Need to configure a response header with DownstreamHeaderTransform containing multiple values being separated by commas

[RahulBorana94]

Hi All,

Currently as per ocelot documentation for headers transformation, it does not support multiple header values using DownstreamHeaderTransform.

we are looking for a way to allow the same without customization and write our own logic for overriding headers like the below which obviously doesn't work:

"DownstreamHeaderTransform": {
  "Access-Control-Allow-Origin": "'*.domain1.com, *.domain2.com'",
  "Access-Control-Allow-Methods": "'GET, POST, PUT, DELETE'"
}

Has someone tried to successfully pass header with multiple values in current ocelot version 23.4.5 using DownstreamHeaderTransform?

If we need to override default DownstreamHeaderTransform functionality, can we replace this with our own implementation logic using DI? Not sure if this particular functionality is available to be replaced using DI.

Would look for suggestions from community on how they have handled this scenario.

Thanks,
Rahul Borana

[raman-m]

Hello, Rahul!
The problem is in used comma char , in header values!
Did you read this discussion? 👉

• How to return a comma in a header using `DownstreamHeaderTransform` json-option? #2249

Don't use comma in header value and everything will be fine. But if downstream services produce such a values with commas then you must encode value. So, the possible solution has provided in #2249 .
Other possible solutions:

• Fork Ocelot repo, develop special HeaderFindAndReplaceCreator class replacing , with something appropriate for your project.
• You are able to develop custom HeaderFindAndReplaceCreator service and replace it in DI container using the IHeaderFindAndReplaceCreator interface service 👇
  

  Ocelot/src/Ocelot/DependencyInjection/OcelotBuilder.cs

  Line 56 in 221a22f

  Services.TryAddSingleton<IHeaderFindAndReplaceCreator, HeaderFindAndReplaceCreator>();

---

Currently as per ocelot documentation for headers transformation, it does not support multiple header values using DownstreamHeaderTransform.

Ocelot doesn't support header which values contain commas , because this char is used for Find and Replace feature

we are looking for a way to allow the same without customization and write our own logic for overriding headers like the below which obviously doesn't work:

"DownstreamHeaderTransform": {
  "Access-Control-Allow-Origin": "'*.domain1.com, *.domain2.com'",
  "Access-Control-Allow-Methods": "'GET, POST, PUT, DELETE'",}

I've explained you above how to develop a custom solution which will support commas in headers. Also, please read #2249

Has someone tried to successfully pass header with multiple values in current ocelot version 23.4.5 using DownstreamHeaderTransform?

👉 #2249

If we need to override default DownstreamHeaderTransform functionality, can we replace this with our own implementation logic using DI? Not sure if this particular functionality is available to be replaced using DI.

Yes, we can! Replace the following interface service:

Ocelot/src/Ocelot/DependencyInjection/OcelotBuilder.cs

Line 56 in 221a22f

Services.TryAddSingleton<IHeaderFindAndReplaceCreator, HeaderFindAndReplaceCreator>();

Hope it helps!
Raman

[RahulBorana94]

thanks for providing possible solution approaches

currently, we use metadata for passing header
will also try your suggested solution approach

[raman-m]

I'm glad that you will try to implement our proposed solution.
Good luck!