Can I use C# Serialization to read a binary file in custom format?

问题

I have a custom binary file which I want to read into my C# program.

There are several different formats, some MSB first, some LSB first and some with the variables in different orders.

Currently, I have a class which reads the right number of bytes, one at a time.

It is very slow and so I am looking to improve performance any way I can.

Is serialization likely to perform better? If so, is this possible with the scenario I have decsribed? Is it possible to customise the BinaryFormatter for big/little-endian format?

Thanks.

回答1:

You can't do that with BinaryFormatter - it will expect additional meta-data/padding around object. You would have to read manually either from a Stream or similarly via a binary reader.

Having done some very similar code, I would write my own reader that sits on top of a stream, with methods like: ReadInt32LittleEndian, ReadInt32BigEndian (etc for everything you need) - and use shift (<< / >>) to assemble the bytes. But importantly I would use a backing buffer to reduce the amount of calls to the underlying stream (even with a buffer, this can be unacceptably slow).

Let me refer you to some code from protobuf-net that does this... in particular ProtoReader, taking an example:

    /// <summary>
    /// Reads an unsigned 32-bit integer from the stream; supported wire-types: Variant, Fixed32, Fixed64
    /// </summary>
    public uint ReadUInt32()
    {
        switch (wireType)
        {
            case WireType.Variant:
                return ReadUInt32Variant(false);
            case WireType.Fixed32:
                if (available < 4) Ensure(4, true);
                position += 4;
                available -= 4;
                return ((uint)ioBuffer[ioIndex++])
                    | (((uint)ioBuffer[ioIndex++]) << 8)
                    | (((uint)ioBuffer[ioIndex++]) << 16)
                    | (((uint)ioBuffer[ioIndex++]) << 24);
            case WireType.Fixed64:
                ulong val = ReadUInt64();
                checked { return (uint)val; }
            default:
                throw CreateException();
        }
    }

(here wireType broadly acts as an indicater of endianness etc, but that isn't important)

Looking at the Fixed32 implementation:

The Ensure makes sure that we have at least 4 more bytes in our backing buffer (fetching more if we desire)
we increment some counters so we can track our position in the logical buffer
we read the data from the buffer

One you have a reader for your format, deserialization should be much easier.

回答2:

No it wont work. Well it could, but the overhead from a transformation will likely kill performance.

来源：https://stackoverflow.com/questions/4154230/can-i-use-c-sharp-serialization-to-read-a-binary-file-in-custom-format

标签

serialization

binary-data