Develop Reference

MultipartFormDataContent.Add StringContent is adding carraige return/linefeed to the name

formData.Add(sJobId,"job_id"); is sending "job_id\r\n" to the server
Here is my C# method:
public static async Task UploadAsync(string url, int job_id, string filename, string filePath) {
try {
// Submit the form using HttpClient and
// create form data as Multipart (enctype="multipart/form-data")
using (var fileStream = new StreamContent(System.IO.File.Open(filePath, FileMode.Open, FileAccess.Read)))
using (var formData = new MultipartFormDataContent()) {
StringContent sJobId = new StringContent(job_id.ToString());
StringContent sOthId = new StringContent(job_id.ToString());
// Try as I might C# adds a CrLf to the end of the job_id tag - so have to strip it in ruby
formData.Add(sOthId, "oth_id");
formData.Add(sJobId,"job_id");
fileStream.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
formData.Add(fileStream, "dt_file", filename);
HttpResponseMessage response = await HttpClient.PostAsync(url, formData);
// If the upload failed there is not a lot we can do
return;
}
} catch (Exception ex) {
// Not a lot we can do here - so just ignore it
System.Diagnostics.Debug.WriteLine($"Upload failed {ex.Message}");
}
}
This is what my Ruby puma server is receiving - see how oth_id and job_id have \r\n appended but "dt_file" does not.
Parameters: {"oth_id\r\n"=>"42157", "job_id\r\n"=>"42157", "dt_file"=>#<ActionDispatch::Http::UploadedFile:0x007f532817dc98 #tempfile=#<Tempfile:/tmp/RackMultipart20190715-37897-189ztb6.msg>, #original_filename="2019-07-15 164600.msg", #content_type="application/octet-stream", #headers="Content-Type: application/octet-stream\r\nContent-Disposition: form-data; name=dt_file; filename=\"2019-07-15 164600.msg\"; filename*=utf-8''2019-07-15%20164600.msg\r\n">}
How do I stop the formData.Add appending a \r\n to the name?

The raw message the application is sending to the server is
POST https://example.com/ HTTP/1.1
Host: example.com
Content-Type: multipart/form-data; boundary="93655e5a-b6b3-48d6-82c9-0d9aa99164cc"
Content-Length: 522
--93655e5a-b6b3-48d6-82c9-0d9aa99164cc
Content-Type: text/plain; charset=utf-8
Content-Disposition: form-data; name=oth_id
1234
--93655e5a-b6b3-48d6-82c9-0d9aa99164cc
Content-Type: text/plain; charset=utf-8
Content-Disposition: form-data; name=job_id
1234
--93655e5a-b6b3-48d6-82c9-0d9aa99164cc
Content-Type: application/octet-stream
Content-Disposition: form-data; name=dt_file; filename=myfile.txt; filename*=utf-8''myfile.txt
a,b,c,d
aa,"b,b","c
c",dd
aaa
--93655e5a-b6b3-48d6-82c9-0d9aa99164cc--
Have a look at the name values.
Looking at RFC 7578 I can see in every example, that the value for name is always quoted.
Content-Disposition: form-data; name="user"
I did not find any hint if it is mandantory or not to quote the values, so I cannot judge who is wrong here.
To get such quoted name values you only have to quote the values in code.
public static async Task UploadAsync(string url, int job_id, string filename, string filePath) {
try {
// Submit the form using HttpClient and
// create form data as Multipart (enctype="multipart/form-data")
using (var fileStream = new StreamContent(System.IO.File.Open(filePath, FileMode.Open, FileAccess.Read)))
using (var formData = new MultipartFormDataContent()) {
StringContent sJobId = new StringContent(job_id.ToString());
StringContent sOthId = new StringContent(job_id.ToString());
// Try as I might C# adds a CrLf to the end of the job_id tag - so have to strip it in ruby
formData.Add(sOthId, "\"oth_id\"");
formData.Add(sJobId,"\"job_id\"");
fileStream.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
formData.Add(fileStream, "\"dt_file\"", filename);
HttpResponseMessage response = await HttpClient.PostAsync(url, formData);
// If the upload failed there is not a lot we can do
return;
}
} catch (Exception ex) {
// Not a lot we can do here - so just ignore it
System.Diagnostics.Debug.WriteLine($"Upload failed {ex.Message}");
}
}
which will now post this
POST https://example.com/ HTTP/1.1
Host: example.com
Content-Type: multipart/form-data; boundary="c33cdc86-db44-40ef-8e6e-3e13a96218d1"
Content-Length: 528
--c33cdc86-db44-40ef-8e6e-3e13a96218d1
Content-Type: text/plain; charset=utf-8
Content-Disposition: form-data; name="oth_id"
1234
--c33cdc86-db44-40ef-8e6e-3e13a96218d1
Content-Type: text/plain; charset=utf-8
Content-Disposition: form-data; name="job_id"
1234
--c33cdc86-db44-40ef-8e6e-3e13a96218d1
Content-Type: application/octet-stream
Content-Disposition: form-data; name="dt_file"; filename=myfile.txt; filename*=utf-8''myfile.txt
a,b,c,d
aa,"b,b","c
c",dd
aaa
--c33cdc86-db44-40ef-8e6e-3e13a96218d1--
Just found a pull request for PowerShell
// .NET does not enclose field names in quotes, however, modern browsers and curl do.
contentDisposition.Name = $"\"{LanguagePrimitives.ConvertTo<String>(fieldName)}\"";

