I'm working with a device that sends back an image, and when I request an image, there is some undocumented information that comes before the image data. I was only able to realize this by looking through the binary data and identifying the image header information inside.
I originally had a normal method and converted it to an extension method. The original question here was related to the compiler complaining about not having Array as the first parameter (I had Byte[]), but it turns out that I had made an error and forgot to delete the first argument in the calling code. In other words, I used to have:
Byte[] new_buffer = RemoveUpToByteArray(buffer, new byte[] { 0x42, 0x4D });
and after changing to an extension method, I had erroneously used:
buffer.RemoveUpToByteArray( buffer, new byte[] { 0x42, 0x4D });
Anyhow, that's all fixed now because I realized my mistake as I was entering the code example into SO. However, I have a new problem that is simply lack of understanding of extension methods and reference vs. value types. Here's the code:
public static void RemoveFromByteArrayUntil(this Byte[] array, Byte[] until)
{
Debug.Assert(until.Count() > 0);
int num_header_bytes = until.Count();
int header_start_pos = 0; // the position of the header bytes, defined by [until]
byte first_header_byte = until[0];
while(header_start_pos != -1) {
header_start_pos = Array.IndexOf(array, first_header_byte, header_start_pos);
if(header_start_pos == -1)
break;
// if we get here, then we've found the first header byte, and we need to look
// for the next ones sequentially
for(int header_ctr=1; header_ctr<num_header_bytes; header_ctr++) {
// we're going to loop over each of the header bytes, but will
// bail out of this loop if there isn't a match
if(array[header_start_pos + header_ctr] != until[header_ctr]) {
// no match, so bail out. but before doing that, advance
// header_start_pos so the outer loop won't find the same
// occurrence of the first header byte over and over again
header_start_pos++;
break;
}
}
// if we get here, we've found the header!
// create a new byte array of the new size
int new_size = array.Count() - header_start_pos;
byte[] output_array = new byte[new_size];
Array.Copy(array, header_start_pos, output_array, 0, new_size);
// here is my problem -- I want to change what array points to, but
// when this code returns, array goes back to its original value, which
// leads me to believe that the first argument is passed by value.
array = output_array;
return;
}
// if we get here, we didn't find a header, so throw an exception
throw new HeaderNotInByteArrayException();
}
My problem now is that it looks like the first this argument to the extension method is passed by value. I want to reassign what array points to, but in this case, it looks like I'll have to just manipulate array's data instead.
Extension methods are static methods that only appear to be instance methods. You can consider the instance the extension method is working on to be read only (by value). Assigning to the instance method of byte[] that is the first parameter of your extension won't work. You won't be able to get away from assigning, but you could modify your extension then write your assignment like this:
buffer = buffer.RemoveUpToByteArray(header);
Make your extension return the byte array result, and don't try to assign to buffer within the extension. Your extension would then be something like this:
public static class MyExtensionMethods
{
public static byte[] RemoveUpToByteArray(this byte[] buffer, byte[] header)
{
byte[] result = buffer;
// your logic to remove header from result
return result;
}
}
I hope this helps.
EDIT:
The above is correct for value types only. If the type you are extending is a reference type, then you would not have an issue operating directly on the type like you are trying to do above. Sadly, a byte array is a struct, and thus derived from System.ValueType. Consider the following, which would be perfectly legal inside an extension, and would give the desired result:
public class MyBytes
{
public byte[] ByteArray { get; set; }
}
public static class MyExtensionMethods
{
// Notice the void return here...
public static void MyClassExtension(this MyBytes buffer, byte[] header)
{
buffer.ByteArray = header;
}
}
I am sorry that I do not know what specific problem you are encountering, or how to resolve it [certainly checking namespace is referenced and resolving any conflicts with similarly named methods is a start], but I did notice one or two oddities.
Consider the following sample solution,
using System.Linq;
namespace Sample.Extensions
{
public static class ByteExtensions
{
public static void RemoveHeader (this byte[] buffer, byte[] header)
{
// take first sequence of bytes, compare to header, if header
// is present, return only content
//
// NOTE: Take, SequenceEqual, and Skip are standard Linq extensions
if (buffer.Take (header.Length).SequenceEqual (header))
{
buffer = buffer.Skip (header.Length).ToArray ();
}
}
}
}
This compiles and runs in VS2010RC. To demonstrate usage,
using Sample.Extensions;
namespace Sample
{
class Program
{
static void Main (string[] args)
{
byte[] buffer = new byte[] { 00, 01, 02 };
byte[] header = new byte[] { 00, 01 };
buffer.RemoveHeader (header);
// hm, so everything compiles and runs, but buffer == { 00, 01, 02 }
}
}
}
So we will not receive a compile or run-time error but clearly it will not operate as intended. This is because extensions must still comply with standard method semantics, meaning parameters are passed by value. We cannot change buffer to point to our new array.
