Rest request body is sometimes truncated

moondaddy 911

I have an Asp.net API app where one of the API’s requests are randomly missing some of the body’s content starting from the end. All of the other APIs are very small in size so we don’t notice any issues with them. This API receives a serialized images from mobile devices and the request is no larger than 20mb in size.

Most of the time everything is OK, but randomly some requests are truncated. Its not because they are too big as some as theh would be less than 10mb in size if they were not truncated.

This is not an issue with the API because we use a logger module to log every request as a text file before it hits the endpoint so we can see exactly what is coming into the server. These requests are truncated by the time they hit the server and before they get to the endpoint/API.

Also, we know that the requests are in good shape when it leave the device.

This is an example of one of the requests:

HEADERS  
Content-Length : 11237420  
Content-Type : text/plain; charset=utf-8  
Accept-Encoding : gzip  
Host : cmtafr-prod.nwis.net  
User-Agent : Dart/2.17 (dart:io)  
deviceid : xxxx  
appversion : 2.21.9  
cap2.0_tokenkey : xxxx  
osversion : 31  
devicebrand : Android  
devicemodel : SM-G973U  
  
PATH  
/api/IssueController/ExecuteIssue_UploadImageV2/5c2b4f27-6026-434e-a52f-a9dc495023a8  
  
BODY  
{"Isu_Id":"EC47DA70-672F-42A7-B6C2-F727DCFA8B56","ImageData":"/9j/4AAQSkZJRgABAQAAAQABAAD/2wC....

We have talked to the datacenter where this is hosted and they don’t know of anything in their environment that could be causing this (but its possible there could still be a problem in their environment).

I am really stuck and this is a huge problem. Can anyone suggest a way to trouble shoot this and/or a way to make uploading serialized image to an API “bullet proof”?

Thank you

Lan Huang-MSFT 25,556 Reputation points Microsoft Vendor

2022-10-31T08:29:45.773+00:00
Hi @moondaddy ,
First, I think you can enable tracing, check the trace log.
https://learn.microsoft.com/en-us/aspnet/web-api/overview/testing-and-debugging/tracing-in-aspnet-web-api
Second, you can check if the problem is caused by the following points.

Is there a limit to the send buffer size in your application settings? Or set up middleware for response interception?

Check if you can use JSonConvert.SerializeObject() to serialize the json object before returning and fix any issues you find.

Check the Content-Type.

Best regards,
Lan Huang
AgaveJoe 26,136 Reputation points

2022-10-31T12:50:16.423+00:00

Can anyone suggest a way to trouble shoot this and/or a way to make uploading serialized image to an API “bullet proof”?

Keep in mind, you've provided no code or explained the design details. What does serialized image mean? Base64 encoding??? Not Base64 encoding the image while using text/pain content-type is problematic.

I would troubleshoot the client code since since it creates the request. Look at the the HTTP headers you are using a HttpClient library named Dart.IO??? Have you reached out to Dart.IO support? What troubleshooting steps have you preformed on the client?

How are you determining the text is truncated? The content-length header does not match the actual bytes in the HTTP body?
moondaddy 911 Reputation points

2022-10-31T15:09:23.977+00:00

Thanks @Lan Huang-MSFT . There is no buffer limit in the app. Requests up to 20mb in size are often processed with no problem while smaller requests can have this problem. Can you please clarify these 3 point as I don't understand: 1) set up middleware for response interception? 2) Check if you can use JSonConvert.SerializeObject() to serialize the json object before returning and fix any issues you find. 3) Check the Content-Type. - the content type is text.
moondaddy 911 Reputation points

2022-10-31T15:20:27.637+00:00

Thanks @AgaveJoe . Yes its Base64 encoding. How do I determine the text is truncated? its obvious for 2 reasons - its json and is missing he ending curly bracket and usually the smallest requests are 5mb in size and if its much smaller its always truncated - and I can confirm by seeing its missing the curly bracket. What is to trouble shoot in client-side code? if it created json missing and ending bracket, then we would get an exception before it leaves the client
AgaveJoe 26,136 Reputation points

2022-10-31T15:48:24.553+00:00

if it created json missing and ending bracket, then we would get an exception before it leaves the client

I'm simply going by the HTTP header you provided which defines the content as plain text (Content-Type : text/plain; charset=utf-8) not JSON. As far as the client and server is concerned the payload is text not JSON.

Does the content-length header match the number of bytes in the HTTP message body? Have you tried contacting Dart.IO support to make sure the library is being used correctly?
moondaddy 911 Reputation points

2022-10-31T16:06:10.007+00:00

Hi @AgaveJoe the length does of the request does not match the length in the header. I'm looking at one now "Content-Length : 9595788", but the actual request size that hi the server is 765kb. i have not tried reaching out to Dart support. I had also been able to reproduce this (but not very often) using postman which has nothing to do with dart.
Lan Huang-MSFT 25,556 Reputation points Microsoft Vendor

2022-11-01T07:33:20.75+00:00

Hi @moondaddy ,

its json and is missing he ending curly bracket

You can use JSonConvert.SerializeObject() to serialize the json object before returning and fix any issues you find.

Check the Content-Type.

You said your content-type was text, but you mentioned JSON. Have you checked that your types are consistent.

the smallest requests are 5mb in size and if its much smaller its always truncated

From your description, it seems to only truncate when the request is small. In the question you said they would be less than 10mb in size if not truncated, then you said the minimum request size is 5MB. Have you configured limit request size. It may be truncated because the minimum request is limited. It is best to check whether the configuration of the client and the server is consistent.
moondaddy 911 Reputation points

2022-11-04T05:42:34.88+00:00

where would a size limit be set? nothing is set in the webconfig.
moondaddy 911 Reputation points

2022-11-04T05:45:51.25+00:00

Does it matter if the header says text and the content is json? json is just text anyway.

No the header content-length and actual content sizes do not match. the header content-length is always correct for what the image should be.

No i have not contacted dart. thats google and I have never had good response from anything google.
Lan Huang-MSFT 25,556 Reputation points Microsoft Vendor

2022-11-04T10:01:44.317+00:00

Hi @moondaddy ,
You can check maxRequestLength and maxAllowedContentLength in web.config.
See the documentation for details:
https://learn.microsoft.com/en-us/dotnet/api/system.web.configuration.httpruntimesection.maxrequestlength?view=netframework-4.8
https://learn.microsoft.com/en-us/iis/configuration/system.webserver/security/requestfiltering/requestlimits/#attributes
AgaveJoe 26,136 Reputation points

2022-11-04T11:23:39.477+00:00

Does it matter if the header says text and the content is json? json is just text anyway.

Of course it matters! HTTP is a text based protocol. Since everything is text, the content-type header tells the receiver what data format to expect. Otherwise the receiver must guess or know the data format ahead of time.

You've shared no code so it is impossible to figure out what's wrong. I suspect a bug in middleware that reads the HTTP stream but that is just a guess.