/*
    * Copyright 2014 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    *   https://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 io.netty.handler.codec.haproxy;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.handler.codec.haproxy.HAProxyProxiedProtocol.AddressFamily;
  import io.netty.util.AbstractReferenceCounted;
  import io.netty.util.CharsetUtil;
  import io.netty.util.NetUtil;
  import io.netty.util.ResourceLeakDetector;
  import io.netty.util.ResourceLeakDetectorFactory;
  import io.netty.util.ResourceLeakTracker;
  import io.netty.util.internal.ObjectUtil;
  import io.netty.util.internal.StringUtil;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  /**
   * Message container for decoded HAProxy proxy protocol parameters
   */
  public final class HAProxyMessage extends AbstractReferenceCounted {
  
      // Let's pick some conservative limit here.
      private static final int MAX_NESTING_LEVEL = 128;
      private static final ResourceLeakDetector<HAProxyMessage> leakDetector =
              ResourceLeakDetectorFactory.instance().newResourceLeakDetector(HAProxyMessage.class);
  
      private final ResourceLeakTracker<HAProxyMessage> leak;
      private final HAProxyProtocolVersion protocolVersion;
      private final HAProxyCommand command;
      private final HAProxyProxiedProtocol proxiedProtocol;
      private final String sourceAddress;
      private final String destinationAddress;
      private final int sourcePort;
      private final int destinationPort;
      private final List<HAProxyTLV> tlvs;
  
      /**
       * Creates a new instance
       */
      private HAProxyMessage(
              HAProxyProtocolVersion protocolVersion, HAProxyCommand command, HAProxyProxiedProtocol proxiedProtocol,
              String sourceAddress, String destinationAddress, String sourcePort, String destinationPort) {
          this(
                  protocolVersion, command, proxiedProtocol,
                  sourceAddress, destinationAddress, portStringToInt(sourcePort), portStringToInt(destinationPort));
      }
  
      /**
       * Creates a new instance of HAProxyMessage.
       * @param protocolVersion the protocol version.
       * @param command the command.
       * @param proxiedProtocol the protocol containing the address family and transport protocol.
       * @param sourceAddress the source address.
       * @param destinationAddress the destination address.
       * @param sourcePort the source port. This value must be 0 for unix, unspec addresses.
       * @param destinationPort the destination port. This value must be 0 for unix, unspec addresses.
       */
      public HAProxyMessage(
              HAProxyProtocolVersion protocolVersion, HAProxyCommand command, HAProxyProxiedProtocol proxiedProtocol,
              String sourceAddress, String destinationAddress, int sourcePort, int destinationPort) {
  
          this(protocolVersion, command, proxiedProtocol,
               sourceAddress, destinationAddress, sourcePort, destinationPort, Collections.<HAProxyTLV>emptyList());
      }
  
      /**
       * Creates a new instance of HAProxyMessage.
       * @param protocolVersion the protocol version.
       * @param command the command.
       * @param proxiedProtocol the protocol containing the address family and transport protocol.
       * @param sourceAddress the source address.
       * @param destinationAddress the destination address.
       * @param sourcePort the source port. This value must be 0 for unix, unspec addresses.
       * @param destinationPort the destination port. This value must be 0 for unix, unspec addresses.
       * @param tlvs the list of tlvs.
       */
      public HAProxyMessage(
              HAProxyProtocolVersion protocolVersion, HAProxyCommand command, HAProxyProxiedProtocol proxiedProtocol,
              String sourceAddress, String destinationAddress, int sourcePort, int destinationPort,
              List<? extends HAProxyTLV> tlvs) {
  
