toCurl drops multipart filename, content-type, and per-part headers

[haskiindahouse]

request.toCurl is great for sharing a request to debug, but for multipart bodies it silently throws away Part.fileName, Part.contentType, and Part.headers. The resulting curl command sends a different request than the original.

Reproducer (scala-cli):

//> using scala 3.8.3
//> using dep com.softwaremill.sttp.client4::core::4.0.5

import sttp.client4.*
import sttp.model.*

@main def run(): Unit =
  val request = basicRequest
    .post(uri"http://example.com/upload")
    .multipartBody(
      multipart("file", "file content")
        .fileName("document.pdf")
        .contentType("application/pdf"),
      multipart("field", "value")
    )
  println(request.toCurl)

Output:

curl \
  --request POST \
  --url 'http://example.com/upload' \
  --form 'file=file content' \
  --form 'field=value' \
  --location \
  --max-redirs 32

Expected something like --form 'file=file content;filename=document.pdf;type=application/pdf'.

Source:

sttp/core/src/main/scala/sttp/client4/internal/ToCurlConverter.scala

Lines 58 to 67 in 6b817f7

	def handleMultipartBody(parts: Seq[Part[GenericRequestBody[_]]]): String =
	parts
	.map { p =>
	p.body match {
	case StringBody(s, _, _) => s"--form '${p.name}=$s'"
	case FileBody(f, _) => s"--form '${p.name}=@${f.name}'"
	case _ => s"--data-binary <PLACEHOLDER>"
	}
	}
	.mkString(newline)

def handleMultipartBody(parts: Seq[Part[GenericRequestBody[_]]]): String =
  parts.map { p =>
    p.body match {
      case StringBody(s, _, _) => s"--form '${p.name}=$s'"
      case FileBody(f, _)      => s"--form '${p.name}=@${f.name}'"
      case _                   => s"--data-binary <PLACEHOLDER>"
    }
  }.mkString(newline)

p.fileName, p.contentType, and p.headers aren't read at all, and any non-StringBody/FileBody part collapses to a literal placeholder. curl supports the metadata via the ;filename=...;type=... and ;headers=@... extensions, so a faithful renderer is feasible.

A sketch (StringBody case):

case StringBody(s, _, _) =>
  val tail = (p.fileName.map(fn => s";filename=$fn").toList ++
              p.contentType.map(ct => s";type=$ct").toList).mkString
  s"--form '${p.name}=$s$tail'"

Happy to PR with full coverage of the four part-body shapes plus a unit test.

[adamw]

Thanks for the report - PRs welcome!