我正在尝试解析表示消息的传入字节流.
我需要拆分流并为每个部分创建一个消息结构.
我需要拆分流并为每个部分创建一个消息结构.
消息始终以0x81(BOM)开头,以0x82(EOM)结束.
start: 0x81 header: 3 bytes data: arbitrary length stop: 0x82
数据部分使用转义字节0x1B(ESC)进行转义：只要数据部分中的一个字节包含控制字节{ESC,BOM,EOM}之一,它就会以ESC为前缀.
标题部分未转义,可能包含控制字节.
我想使用Rx.Net以功能性的反应式编码,通过使用IObservable< byte>并将其转换为IObservable< Message>.
最常用的方法是什么？
一些例子：
[81 01 02 03 82] single message
[81 82 81 82 82] single message,header = [82 81 82]
[81 01 02 1B 82] single message,header = [01 02 1B].
[81 01 02 03 1B 82 82] single message,header = [01 02 03],(unescaped) data = [82]
[81 01 02 03 1B 1B 82 82] single message + dangling [82] which should be ignored.
header = [01 02 03],(unescaped) data = [1B]
这是一个状态机绘图：
解决方法
如果你正在寻找“功能更强大”的东西,那么这可能会有所帮助,但@Evk的答案也会通过这些测试.
首先我可以建议,为了提供一个可验证的答案,你可以提供一个测试套件来实现这样的复杂问题.
像这样的东西会非常有帮助.
var scheduler = new TestScheduler();
var source = scheduler.CreateColdobservable<byte>(
ReactiveTest.OnNext<byte>(01,0x81),//BOM m1
ReactiveTest.OnNext<byte>(02,0x01),ReactiveTest.OnNext<byte>(03,0x02),ReactiveTest.OnNext<byte>(04,0x03),ReactiveTest.OnNext<byte>(05,0x82),//EOM m1
ReactiveTest.OnNext<byte>(06,//BOM m2
ReactiveTest.OnNext<byte>(07,ReactiveTest.OnNext<byte>(08,ReactiveTest.OnNext<byte>(09,ReactiveTest.OnNext<byte>(10,//EOM m2
ReactiveTest.OnNext<byte>(11,//BOM m3
ReactiveTest.OnNext<byte>(12,ReactiveTest.OnNext<byte>(13,ReactiveTest.OnNext<byte>(14,0x1B),ReactiveTest.OnNext<byte>(15,//EOM m3
ReactiveTest.OnNext<byte>(16,//BOM m4
ReactiveTest.OnNext<byte>(17,ReactiveTest.OnNext<byte>(18,ReactiveTest.OnNext<byte>(19,ReactiveTest.OnNext<byte>(20,//Control character
ReactiveTest.OnNext<byte>(21,//Data
ReactiveTest.OnNext<byte>(22,//EOM m4
ReactiveTest.OnNext<byte>(23,//BOM m5
ReactiveTest.OnNext<byte>(24,ReactiveTest.OnNext<byte>(25,ReactiveTest.OnNext<byte>(26,ReactiveTest.OnNext<byte>(27,//Control character
ReactiveTest.OnNext<byte>(28,//Data
ReactiveTest.OnNext<byte>(29,//EOM m5
ReactiveTest.OnNext<byte>(30,0x82));//Ignored (expected 0x81)
var observer = scheduler.CreateObserver<Message>();
//CurrentAnswer(source)
MyAnswer(source)
.Subscribe(observer);
scheduler.Start();
ReactiveAssert.AreElementsEqual(
new[] {
ReactiveTest.OnNext(05,new Message(){Header=new byte[]{0x01,0x02,0x03},Data=new byte[0]{}}),ReactiveTest.OnNext(10,new Message(){Header=new byte[]{0x82,0x81,0x82},ReactiveTest.OnNext(15,0x1B},ReactiveTest.OnNext(22,Data=new byte[]{ 0x82}}),ReactiveTest.OnNext(29,Data=new byte[]{ 0x1B}}),},observer.Messages);
我还写了一个允许我验证代码的Message版本
public class Message
{
public static readonly byte BOM = 0x81;
public static readonly byte EOM = 0x82;
public static readonly byte Control = 0x1B;
public byte[] Header { get; set; }
public byte[] Data { get; set; }
public static Message Create(byte[] bytes)
{
if(bytes==null)
throw new ArgumentNullException(nameof(bytes));
if(bytes.Length<3)
throw new ArgumentException("bytes<3").Dump();
var header = new byte[3];
Array.copy(bytes,header,3);
var body = new List<byte>();
var escapeNext = false;
for (int i = 3; i < bytes.Length; i++)
{
var b = bytes[i];
if (b == Control && !escapeNext)
{
escapeNext = true;
}
else
{
body.Add(b);
escapeNext = false;
}
