Allow PcapWriteHandler instances to write to the same OutputStream (#…

…13118)

Motivation:
Currently, PcapWriteHandler expects a dedicated OutputStream, and cannot support multiple streams written to a single PCAP file. These modifications are intended to support sharing the OutputStream between multiple concurrent PcapWriteHandler instances.

Modification:
Added a "shareOutputStream" flag to PcapWriteHandler (and PcapWriter) to enable synchronization on the OutputStream in order to prevent interleaved writes. Also, provide a method to write the PCAP Global Header to the OutputStream.

Result:
Allows multiple channels to write to the same PCAP file.

This PR adds further improvement done in PR #12337 and supersedes it.
Original Author: @RoganDawes

handler/src/main/java/io/netty/handler/pcap/EthernetPacket.java

@@ -50,7 +50,7 @@ private EthernetPacket() {
      * @param payload Payload of IPv4
      */
     static void writeIPv4(ByteBuf byteBuf, ByteBuf payload) {
-        EthernetPacket.writePacket(byteBuf, payload, DUMMY_SOURCE_MAC_ADDRESS, DUMMY_DESTINATION_MAC_ADDRESS, V4);
+        writePacket(byteBuf, payload, DUMMY_SOURCE_MAC_ADDRESS, DUMMY_DESTINATION_MAC_ADDRESS, V4);
     }
 
     /**
@@ -60,7 +60,7 @@ static void writeIPv4(ByteBuf byteBuf, ByteBuf payload) {
      * @param payload Payload of IPv6
      */
     static void writeIPv6(ByteBuf byteBuf, ByteBuf payload) {
-        EthernetPacket.writePacket(byteBuf, payload, DUMMY_SOURCE_MAC_ADDRESS, DUMMY_DESTINATION_MAC_ADDRESS, V6);
+        writePacket(byteBuf, payload, DUMMY_SOURCE_MAC_ADDRESS, DUMMY_DESTINATION_MAC_ADDRESS, V6);
     }
 
     /**

handler/src/main/java/io/netty/handler/pcap/PcapHeaders.java

@@ -17,6 +17,9 @@
 
 import io.netty.buffer.ByteBuf;
 
+import java.io.IOException;
+import java.io.OutputStream;
+
 final class PcapHeaders {
 
     /**
@@ -31,20 +34,21 @@ final class PcapHeaders {
      *      <li> network </li>
      * </ol>
      */
-    private static final byte[] GLOBAL_HEADER = new byte[]{-95, -78, -61, -44, 0, 2, 0, 4, 0, 0,
+    private static final byte[] GLOBAL_HEADER = {-95, -78, -61, -44, 0, 2, 0, 4, 0, 0,
             0, 0, 0, 0, 0, 0, 0, 0, -1, -1, 0, 0, 0, 1};
 
     private PcapHeaders() {
         // Prevent outside initialization
     }
 
     /**
-     * Write Pcap Global Header
+     * Writes the Pcap Global Header to the provided {@code OutputStream}
      *
-     * @param byteBuf byteBuf where we'll write header data
+     * @param outputStream OutputStream where Pcap data will be written.
+     * @throws IOException if there is an error writing to the {@code OutputStream}
      */
-    public static void writeGlobalHeader(ByteBuf byteBuf) {
-        byteBuf.writeBytes(GLOBAL_HEADER);
+    static void writeGlobalHeader(OutputStream outputStream) throws IOException {
+        outputStream.write(GLOBAL_HEADER);
     }
 
     /**