Formatting of multipart HTTP request body output with restsharp

I am creating a restsharp request in order to trigger a batch direct send push request off to Azure notification hub.
I am receiving a 400 Bad Request response, with the message; Could not find 'notifications' part in the multipart content supplied.
The request looks like such;
const string multipartContentType = "multipart/form-data; boundary=\"simple-boundary\"";
const string authSignature = "myvalidauthsignature";
const string url = "mynotificanhuburl";
const string message = "Some message";
var restClient = new RestClient
{
BaseUrl = new Uri(url),
Proxy = new WebProxy("127.0.0.1", 8888),
};
var request = new RestSharp.RestRequest(Method.POST)
{
RequestFormat = DataFormat.Json,
AlwaysMultipartFormData = true
};
request.AddHeader("Content-Type", multipartContentType);
request.AddHeader("Authorization", authSignature);
request.AddHeader("ServiceBusNotification-Format", "gcm");
request.AddParameter("notification", JsonConvert.SerializeObject(new { data = new { message } }), ParameterType.GetOrPost);
request.AddParameter("devices", JsonConvert.SerializeObject(new List<string> { "123", "456" }), ParameterType.GetOrPost);
var response = restClient.Execute(request);
I can see the raw request via Fiddler;
POST https://xxxxx.servicebus.windows.net/xxx/messages/$batch?direct&api-version=2015-04 HTTP/1.1
Authorization: [redacted]
ServiceBusNotification-Format: gcm
Accept: application/json, application/xml, text/json, text/x-json, text/javascript, text/xml
User-Agent: RestSharp/105.2.3.0
Content-Type: multipart/form-data; boundary=-----------------------------28947758029299
Host: [redacted]
Content-Length: 412
Accept-Encoding: gzip, deflate
Connection: Keep-Alive
-------------------------------28947758029299
Content-Disposition: form-data; name="notification"
{"data":{"message":"Some message"}}
-------------------------------28947758029299
Content-Disposition: form-data; name="devices"
["123","456"]
-------------------------------28947758029299--
Which looks about right. If I copy this into postman with the headers etc, I can see the same error response. HOWEVER in postman when I remove the quote marks around the parameter names, it works and returns a 201 Created response.
So this works....
Content-Disposition: form-data; name=notification
This doesn't
Content-Disposition: form-data; name="notification"
Which seems really peculiar. As we are using restsharp however I don't think I have any direct control over the raw output for the request body. I am wondering;
Is there a restsharp setting to manage these quote, perhaps a formatting setting
Why would the Azure endpoint reject a parameter name with quotes
It is possible that the issue is elsewhere and this is a red herring, but this does seem to be responsible.
Appreciate any help...