}
var msg = new Message { Header = header,Data = body.ToArray()};
return msg;
}
public override string ToString()
{
return string.Format("Message(Header=[{0}],Data=[{1}])",ByteArrayString(Header),ByteArrayString(Data));
}
private static string ByteArrayString(byte[] bytes)
{
return string.Join(",",bytes.Select(b => b.ToString("X")));
}
public override bool Equals(object obj)
{
var other = obj as Message;
if(obj==null)
return false;
return Equals(other);
}
protected bool Equals(Message other)
{
return IsSequenceEqual(Header,other.Header)
&& IsSequenceEqual(Data,other.Data);
}
private bool IsSequenceEqual<T>(IEnumerable<T> expected,IEnumerable<T> other)
{
if(expected==null && other==null)
return true;
if(expected==null || other==null)
return false;
return expected.SequenceEqual(other);
}
public override int GetHashCode()
{
unchecked
{
return ((Header != null ? Header.GetHashCode() : 0) * 397) ^ (Data != null ? Data.GetHashCode() : 0);
}
}
}
现在我拥有了所有的管道,我可以专注于实际的问题.
public static IObservable<Message> MyAnswer(IObservable<byte> source)
{
return source.Publish(s =>
{
return
Observable.Defer(()=>
//Start consuming once we see a BOM
s.Skipwhile(b => b != Message.BOM)
.Scan(new Accumulator(),(acc,cur)=>acc.Accumulate(cur))
)
.TakeWhile(acc=>!acc.IsEndOfMessage())
.Where(acc=>!acc.IsBeginingOfMessage())
.Select(acc=>acc.Value())
.ToArray()
.Where(buffer=>buffer.Any())
.Select(buffer => Message.Create(buffer))
.Repeat();
});
}
public class Accumulator
{
private int _index = 0;
private byte _current =0;
private bool _isCurrentEscaped = false;
private bool _isNextEscaped = false;
public Accumulator Accumulate(byte b)
{
_index++;
_current = b;
_isCurrentEscaped = _isNextEscaped;
_isNextEscaped = (!IsHeader() && !_isCurrentEscaped && b==Message.Control);
return this;
}
public byte Value()
{
return _current;
}
private bool IsHeader()
{
return _index < 5;
}
public bool IsBeginingOfMessage()
{
return _index == 1 && _current == Message.BOM;
}
public bool IsEndOfMessage()
{
return !IsHeader()
&& _current == Message.EOM
&& !_isCurrentEscaped;
}
}
为了完整起见,这里是@Evk的答案的胆量,所以你可以轻松地交换实现.
public static IObservable<Message> CurrentAnswer(IObservable<byte> source)
{
return Observable.Create<Message>(o =>
{
// some crude parsing code for the sake of example
bool nextIsEscaped = false;
bool readingHeader = false;
bool readingBody = false;
List<byte> body = new List<byte>();
List<byte> header = new List<byte>();
return source.Subscribe(b =>
{
if (b == 0x81 && !nextIsEscaped && !readingHeader)
{
// start
readingHeader = true;
readingBody = false;
nextIsEscaped = false;
}
else if (b == 0x82 && !nextIsEscaped && !readingHeader)
{
// end
readingHeader = false;
readingBody = false;
if (header.Count > 0 || body.Count > 0)
{
o.OnNext(new Message()
{
Header = header.ToArray(),Data = body.ToArray()
});
header.Clear();
body.Clear();
}
nextIsEscaped = false;
}
else if (b == 0x1B && !nextIsEscaped && !readingHeader)
{
nextIsEscaped = true;
}
else
{
if (readingHeader)
{
header.Add(b);
if (header.Count == 3)
{
readingHeader = false;
readingBody = true;
}
}
else if (readingBody)
body.Add(b);
nextIsEscaped = false;
}
});
});
}