          ObjectUtil.checkNotNull(protocolVersion, "protocolVersion");
          ObjectUtil.checkNotNull(proxiedProtocol, "proxiedProtocol");
         ObjectUtil.checkNotNull(tlvs, "tlvs");
         AddressFamily addrFamily = proxiedProtocol.addressFamily();
 
         checkAddress(sourceAddress, addrFamily, protocolVersion);
         checkAddress(destinationAddress, addrFamily, protocolVersion);
         checkPort(sourcePort, addrFamily);
         checkPort(destinationPort, addrFamily);
 
         this.protocolVersion = protocolVersion;
         this.command = command;
         this.proxiedProtocol = proxiedProtocol;
         this.sourceAddress = sourceAddress;
         this.destinationAddress = destinationAddress;
         this.sourcePort = sourcePort;
         this.destinationPort = destinationPort;
         this.tlvs = Collections.unmodifiableList(tlvs);
 
         leak = leakDetector.track(this);
     }
 
     /**
      * Decodes a version 2, binary proxy protocol header.
      *
      * @param header                     a version 2 proxy protocol header
      * @return                           {@link HAProxyMessage} instance
      * @throws HAProxyProtocolException  if any portion of the header is invalid
      */
     static HAProxyMessage decodeHeader(ByteBuf header) {
         ObjectUtil.checkNotNull(header, "header");
 
         if (header.readableBytes() < 16) {
             throw new HAProxyProtocolException(
                     "incomplete header: " + header.readableBytes() + " bytes (expected: 16+ bytes)");
         }
 
         // Per spec, the 13th byte is the protocol version and command byte
         header.skipBytes(12);
         final byte verCmdByte = header.readByte();
 
         HAProxyProtocolVersion ver;
         try {
             ver = HAProxyProtocolVersion.valueOf(verCmdByte);
         } catch (IllegalArgumentException e) {
             throw new HAProxyProtocolException(e);
         }
 
         if (ver != HAProxyProtocolVersion.V2) {
             throw new HAProxyProtocolException("version 1 unsupported: 0x" + Integer.toHexString(verCmdByte));
         }
 
         HAProxyCommand cmd;
         try {
             cmd = HAProxyCommand.valueOf(verCmdByte);
         } catch (IllegalArgumentException e) {
             throw new HAProxyProtocolException(e);
         }
 
         if (cmd == HAProxyCommand.LOCAL) {
             return unknownMsg(HAProxyProtocolVersion.V2, HAProxyCommand.LOCAL);
         }
 
         // Per spec, the 14th byte is the protocol and address family byte
         HAProxyProxiedProtocol protAndFam;
         try {
             protAndFam = HAProxyProxiedProtocol.valueOf(header.readByte());
         } catch (IllegalArgumentException e) {
             throw new HAProxyProtocolException(e);
         }
 
         if (protAndFam == HAProxyProxiedProtocol.UNKNOWN) {
             return unknownMsg(HAProxyProtocolVersion.V2, HAProxyCommand.PROXY);
         }
 
         int addressInfoLen = header.readUnsignedShort();
 
         String srcAddress;
         String dstAddress;
         int addressLen;
         int srcPort = 0;
         int dstPort = 0;
 
         AddressFamily addressFamily = protAndFam.addressFamily();
 
         if (addressFamily == AddressFamily.AF_UNIX) {
             // unix sockets require 216 bytes for address information
             if (addressInfoLen < 216 || header.readableBytes() < 216) {
                 throw new HAProxyProtocolException(
                     "incomplete UNIX socket address information: " +
                             Math.min(addressInfoLen, header.readableBytes()) + " bytes (expected: 216+ bytes)");
             }
             int startIdx = header.readerIndex();
             int addressEnd = header.indexOf(startIdx, startIdx + 108, (byte) 0); // FIND_NUL
             if (addressEnd == -1) {
                 addressLen = 108;
             } else {
                 addressLen = addressEnd - startIdx;
             }
             srcAddress = header.toString(startIdx, addressLen, CharsetUtil.US_ASCII);
 
             startIdx += 108;
 
