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/**
 * Copyright (C) 2013-2017 Expedia Inc.
 *
 * 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.hotels.styx.server.handlers;

import com.google.common.io.Files;
import com.google.common.net.MediaType;
import com.hotels.styx.api.HttpHandler;
import com.hotels.styx.api.HttpRequest;
import com.hotels.styx.api.HttpResponse;
import org.slf4j.Logger;
import rx.Observable;

import java.io.File;
import java.io.IOException;
import java.util.Optional;

import static com.google.common.base.Throwables.propagate;
import static com.hotels.styx.api.HttpHeaderNames.CONTENT_TYPE;
import static com.hotels.styx.api.HttpResponse.Builder.response;
import static com.hotels.styx.api.MediaTypes.mediaTypeOf;
import static com.hotels.styx.api.http.handlers.NotFoundHandler.NOT_FOUND_HANDLER;
import static io.netty.handler.codec.http.HttpResponseStatus.INTERNAL_SERVER_ERROR;
import static java.nio.charset.StandardCharsets.UTF_8;
import static org.slf4j.LoggerFactory.getLogger;
import static rx.Observable.just;

/**
 * HTTP handler that provides a static file.
 */
public class StaticFileHandler implements HttpHandler {
    private static final Logger LOG = getLogger(StaticFileHandler.class);
    private final File dir;

    /**
     * Constructor.
     *
     * @param dir directory to find files in
     */
    public StaticFileHandler(File dir) {
        this.dir = dir;
    }

    @Override
    public Observable handle(HttpRequest request) {
        try {
            return resolveFile(request.path())
                    .map(ResolvedFile::new)
                    .map(resolvedFile -> response()
                            .addHeader(CONTENT_TYPE, resolvedFile.mediaType)
                            .body(resolvedFile.content)
                            .build())
                    .map(Observable::just)
                    .orElseGet(() -> NOT_FOUND_HANDLER.handle(request));
        } catch (IOException e) {
            return just(response(INTERNAL_SERVER_ERROR).build());
        }
    }

    private static class ResolvedFile {
        private final String content;
        private final MediaType mediaType;

        private ResolvedFile(File file) {
            this.content = readLines(file);
            this.mediaType = mediaTypeOf(file.getName());
        }
    }

    private static String readLines(File file) {
        try {
            return Files.toString(file, UTF_8);
        } catch (IOException e) {
            throw propagate(e);
        }
    }

    /**
     * Resolve path to actual file.
     *
     * @param path file path
     * @return file if it exists
     * @throws IOException I/O exception
     */
    private Optional resolveFile(String path) throws IOException {
        File result = new File(dir, path).getCanonicalFile();
        LOG.debug("Resolved path={}", result);

        if (!result.exists()) {
            return Optional.empty();
        }

        // For security, check file really does exist under root.
        String fullPath = result.getPath();
        if (!fullPath.startsWith(dir.getCanonicalPath() + File.separator) && !fullPath.equals(dir.getCanonicalPath())) {
            // Prevent paths like http://foo/../../etc/passwd
            result = null;
        }

        return Optional.ofNullable(result);
    }
}