We can resolve this issue by rewriting our method to conventional function semantics,
public static byte[] RemoveHeaderFunction (this byte[] buffer, byte[] header)
{
byte[] stripped = null;
if (stripped.Take (header.Length).SequenceEqual (header))
{
stripped = stripped.Skip (header.Length).ToArray ();
}
else
{
stripped = buffer.ToArray ();
}
return stripped;
}
Now
using Sample.Extensions;
namespace Sample
{
class Program
{
static void Main (string[] args)
{
byte[] buffer = new byte[] { 00, 01, 02 };
byte[] header = new byte[] { 00, 01 };
// old way, buffer will still contain { 00, 01, 02 }
buffer.RemoveHeader (header);
// new way! as a function, we obtain new array of { 02 }
byte[] stripped = buffer.RemoveHeaderFunction (header);
}
}
}
Unfortunately, arrays are immutable value types [may be using these terms incorrectly]. The only way to modify your "array" in-place is to change the container to a mutable reference-type, like a List<byte>.
If you are really keen on "passing by ref", in-place, side-effect semantics, then one option may be the following
using System.Linq;
namespace Sample.Extensions
{
public static class ListExtensions
{
public static void RemoveHeader<T> (this List<T> list, List<T> header)
{
if (list.Take (header.Count).SequenceEqual (header))
{
list.RemoveRange (0, header.Count);
}
}
}
}
As for usage,
static void Main (string[] args)
{
byte[] buffer = new byte[] { 00, 01, 02 };
byte[] header = new byte[] { 00, 01 };
List<byte> bufferList = buffer.ToList ();
// in-place side-effect header removal
bufferList.RemoveHeader (header.ToList ());
}
Under the hood, List<T> is maintaining an array of type T. At certain thresholds, it is simply manipulating the underlying array and\or instantiating new arrays for us.
Hope this helps! :)
Related
If someone passes me an ArraySegment<byte> foo and this segment points into a larger buffer, what's the idiomatic way to copy this segment into a fresh new byte[] ?
I tried accessing at foo.Array but this seems to point to the beginning of the larger buffer, not the beginning of the segment.
e.g. the larger buffer could be "blahfoobar" and the ArraySegment points to "foo". I want to get a byte[] with just "foo".
I'm sure it's dead simple, but coming from C++, I can't figure the lingo used in c#.
Creating a new array would be entirely to miss the point of the API, which is to represent a pre-existing segment. In more recent .NET version, Span<T> and ReadOnlySpan<T> would be better choices - they allow you to create an abstraction over contiguous memory without needing the consumer to worry about the Offset etc, as that can be imposed externally. There are constructors on Span<T> and ReadOnlySpan<T> that allow you to deal with aspects so that the consumer never needs to know about them, with the knowledge that on recent runtimes: the JIT will elide bounds checks on spans.
using System;
using System.Text;
namespace ConsoleApp1
{
class Program
{
private static readonly byte[] _initArray = Encoding.ASCII.GetBytes("blahfoobar");
//private static byte[] ArraySegmentToArray(ArraySegment<byte> segment)
//{
// var result = new byte[segment.Count];
// for (int i = 0; i < segment.Count; i++)
// {
// result[i] = segment.Array[i + segment.Offset];
// }
// return result;
//}
private static byte[] ArraySegmentToArray(ArraySegment<byte> segment) =>
segment.ToArray();
static void Main(string[] args)
{
var segFoo = new ArraySegment<byte>(_initArray, 4, 3);
var test = ArraySegmentToArray(segFoo);
}
}
}
But of course it is bad practice. Because if you turn segment to array you allocate memory, and if you use ArraySegment stuff as pointers , you don't allocate memory, actually, that is the main idea of using ArraySegment, because if not the array could be provided as parameters :)
P.S. Commented code just for understanding the idea.
byte[] bytes = Call("getBytes") ; where getBytes function returns a byte[].
above function is called to fetch image rgb data in csharp. Returned byte[] is deep copied into the bytes array.
