Sort cookies as per FRC6265, close AsyncHttpClient#1048

Author: slandelle

client/src/main/java/org/asynchttpclient/cookie/CookieEncoder.java

@@ -12,20 +12,63 @@
  */
 package org.asynchttpclient.cookie;
 
-import org.asynchttpclient.util.StringUtils;
-
+import java.util.Arrays;
 import java.util.Collection;
+import java.util.Comparator;
+
+import org.asynchttpclient.util.StringUtils;
 
 public final class CookieEncoder {
 
+    /**
+     * Sort cookies into decreasing order of path length, breaking ties by sorting into increasing chronological order of creation time, as recommended by RFC 6265.
+     */
+    private static final Comparator<Cookie> COOKIE_COMPARATOR = new Comparator<Cookie>() {
+        @Override
+        public int compare(Cookie c1, Cookie c2) {
+            String path1 = c1.getPath();
+            String path2 = c2.getPath();
+            // Cookies with unspecified path default to the path of the request. We don't
+            // know the request path here, but we assume that the length of an unspecified
+            // path is longer than any specified path (i.e. pathless cookies come first),
+            // because setting cookies with a path longer than the request path is of
+            // limited use.
+            int len1 = path1 == null ? Integer.MAX_VALUE : path1.length();
+            int len2 = path2 == null ? Integer.MAX_VALUE : path2.length();
+            int diff = len2 - len1;
+            if (diff != 0) {
+                return diff;
+            }
+            // Rely on Java's sort stability to retain creation order in cases where
+            // cookies have same path length.
+            return -1;
+        }
+    };
+
     private CookieEncoder() {
     }
 
     public static String encode(Collection<Cookie> cookies) {
         StringBuilder sb = StringUtils.stringBuilder();
 
-        for (Cookie cookie : cookies) {
-            add(sb, cookie.getName(), cookie.getValue(), cookie.isWrap());
+        if (cookies.isEmpty()) {
+            return "";
+
+        } else if (cookies.size() == 1) {
+            Cookie cookie = cookies.iterator().next();
+            if (cookie != null) {
+                add(sb, cookie.getName(), cookie.getValue(), cookie.isWrap());
+            }
+
+        } else {
+            Cookie[] cookiesSorted = cookies.toArray(new Cookie[cookies.size()]);
+            Arrays.sort(cookiesSorted, COOKIE_COMPARATOR);
+            for (int i = 0; i < cookiesSorted.length; i++) {
+                Cookie cookie = cookiesSorted[i];
+                if (cookie != null) {
+                    add(sb, cookie.getName(), cookie.getValue(), cookie.isWrap());
+                }
+            }
         }
 
         if (sb.length() > 0) {