I'm trying to write a plugin that alters HTML files served by Ktor. In `onCallRespond` / `transformB...

# ktor

[Marc Plano-Lesay]

I'm trying to write a plugin that alters HTML files served by Ktor. In onCallRespond / transformBody, the data argument I get is Any. When printing its type when a static HTML file is served, I get a io.ktor.server.http.content.PreCompressedResponse (I don't have compression configured on this server). Is there a way to get the actual body?

[Marc Plano-Lesay]

I'm also not too sure how to get the served file type - how to determined whether it's an HTML file or not. I could do without that though.

[Aleksei Tirman [JB]]

You can call the readFrom() method of the PreCompressedResponse object to get a ByteReadChannel which can be used to read a content. A content of a file isn’t actually compressed.

[Marc Plano-Lesay]

That's what I just found - I had to dig a bit as as far as I can tell, PreCompressedResponse isn't in the documentation. I also have to cast it, as it comes out as an Any, but I can live with that.

[Marc Plano-Lesay]

I figured out how to read the content, but how can I write, or replace the content? Just returning a String from transformBody results in a 406 Not Acceptable

[Marc Plano-Lesay]

I take that back - returning a String returns it as plain text

[Marc Plano-Lesay]

I need to set the content type somehow I guess

[Aleksei Tirman [JB]]

Doesn’t the contentType property of PreCompressedResponse contain a value for the Content-Type header?

[Marc Plano-Lesay]

Err sorry you're right, I was so focused on reading the channel that I didn't look at the other OutgoingContent.ReadChannelContent attributes. It does have the Content-Type set to text/html, which is great. I can filter out HTML files easily.

Now is there a canonical way to replace the response body by conserving the headers etc?

[Marc Plano-Lesay]

(I'm actually a bit surprised that transformBody doesn't do just that)

[Aleksei Tirman [JB]]

Should the Content-Length header be modified too?

[Marc Plano-Lesay]

I assume it would need to be modified indeed, but returning a String from transformBody seems to override every header regardless - Firefox receives a text/plain with the proper Content-Length

[Marc Plano-Lesay]

I assume I need to construct some sort of response object, but I really don't know where to start looking at, the documentation around plugins seems to be a bit scarce

[Marc Plano-Lesay]

Oh, actually, I guess any kind of OutgoingContent subclass would do...

[Marc Plano-Lesay]

Yep, using a WriterContent setting both the body and contentType works just fine

[Marc Plano-Lesay]

Thanks a lot!