Aleyna Aleyna - 15 days ago 8
C# Question

C# - StreamReader.ReadLine does not work properly!

Simply I have been trying to implement what

BufferedStreamReader
does in Java. I have a socket stream open and just want to read it in a line-oriented fashion - line by line.

I have the following server-code.

while (continueProcess)
{
try
{
StreamReader reader = new StreamReader(Socket.GetStream(), Encoding.UTF8);
string command = reader.ReadLine();
if (command == null)
break;

OnClientExecute(command);
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}


And the following client-code:

TcpClient tcpClient = new TcpClient();
try
{
tcpClient.Connect("localhost", serverPort);
StreamWriter writer = new StreamWriter(tcpClient.GetStream(), Encoding.UTF8);
writer.AutoFlush = true;
writer.WriteLine("login>user,pass");
writer.WriteLine("print>param1,param2,param3");
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
finally
{
tcpClient.Close();
}


The server reads only the very first line (
login>user,pass
) and then
ReadLine
returns null!

What's the easiest way of achieving this line-oriented reader as it is in Java's
BufferedStreamReader
? :s

Answer

A typical line-reader is something like:

using(StreamReader reader = new StreamReader(Socket.GetStream(), Encoding.UTF8)) {
    string line;
    while((line = reader.ReadLine()) != null) {
        // do something with line
    }
}

(note the using to ensure we Dispose() it even if we get an error, and the loop)

If you want, you could abstract this (separation of concerns) with an iterator block:

static IEnumerable<string> ReadLines(Stream source, Encoding encoding) {
    using(StreamReader reader = new StreamReader(source, encoding)) {
        string line;
        while((line = reader.ReadLine()) != null) {
            yield return line;
        }
    }
}

(note we've moved this into a function and removed the "do something", replacing it with "yield return", which creates an iterator (a lazily iterated, non-buffering state machine)

We would then consume this as simply as:

foreach(string line in ReadLines(Socket.GetStream(), Encoding.UTF8)) {
    // do something with line
}

Now our processing code doesn't need to worry about how to read lines - simply given a sequence of lines, do something with them.

Note that the using (Dispose()) applies to TcpClient too; you should make a habit of checking for IDisposable; for example (still including your error-logging):

using(TcpClient tcpClient = new TcpClient()) {
    try {
       tcpClient.Connect("localhost", serverPort);
       StreamWriter writer = new StreamWriter(tcpClient.GetStream(), Encoding.UTF8);
       writer.AutoFlush = true;
       writer.WriteLine("login>user,pass");
       writer.WriteLine("print>param1,param2,param3");
    } catch (Exception ex) {
        Console.Error.WriteLine(ex.ToString());
    }
}
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