V4.1 Fix "=" character in HttpPostRequestDecoder

Motivation
Issue #3004 shows that "=" character was not supported as it should in
the HttpPostRequestDecoder in form-data boundary.

Modifications:
Add 2 methods in StringUtil
- split with maxPart argument: String split with max parts only (to prevent multiple '='
to be source of extra split while not needed)
- substringAfter: String part after delimiter (since first part is not
needed)
Use those methods in HttpPostRequestDecoder.
Change and the HttpPostRequestDecoderTest to check using a boundary
beginning with "=".

Results:
The fix implies more stability and fix the issue.

codec-http/src/main/java/io/netty/handler/codec/http/multipart/HttpPostMultipartRequestDecoder.java

@@ -672,7 +672,7 @@ public class HttpPostMultipartRequestDecoder implements InterfaceHttpPostRequest
                 if (checkSecondArg) {
                     // read next values and store them in the map as Attribute
                     for (int i = 2; i < contents.length; i++) {
-                        String[] values = StringUtil.split(contents[i], '=');
+                        String[] values = StringUtil.split(contents[i], '=', 2);
                         Attribute attribute;
                         try {
                             String name = cleanString(values[0]);
@@ -721,8 +721,8 @@ public class HttpPostMultipartRequestDecoder implements InterfaceHttpPostRequest
                 // Take care of possible "multipart/mixed"
                 if (contents[1].equalsIgnoreCase(HttpPostBodyUtil.MULTIPART_MIXED)) {
                     if (currentStatus == MultiPartStatus.DISPOSITION) {
-                        String[] values = StringUtil.split(contents[2], '=');
+                        String values = StringUtil.substringAfter(contents[2], '=');
-                        multipartMixedBoundary = "--" + values[1];
+                        multipartMixedBoundary = "--" + values;
                         currentStatus = MultiPartStatus.MIXEDDELIMITER;
                         return decodeMultipart(MultiPartStatus.MIXEDDELIMITER);
                     } else {
@@ -731,11 +731,11 @@ public class HttpPostMultipartRequestDecoder implements InterfaceHttpPostRequest
                 } else {
                     for (int i = 1; i < contents.length; i++) {
                         if (contents[i].toLowerCase().startsWith(HttpHeaders.Values.CHARSET)) {
-                            String[] values = StringUtil.split(contents[i], '=');
+                            String values = StringUtil.substringAfter(contents[i], '=');
                             Attribute attribute;
                             try {
                                 attribute = factory.createAttribute(request, HttpHeaders.Values.CHARSET,
-                                        cleanString(values[1]));
+                                        cleanString(values));
                             } catch (NullPointerException e) {
                                 throw new ErrorDataDecoderException(e);
                             } catch (IllegalArgumentException e) {

codec-http/src/main/java/io/netty/handler/codec/http/multipart/HttpPostRequestDecoder.java

@@ -169,25 +169,25 @@ public class HttpPostRequestDecoder implements InterfaceHttpPostRequestDecoder {
             } else {
                 return null;
             }
-            String[] boundary = StringUtil.split(headerContentType[mrank], '=');
+            String boundary = StringUtil.substringAfter(headerContentType[mrank], '=');
-            if (boundary.length != 2) {
+            if (boundary == null) {
                 throw new ErrorDataDecoderException("Needs a boundary value");
             }
-            if (boundary[1].charAt(0) == '"') {
+            if (boundary.charAt(0) == '"') {
-                String bound = boundary[1].trim();
+                String bound = boundary.trim();
                 int index = bound.length() - 1;
                 if (bound.charAt(index) == '"') {
-                    boundary[1] = bound.substring(1, index);
+                    boundary = bound.substring(1, index);
                 }
             }
             if (headerContentType[crank].toLowerCase().startsWith(
                     HttpHeaders.Values.CHARSET)) {
-                String[] charset = StringUtil.split(headerContentType[crank], '=');
+                String charset = StringUtil.substringAfter(headerContentType[crank], '=');
-                if (charset.length > 1) {
+                if (charset != null) {
-                    return new String[] {"--" + boundary[1], charset[1]};
+                    return new String[] {"--" + boundary, charset};
                 }
             }
-            return new String[] {"--" + boundary[1]};
+            return new String[] {"--" + boundary};
         }
         return null;
     }

common/src/main/java/io/netty/util/internal/StringUtil.java

@@ -111,6 +111,63 @@ public final class StringUtil {
         return res.toArray(new String[res.size()]);
     }
 
+    /**
+     * Splits the specified {@link String} with the specified delimiter in maxParts maximum parts.
+     * This operation is a simplified and optimized
+     * version of {@link String#split(String, int)}.
+     */
+    public static String[] split(String value, char delim, int maxParts) {
+        final int end = value.length();
+        final List<String> res = new ArrayList<String>();
+
+        int start = 0;
+        int cpt = 1;
+        for (int i = 0; i < end && cpt < maxParts; i ++) {
+            if (value.charAt(i) == delim) {
+                if (start == i) {
+                    res.add(EMPTY_STRING);
+                } else {
+                    res.add(value.substring(start, i));
+                }
+                start = i + 1;
+                cpt++;
+            }
+        }
+
+        if (start == 0) { // If no delimiter was found in the value
+            res.add(value);
+        } else {
+            if (start != end) {
+                // Add the last element if it's not empty.
+                res.add(value.substring(start, end));
+            } else {
+                // Truncate trailing empty elements.
+                for (int i = res.size() - 1; i >= 0; i --) {
+                    if (res.get(i).isEmpty()) {
+                        res.remove(i);
+                    } else {
+                        break;
+                    }
+                }
+            }
+        }
+
+        return res.toArray(new String[res.size()]);
+    }
+
+    /**
+     * Get the item after one char delim if the delim is found (else null).
+     * This operation is a simplified and optimized
+     * version of {@link String#split(String, int)}.
+     */
+    public static String substringAfter(String value, char delim) {
+        int pos = value.indexOf(delim);
+        if (pos >= 0) {
+            return value.substring(pos + 1);
+        }
+        return null;
+    }
+
     /**
      * Converts the specified byte value into a 2-digit hexadecimal integer.
      */

common/src/test/java/io/netty/util/internal/StringUtilTest.java

@@ -70,4 +70,15 @@ public class StringUtilTest {
     public void splitWithDelimiterAtBeginning() {
         assertArrayEquals(new String[] { "", "foo", "bar" }, split("#foo#bar", '#'));
     }
+
+    @Test
+    public void splitMaxPart() {
+        assertArrayEquals(new String[] { "foo", "bar:bar2" }, split("foo:bar:bar2", ':', 2));
+        assertArrayEquals(new String[] { "foo", "bar", "bar2" }, split("foo:bar:bar2", ':', 3));
+    }
+
+    @Test
+    public void substringAfterTest() {
+        assertEquals("bar:bar2", substringAfter("foo:bar:bar2", ':'));
+    }
 }