R – ASP.NET Response Filter to Reformat the rendered output of ASPX pages

asp.netfilterhttpmoduleresponsestream

I've created a simple HttpModule and response stream to reformat the rendered output of web pages (see code snippets below).

In the HttpModule I set the Response.Filter to my PageStream:

m_Application.Context.Response.Filter = new PageStream(m_Application.Context);

In the PageStream I overwrite the Write method in order to do my reformatting of the rendered output:

public override void Write(byte[] buffer, int offset, int count)
{
    string html = System.Text.Encoding.UTF8.GetString(buffer);
    //Do some string resplace operations here...
    byte[] input = System.Text.Encoding.UTF8.GetBytes(html);
    m_DefaultStream.Write(input, 0, input.Length);
}

And this work fine when using it on simple HTML pages (.html), but when I use this method on ASPX pages (.aspx), the Write method is called several times, splitting up the reformatting into different steps, and potentially destroying the string replacement operations.

How do I solve this? Is there a way to let the ASPX page NOT call Write several times, e.g. by changing its buffer size, or have I chosen the wrong approach entirely, by using this Response.Filter method to manipulate the rendered output?

Best Answer

I would just buffer the data in the Write method, and do the string operations in the Close method, like this:

private readonly Stream _forwardStream;
private readonly StringBuilder _sb;

// snip

public override void Write (byte[] buffer, int offset, int count)
{
  string chunk = Encoding.UTF8.GetString (buffer, offset, count);
  _sb.Append (chunk);
}

public override void Close ()
{
  string result = GetManipulatedString ();

  byte[] rawResult = Encoding.UTF8.GetBytes (result);
  _forwardStream.Write (rawResult, 0, rawResult.Length);

  base.Close ();
  _forwardStream.Close ();
}

(Maybe even better if you collect the data in a MemoryStream)

Related Solutions

Java – How to filter a Java Collection (based on predicate)

Java 8 (2014) solves this problem using streams and lambdas in one line of code:

List<Person> beerDrinkers = persons.stream()
    .filter(p -> p.getAge() > 16).collect(Collectors.toList());

Here's a tutorial.

Use Collection#removeIf to modify the collection in place. (Notice: In this case, the predicate will remove objects who satisfy the predicate):

persons.removeIf(p -> p.getAge() <= 16);

lambdaj allows filtering collections without writing loops or inner classes:

List<Person> beerDrinkers = select(persons, having(on(Person.class).getAge(),
    greaterThan(16)));

Can you imagine something more readable?

Disclaimer: I am a contributor on lambdaj

C# – How to retrieve response html from within a HttpModule

Fun little challenge.

Here's the code:

StreamWatcher.cs

    public class StreamWatcher : Stream
    {
        private Stream _base;
        private MemoryStream _memoryStream = new MemoryStream();

        public StreamWatcher(Stream stream)
        {
            _base = stream;
        }

        public override void Flush()
        {
            _base.Flush();
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            return _base.Read(buffer, offset, count);
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            _memoryStream.Write(buffer, offset, count);
            _base.Write(buffer, offset, count);
        }

        public override string ToString()
        {
            return Encoding.UTF8.GetString(_memoryStream.ToArray());
        }

        #region Rest of the overrides
        public override bool CanRead
        {
            get { throw new NotImplementedException(); }
        }

        public override bool CanSeek
        {
            get { throw new NotImplementedException(); }
        }

        public override bool CanWrite
        {
            get { throw new NotImplementedException(); }
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            throw new NotImplementedException();
        }

        public override void SetLength(long value)
        {
            throw new NotImplementedException();
        }

        public override long Length
        {
            get { throw new NotImplementedException(); }
        }

        public override long Position
        {
            get
            {
                throw new NotImplementedException();
            }
            set
            {
                throw new NotImplementedException();
            }
        }
        #endregion
    }

TitleModule.cs

public class TitleModule : IHttpModule
{
    public void Dispose()
    {
    }

    private static Regex regex = new Regex(@"(?<=<title>)[\w\s\r\n]*?(?=</title)", RegexOptions.Compiled | RegexOptions.IgnoreCase);
    private StreamWatcher _watcher;
    public void Init(HttpApplication context)
    {
        context.BeginRequest += (o, e) => 
        {
            _watcher = new StreamWatcher(context.Response.Filter);
            context.Response.Filter = _watcher;
        };


        context.EndRequest += (o, e) =>
        {
            string value = _watcher.ToString();
            Trace.WriteLine(regex.Match(value).Value.Trim());
        };
    }
}

Best Answer

Related Solutions

Java – How to filter a Java Collection (based on predicate)

C# – How to retrieve response html from within a HttpModule

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