[users@httpd] mod_ext_filter with Mono problem

[Tero Armando De La Rosa]

Hello,

I'm trying to create a simple Mono program that is configured as an external 
filter that simply reads from stdin and writes to stdout a modified version of 
a media file (images, videos...).

Prior to reading from stdin I'm trying to craft a POC which simply replaces all 
requests' content with a hardcoded file ("Capture.PNG" in my case).

The problem is that a timeout always occurs when I do this.

[Wed Apr 13 11:26:51.906231 2016] [ext_filter:error] [pid 1899:tid 
139929490360064] (70007)The timeout specified has expired: [client 
10.0.216.137:15328] AH01466: apr_file_read(child output), len 
18446744073709551615
[Wed Apr 13 11:26:51.906342 2016] [ext_filter:error] [pid 1899:tid 
139929490360064] (70007)The timeout specified has expired: [client 
10.0.216.137:15328] AH01468: ef_unified_filter() failed


However, if I replace the filter line with this: "/bin/cat 
/var/www/html/Capture.PNG" it will always work correctly.

Can anyone shed some light on this? Thank you in advance.

PD. Find enclosed the source code and apache configuration I'm using. I'm also 
running Apache 2.4.7 on Ubuntu Server 14.04 which comes by default.

using System;
using System.IO;

namespace ApacheFilterExample1
{
    class Program
    {
#if WINDOWS
        const string Sample1 = @"C:\Apache24\htdocs\Capture.PNG";
#else
        const string Sample1 = "/var/www/html/Capture.PNG";
#endif

        static int Main(string[] args)
        {
            try
            {
                byte[] bytes;
                                
                using (Stream output = System.Console.OpenStandardOutput())
                {
                    bytes = File.ReadAllBytes(Sample1);
                    output.Write(bytes, 0, bytes.Length);
                }

                Console.Error.WriteLine(String.Format("{0} bytes written.", 
bytes.Length.ToString()));

                return 0;
            }
            catch (Exception e)
            {
                Console.Error.WriteLine(e.Message);

                return -1;
            }
                }
                
    }
}

using System;
using System.IO;

namespace ApacheFilterExample2
{
    class Program
    {
#if WINDOWS
        const string Success = @"C:\Apache24\htdocs\Capture.PNG";
        const string Failure = @"C:\Apache24\htdocs\Capture2.PNG";
#else
        const string Success = "/var/www/html/Capture.PNG";
        const string Failure = "/var/www/html/Capture2.PNG";
#endif

        static int Main(string[] args)
        {
            try
            {
                //// if nothing is being piped in, then exit  (not working 
correctly)
                //if (!IsPipedInput())
                //{
                //    Console.Error.WriteLine("Nothing being piped in, 
waiting...");
                //    Thread.Sleep(250);
                //    //return 0;
                //}

                Console.Error.WriteLine("Waiting for input.");

                byte[] fileBytes;

                if (System.Console.In.Peek() != -1)
                {
                    Console.Error.WriteLine("Input available, opening 
stream...");

                    using (Stream s = System.Console.OpenStandardInput())
                    {
                        Console.Error.WriteLine("Input stream open, reading 
from stream...");

                        byte[] buffer = new byte[4096];
                        using (MemoryStream ms = new MemoryStream())
                        {
                            int read;

                            while ((read = s.Read(buffer, 0, buffer.Length)) > 
0)
                            {
                                ms.Write(buffer, 0, buffer.Length);
                            }

                            fileBytes = ms.ToArray();
                                                        
                            Console.Error.WriteLine(String.Format("{0} bytes 
read from input stream. Opening output stream...", 
fileBytes.Length.ToString()));
                        }
                    }

                    using (Stream output = System.Console.OpenStandardOutput())
                    {
                        fileBytes = File.ReadAllBytes(Success);

                        output.Write(fileBytes, 0, fileBytes.Length);

                        Console.Error.WriteLine(String.Format("{0} bytes 
written to output stream.", fileBytes.Length.ToString()));
                        output.Dispose();
                    }

                }
                else
                {
                    Console.Error.WriteLine("Error, no data available to 
read.");

                    using (Stream output = System.Console.OpenStandardOutput())
                    {
                        fileBytes = File.ReadAllBytes(Failure);

                        output.Write(fileBytes, 0, fileBytes.Length);

                        Console.Error.WriteLine(String.Format("{0} bytes 
written to output stream (NO INPUT).", fileBytes.Length.ToString()));
                        output.Dispose();
                    }
                }

                return 0;
            }
            catch (Exception ex)
            {
                Console.Error.WriteLine(String.Format("Error: \n{0}", 
ex.ToString()));

                using (Stream output = System.Console.OpenStandardOutput())
                {
                    byte[] fileBytes = File.ReadAllBytes(Failure);
                                        
                                        output.Write(fileBytes, 0, 
fileBytes.Length);

                    Console.Error.WriteLine(String.Format("{0} bytes written to 
output stream (ERROR).", fileBytes.Length.ToString()));
                    output.Dispose();
                }

                return 0;
            }

        }

        private static bool IsPipedInput()
        {
            try
            {
                bool isKey = System.Console.KeyAvailable;
                return false;
            }
            catch
            {
                return true;
            }
        }
    }
}

apache2.conf
Description: apache2.conf

FilterScript.sh
Description: FilterScript.sh

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