According our documentation, request should look like this:
POST https://{Namespace}.servicebus.windows.net/{Notification Hub}/messages/$batch?direct&api-version=2015-08 HTTP/1.1
Content-Type: multipart/mixed; boundary="simple-boundary"
Authorization: SharedAccessSignature sr=https%3a%2f%2f{Namespace}.servicebus.windows.net%2f{Notification Hub}%2fmessages%2f%24batch%3fdirect%26api-version%3d2015-08&sig={Signature}&skn=DefaultFullSharedAccessSignature
ServiceBusNotification-Format: gcm
Host: {Namespace}.servicebus.windows.net
Content-Length: 431
Expect: 100-continue
Connection: Keep-Alive
--simple-boundary
Content-Type: application/json
Content-Disposition: inline; name=notification
{"data":{"message":"Hello via Direct Batch Send!!!"}}
--simple-boundary
Content-Type: application/json
Content-Disposition: inline; name=devices
["Device Token1","Device Token2","Device Token3"]
--simple-boundary--
So, the name parameter's value is not quoted (name=devices). I've not found any RFC which would explicitly specify requirements regarding the situation. However, in examples inside of RFCs a values appear quoted. And because of that I'm going to fix the service to support both options. Fix should come with next deployment in a week or so.

I was plagued by this for a few days and was diligently searching for a solution with RestSharp and was unable to find one as it always default the content type to "multipart/form-data". I know the OP was looking for a way to do this with RestSharp but I don't believe there is currently.My solution comes from a few different posts over a few days so I apologize for not linking to them. Below is a sample Function to perform a multipart/related POST with json body and base64 pdf string as the file.
public static void PostBase64PdfHttpClient(string recordID, string docName, string pdfB64)
{
string url = $"baseURL";
HttpClient client = new HttpClient();
var myBoundary = "------------ThIs_Is_tHe_bouNdaRY_";
string auth = Convert.ToBase64String(Encoding.UTF8.GetBytes($"UN:PW"));
client.DefaultRequestHeaders.Add("Authorization", $"Basic {auth}");
HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, $"{url}/api-endpoint");
request.Headers.Date = DateTime.UtcNow;
request.Headers.Add("Accept", "application/json; charset=utf-8");
MultipartContent mpContent = new MultipartContent("related", myBoundary);
mpContent.Headers.TryAddWithoutValidation("Content-Type", $"multipart/related; boundary={myBoundary}");
dynamic jObj = new Newtonsoft.Json.Linq.JObject(); jObj.ID = recordID; jObj.Name = docName;
var jsonSerializeSettings = new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore };
var json = JsonConvert.SerializeObject(jObj, jsonSerializeSettings);
mpContent.Add(new StringContent(json, Encoding.UTF8, "application/json"));
mpContent.Add(new StringContent(pdfB64, Encoding.UTF8, "application/pdf"));
request.Content = mpContent;
HttpResponseMessage response = client.SendAsync(request).Result;
}

How to flash a spark core from C#

I am trying to flash a spark core from a C# application. I keep getting { error: Nothing to do? } response.
Below is my code
var url = string.Format("https://api.spark.io/v1/devices/{0}", sparkDeviceID);
using (var client = new HttpClient())
{
client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", accesstoken);
using (var formData = new MultipartFormDataContent())
{
HttpContent fileContent = new ByteArrayContent(Encoding.ASCII.GetBytes(rom));
//client.SendAsync()
formData.Add(fileContent, "file", "file");
var response = client.PutAsync(url, formData).Result;
if (!response.IsSuccessStatusCode)
throw new Exception("An error occurred during rom flash!");
var responseStream = response.Content.ReadAsStreamAsync().Result;
using (var reader = new StreamReader(responseStream, true))
{
var result = reader.ReadToEnd();
}
}
return true;
}
The documentation reads:
The API request should be encoded as multipart/form-data with a file field populated.
I believe the problem is the endpoint doesn't see the file. Any idea on how to resolve this?