Since return byte array is large, deep copying adds more time.
how to make bytes array in csharp to hold only reference of java byte[]?
public class TestUtil : MonoBehaviour
{
public static string TAG = "--------TestUtil------------> ";
private static AndroidJavaObject pluginClass;
public static List<byte[]> rgbList = new List<byte[]>();
void Start()
{
Debug.Log(TAG + "start called");
//mainDataArray = new byte[1280*720*4];
Debug.Log(TAG + "creating java object");
initializePlayer();
}
public void initializePlayer()
{
// StreamHandler is the Javaclass. here i am creating a object StreamHandler
pluginClass = new AndroidJavaObject("com.test.android.decoder.StreamHandler");
// using this code to get the context
AndroidJavaClass unityPlayer = new AndroidJavaClass("com.unity3d.player.UnityPlayer");
AndroidJavaObject activity = unityPlayer.GetStatic<AndroidJavaObject>("currentActivity");
// setting context StreamHandler object
pluginClass.Call("setActivity", activity);
// setting the interface object, where java class will call the respective function
pluginClass.Call("setOnDecodeListener", new AndroidPluginCallback());
// initializing the player
pluginClass.Call("init", ipAddress, port, outWidth, outHeight);
Debug.Log(TAG + " Initialization done");
}
public void quitApplication(string sid)
{
Application.Quit();
}
private void Update()
{
if (Input.GetKey(KeyCode.Escape)) {
Debug.Log(TAG + "Escape");
quitApplication(sId);
}
}
int count;
private void LateUpdate()
{
if (0 != rgbList.Count) {
// here i am updating the rgb texture to Quad gameobject
}
}
class AndroidPluginCallback : AndroidJavaProxy
{
public AndroidPluginCallback() : base("com.test.android.OnDecodeListener") { }
public void success(byte[] videoPath)
{
}
public void onFrameAvailable()
{
// Called when java code successfully generate RGBA data
long startTime = DateTimeOffset.Now.ToUnixTimeMilliseconds();
// Need to call "getBytes()" to get the RGBA frame.
//Note: generally if you call same function from another java class it do shallow copy to byte[] object
// but in this case it is doing deep copy or i am not sure whats going on.
byte[] rawBytes = pluginClass.Call<byte[]>("getBytes"); // width and height of frame is 1088x1088
rgbList.Add(rawBytes);
long diff = DateTimeOffset.Now.ToUnixTimeMilliseconds() - startTime;
Debug.Log(TAG + "Entered into onFrameAvailable callback. time taken to copy to rawbytes: " + diff); // diff is 14ms on average. Not sure why.
}
public void fail(string errorMessage)
{
Debug.Log(TAG + "ENTER callback onError: " + errorMessage);
}
}
}
AndroidJavaObject uses the JNI (Java Native Interface) to marshal data to and from Java land. Depending on how Java stores the arrays in memory, the JNI may need to do a deep copy to form an array that C# would understand, such as if the JVM originally stored the array in non-contiguous blocks.
Here's IBM's description:
JNI provides a clean interface between Java code and native code. To maintain this separation, arrays are passed as opaque handles, and native code must call back to the JVM in order to manipulate array elements using set and get calls. The Java specification leaves it up to the JVM implementation whether these calls provide direct access to the arrays or return a copy of the array. For example, the JVM might return a copy when it has optimized arrays in a way that does not store them contiguously.
These calls, then, might cause copying of the elements being manipulated. For example, if you call GetLongArrayElements() on an array with 1,000 elements, you might cause the allocation and copy of at least 8,000 bytes (1,000 elements * 8 bytes for each long). When you then update the array's contents with ReleaseLongArrayElements(), another copy of 8,000 bytes might be required to update the array. Even when you use the newer GetPrimitiveArrayCritical(), the specification still permits the JVM to make copies of the full array.
So basically, try to avoid marshalling arrays across the JNI (such as with AndroidJavaObject as much as possible, because it's not up to the C# on whether the JNI makes a deep copy or not.
I am having a problem with the camera CallBack Buffer. The camera adds 4 new callbackbuffers, and also associates the byte Array to a dictionary mBytesToByteBuffer with the form (Byte[], ByteBuffer). I believe the problem lies with the fact the dictionary never updates its keys to the most recent frame. Leading to comparisons with current frame data failing. And the code not progressing past that point.
I have looked through the google example I have been working through, and it seems that they do not update their mBytesToByteBuffer at all, but that it seems to work.
From having looked at the source code for both AddCallbackBuffer and SetPreviewCallbackWithBuffer, it seems that they do not do anything with the byte arrays passed to them.
