Comment by GGFPC for You would have to structure the InputStream data so that it could be divided into packets. For example, if you're writing raw packet data to the stream, before each packet you would write a number giving the size of the packet, in bytes.Then, when reading the stream and writing a pcap file, you would read the number first, and then read that number of bytes of packet data. You would also have to ensure, in each iteration of the loop, the buffer would have to have exactly that number of bytes, so that dumper.dumpRaw knows how many bytes are in the packet.This probably means that you should allocate the packet buffer separately, for every packet, and allocate it so that it's exactly the size of the packet data.Without doing that, your code will NOT work.

I'm trying that with the following code IpV4Packet p = new IpV4Packet.Builder() .dstAddr((Inet4Address) Inet4Address.getByName("172.0.0.1")) .srcAddr((Inet4Address) Inet4Address.getByName("172.0.0.2")) .version(IpVersion.IPV4) .protocol(IpNumber.TCP) .ttl(new Integer(64).byteValue()) .options(Collections.singletonList(IpV4NoOperationOption.getInstance())) .tos(new IpV4Rfc1349Tos.Builder().tos(IpV4TosTos.DEFAULT).precedence(IpV4TosPrecedence.ROUTINE).build()) .build(); TcpPacket t = new TcpPacket.Builder() .dstPort(new TcpPort((short)9042, "CQL")) .srcPort(new TcpPort((short)47014, "Host")) .correctLengthAtBuild(true) .sequenceNumber(6) .ack(true) .psh(true) .urgentPointer((short) 0) .window((short) 229) .build(); byte[] arr = ArrayUtils.addAll(ArrayUtils.addAll(p.getHeader().getRawData(), t.getHeader().getRawData()),Arrays.copyOfRange(buffer, 0, bytesRead )); 'arr' is what I'm writing the file, but for some reason wireshark loads the packets as "Bogus Length, must be at least 20". If I add correctLengthAtBuild(true) it shows length 20 but malformed tcp packets. Is this what you meant?