How to set large string inside HttpContent when using HttpClient?

Question

So, I created a HttpClient and am posting data using HttpClient.PostAsync().

I set the HttpContent using

HttpContent content = new FormUrlEncodedContent(post_parameters); where post_parameters is a list of Key value pairs List<KeyValuePair<string, string>>

Problem is, when the HttpContent has a large value (an image converted to base64 to be transmitted) I get a URL is too long error. That makes sense - cause the url cant go beyond 32,000 characters. But how do I add the data into the HttpContent if not this way?

Please help.

I am confused...when you use any kind of `HttpContent`(including `FormUrlEncodedContent`) the data is in the body and not in Url..so how why are you seeing the data in the Url? — Kiran, May 17 '14 at 17:47
When I make the following call, dict.Add(new KeyValuePair("Base64FileData", image)); (Where image is the base 64 converted string). An exception is thrown. — Muraad, May 20 '14 at 14:22

score 69 · Accepted Answer · answered May 23 '14 at 17:36

69

I figured it out with the help of my friend. What you would want to do is avoid using FormUrlEncodedContent(), because it has restrictions on the size of the uri. Instead, you can do the following :

    var jsonString = JsonConvert.SerializeObject(post_parameters);
    var content = new StringContent(jsonString, Encoding.UTF8, "application/json");

Here, we don't need to use HttpContent to post to the server, StringContent gets the job done !

answered May 23 '14 at 17:36

Muraad

1,110
1
9
14

5

> Here, we don't need to use HttpContent to post to the server, StringContent gets the job done ! `StringContent` actually is `HttpContent` (it is derived from abstract `HttpContent` similarly to `FormUrlEncodedContent`) – eXavier Jun 09 '15 at 11:32
This is by far the easiest way. Anything else I've seen on here up to early 2016 is a PITA. – mafu Mar 11 '16 at 21:49
1

Worked for me, Thanks for the help. – Parveen Dec 19 '18 at 07:39

score 31 · Answer 2 · edited May 23 '17 at 12:02

31

FormUrlEncodedContent internally uses Uri.EscapeDataString : from reflection, I can see that this method has constants limiting the size of request length.

A possible solution is to create a new implementation of FormUrlEncodedContent by using System.Net.WebUtility.UrlEncode (.net 4.5) to bypass this limitation.

public class MyFormUrlEncodedContent : ByteArrayContent
{
    public MyFormUrlEncodedContent(IEnumerable<KeyValuePair<string, string>> nameValueCollection)
        : base(MyFormUrlEncodedContent.GetContentByteArray(nameValueCollection))
    {
        base.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded");
    }
    private static byte[] GetContentByteArray(IEnumerable<KeyValuePair<string, string>> nameValueCollection)
    {
        if (nameValueCollection == null)
        {
            throw new ArgumentNullException("nameValueCollection");
        }
        StringBuilder stringBuilder = new StringBuilder();
        foreach (KeyValuePair<string, string> current in nameValueCollection)
        {
            if (stringBuilder.Length > 0)
            {
                stringBuilder.Append('&');
            }

            stringBuilder.Append(MyFormUrlEncodedContent.Encode(current.Key));
            stringBuilder.Append('=');
            stringBuilder.Append(MyFormUrlEncodedContent.Encode(current.Value));
        }
        return Encoding.Default.GetBytes(stringBuilder.ToString());
    }
    private static string Encode(string data)
    {
        if (string.IsNullOrEmpty(data))
        {
            return string.Empty;
        }
        return System.Net.WebUtility.UrlEncode(data).Replace("%20", "+");
    }
}

To send large content, it's better to use StreamContent.

edited May 23 '17 at 12:02

Community

1
1

answered May 19 '14 at 14:27

Cybermaxs

24,378
8
83
112

I cannot use this solution because i am using .Net 4.0 and i do not have the access to the method UrlEncode(). I cannot upgrade due to work restrictions, any other thoughts? – Muraad May 20 '14 at 19:41
by adding a System.Web dependency, you could find a similar method HttpUtility.UrlEncode – Cybermaxs May 20 '14 at 19:59
the implementation you gave me has the same restrictions as FormUrlEcondedContent() , but now instead of throwing an exception it skips the call to post to the server. – Muraad May 21 '14 at 13:34
1

This solution has worked for me. I have some restriction in the api that I am consuming and I had to consume that using "application/x-www-form-urlencoded". Thanks. – jvrdelafuente Feb 13 '15 at 11:06
2

Just out of interest, whats happening here? .Replace("%20", "+") – GregoryBrad Oct 01 '15 at 04:09
1

Never said this to anyone on stack overflow. You're a total badass! – Mr. B Sep 15 '16 at 01:19
Was facing this issue do to an out of control viewstate on a site i dont control but need to interface with... this custom class saved my ass. :P thanks – Sicae Jun 09 '19 at 02:32

score 5 · Answer 3 · answered Jan 17 '18 at 18:19

This code works for me, basically you send post data "application/x-www-form-urlencoded" within string content over http client, hope this can help anyone with the same problem like me

void sendDocument()
    {
        string url = "www.mysite.com/page.php";
        StringBuilder postData = new StringBuilder();
        postData.Append(String.Format("{0}={1}&", HttpUtility.HtmlEncode("prop"), HttpUtility.HtmlEncode("value")));
        postData.Append(String.Format("{0}={1}", HttpUtility.HtmlEncode("prop2"), HttpUtility.HtmlEncode("value2")));
        StringContent myStringContent = new StringContent(postData.ToString(), Encoding.UTF8, "application/x-www-form-urlencoded");
        HttpClient client = new HttpClient();
        HttpResponseMessage message = client.PostAsync(url, myStringContent).GetAwaiter().GetResult();
        string responseContent = message.Content.ReadAsStringAsync().GetAwaiter().GetResult();
    }

But the OPs problem was posting large amounts of data, which you have not demonstrated can be done in this way. However I see what you are doing - using `application/x-www-form-urlencoded` but bypassing using `class FormUrlEncodedContent ` which seems to have the content length restriction. — HankCa, Feb 28 '18 at 03:47
This basically worked for me. The thing I changed was to use the `WebUtility.UrlEncode("prop2")` instead of `HtmlEncode`. I had a weird API end point that required a JSON array inside a form post body. Sometimes that array could be massive which is why I needed something like this. Good stuff! — Hallmanac, May 01 '18 at 10:45

How to set large string inside HttpContent when using HttpClient?

3 Answers3

Linked