Finally got it working.
The issue was the way .NET generated the content-disposition header for the file form data.
I used fiddler to compare the output of a successful put request to the put request that my code was generating:
Successful PUT request generated using CURL:
PUT http://127.0.0.1:8888/ HTTP/1.1
User-Agent: curl/7.33.0
Host: 127.0.0.1:8888
Accept: */*
Content-Length: 2861
Expect: 100-continue
Content-Type: multipart/form-data; boundary=------------------------5efcf64a370f13c8
--------------------------5efcf64a370f13c8
Content-Disposition: form-data; name="file"; filename="ms.ino"
Content-Type: application/octet-stream
...
My PUT request (unsuccessful):
PUT https://api.spark.io/v1/devices/{deviceid} HTTP/1.1
Authorization: Bearer {access_token}
Content-Type: multipart/form-data; boundary="135f5425-9342-4ffa-a645-99c04834026f"
Host: api.spark.io
Content-Length: 2878
Expect: 100-continue
--135f5425-9342-4ffa-a645-99c04834026f
Content-Type: application/octet-stream
Content-Disposition: form-data; name=file; filename=file.ino; filename*=utf-8''file.ino
...
If you'll notice the difference in the Content-Type for the actual file being sent:
Successful: Content-Disposition: form-data; name="file"; filename="ms.ino"
Unsuccessful: Content-Disposition: form-data; name=file; filename=file.ino; filename*=utf-8''file.ino
Most specifically, the resolution was to add quotes around the name attribute.
Resolution:
formData.Add(fileContent, "\"file\"", "file.ino");

A JSONObject text must begin with '{' at character 0 when posting multipart

I am trying to do a multipart call in C# from windows phone.
I am sending the exact same json of a working android call but from wp I am getting this response body:
"errorNumber":90 - A JSONObject text must begin with '{' at character 0 of "}
The first char I am sending is {.
Why does it happen?
Here is my code:
public async Task postHttpClient(string serviceUrl, string requestObj)
{
Debug.WriteLine("postHttpClient");
try
{
var client = new HttpClient();
client.DefaultRequestHeaders.TryAddWithoutValidation("Content-Type", "multipart/form-data");
Debug.WriteLine("requestObj: " + requestObj);
Debug.WriteLine("curly brace should be expected: " + (int)requestObj.Trim().ElementAt(0));
MultipartFormDataContent content = new MultipartFormDataContent();
var contentData = new StringContent(requestObj.Trim());
content.Add(contentData);
var responseVar = await client.PostAsync(serviceUrl, content);
responseVar.EnsureSuccessStatusCode();
Debug.WriteLine("responseVar: " + responseVar.ToString());
var body = await responseVar.Content.ReadAsStringAsync();
Debug.WriteLine("body: " + body);
}
catch (Exception e)
{
Debug.WriteLine("e: " + e.ToString());
}
}
and my fiddler:
Raw Headers
POST /MyServer/SendActivity/ HTTP/1.1
Accept: /
Content-Length: 703
Accept-Encoding: identity
Content-Type: multipart/form-data; boundary="e8763d7d-a53d-4baa-a6c7-c3bc37bd52a6"
User-Agent: NativeHost
Host: merp.techmobile.eu:8080
Connection: Keep-Alive
Pragma: no-cache
Textview tab
--e8763d7d-a53d-4baa-a6c7-c3bc37bd52a6
Content-Type: text/plain; charset=utf-8
Content-Disposition: form-data
{"SendActivityRequest":{"activity":{...

