Implement respondBytes similar to responding with text

[thomasweitzel]

I have a resources page that delivers binary content in a safe way, either from a backing file, a resource, or dynamically calculated content (like PNG, SVG, ICO, MP3, ...):

call.response.contentType(content.type)
call.respond(content.bytes)

Since 0.9.1 I get an exception (was no problem in 0.9.0):

io.ktor.response.UnsafeHeaderException:
Header Content-Type is controlled by the engine and cannot be set explicitly

When I omit the setting of the content type, the browser rightfully complains:

Resource interpreted as Stylesheet but transferred with MIME type text/plain:
https://domain.tld/resources?name=screen&ext=css

Resource interpreted as Document but transferred with MIME type application/zip:
https://domain.tld/resources?privileged=1&name=simulation&ext=xlsx

How can I solve the situation and still have a generic content producer page?

[orangy]

I was pretty sure we have respondBytes, but looks like it is an unfortunate omission… We will add it.
As a workaround, you may write your own low level OutgoingContent and a helper function:

class ByteContent(val bytes: ByteArray, override val contentType: ContentType, override val status: HttpStatusCode? = null): OutgoingContent.ByteArrayContent(){
    override val contentLength: Long
        get() = bytes.size.toLong()

    override fun bytes(): ByteArray = bytes

    override fun toString() = "ByteContent[$contentType] ${bytes.size} bytes"
}

suspend fun ApplicationCall.respondBytes(bytes: ByteArray, contentType: ContentType? = null, status: HttpStatusCode? = null, configure: OutgoingContent.() -> Unit = {}) {
    val message = ByteContent(bytes, defaultTextContentType(contentType), status).apply(configure)
    return respond(message)
}

And use it like

call.respondBytes(content.bytes, content.type)

[thomasweitzel]

Thank you for the workaround: it works. Looking forward to the next ktor release.