java - MappedbyteBuffer.get() increments position by too much -


the relevant part of file this:

82 0a 96 c9 82 0a 96 d3 00 66 13 08

i open file in mappedbytebuffer , set position beginning. this:

mappedbytebuffer buffer = channel.map(filechannel.mapmode.read_only, 0, channel.size()); ... buffer.position(packetinfos.get(idpacket).getstartpos());  //getting time packet header time = math.addexact(math.multiplyexact((long) buffer.order(byteorder.little_endian).getint(), 1000), math.floordiv(buffer.order(byteorder.little_endian).getint(), 1000));  //getting source ip ip frame buffer.position(packetinfos.get(idpacket).getstartpos() + packet_ipsource_offs); // puts buffers position @ part of file shown above source = bytetounsigned(buffer.get()) + "." + bytetounsigned(buffer.get()) + "." + bytetounsigned(buffer.get()) + "." + bytetounsigned(buffer.get());  //getting destination ip ip frame destination = bytetounsigned(buffer.get()) + "." + bytetounsigned(buffer.get()) + "." + bytetounsigned(buffer.get()) + "." + bytetounsigned(buffer.get());

the bytetounsigned method does: 

public static int bytetounsigned(byte b){     return b & 0xff; }

source ends being: "130.10.150.211" when should "130.10.150.201". reason get() method increments position of buffer 1 in cases, 5 after third time? might have guessed i'm trying decode destination ip afterwards , starts reading after "d3", resulting in "0.102.19.8"

even before bytetounsigned calls source ip "-126.10.-106.-45".

after debugging step step through line:

source = bytetounsigned(buffer.get()) + "." + bytetounsigned(buffer.get()) + "." + bytetounsigned(buffer.get()) + "." + bytetounsigned(buffer.get());

watching buffer.position() , buffer.get(), see following:

  • first get(): buffer.position()=70, buffer.get()=-126
  • second get(): buffer.position()=71, buffer.get()=10
  • third get(): buffer.position()=72, buffer.get()=-106
  • fourth get(): buffer.position()=73, buffer.get()=-45

so position incremented correctly, bytes between 72nd , 77th not visible buffer somehow?

the api plainly states:

public abstract byte get() relative method. reads byte @ buffer's current position, , increments position.

what missing?

turns out i'm enormous idiot. did not notice bytes 82 0a 96 repeat few bytes right. accidentally placed position of buffer. don't worry, i'm ashamed.


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