It might help someone to know that I fixed it by adding a key to my json,
By changing this line: content.Add(contentData);
to this content.Add(contentData, "request");

c# .NET multipart/form-data Upload A File

I want to create an application to automaticly upload a file to googles SearchbyImage-tool
https://www.google.de/searchbyimage/upload
Google is using a multipart/form-data for submitting the file, something like that:
Content-Type: multipart/form-data; boundary=---------------------------265001916915724
Content-Length: 9989
-----------------------------265001916915724
Content-Disposition: form-data; name="image_url"
-----------------------------265001916915724
Content-Disposition: form-data; name="encoded_image"; filename=""
Content-Type: application/octet-stream
-----------------------------265001916915724
Content-Disposition: form-data; name="image_content"
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XZ8MZzjx-2QGRGr-hjrsLQyPDBp8Heu0dfGIizTAMo25YNNnItJ4WtTpdori_Yq68yL6tbeiBbsPNTuGgbUhIjau9qyIQo58xtXXvminyA5mxrSaR5w8zx98nTVI9h3RnriPKa2vfSuiYbXNvyciXuK9FgGx2ldpHWJCvJ9bzxCMbWj_veMZaaeLyAiS53PBkMm-y_Gr9v39c3_uvV--P7elACdu-nsk_vgS1I1_DXqdrqlWt4rV-hyua8fqbTVOTUDo-Lzy1sfjkXfo_LFIC2MnBSNuPy9svtj44uqDVz9Y-2puRYQobf0x6a9XH-R7BVJ4Lbus2d2FBVbN7mStZvdQQts4jetD9dcEhXhE0zCeqPFzOfIor_08bT259NFikI3rRbLyQp6B6y--vHT74rU39N5tf0keJA9aL-b9z48vzPa5L8ovyNlVJy8384OSGKN7kp28vHhxje3o8u_dffdk4eQ2NEE4vJ_sqMJTTy7LsLNrcDYz7ey6nFrO5sZxdk39Mji7hv31V4_fi6dzRuKRe27FgyN_jPtG3IDxM1aglmW_sSNo0NzVgaqzbdhc3YaZW45h2D2_xLKPy2xMG41ndf2Lxkf8VF0f_gzFtwpHMRLItJ_HwgcXuP_78IaWsRcb30bh3ZDPNWdXzofHP7hOzyDU8KoBTxrlz_FpbPwfz97o-LCNlYDyIFZjUxILNnXhyieAlctmozuRC6y5HA98fDPWla3Av8z9OvBvV7L40kqXPxbuj4TgM9f4ZZmcOMPIJz-vPL3v1X7sxe8a_rPmSOJvk_-l4Un9-Qb9sZ1ilz-Xin8QjB9czi6PqChnVx59n0QjS1_mbBVPy6xidbqHGYDfV9mC4sPN2Fna5HJ2RURGc6ZsD99ySGUExXFIeY2rYLSs78jvO8J23sv73O1bER7N2RWnAGvgXdTsav2xGTTrGc7nkjIXEbSw_itGVo3HGq86VMg3XqsGWY3R6b8WoXE9zys___svr7gcX_3JJWj7YjfWbCzEwvc_spndU80d9v95rW55QzsO1LZh5ZaEcHYj58fqrzTIGgNuydSRr1ToqPnjETdnfsPmK157Zv2QfeVzIOcvXf2xMgRizAdfIyaQUn9KZj7wgFBZgmU_6FFiIU_D_HJDYTmnzufSOIgIl2bMxefCsMg1pLfnHr9zyrWdxszvVzUVloFPuNaLpv-W8Rc1KkKepvUXX17u9e0YI6M8Ysif2lPrM9peuO0Z3U_yoPWXDfsR5OzyQ2uK7v2-uE6x0iPO7M6adRRr1h6xvzJ8-G_xoxtexphXcnG4PonXpxTijjsYC-R7pcnsWnW84WnEUSczx6jj5ayu-lkk7eeLVL2u-flBadDuwUu8Em3fFq0sxKbK06