             addressEnd = header.indexOf(startIdx, startIdx + 108, (byte) 0); // FIND_NUL
             if (addressEnd == -1) {
                 addressLen = 108;
             } else {
                 addressLen = addressEnd - startIdx;
             }
             dstAddress = header.toString(startIdx, addressLen, CharsetUtil.US_ASCII);
             // AF_UNIX defines that exactly 108 bytes are reserved for the address. The previous methods
             // did not increase the reader index although we already consumed the information.
             header.readerIndex(startIdx + 108);
         } else {
             if (addressFamily == AddressFamily.AF_IPv4) {
                 // IPv4 requires 12 bytes for address information
                 if (addressInfoLen < 12 || header.readableBytes() < 12) {
                     throw new HAProxyProtocolException(
                         "incomplete IPv4 address information: " +
                                 Math.min(addressInfoLen, header.readableBytes()) + " bytes (expected: 12+ bytes)");
                 }
                 addressLen = 4;
             } else if (addressFamily == AddressFamily.AF_IPv6) {
                 // IPv6 requires 36 bytes for address information
                 if (addressInfoLen < 36 || header.readableBytes() < 36) {
                     throw new HAProxyProtocolException(
                         "incomplete IPv6 address information: " +
                                 Math.min(addressInfoLen, header.readableBytes()) + " bytes (expected: 36+ bytes)");
                 }
                 addressLen = 16;
             } else {
                 throw new HAProxyProtocolException(
                     "unable to parse address information (unknown address family: " + addressFamily + ')');
             }
 
             // Per spec, the src address begins at the 17th byte
             srcAddress = ipBytesToString(header, addressLen);
             dstAddress = ipBytesToString(header, addressLen);
             srcPort = header.readUnsignedShort();
             dstPort = header.readUnsignedShort();
         }
 
         final List<HAProxyTLV> tlvs = readTlvs(header);
 
         return new HAProxyMessage(ver, cmd, protAndFam, srcAddress, dstAddress, srcPort, dstPort, tlvs);
     }
 
     private static List<HAProxyTLV> readTlvs(final ByteBuf header) {
         HAProxyTLV haProxyTLV = readNextTLV(header, 0);
         if (haProxyTLV == null) {
             return Collections.emptyList();
         }
         // In most cases there are less than 4 TLVs available
         List<HAProxyTLV> haProxyTLVs = new ArrayList<HAProxyTLV>(4);
 
         try {
             do {
                 haProxyTLVs.add(haProxyTLV);
                 if (haProxyTLV instanceof HAProxySSLTLV) {
                     haProxyTLVs.addAll(((HAProxySSLTLV) haProxyTLV).encapsulatedTLVs());
                 }
             } while ((haProxyTLV = readNextTLV(header, 0)) != null);
         } catch (Throwable t) {
             // Release all previously read TLVs before rethrowing as otherwise we would leak.
             releaseTlvs(haProxyTLVs);
             throw t;
         }
         return haProxyTLVs;
     }
 
     private static void releaseDeep(List<HAProxyTLV> children) {
         for (HAProxyTLV child : children) {
             child.release();
             if (child instanceof HAProxySSLTLV) {
                 releaseDeep(((HAProxySSLTLV) child).encapsulatedTLVs());
             }
         }
     }
 
     private static void releaseTlvs(List<HAProxyTLV> tlvs) {
         int skip = 0;
         for (HAProxyTLV tlv : tlvs) {
             if (skip > 0) {
                 skip--;
                 // This TLV is a flattened depth-1 child. If it encapsulates anything (depth-2+),
                 // those deeper children were NOT flattened, so we must release them recursively.
                 if (tlv instanceof HAProxySSLTLV) {
                     releaseDeep(((HAProxySSLTLV) tlv).encapsulatedTLVs());
                 }
             } else if (tlv instanceof HAProxySSLTLV) {
                 // This is a top-level (depth-0) SSL TLV.
                 // Its immediate children (depth-1) were flattened into this list,
                 // so we must skip them in the outer loop to avoid treating them as top-level TLVs.
                 skip = ((HAProxySSLTLV) tlv).encapsulatedTLVs().size();
             }
             tlv.release();
         }
     }
 
     private static HAProxyTLV readNextTLV(final ByteBuf header, int nestingLevel) {
         if (nestingLevel > MAX_NESTING_LEVEL) {
             throw new HAProxyProtocolException(
                     "Maximum TLV nesting level reached: " + nestingLevel + " (expected: < " + MAX_NESTING_LEVEL + ')');
         }
         // We need at least 4 bytes for a TLV
         if (header.readableBytes() < 4) {
             return null;
         }
 
         final byte typeAsByte = header.readByte();
         final HAProxyTLV.Type type = HAProxyTLV.Type.typeForByteValue(typeAsByte);
 