Declaration of mBytesToByteBuffer
public ConcurrentDictionary<byte[], ByteBuffer> mBytesToByteBuffer = new ConcurrentDictionary<byte[], ByteBuffer>();
Adding the CallbackBuffers:
camera.AddCallbackBuffer(createPreviewBuffer(mPreviewSize));
camera.AddCallbackBuffer(createPreviewBuffer(mPreviewSize));
camera.AddCallbackBuffer(createPreviewBuffer(mPreviewSize));
camera.AddCallbackBuffer(createPreviewBuffer(mPreviewSize));
camera.SetPreviewCallbackWithBuffer(new CameraPreviewCallback(this));
The dictionary mBytesToByteBuffer contains the correct size of byteArray, however this is never populated.
The Byte Buffer Dictionary is created here.
private byte[] createPreviewBuffer(Size previewSize)
{
int bitsPerPixel = ImageFormat.GetBitsPerPixel(ImageFormatType.Nv21);
long sizeInBits = previewSize.Height * previewSize.Width * bitsPerPixel;
int bufferSize = (int)System.Math.Ceiling(sizeInBits / 8.0d) + 1;
byte[] byteArray = new byte[bufferSize];
ByteBuffer buffer = ByteBuffer.Wrap(byteArray);
if (!buffer.HasArray)
{
throw new IllegalStateException("Failed to create valid buffer for camera source.");
}
mBytesToByteBuffer[byteArray] = buffer; //(byteArray, buffer);
return byteArray;
}
The callBackBuffer is called here through mBytesToByteBuffer
public void setNextFrame(byte[] data, Android.Hardware.Camera camera)
{
lock (mLock)
{
if (mPendingFrameData != null)
{
camera.AddCallbackBuffer(mPendingFrameData.ToArray<System.Byte>());
mPendingFrameData = null;
}
if (!cameraSource.mBytesToByteBuffer.ContainsKey(data))
{
Log.Debug(TAG, "Skipping Frame, Could not Find ByteBuffer Associated with image");
return;
}
mPendingTimeMillis = SystemClock.ElapsedRealtime() - mStartTimeMillis;
mPendingFrameId++;
mPendingFrameData = cameraSource.mBytesToByteBuffer[data];
Monitor.PulseAll(mLock);
}
}
But the code never gets past
if(!cameraSource.mBytesToByteBuffer.containsKey(data)
Data is fully populated.
CameraPreviewCallback:
private class CameraPreviewCallback : Java.Lang.Object, Android.Hardware.Camera.IPreviewCallback
{
CameraSource cameraSource;
public CameraPreviewCallback(CameraSource cs)
{
cameraSource = cs;
}
public void OnPreviewFrame(byte[] data, Android.Hardware.Camera camera)
{
cameraSource.mFrameProcessor.setNextFrame(data, camera);
}
}
I have been working through the Google Vison Example Camera Source
My Full Camera Source
MFC CArray was Serialized and saved to a database. I need to read this data into a C# project. I am able to retrieve the data as byte[] from the database. I then write the byte[] to a MemoryStream. Now I need to read the data from the MemoryStream.
Someone has apparently solved this before, but did not write their solution.
http://social.msdn.microsoft.com/Forums/eu/csharpgeneral/thread/17393adc-1f1e-4e12-8975-527f42e5393e
I followed these projects in my attempt to solve the problem.
http://www.codeproject.com/Articles/32741/Implementing-MFC-Style-Serialization-in-NET-Part-1
http://www.codeproject.com/Articles/32742/Implementing-MFC-Style-Serialization-in-NET-Part-2
The first thing in the byte[] is the size of the array, and I can retrieve that with binaryReader.readInt32(). However, I cannot seem to get back the float values. If I try binaryReader.readSingle() or
public void Read(out float d) {
byte[] bytes = new byte[4];
reader.Read(bytes, m_Index, 4);
d = BitConverter.ToSingle(bytes, 0);
}
I do not get back the correct data. What am I missing?
EDIT Here is the C++ code that serializes the data
typedef CArray<float, float> FloatArray;
FloatArray floatArray;
// fill floatArray
CSharedFile memoryFile(GMEM_MOVEABLE | GMEM_ZEROINIT);
CArchive ar(&memoryFile, CArchive::store);
floatArray.Serialize(ar);
ar.Close();
EDIT 2
By reading backward, I was able to get all of the floats, and was also able to determine that the size for CArray is byte[2], or Int16. Does anyone know if this is always the case?
Using the codeproject articles above, here is a C# implementation of CArray which will allow you to deserialize a serialized MFC CArray.
