;
+import org.apache.lucene.queryparser.classic.QueryParser;
+import org.apache.lucene.search.IndexSearcher;
+import org.apache.lucene.search.Query;
+import org.apache.lucene.search.ScoreDoc;
+import org.apache.lucene.search.TopDocs;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.IndexOutput;
+import org.apache.lucene.store.RAMDirectory;
+import org.apache.lucene.util.Version;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.List;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipInputStream;
+
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+@Singleton
+public class QueryDocumentationFilter implements Filter {
+  private static final Logger log =
+      LoggerFactory.getLogger(QueryDocumentationFilter.class);
+
+  private static final String INDEX_PATH = "index.zip";
+  private static final Version LUCENE_VERSION = Version.LUCENE_44;
+
+  private IndexSearcher searcher;
+  private QueryParser parser;
+
+  protected static class DocResult {
+    public String title;
+    public String url;
+    public String content;
+  }
+
+  @Inject
+  QueryDocumentationFilter() {
+  }
+
+  @Override
+  public void init(FilterConfig filterConfig) {
+    try {
+      Directory dir = readIndexDirectory();
+      if (dir == null) {
+        searcher = null;
+        parser = null;
+        return;
+      }
+      IndexReader reader = DirectoryReader.open(dir);
+      searcher = new IndexSearcher(reader);
+      StandardAnalyzer analyzer = new StandardAnalyzer(LUCENE_VERSION);
+      parser = new QueryParser(LUCENE_VERSION, Constants.DOC_FIELD, analyzer);
+    } catch (IOException e) {
+      log.error("Cannot initialize documentation full text index", e);
+      searcher = null;
+      parser = null;
+    }
+  }
+
+  @Override
+  public void destroy() {
+  }
+
+  @Override
+  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
+      throws IOException, ServletException {
+    HttpServletRequest req = (HttpServletRequest) request;
+    if ("GET".equals(req.getMethod())
+        && !Strings.isNullOrEmpty(req.getParameter("q"))) {
+      HttpServletResponse rsp = (HttpServletResponse) response;
+      try {
+        List<DocResult> result = doQuery(request.getParameter("q"));
+        Multimap<String, String> config = LinkedHashMultimap.create();
+        RestApiServlet.replyJson(req, rsp, config, result);
+      } catch (DocQueryException e) {
+        rsp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
+      }
+    } else {
+      chain.doFilter(request, response);
+    }
+  }
+
+  private List<DocResult> doQuery(String q) throws DocQueryException {
+    if (parser == null || searcher == null) {
+      throw new DocQueryException("Not initialized");
+    }
+    try {
+      Query query = parser.parse(q);
+      TopDocs results = searcher.search(query, Integer.MAX_VALUE);
+      ScoreDoc[] hits = results.scoreDocs;
+      int totalHits = results.totalHits;
+
+      List<DocResult> out = Lists.newArrayListWithCapacity(totalHits);
+      for (int i = 0; i < totalHits; i++) {
+        DocResult result = new DocResult();
+        Document doc = searcher.doc(hits[i].doc);
+        result.url = doc.get(Constants.URL_FIELD);
+        result.title = doc.get(Constants.TITLE_FIELD);
+        out.add(result);
+      }
+      return out;
+    } catch (IOException e) {
+      throw new DocQueryException(e);
+    } catch (ParseException e) {
+      throw new DocQueryException(e);
+    }
+  }
+
+  protected Directory readIndexDirectory() throws IOException {
+    Directory dir = new RAMDirectory();
+    byte[] buffer = new byte[4096];
+    InputStream index =
+        QueryDocumentationFilter.class.getClassLoader().getResourceAsStream(INDEX_PATH);
+    if (index == null) {
+      log.warn("No index available");
+      return null;
+    }
+    ZipInputStream zip = new ZipInputStream(index);
+    try {
+      ZipEntry entry;
+      while ((entry = zip.getNextEntry()) != null) {
+        IndexOutput out = dir.createOutput(entry.getName(), null);
+        int count;
+        while ((count = zip.read(buffer)) != -1) {
+          out.writeBytes(buffer, count);
+        }
+        out.close();
+      }
+    } finally {
+      zip.close();
+    }
+    // We must NOT call dir.close() here, as DirectoryReader.open() expects an opened directory.
+    return dir;
+  }
+
+  private static class DocQueryException extends Exception {
+    public DocQueryException() {
+    }
+
+    public DocQueryException(String msg) {
+      super(msg);
+    }
+
+    public DocQueryException(String msg, Throwable e) {
+      super(msg, e);
+    }
+
+    public DocQueryException(Throwable e) {
+      super(e);
+    }
+  }
+}