Support byte ranges in ResourceHttpRequestHandler

This commit introduces support for HTTP byte ranges in the
ResourceHttpRequestHandler. This support consists of a number of
changes:

- Parsing of HTTP Range headers in HttpHeaders, using a new HttpRange
  class and inner ByteRange/SuffixByteRange subclasses.
- MIME boundary generation moved from FormHttpMessageConverter to
  MimeTypeUtils.
- writePartialContent() method introduced in ResourceHttpRequestHandler,
  handling the byte range logic
- Additional partial content tests added to
  ResourceHttpRequestHandlerTests.

Issue: SPR-10805

Author: poutsma

spring-core/src/main/java/org/springframework/util/MimeTypeUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 
 package org.springframework.util;
 
+import java.nio.charset.Charset;
 import java.nio.charset.UnsupportedCharsetException;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -25,6 +26,7 @@
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Random;
 
 import org.springframework.util.MimeType.SpecificityComparator;
 
@@ -37,6 +39,17 @@
  */
 public abstract class MimeTypeUtils {
 
+	private static final byte[] BOUNDARY_CHARS =
+			new byte[] {'-', '_', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', 'a', 'b', 'c', 'd', 'e', 'f', 'g',
+					'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'A',
+					'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U',
+					'V', 'W', 'X', 'Y', 'Z'};
+
+	private static final Random RND = new Random();
+
+	private static Charset US_ASCII = Charset.forName("US-ASCII");
+
+
 	/**
 	 * Public constant mime type that includes all media ranges (i.e. "*/*").
 	 */
@@ -319,6 +332,25 @@ public static void sortBySpecificity(List<MimeType> mimeTypes) {
 		}
 	}
 
+	/**
+	 * Generate a random MIME boundary as bytes, often used in multipart mime types.
+	 */
+	public static byte[] generateMultipartBoundary() {
+		byte[] boundary = new byte[RND.nextInt(11) + 30];
+		for (int i = 0; i < boundary.length; i++) {
+			boundary[i] = BOUNDARY_CHARS[RND.nextInt(BOUNDARY_CHARS.length)];
+		}
+		return boundary;
+	}
+
+	/**
+	 * Generate a random MIME boundary as String, often used in multipart mime types.
+	 */
+	public static String generateMultipartBoundaryString() {
+		return new String(generateMultipartBoundary(), US_ASCII);
+	}
+
+
 
 	/**
 	 * Comparator used by {@link #sortBySpecificity(List)}.

spring-web/src/main/java/org/springframework/http/HttpHeaders.java

@@ -1,11 +1,11 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * 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
+ *      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,
@@ -744,6 +744,23 @@ public String getPragma() {
 		return getFirst(PRAGMA);
 	}
 
+	/**
+	 * Sets the (new) value of the {@code Range} header.
+	 */
+	public void setRange(List<HttpRange> ranges) {
+		String value = HttpRange.toString(ranges);
+		set(RANGE, value);
+	}
+
+	/**
+	 * Returns the value of the {@code Range} header.
+	 * <p>Returns an empty list when the range is unknown.
+	 */
+	public List<HttpRange> getRange() {
+		String value = getFirst(RANGE);
+		return HttpRange.parseRanges(value);
+	}
+
 	/**
 	 * Set the (new) value of the {@code Upgrade} header.
 	 */