How to return a comma in a header using DownstreamHeaderTransform json-option?

[flfaure-pro]

I would like to return the following header using DownstreamHeaderTransform:
Cache-Control: public, max-age=1800

So I added the following code to my route:

"DownstreamHeaderTransform": {
    "Cache-Control": "public, max-age=1800"
},

However, the comma is used to replace values, so it doesn't work: Find and Replace

Is there any way to escape it?

[raman-m]

Try to encode the header value by online tool: https://www.urlencoder.io/
Try to escape comma explicitly in the value and define the following transformation:

{
  "DownstreamHeaderTransform": {
    "Cache-Control": "public%2C max-age=1800"
  },
  // ..
}

I believe the browsers should understand it.

[flfaure-pro]

Thx for your answer. I tested but it doesn't fix my problem because the encoded chars are not replaced by ocelot and they are forwarded like that.

[raman-m]

The comma syntax is an old convention for header transformations. If the header value contains a comma, Ocelot gets confused and attempts to perform a Find and Replace operation, resulting in the header being absent in the response. Therefore, we need an alternative solution...

[raman-m]

The comma is hard-coded as a delimiter in the HeaderFindAndReplaceCreator class, lines below 47:

Ocelot/src/Ocelot/Configuration/Creator/HeaderFindAndReplaceCreator.cs

Lines 47 to 49 in d1ecfaf

	foreach (var input in fileRoute.DownstreamHeaderTransform)
	{
	if (input.Value.Contains(","))

Ocelot has no options to specify custom delimiter. It needs to be developed. No such sub-feature.

To implement this solution using C#, you need to:

• Override PreErrorResponderMiddleware using the Middleware Injection feature. In the response, locate the Cache-Control header with an invalid value and correct it.
• Keep the escaped string in JSON: "Cache-Control": "public%2C max-age=1800" to allow Ocelot to add the header to response
• In the overridden PreErrorResponderMiddleware, find the header from context.Response.Headers and decode the value using the HttpUtility.UrlDecode method

[flfaure-pro]

Thx for the solution. I'll try this as soon as I can.

[raman-m]

What I wonder is Why do you transform downstream response headers including Cache-Control?
Does Ocelot swallow it or change somehow?

[flfaure-pro]

It's not really a transformation, it's more an addition. I don't want my downstream services to manage that header. I want to add it at the gateway level : https://ocelot.readthedocs.io/en/latest/features/headerstransformation.html#add-to-response

[raman-m]

Got it! My answer with the solution to implement with custom C# code.
Are you a C# developer, or do you prefer to write JSON in route configuration?

[flfaure-pro]

Yes I am a C# developer. But having the possiblity to implement the solution directly in the JSON route config might be useful as well :)

[raman-m]

If you would like this feature, you need to contribute by proposing the "delimiter in JSON" feature. Any pull requests are welcome!
Our development process can be found here: Development Process