Implementing HTTP byte-range requests in Spring MVC

Recently I needed to implement HTTP byte-range requests in Spring MVC for serving some media files. In my case those were not really static files though.

This is actually like implementing Tomcat's DefaultServlet (http://tomcat.apache.org/tomcat-6.0-doc/default-servlet.html) in order to serve static files. So first thing that comes to mind is, is there any way to simply re-use  implementation of org.apache.catalina.servlets.DefaultServlet by sub-classing it or by simply invoking some methods from the class. But after looking at the DefaultServlet source code, I decided against it as it looked difficult to retrofit that in Spring MVC paradigm. After little more googling, I found this excellent blog-post by Bauke Scholtz - http://balusc.blogspot.in/2009/02/fileservlet-supporting-resume-and.html. The blog-post talks about supporting byte-range or part-range requests as received from the client browser or any HTTP-based client who wishes to send such requests.

I refactored this code for a Spring View. Here is the code -

/**
 * net/balusc/webapp/FileServlet.java
 *
 * Copyright (C) 2009 BalusC
 *
 * This program is free software: you can redistribute it and/or modify it under the terms of the
 * GNU Lesser General Public License as published by the Free Software Foundation, either version 3
 * of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
 * even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License along with this library.
 * If not, see .
 */

import org.springframework.web.servlet.view.AbstractView;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Map;

/**
 * LGPL code from http://balusc.blogspot.in/2009/02/fileservlet-supporting-resume-and.html adopted
 * as Spring View for streaming binary files. 
 *
 * @author Atul M Dambalkar (Adapted for Spring View)
 */
public class StreamingViewRenderer extends AbstractView {

    // Constants ----------------------------------------------------------------------------------

    private static final int DEFAULT_BUFFER_SIZE = 20480; // ..bytes = 20KB.
    private static final long DEFAULT_EXPIRE_TIME = 604800000L; // ..ms = 1 week.
    private static final String MULTIPART_BOUNDARY = "MULTIPART_BYTERANGES";

    @Override
    protected void renderMergedOutputModel(Map objectMap,
            HttpServletRequest request, HttpServletResponse response)
            throws Exception {

        InputStream dataStream =  (InputStream) objectMap.get(DownloadConstants.INPUT_STREAM);
        
        if (dataStream == null) {
            response.sendError(HttpServletResponse.SC_NOT_FOUND);
            return;
        }
        long length = (Long) objectMap.get(DownloadConstants.CONTENT_LENGTH); 
        String fileName = (String) objectMap.get(DownloadConstants.FILENAME);
        Date lastModifiedObj = (Date)objectMap.get(DownloadConstants.LAST_MODIFIED);

        if (StringUtils.isEmpty(fileName) || lastModifiedObj == null) {
            response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
            return;
        }
        long lastModified = lastModifiedObj.getTime();
        String contentType = (String) objectMap.get(DownloadConstants.CONTENT_TYPE);

        // Validate request headers for caching ---------------------------------------------------

        // If-None-Match header should contain "*" or ETag. If so, then return 304.
        String ifNoneMatch = request.getHeader("If-None-Match");
        if (ifNoneMatch != null && HttpUtils.matches(ifNoneMatch, fileName)) {
            response.setHeader("ETag", fileName); // Required in 304.
            response.sendError(HttpServletResponse.SC_NOT_MODIFIED);
            return;
        }

        // If-Modified-Since header should be greater than LastModified. If so, then return 304.
        // This header is ignored if any If-None-Match header is specified.
        long ifModifiedSince = request.getDateHeader("If-Modified-Since");
        if (ifNoneMatch == null && ifModifiedSince != -1 && ifModifiedSince + 1000 > lastModified) {
            response.setHeader("ETag", fileName); // Required in 304.
            response.sendError(HttpServletResponse.SC_NOT_MODIFIED);
            return;
        }

        // Validate request headers for resume ----------------------------------------------------

        // If-Match header should contain "*" or ETag. If not, then return 412.
        String ifMatch = request.getHeader("If-Match");
        if (ifMatch != null && !HttpUtils.matches(ifMatch, fileName)) {
            response.sendError(HttpServletResponse.SC_PRECONDITION_FAILED);
            return;
        }

        // If-Unmodified-Since header should be greater than LastModified. If not, then return 412.
        long ifUnmodifiedSince = request.getDateHeader("If-Unmodified-Since");
        if (ifUnmodifiedSince != -1 && ifUnmodifiedSince + 1000 <= lastModified) {
            response.sendError(HttpServletResponse.SC_PRECONDITION_FAILED);
            return;
        }
        