hsA_Y3tmPXsXNYd7AFryz7HNcN5-eacJykrgg863qeCd8o51aC9QSvKdScAYk_g_ZXpz3uADj414RvdDwQ8nkm9n_NOZd418F4wfg2Cu8Gfc7b52SRTJE14hFff9z-hcKywfJXzlkc_B-tX4oMMeHD_3yT6UNpNy6_h5UuVC1C_dzLsKpsA4Yu-VsUTbsL3YzMwlWXe_wh3V5bDLnL_wjQH1XjbDvzVkatER-H6Y_j7Lrxv1pvVvqy8Ad0_Q7Dk-p5Un9sf0P4h4ocNK-naH8xeH8Tzq4ewVLObqt1IiD_jbc6BuKrWVrmEVanywH8niPN2HWgCVu_Oudydv0RVTkRzksO0n6eUFTtxVOHvR4975-IAOj3ccYwLCKhRXhcVL5iiP0MrYzu-Ptin1LrjVi42nUYavsAIDEWFZFwt-tjgH2McnAEadcbb6DsL_4UDUcTxhrdo8zJ5XW6ZSx9-eCxNuyvcZzdlOfHxYAbIj6R82cdDpZgv6PLZOHIxjR_Zln59UGLMBnmlo_R_l0yaw7i6U98RomvEQ5SWlk0Pn_Tl3hfMLtb2GnMn9qnMR9gaf5flbdErA8pE1ET4mLcrYwB1X_1u9NcjdhhX3YGQ8D4ZY2MfPEDqpyMB-2wNutnjuR6lOtBFvnLl71JBK6_-PLqz4xMnIwLGl-8iHdfZNxofilDozfWr98xhSAW-B5y8Eg19h6oYgfVVGJLcSUmTz4imN3WdqCFMZC1rLj0i9JT7ORgfnpwPUrrgeG3TPM06f2dXa_z6X5vHxRlPKBK1fpmOo1Z72MOchSzK0biPjjLfECVVoPsGX0qGTFj5uXhk9p2fFLTjbUV7Xjr4wrc-fgk_HbMA54MvFQy8qLwkXLCgjIAw_CtzIhUQXE3vonImHPh6XT2f9m-jg0cBi8uvjXgbRfe8f_ObvXymfbhR3x9qvroUdZ4zP3xMMQufBoifzuDNAr_x8s40fEhP1WdB7H4qeossRXLtnTgsjvq0X1gHEqnXor_2ToCxcd34MYP_w4duQtR_9eXGTJkIzJCjf6RPtfF4ictFRHo4EHp6Ie_V_uD15fj2FLNkcSvTg17GJ40ZUAouev-YdR64lg4wF8M8KeEs6tHxNREeQ3wx0XlWLflCFZtKhOpHuqy6xuIkQmJyMSLCMWNOBdMmY5k42kcLC_H_rJyFB-oRNFXldi8pwqf7q5CflEC63Yk8MHWhGB1FbMbt_04EdKLmSEJAimmNZL19eGKKBMjGJcBuJj1m9Z_Zu01yZPkGeTsuplEySjOnVOKLTtrwM4DFY4uv8oakuLiju6SvMO4847JpiYv2r-laq8ffnUBxi4qwnMzP8Wtj03FxBduxukDE7D4HVMGXKb1VzGWfWU_NjGGUYxetjJEvIxfPEY_Vf24kPtN-LDkQC2-_iAw_v1WXHpLKbq_eBj7pl6C0dtuxidH1-D6ed9Cx3tTUPqNS2NlKFxI_3p-PwrTp-zNl7Fm12SAo_5GEfLeiZAn_-prOPLNP8ADN9zuSbnR02_M_--NCHYqEdb-2h9uzKLWg_fzbK0Pwaa7aniJkSWGMV6Eur-uT5pfmt9s2dug_S8VL3T27L2YNuNz4fByR7fqFEu5TSSxu6IDm_aexsOPrcDUqetSaXLA33uh833b7cNRNPMfcPrg77Bk2ugIhvcC15dVuiROcfZkdGXnfVhNbVANZ-_gXb88-lp__HjKhA-nzVuFy0Y247FZCVzy433C0eXXTz67BksOzcD1c76F1gm_wr4rLgmp2e0r-hKl_1E12lHf75nPfTW7fTtikOkIW_9rr_qRe7H8ppusmtr-13_Sr56OiLp_V1oc-e-qie_p51P7lEHRVxgLso9kb_uGPUrV25w7ZyfGv16I1XmVWLryIKbNK8acBV_iIfZ7u2PHsJ8uoZdLApnI2Bkx4lZ2puZ38OxDN_YMvrJP_fWfuZGJ_qfP2IXV1HprgLO9nvpaf-LL44-GVwpHl19qvodtGIzpe8fj-2__pXB0dWc3_fnM9v4bVaOdnf75anYvNEJG389WxIsYO2J0eiYiRgxff4mo0vzT_kP7T1-0V-n4pjOmb8Hzz32AUaMW4PbbZ-P-_56OSRPXptPUgP9OphjR5559BgX5S_sI40r2fKDb86Ervo1hK_4R3534tQHA6PZtffXV7GY3wpQdj7__RlBIXqSv2auBIAaT1h-tP1p_tH9GZxBsKdoz4B3ObA1w--79nl_RiJ4PyniIz0jS-iZ9GgjrxVezm6kI2UCPyND4iEHoiwwCrV_KcKAMh74dYab5ufjmJ-fJcSivqsmWPzhgn