add empty source handler

satrs-core/src/cfdp/mod.rs

@@ -14,6 +14,8 @@ use serde::{Deserialize, Serialize};
 
 #[cfg(feature = "std")]
 pub mod dest;
+#[cfg(feature = "std")]
+pub mod source;
 pub mod user;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]

satrs-core/src/cfdp/source.rs

@@ -0,0 +1,16 @@
+use spacepackets::util::UnsignedByteField;
+
+pub struct SourceHandler {
+    id: UnsignedByteField,
+}
+
+impl SourceHandler {
+    pub fn new(id: impl Into<UnsignedByteField>) -> Self {
+        Self { id }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+}