        // Validate and process range -------------------------------------------------------------

        // Prepare some variables. The full Range represents the complete file.
        Range full = new Range(0, length - 1, length);
        List ranges = new ArrayList();

        // Validate and process Range and If-Range headers.
        String range = request.getHeader("Range");
        if (range != null) {

            // Range header should match format "bytes=n-n,n-n,n-n...". If not, then return 416.
            if (!range.matches("^bytes=\\d*-\\d*(,\\d*-\\d*)*$")) {
                response.setHeader("Content-Range", "bytes */" + length); // Required in 416.
                response.sendError(HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE);
                return;
            }

            String ifRange = request.getHeader("If-Range");
            if (ifRange != null && !ifRange.equals(fileName)) {
                try {
                    long ifRangeTime = request.getDateHeader("If-Range"); // Throws IAE if invalid.
                    if (ifRangeTime != -1) {
                        ranges.add(full);
                    }
                } catch (IllegalArgumentException ignore) {
                    ranges.add(full);
                }
            }

            // If any valid If-Range header, then process each part of byte range.
            if (ranges.isEmpty()) {
                for (String part : range.substring(6).split(",")) {
                    // Assuming a file with length of 100, the following examples returns bytes at:
                    // 50-80 (50 to 80), 40- (40 to length=100), -20 (length-20=80 to length=100).
                    long start = StringUtils.sublong(part, 0, part.indexOf("-"));
                    long end = StringUtils.sublong(part, part.indexOf("-") + 1, part.length());

                    if (start == -1) {
                        start = length - end;
                        end = length - 1;
                    } else if (end == -1 || end > length - 1) {
                        end = length - 1;
                    }

                    // Check if Range is syntactically valid. If not, then return 416.
                    if (start > end) {
                        response.setHeader("Content-Range", "bytes */" + length); // Required in 416.
                        response.sendError(HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE);
                        return;
                    }

                    // Add range.                    
                    ranges.add(new Range(start, end, length));
                }
            }
        }

        // Prepare and initialize response --------------------------------------------------------

        // Get content type by file name and set content disposition.
        String disposition = "inline";

        // If content type is unknown, then set the default value.
        // For all content types, see: http://www.w3schools.com/media/media_mimeref.asp
        // To add new content types, add new mime-mapping entry in web.xml.
        if (contentType == null) {
            contentType = "application/octet-stream";
        } else if (!contentType.startsWith("image")) {
            // Else, expect for images, determine content disposition. If content type is supported by
            // the browser, then set to inline, else attachment which will pop a 'save as' dialogue.
            String accept = request.getHeader("Accept");
            disposition = accept != null && HttpUtils.accepts(accept, contentType) 
                                    ? "inline" : "attachment";
        }

        // Initialize response.
        response.reset();
        response.setBufferSize(DEFAULT_BUFFER_SIZE);
        response.setHeader("Content-Disposition", disposition + ";filename=\"" + fileName + "\"");
        response.setHeader("Accept-Ranges", "bytes");
        response.setHeader("ETag", fileName);
        response.setDateHeader("Last-Modified", lastModified);
        response.setDateHeader("Expires", System.currentTimeMillis() + DEFAULT_EXPIRE_TIME);

        // Send requested file (part(s)) to client ------------------------------------------------

        // Prepare streams.
        InputStream input = null;
        OutputStream output = null;

        try {
            // Open streams.
            input = new BufferedInputStream(dataStream);
            output = response.getOutputStream();

            if (ranges.isEmpty() || ranges.get(0) == full) {

                // Return full file.
                Range r = full;
                response.setContentType(contentType);
                response.setHeader("Content-Range", "bytes " + r.start + "-" + r.end + "/" + r.total);
                response.setHeader("Content-Length", String.valueOf(r.length));
                copy(input, output, length, r.start, r.length);
                
            } else if (ranges.size() == 1) {

                // Return single part of file.
                Range r = ranges.get(0);
                response.setContentType(contentType);
                response.setHeader("Content-Range", "bytes " + r.start + "-" + r.end + "/" + r.total);
                response.setHeader("Content-Length", String.valueOf(r.length));
                response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT); // 206.

                // Copy single part range.
                copy(input, output, length, r.start, r.length);

            } else {

                // Return multiple parts of file.
                response.setContentType("multipart/byteranges; boundary=" + MULTIPART_BOUNDARY);
                response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT); // 206.