         final int length = header.readUnsignedShort();
         switch (type) {
         case PP2_TYPE_SSL:
             if (length < 5) {
                 throw new HAProxyProtocolException("TLV length must be at least 5 but was: " + length);
             }
             if (length > header.readableBytes()) {
                 throw new HAProxyProtocolException("TLV length must be smaller or equal the readable bytes (" +
                         header.readableBytes() + ") but was: " + length);
             }
             // Slice the rawContent but only retain it if we didn't see an error as otherwise we might
             // leak.
             final ByteBuf rawContent = header.slice(header.readerIndex(), length);
             final ByteBuf byteBuf = header.readSlice(length);
             final byte client = byteBuf.readByte();
             final int verify = byteBuf.readInt();
 
             if (byteBuf.readableBytes() >= 4) {
 
                 final List<HAProxyTLV> encapsulatedTlvs = new ArrayList<HAProxyTLV>(4);
                 try {
                     do {
                         final HAProxyTLV haProxyTLV = readNextTLV(byteBuf, nestingLevel + 1);
                         if (haProxyTLV == null) {
                             break;
                         }
                         encapsulatedTlvs.add(haProxyTLV);
                     } while (byteBuf.readableBytes() >= 4);
                 }  catch (Throwable t) {
                     // Release all previously read TLVs before rethrowing as otherwise we would leak.
                     releaseTlvs(encapsulatedTlvs);
                     throw t;
                 }
 
                 return new HAProxySSLTLV(verify, client, encapsulatedTlvs, rawContent.retain());
             }
             return new HAProxySSLTLV(verify, client, Collections.<HAProxyTLV>emptyList(), rawContent.retain());
         // If we're not dealing with an SSL Type, we can use the same mechanism
         case PP2_TYPE_ALPN:
         case PP2_TYPE_AUTHORITY:
         case PP2_TYPE_SSL_VERSION:
         case PP2_TYPE_SSL_CN:
         case PP2_TYPE_NETNS:
         case OTHER:
             return new HAProxyTLV(type, typeAsByte, header.readRetainedSlice(length));
         default:
             return null;
         }
     }
 
     /**
      * Decodes a version 1, human-readable proxy protocol header.
      *
      * @param header                     a version 1 proxy protocol header
      * @return                           {@link HAProxyMessage} instance
      * @throws HAProxyProtocolException  if any portion of the header is invalid
      */
     static HAProxyMessage decodeHeader(String header) {
         if (header == null) {
             throw new HAProxyProtocolException("header");
         }
 
         String[] parts = header.split(" ");
         int numParts = parts.length;
 
         if (numParts < 2) {
             throw new HAProxyProtocolException(
                     "invalid header: " + header + " (expected: 'PROXY' and proxied protocol values)");
         }
 
         if (!"PROXY".equals(parts[0])) {
             throw new HAProxyProtocolException("unknown identifier: " + parts[0]);
         }
 
         HAProxyProxiedProtocol protAndFam;
         try {
             protAndFam = HAProxyProxiedProtocol.valueOf(parts[1]);
         } catch (IllegalArgumentException e) {
             throw new HAProxyProtocolException(e);
         }
 
         if (protAndFam != HAProxyProxiedProtocol.TCP4 &&
                 protAndFam != HAProxyProxiedProtocol.TCP6 &&
                 protAndFam != HAProxyProxiedProtocol.UNKNOWN) {
             throw new HAProxyProtocolException("unsupported v1 proxied protocol: " + parts[1]);
         }
 
         if (protAndFam == HAProxyProxiedProtocol.UNKNOWN) {
             return unknownMsg(HAProxyProtocolVersion.V1, HAProxyCommand.PROXY);
         }
 
         if (numParts != 6) {
             throw new HAProxyProtocolException("invalid TCP4/6 header: " + header + " (expected: 6 parts)");
         }
 
         try {
             return new HAProxyMessage(
                     HAProxyProtocolVersion.V1, HAProxyCommand.PROXY,
                     protAndFam, parts[2], parts[3], parts[4], parts[5]);
         } catch (RuntimeException e) {
             throw new HAProxyProtocolException("invalid HAProxy message", e);
         }
     }
 