1vfcAq__PXUnq2xtcqAaL-nDCfCV_0XXzFndxQzFPKSERx6T_IgfaD1QPaA7CHtB7QfEh4gPEB4gPAA4QHCA_0bDwhnV0asnE2N3pM8SB9oPSgdIHtA9oDsAdkDsgdSB8gekj0ke0j2kOxh_7KHwtmliEX_jljQ_NH8EQNFDBQxUMRA0X5OeIbwAOEBwgOEBwgPuPGAK42ZIpYUsaSIJUUsKWLZvyKWNF80X8Q4EuNK-I3wG-E3wm-EB8x4gGp2qUaZarapZp1q9inDhTJ86MwKOrOD8ADhAcIDhAcIDww4PEA1u1SDQzVIVLNONft0ZoGtA8QQEUNEDBExRMQQUcYIZYxQxshAwQP_D1qk899cHOG9AAAAAElFTkSuQmCC
-----------------------------265001916915724
Content-Disposition: form-data; name="filename"
filename.bmp
-----------------------------265001916915724
Content-Disposition: form-data; name="num"
10
-----------------------------265001916915724
Content-Disposition: form-data; name="hl"
de
-----------------------------265001916915724
Content-Disposition: form-data; name="bih"
976
-----------------------------265001916915724
Content-Disposition: form-data; name="biw"
1920
-----------------------------265001916915724--
I have absolutely no idea on how to do that in C#... Any suggestions?

using c# you can use HttpClient to do the Post Multi-part Form Data.
below is the code snippet that i tried and worked for me..
give it a try!!
using (var client = new HttpClient())
{
//client.DefaultRequestHeaders.Add("User-Agent", "CBS Brightcove API Service");
string authorization = GenerateBase64();
client.DefaultRequestHeaders.Add("Authorization", authorization);
using (var content = new MultipartFormDataContent())
{
string fileName = Path.GetFileName(textBox1.Text);
//Content-Disposition: form-data; name="json"
var stringContent = new StringContent(InstancePropertyObject);
stringContent.Headers.Remove("Content-Type");
stringContent.Headers.Add("Content-Type", "application/json");
stringContent.Headers.Add("Content-Disposition", "form-data; name=\"instance\"");
content.Add(stringContent, "instance");
var fileContent = new ByteArrayContent(filecontent);
fileContent.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
{
FileName = fileName
};
content.Add(fileContent);
var result = client.PostAsync(targetURL, content).Result;
Console.Read();
}
}

You could use WebClient's upload file method. You could use headers property to assign packet's headers. A few caveats with WebClient are: setting timeout, unzipping gzipped responses and finally if you intend to make multiple simultaneous requests removing connections limit