asp.net MVC 3/4 equivalent to a response.filter

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I am in a need to intercept all of the html that will be sent to the browser and replace some tags that are there. this will need to be done globally and for every view. wha

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慢半拍i

2020-12-06 08:25

You could still use a response filter in ASP.NET MVC:

public class ReplaceTagsFilter : MemoryStream
{
    private readonly Stream _response;
    public ReplaceTagsFilter(Stream response)
    {
        _response = response;
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        var html = Encoding.UTF8.GetString(buffer);
        html = ReplaceTags(html);
        buffer = Encoding.UTF8.GetBytes(html);
        _response.Write(buffer, offset, buffer.Length);
    }

    private string ReplaceTags(string html)
    {
        // TODO: go ahead and implement the filtering logic
        throw new NotImplementedException();
    }
}

and then write a custom action filter which will register the response filter:

public class ReplaceTagsAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        var response = filterContext.HttpContext.Response;
        response.Filter = new ReplaceTagsFilter(response.Filter);
    }
}

and now all that's left is decorate the controllers/actions that you want to be applied this filter:

[ReplaceTags]
public ActionResult Index()
{
    return View();
}

or register it as a global action filter in Global.asax if you want to apply to all actions.

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我在风中等你

2020-12-06 08:38

The answer is correct but. After using it for a while I came across a case when the response is split in many parts so that html is incorrect

Part 1: 
<html>.....<labe

Part 2: 
l/>...</html>

Also partial renders may make unexpected cases. Their html is out of the main stream too. So my solution is to do it in the Flush method after all streaming is done.

    /// <summary>
    /// Insert messages and script to display on client when a partial view is returned
    /// </summary>
    private class ResponseFilter : MemoryStream
    {
        private readonly Stream _response;
        private readonly IList<object> _detachMessages;

        public override void Flush()
        {

            // add messages and remove
            // filter is called for a number of methods on one page (BeginForm, RenderPartial...)
            // so that we don't need to add it more than once

            var html = MessageAndScript(_detachMessages);
            var buffer = Encoding.UTF8.GetBytes(html);
            _detachMessages.Clear();
            _response.Write(buffer, 0, buffer.Length);

            base.Flush();
        }

        public ResponseFilter(Stream response, IList<object> detachMessages)
        {
            _response = response;
            _detachMessages = detachMessages;
        }

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

        private static string MessageAndScript(IList<object> detachMessages)
        {

            if (detachMessages.Count == 0)
                return null;

            var javascript = CustomJavaScriptSerializer.Instance.Serialize(detachMessages);

            return "$(function(){var messages = " + javascript + @";
// display messages
base.ajaxHelper.displayMessages(messages);
})";
        }
    }

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