     /**
      * Proxy protocol message for 'UNKNOWN' proxied protocols. Per spec, when the proxied protocol is
      * 'UNKNOWN' we must discard all other header values.
      */
     private static HAProxyMessage unknownMsg(HAProxyProtocolVersion version, HAProxyCommand command) {
         return new HAProxyMessage(version, command, HAProxyProxiedProtocol.UNKNOWN, null, null, 0, 0);
     }
 
     /**
      * Convert ip address bytes to string representation
      *
      * @param header     buffer containing ip address bytes
      * @param addressLen number of bytes to read (4 bytes for IPv4, 16 bytes for IPv6)
      * @return           string representation of the ip address
      */
     private static String ipBytesToString(ByteBuf header, int addressLen) {
         StringBuilder sb = new StringBuilder();
         final int ipv4Len = 4;
         final int ipv6Len = 8;
         if (addressLen == ipv4Len) {
             for (int i = 0; i < ipv4Len; i++) {
                 sb.append(header.readByte() & 0xff);
                 sb.append('.');
             }
         } else {
             for (int i = 0; i < ipv6Len; i++) {
                 sb.append(Integer.toHexString(header.readUnsignedShort()));
                 sb.append(':');
             }
         }
         sb.setLength(sb.length() - 1);
         return sb.toString();
     }
 
     /**
      * Convert port to integer
      *
      * @param value                      the port
      * @return                           port as an integer
      * @throws IllegalArgumentException  if port is not a valid integer
      */
     private static int portStringToInt(String value) {
         int port;
         try {
             port = Integer.parseInt(value);
         } catch (NumberFormatException e) {
             throw new IllegalArgumentException("invalid port: " + value, e);
         }
 
         if (port <= 0 || port > 65535) {
             throw new IllegalArgumentException("invalid port: " + value + " (expected: 1 ~ 65535)");
         }
 
         return port;
     }
 
     /**
      * Validate an address (IPv4, IPv6, Unix Socket)
      *
      * @param address    human-readable address
      * @param addrFamily the {@link AddressFamily} to check the address against
      * @param version    the protocol version
      * @throws IllegalArgumentException if the address is invalid
      */
     private static void checkAddress(String address, AddressFamily addrFamily, HAProxyProtocolVersion version) {
         ObjectUtil.checkNotNull(addrFamily, "addrFamily");
 
         switch (addrFamily) {
             case AF_UNSPEC:
                 if (address != null) {
                     throw new IllegalArgumentException("unable to validate an AF_UNSPEC address: " + address);
                 }
                 return;
             case AF_UNIX:
                 ObjectUtil.checkNotNull(address, "address");
                 if (address.getBytes(CharsetUtil.US_ASCII).length > 108) {
                     throw new IllegalArgumentException("invalid AF_UNIX address: " + address);
                 }
                 if (version == HAProxyProtocolVersion.V1) {
                     // V1 is text-based and uses CR LF as header delimiters, and space as field delimiter.
                     for (int i = 0, len = address.length(); i < len; i++) {
                         char c = address.charAt(i);
                         if (c == '\r' || c == '\n' || c == ' ') {
                             throw new IllegalArgumentException("invalid AF_UNIX address: " + address);
                         }
                     }
                 }
                 return;
         }
 
         ObjectUtil.checkNotNull(address, "address");
 
         switch (addrFamily) {
             case AF_IPv4:
                 if (!NetUtil.isValidIpV4Address(address)) {
                     throw new IllegalArgumentException("invalid IPv4 address: " + address);
                 }
                 break;
             case AF_IPv6:
                 if (!NetUtil.isValidIpV6Address(address)) {
                     throw new IllegalArgumentException("invalid IPv6 address: " + address);
                 }
                 break;
             default:
                 throw new IllegalArgumentException("unexpected addrFamily: " + addrFamily);
         }
     }
 
     /**
      * Validate the port depending on the addrFamily.
      *
      * @param port                       the UDP/TCP port
      * @throws IllegalArgumentException  if the port is out of range (0-65535 inclusive)
      */
     private static void checkPort(int port, AddressFamily addrFamily) {
         switch (addrFamily) {
         case AF_IPv6:
         case AF_IPv4:
             if (port < 0 || port > 65535) {
                 throw new IllegalArgumentException("invalid port: " + port + " (expected: 0 ~ 65535)");
             }
             break;
         case AF_UNIX:
         case AF_UNSPEC:
             if (port != 0) {
                 throw new IllegalArgumentException("port cannot be specified with addrFamily: " + addrFamily);
             }
             break;
         default:
             throw new IllegalArgumentException("unexpected addrFamily: " + addrFamily);
         }
     }
 