                // Cast back to ServletOutputStream to get the easy println methods.
                ServletOutputStream sos = (ServletOutputStream) output;

                // Copy multi part range.
                for (Range r : ranges) {
                    // Add multipart boundary and header fields for every range.
                    sos.println();
                    sos.println("--" + MULTIPART_BOUNDARY);
                    sos.println("Content-Type: " + contentType);
                    sos.println("Content-Range: bytes " + r.start + "-" + r.end + "/" + r.total);

                    // Copy single part range of multi part range.
                    copy(input, output, length, r.start, r.length);
                }

                // End with multipart boundary.
                sos.println();
                sos.println("--" + MULTIPART_BOUNDARY + "--");
            }
        } finally {
            // Gently close streams.
            close(output);
            close(input);
            close(dataStream);
        }

    }

    /**
     * Close the given resource.
     * @param resource The resource to be closed.
     */
    private static void close(Closeable resource) {
        if (resource != null) {
            try {
                resource.close();
            } catch (IOException ignore) {
                // Ignore IOException. If you want to handle this anyway, it might be useful to know
                // that this will generally only be thrown when the client aborted the request.
            }
        }
    }
    
    /**
     * Copy the given byte range of the given input to the given output.
     * @param input The input to copy the given range to the given output for.
     * @param output The output to copy the given range from the given input for.
     * @param start Start of the byte range.
     * @param length Length of the byte range.
     * @throws IOException If something fails at I/O level.
     */
    private static void copy(InputStream input, OutputStream output, 
                             long inputSize, long start, long length)
        throws IOException
    {
        byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
        int read;

        if (inputSize == length) {
            // Write full range.
            while ((read = input.read(buffer)) > 0) {
                output.write(buffer, 0, read);
                output.flush();
            }
        } else {
            input.skip(start);
            long toRead = length;

            while ((read = input.read(buffer)) > 0) {
                if ((toRead -= read) > 0) {
                    output.write(buffer, 0, read);
                    output.flush();
                } else {
                    output.write(buffer, 0, (int) toRead + read);
                    output.flush();
                    break;
                }
            }
        }
    }

    // Inner classes ------------------------------------------------------------------------------

    /**
     * This class represents a byte range.
     */
    protected class Range {
        long start;
        long end;
        long length;
        long total;

        /**
         * Construct a byte range.
         * @param start Start of the byte range.
         * @param end End of the byte range.
         * @param total Total length of the byte source.
         */
        public Range(long start, long end, long total) {
            this.start = start;
            this.end = end;
            this.length = end - start + 1;
            this.total = total;
        }
    }
}

public class DownloadConstants {

 public static final String INPUT_STREAM = "inputStream";
 public static final String CONTENT_TYPE = "contentType";

 public static final String CONTENT_LENGTH = "contentLength";
 public static final String FILENAME = "filename";
    public static final String LAST_MODIFIED = "lastModified";
}

public class HttpUtils {
    
    /**
     * Returns true if the given accept header accepts the given value.
     * @param acceptHeader The accept header.
     * @param toAccept The value to be accepted.
     * @return True if the given accept header accepts the given value.
     */
    public static boolean accepts(String acceptHeader, String toAccept) {
        String[] acceptValues = acceptHeader.split("\\s*(,|;)\\s*");
        Arrays.sort(acceptValues);
        return Arrays.binarySearch(acceptValues, toAccept) > -1
            || Arrays.binarySearch(acceptValues, toAccept.replaceAll("/.*$", "/*")) > -1
            || Arrays.binarySearch(acceptValues, "*/*") > -1;
    }

    /**
     * Returns true if the given match header matches the given value.
     * @param matchHeader The match header.
     * @param toMatch The value to be matched.
     * @return True if the given match header matches the given value.
     */
    public static boolean matches(String matchHeader, String toMatch) {
        String[] matchValues = matchHeader.split("\\s*,\\s*");
        Arrays.sort(matchValues);
        return Arrays.binarySearch(matchValues, toMatch) > -1
            || Arrays.binarySearch(matchValues, "*") > -1;
    }
}

public class StringUtils {

    /**
     * Returns a substring of the given string value from the given begin index to the given end
     * index as a long. If the substring is empty, then -1 will be returned
     * @param value The string value to return a substring as long for.
     * @param beginIndex The begin index of the substring to be returned as long.
     * @param endIndex The end index of the substring to be returned as long.
     * @return A substring of the given string value as long or -1 if substring is empty.
     */
    public static long sublong(String value, int beginIndex, int endIndex) {
        String substring = value.substring(beginIndex, endIndex);
        return (substring.length() > 0) ? Long.parseLong(substring) : -1;
    }    
    
}

Next, you just need to define the above view class to be a Spring bean and use it in Spring MVC's ModelAndView object.