2 files changed, 14 insertions, 2 deletions

diff --git a/embassy-usb-dfu/src/application.rs b/embassy-usb-dfu/src/application.rs
index 6ad07a78c..4b7b72073 100644
--- a/embassy-usb-dfu/src/application.rs
+++ b/embassy-usb-dfu/src/application.rs
@@ -2,7 +2,7 @@ use embassy_boot::BlockingFirmwareState;
 use embassy_time::{Duration, Instant};
 use embassy_usb::control::{InResponse, OutResponse, Recipient, RequestType};
 use embassy_usb::driver::Driver;
-use embassy_usb::{Builder, Handler};
+use embassy_usb::{Builder, FunctionBuilder, Handler};
 use embedded_storage::nor_flash::NorFlash;
 
 use crate::consts::{
@@ -130,8 +130,14 @@ pub fn usb_dfu<'d, D: Driver<'d>, MARK: DfuMarker, RST: Reset>(
     builder: &mut Builder<'d, D>,
     handler: &'d mut Control<MARK, RST>,
     timeout: Duration,
+    func_modifier: impl Fn(&mut FunctionBuilder<'_, 'd, D>),
 ) {
     let mut func = builder.function(0x00, 0x00, 0x00);
+
+    // Here we give users the opportunity to add their own function level MSOS headers for instance.
+    // This is useful when DFU functionality is part of a composite USB device.
+    func_modifier(&mut func);
+
     let mut iface = func.interface();
     let mut alt = iface.alt_setting(USB_CLASS_APPN_SPEC, APPN_SPEC_SUBCLASS_DFU, DFU_PROTOCOL_RT, None);
     let timeout = timeout.as_millis() as u16;
diff --git a/embassy-usb-dfu/src/dfu.rs b/embassy-usb-dfu/src/dfu.rs
index a98d6ab40..0f39d906b 100644
--- a/embassy-usb-dfu/src/dfu.rs
+++ b/embassy-usb-dfu/src/dfu.rs
@@ -1,7 +1,7 @@
 use embassy_boot::{AlignedBuffer, BlockingFirmwareUpdater, FirmwareUpdaterError};
 use embassy_usb::control::{InResponse, OutResponse, Recipient, RequestType};
 use embassy_usb::driver::Driver;
-use embassy_usb::{Builder, Handler};
+use embassy_usb::{Builder, FunctionBuilder, Handler};
 use embedded_storage::nor_flash::{NorFlash, NorFlashErrorKind};
 
 use crate::consts::{
@@ -186,8 +186,14 @@ impl<'d, DFU: NorFlash, STATE: NorFlash, RST: Reset, const BLOCK_SIZE: usize> Ha
 pub fn usb_dfu<'d, D: Driver<'d>, DFU: NorFlash, STATE: NorFlash, RST: Reset, const BLOCK_SIZE: usize>(
     builder: &mut Builder<'d, D>,
     handler: &'d mut Control<'d, DFU, STATE, RST, BLOCK_SIZE>,
+    func_modifier: impl Fn(&mut FunctionBuilder<'_, 'd, D>),
 ) {
     let mut func = builder.function(USB_CLASS_APPN_SPEC, APPN_SPEC_SUBCLASS_DFU, DFU_PROTOCOL_DFU);
+
+    // Here we give users the opportunity to add their own function level MSOS headers for instance.
+    // This is useful when DFU functionality is part of a composite USB device.
+    func_modifier(&mut func);
+
     let mut iface = func.interface();
     let mut alt = iface.alt_setting(USB_CLASS_APPN_SPEC, APPN_SPEC_SUBCLASS_DFU, DFU_PROTOCOL_DFU, None);
     alt.descriptor(