feat(transcode): support transcoding

src/api/wado/routes.rs

@@ -70,6 +70,7 @@ async fn instance_resource(
 	request: RetrieveInstanceRequest,
 ) -> impl IntoResponse {
 	if let Some(wado) = provider.wado {
+		let transfer_syntax = request.transfer_syntax.clone();
 		let study_instance_uid: UI = request.query.study_instance_uid.clone();
 		let response = wado.retrieve(request).await;
 
@@ -92,6 +93,7 @@ async fn instance_resource(
 					)
 					.body(Body::from_stream(DicomMultipartStream::new(
 						stream.into_stream(),
+						transfer_syntax.as_deref(),
 					)))
 					.unwrap()
 			}
@@ -131,6 +133,7 @@ async fn rendered_resource(
 			trace!("Using default rendering");
 			let instance_request = RetrieveInstanceRequest {
 				query: request.query,
+				transfer_syntax: None,
 			};
 
 			let stream = wado

src/api/wado/service.rs

@@ -52,10 +52,10 @@ pub enum RetrieveError {
 impl IntoResponse for RetrieveError {
 	fn into_response(self) -> Response {
 		match self {
-			RetrieveError::Backend { source } => {
+			Self::Backend { source } => {
 				(StatusCode::INTERNAL_SERVER_ERROR, source.to_string()).into_response()
 			}
-			RetrieveError::Unimplemented => Response::builder()
+			Self::Unimplemented => Response::builder()
 				.status(StatusCode::NOT_IMPLEMENTED)
 				.body(Body::from("This transaction is not implemented."))
 				.unwrap(),
@@ -64,6 +64,7 @@ impl IntoResponse for RetrieveError {
 }
 pub struct RetrieveInstanceRequest {
 	pub query: ResourceQuery,
+	pub transfer_syntax: Option<String>,
 }
 
 pub struct ThumbnailRequest {
@@ -157,6 +158,33 @@ where
 	}
 }
 
+/// Extracts the transfer-syntax parameter from an Accept header value.
+///
+/// According to <https://dicom.nema.org/medical/dicom/current/output/chtml/part18/sect_8.7.3.5.2.html>
+/// the syntax is: transfer-syntax-mtp = OWS ";" OWS %s"transfer-syntax=" ts-value
+///
+/// Examples:
+/// - "application/dicom; transfer-syntax=1.2.840.10008.1.2.4.50"
+/// - "multipart/related; type=\"application/dicom\"; transfer-syntax=1.2.840.10008.1.2.4.50"
+fn extract_transfer_syntax_from_accept(accept_header: &str) -> Option<String> {
+	// Split by semicolons to get individual parameters
+	for part in accept_header.split(';') {
+		let trimmed = part.trim();
+		// Look for the transfer-syntax parameter
+		if let Some(value) = trimmed.strip_prefix("transfer-syntax=") {
+			let value = value.trim();
+			// The value might be quoted or unquoted
+			let transfer_syntax = if value.starts_with('"') && value.ends_with('"') {
+				value.trim_matches('"')
+			} else {
+				value
+			};
+			return Some(transfer_syntax.to_string());
+		}
+	}
+	None
+}
+
 impl<S> FromRequestParts<S> for RetrieveInstanceRequest
 where
 	AppState: FromRef<S>,
@@ -169,7 +197,21 @@ where
 			.await
 			.map_err(PathRejection::into_response)?;
 
-		Ok(Self { query })
+		let accept = parts
+			.headers
+			.get(ACCEPT)
+			.map(|h| String::from(h.to_str().unwrap_or_default()));
+
+		// Extract the requested transfer-syntax from the Accept header if present
+		// https://dicom.nema.org/medical/dicom/current/output/chtml/part18/sect_8.7.3.5.2.html
+		let transfer_syntax = accept
+			.as_ref()
+			.and_then(|accept_str| extract_transfer_syntax_from_accept(accept_str));
+
+		Ok(Self {
+			query,
+			transfer_syntax,
+		})
 	}
 }
 
