How to set large string inside HttpContent when us

问题:

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.

回答1:

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 !

回答2:

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.

回答3:

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();
    }