An example showing how to dynamically set header value for Content-Disposition HTTP header using Tapir

ContentDispositionTapirExample.scala

import cats.effect.IO
import cats.syntax.all.*
import sttp.capabilities.fs2.Fs2Streams
import sttp.model.HeaderNames.ContentDisposition
import sttp.tapir.EndpointIO.Header
import sttp.tapir.*

import java.nio.charset.StandardCharsets

// This is an example showing how to dynamically set the Content-Disposition HTTP header in Tapir
object ContentDispositionTapirExample {

  import ContentDispositionHeader.*

  val route =
    endpoint.get
      .in("download")
      .in(path[String].name("fileName"))
      .out(contentDispositionHeader)
      .out(streamBinaryBody(Fs2Streams[IO])(CodecFormat.OctetStream()))

  val attachmentWithFileNameEndpoint =
    route
      .in("attachment-with-file-name")
      .serverLogicSuccessPure { fileName =>
        attachmentWithFileName(fileName) -> downloadFile(fileName)
      }

  val attachmentWithoutFileNameEndpoint =
    route
      .in("attachment")
      .serverLogicSuccessPure { fileName =>
        attachment -> downloadFile(fileName)
      }

  val inlineContentEndpoint =
    route
      .in("inline")
      .serverLogicSuccessPure { fileName =>
        inline -> downloadFile(fileName)
      }

  def downloadFile(fileName: String) =
    fs2.Stream(s"Contents from file: $fileName".getBytes(StandardCharsets.UTF_8).toSeq*).covary[IO]

  sealed trait ContentDispositionHeader

  object ContentDispositionHeader {

    def attachmentWithFileName(fileName: String): ContentDispositionHeader = ContentDispositionAttachment(fileName.some)
    def attachment: ContentDispositionHeader = ContentDispositionAttachment(none)
    def inline: ContentDispositionHeader = ContentDispositionInline()

    private case class ContentDispositionAttachment(fileName: Option[String]) extends ContentDispositionHeader
    private case class ContentDispositionInline() extends ContentDispositionHeader

    val contentDispositionHeader: Header[ContentDispositionHeader] =
      header[String](ContentDisposition)
        .mapDecode(
          DecodeResult
            .Error(_, new IllegalArgumentException("Content-Disposition header is not expected in HTTP Request"))
        ) {
          case ContentDispositionAttachment(Some(fileName)) => s"attachment; filename=\"$fileName\""
          case ContentDispositionAttachment(None) => "attachment"
          case ContentDispositionInline() => "inline"
        }
  }

}