@@ -456,6 +498,59 @@ mod tests {
 		);
 	}
 
+	#[test]
+	fn test_extract_transfer_syntax_from_accept() {
+		// Test simple case
+		assert_eq!(
+			extract_transfer_syntax_from_accept(
+				"application/dicom; transfer-syntax=1.2.840.10008.1.2.4.50"
+			),
+			Some("1.2.840.10008.1.2.4.50".to_string())
+		);
+
+		// Test with extra whitespace
+		assert_eq!(
+			extract_transfer_syntax_from_accept(
+				"application/dicom;   transfer-syntax=1.2.840.10008.1.2.4.50"
+			),
+			Some("1.2.840.10008.1.2.4.50".to_string())
+		);
+
+		// Test wildcard
+		assert_eq!(
+			extract_transfer_syntax_from_accept("application/dicom; transfer-syntax=*"),
+			Some("*".to_string())
+		);
+
+		// Test multipart/related with type parameter
+		assert_eq!(
+			extract_transfer_syntax_from_accept("multipart/related; type=\"application/dicom\"; transfer-syntax=1.2.840.10008.1.2.4.50"),
+			Some("1.2.840.10008.1.2.4.50".to_string())
+		);
+
+		// Test with quoted value (though not typical for transfer-syntax)
+		assert_eq!(
+			extract_transfer_syntax_from_accept(
+				"application/dicom; transfer-syntax=\"1.2.840.10008.1.2.4.50\""
+			),
+			Some("1.2.840.10008.1.2.4.50".to_string())
+		);
+
+		// Test without transfer-syntax parameter
+		assert_eq!(
+			extract_transfer_syntax_from_accept("application/dicom"),
+			None
+		);
+
+		// Test with other parameters but no transfer-syntax
+		assert_eq!(
+			extract_transfer_syntax_from_accept(
+				"multipart/related; type=\"application/dicom\"; boundary=example"
+			),
+			None
+		);
+	}
+
 	#[test]
 	fn parse_rendered_query_params() {
 		let uri =

src/backend/dimse/cmove/movescu.rs

@@ -87,6 +87,8 @@ pub enum MoveError {
 	#[error(transparent)]
 	Write(#[from] WriteError),
 	#[error(transparent)]
+	Transcode(#[from] dicom::pixeldata::TranscodeError),
+	#[error(transparent)]
 	Association(#[from] PoolError<AssociationError>),
 	#[error("Sub-operation failed")]
 	OperationFailed,

src/backend/dimse/wado.rs

@@ -17,7 +17,10 @@ use async_stream::stream;
 use async_trait::async_trait;
 use dicom::core::VR;
 use dicom::dictionary_std::tags;
+use dicom::encoding::TransferSyntaxIndex;
 use dicom::object::{FileDicomObject, InMemDicomObject};
+use dicom::transfer_syntax::TransferSyntaxRegistry;
+use dicom_pixeldata::Transcode;
 use futures::stream::BoxStream;
 use futures::{Stream, StreamExt};
 use pin_project::pin_project;
@@ -104,6 +107,7 @@ impl WadoService for DimseWadoService {
 	async fn metadata(&self, request: MetadataRequest) -> Result<InstanceResponse, RetrieveError> {
 		self.retrieve(RetrieveInstanceRequest {
 			query: request.query,
+			transfer_syntax: None,
 		})
 		.await
 	}
@@ -263,11 +267,23 @@ impl<'a> DicomMultipartStream<'a> {
 		stream: impl Stream<Item = Result<Arc<FileDicomObject<InMemDicomObject>>, MoveError>>
 			+ Send
 			+ 'a,
+		transfer_syntax_uid: Option<&str>,
 	) -> Self {
+		let transfer_syntax_uid =
+			transfer_syntax_uid.and_then(|ts_uid| TransferSyntaxRegistry.get(ts_uid));
+
 		let multipart_stream = stream
-			.map(|item| {
+			.map(move |item| {
+				let transfer_syntax_uid = transfer_syntax_uid;
 				item.and_then(|object| {
-					Self::write(&object).map_err(|err| MoveError::Write(WriteError::Io(err)))
+					if let Some(ts) = transfer_syntax_uid {
+						let mut transcoded = (*object).clone();
+						transcoded.transcode(ts).map_err(MoveError::Transcode)?;
+						Self::write(&transcoded)
+							.map_err(|err| MoveError::Write(WriteError::Io(err)))
+					} else {
+						Self::write(&object).map_err(|err| MoveError::Write(WriteError::Io(err)))
+					}
 				})
 			})
 			.chain(futures::stream::once(async {
@@ -289,7 +305,11 @@ impl<'a> DicomMultipartStream<'a> {
 		let mut buffer = Vec::new();
 
 		writeln!(buffer, "--boundary\r")?;
-		writeln!(buffer, "Content-Type: application/dicom\r")?;
+		writeln!(
+			buffer,
+			"Content-Type: application/dicom; transfer-syntax=\"{}\"\r",
+			file.meta().transfer_syntax.trim_end_matches('\0')
+		)?;
 		writeln!(buffer, "Content-Length: {file_length}\r")?;
 		writeln!(buffer, "\r")?;
 		buffer.append(&mut dcm);