feat(agent): add a header action to set default value of a header if no present

Author: joelwurtz

src/filter/header_action/header_default.rs

@@ -0,0 +1,44 @@
+use crate::action::UnitTrace;
+use crate::filter::header_action::HeaderAction;
+use crate::http::Header;
+
+#[derive(Debug)]
+pub struct HeaderDefaultAction {
+    pub name: String,
+    pub value: String,
+    // in 3.0 make this mandatory
+    pub id: Option<String>,
+    // in 3.0 make this mandatory
+    pub target_hash: Option<String>,
+}
+
+// Set a header if not present
+impl HeaderAction for HeaderDefaultAction {
+    fn filter(&self, mut headers: Vec<Header>, unit_trace: Option<&mut UnitTrace>) -> Vec<Header> {
+        let mut found = false;
+
+        for header in &headers {
+            if header.name.to_lowercase() == self.name.to_lowercase() {
+                found = true;
+                break;
+            }
+        }
+
+        if !found {
+            headers.push(Header {
+                name: self.name.clone(),
+                value: self.value.clone(),
+            });
+
+            if let (Some(trace), Some(id)) = (unit_trace, &self.id) {
+                trace.add_value_computed_by_unit(id, &self.value);
+
+                if let Some(target_hash) = &self.target_hash {
+                    trace.add_unit_id_with_target(target_hash, id);
+                }
+            }
+        }
+
+        headers
+    }
+}

src/filter/header_action/mod.rs

@@ -1,4 +1,5 @@
 pub mod header_add;
+pub mod header_default;
 pub mod header_override;
 pub mod header_remove;
 pub mod header_replace;
@@ -47,5 +48,14 @@ pub fn create_header_action(header_filter: &HeaderFilter) -> Option<Box<dyn Head
         }));
     }
 
+    if header_filter.action == "default" {
+        return Some(Box::new(header_default::HeaderDefaultAction {
+            id: header_filter.id.clone(),
+            name: header_filter.header.clone(),
+            value: header_filter.value.clone(),
+            target_hash: header_filter.target_hash.clone(),
+        }));
+    }
+
     None
 }