// Deriving from the IMfcArchiveSerialization interface is not mandatory
public class CArray : IMfcArchiveSerialization {
public Int16 size;
public List<float> floatValues;
public CArray() {
floatValues = new List<float>();
}
virtual public void Serialize(MfcArchive ar) {
if(ar.IsStoring()) {
throw new NotImplementedException("MfcArchive can't store");
}
else {
// be sure to read in the order in which they were stored
ar.Read(out size);
for(int i = 0; i < size; i++) {
float floatValue;
ar.Read(out floatValue);
floatValues.Add(floatValue);
}
}
}
}
I need to port code from Java to C#. In the Java code, the methods "ByteBuffer.flip()" and "ByteBuffer.slice" is used, and I don't know how to translate this.
I've read this question (An equivalent of javax.nio.Buffer.flip() in c#), but although an answer is given, I cannot figure how to apply it. According to Tom Hawtin, I should "Set the limit to the current position and then set the position to zero" in the underlying array. I am unsure as of how to change these values. (If you could explain the underlying logic, it would help me a lot :)
As for the ByteBuffer.slice, I have no clue on how to translate it.
EDIT: If it can be clearer with the actual code, I'll post it:
Java:
ByteBuffer buff;
buff.putShort((short) 0);
buff.put(customArray);
buff.flip();
buff.putShort((short) 0);
ByteBuffer b = buff.slice();
short size = (short) (customFunction(b) + 2);
buff.putShort(0, size);
buff.position(0).limit(size);
So far, my translation in C#.NET:
BinaryWriter b = new BinaryWriter(); //ByteBuffer buff;
b.Write((short)0); // buff.putShort((short) 0);
b.Write(paramStream.ToArray()); // buff.put(customArray);
b.BaseStream.SetLength(b.BaseStream.Position); // buff.flip; (not sure)
b.BaseStream.Position = 0; // buff.flip; too (not sure)
b.Write((short)0); // buff.putShort((short) 0)
??? // ByteBuffer b = buff.slice();
// Not done but I can do it, short size = (short) (customFunction(b) + 2);
??? // How do I write at a particular position?
??? // buff.position(0).limit(size); I don't know how to do this
Thank you!
EDIT: Changed b.BaseStream.SetLength(b.BaseStream.Length); to b.BaseStream.SetLength(b.BaseStream.Position);, based on the Java docs.
(See See http://java.sun.com/javase/6/docs/api/java/nio/ByteBuffer.html#slice%28%29 and http://java.sun.com/javase/6/docs/api/java/nio/Buffer.html#flip%28%29 for java's calls)
Flip is a quick way to reset the buffer. So for example
(pseudocode)
void flip()
{
Length = currentPos;
currentPos = 0;
}
Allows you to quickly setup the buffer you presumably just wrote to for reading from the beginning.
Update:
Splice is a bit trickier due to the requirement that "Changes to this buffer's content will be visible in the new buffer, and vice versa; the two buffers' position, limit, and mark values will be independent". There unfortunately is no concept of a shared portion of buffer (that i know of - theres always using arrays, detailed below) without making your own class. The closest thing you could do is this:
Old Code:
ByteBuffer b = buff.slice();
New Code (assuming a List)
List<Byte> b= buff;
int bStart = buffPos; // buffPos is your way of tracking your mark
the downside to the code above is that there is no way for c# to hold the new starting point of the new buffer and still share it. You'll have to manually use the new starting point whenever you do anything, from for loops (for i=bStart;...) to indexing (newList[i + bStart]...)
Your other option is to do use Byte[] arrays instead, and do something like this:
Byte[] b = &buff[buffPos];
... however that requires unsafe operations to be enabled, and I cannot vouch for its saftey, due to the garbage collector and my avoidance of the "unsafe" features.
Outside of that, theres always making your own ByteBuffer class.
Untested, but if I understand the java bits correctly, this would give you an idea on how to implement.
public class ByteBuffer {
private int _Position;
private int _Capacity;
private byte[] _Buffer;
private int _Start;
private ByteBuffer(int capacity, int position, int start, byte[] buffer) {
_Capacity = capacity;
_Position = position;
_Start = start;
_Buffer = buffer;
}
public ByteBuffer(int capacity) : this(capacity, 0 , 0, new byte[capacity]) {
}
public void Write(byte item) {
if (_Position >= _Capacity) {
throw new InvalidOperationException();
}
_Buffer[_Start + _Position++] = item;
}
public byte Read() {
if (_Position >= _Capacity) {
throw new InvalidOperationException();
}
return _Buffer[_Start + _Position++];
}
public void Flip() {
_Capacity = _Position;
_Position = _Start;
}
public ByteBuffer Slice() {
return new ByteBuffer(_Capacity-_Position, 0, _Position, _Buffer);
}
}