     /**
      * Returns the {@link HAProxyProtocolVersion} of this {@link HAProxyMessage}.
      */
     public HAProxyProtocolVersion protocolVersion() {
         return protocolVersion;
     }
 
     /**
      * Returns the {@link HAProxyCommand} of this {@link HAProxyMessage}.
      */
     public HAProxyCommand command() {
         return command;
     }
 
     /**
      * Returns the {@link HAProxyProxiedProtocol} of this {@link HAProxyMessage}.
      */
     public HAProxyProxiedProtocol proxiedProtocol() {
         return proxiedProtocol;
     }
 
     /**
      * Returns the human-readable source address of this {@link HAProxyMessage} or {@code null}
      * if HAProxy performs health check with {@code send-proxy-v2}.
      */
     public String sourceAddress() {
         return sourceAddress;
     }
 
     /**
      * Returns the human-readable destination address of this {@link HAProxyMessage}.
      */
     public String destinationAddress() {
         return destinationAddress;
     }
 
     /**
      * Returns the UDP/TCP source port of this {@link HAProxyMessage}.
      */
     public int sourcePort() {
         return sourcePort;
     }
 
     /**
      * Returns the UDP/TCP destination port of this {@link HAProxyMessage}.
      */
     public int destinationPort() {
         return destinationPort;
     }
 
     /**
      * Returns a list of {@link HAProxyTLV} or an empty list if no TLVs are present.
      * <p>
      * TLVs are only available for the Proxy Protocol V2
      */
     public List<HAProxyTLV> tlvs() {
         return tlvs;
     }
 
     int tlvNumBytes() {
         int tlvNumBytes = 0;
         for (int i = 0; i < tlvs.size(); i++) {
             tlvNumBytes += tlvs.get(i).totalNumBytes();
         }
         return tlvNumBytes;
     }
 
     @Override
     public HAProxyMessage touch() {
         tryRecord();
         return (HAProxyMessage) super.touch();
     }
 
     @Override
     public HAProxyMessage touch(Object hint) {
         if (leak != null) {
             leak.record(hint);
         }
         return this;
     }
 
     @Override
     public HAProxyMessage retain() {
         tryRecord();
         return (HAProxyMessage) super.retain();
     }
 
     @Override
     public HAProxyMessage retain(int increment) {
         tryRecord();
         return (HAProxyMessage) super.retain(increment);
     }
 
     @Override
     public boolean release() {
         tryRecord();
         return super.release();
     }
 
     @Override
     public boolean release(int decrement) {
         tryRecord();
         return super.release(decrement);
     }
 
     private void tryRecord() {
         if (leak != null) {
             leak.record();
         }
     }
 
     @Override
     protected void deallocate() {
         try {
             releaseTlvs(tlvs);
         } finally {
             final ResourceLeakTracker<HAProxyMessage> leak = this.leak;
             if (leak != null) {
                 boolean closed = leak.close(this);
                 assert closed;
             }
         }
     }
 
     @Override
     public String toString() {
         StringBuilder sb = new StringBuilder(256)
                 .append(StringUtil.simpleClassName(this))
                 .append("(protocolVersion: ").append(protocolVersion)
                 .append(", command: ").append(command)
                 .append(", proxiedProtocol: ").append(proxiedProtocol)
                 .append(", sourceAddress: ").append(sourceAddress)
                 .append(", destinationAddress: ").append(destinationAddress)
                 .append(", sourcePort: ").append(sourcePort)
                 .append(", destinationPort: ").append(destinationPort)
                 .append(", tlvs: [");
         if (!tlvs.isEmpty()) {
             for (HAProxyTLV tlv: tlvs) {
                 sb.append(tlv).append(", ");
             }
             sb.setLength(sb.length() - 2);
         }
         sb.append("])");
         return sb.toString();
     }
 }