Add downstream_compliance_region hostcall

crates/adapter/src/fastly/core.rs

@@ -995,9 +995,7 @@ pub mod fastly_http_req {
         nwritten: *mut usize,
     ) -> FastlyStatus {
         alloc_result!(region_out, region_max_len, nwritten, {
-            fastly::api::http_req::downstream_compliance_region(
-                u64::try_from(region_max_len).trapping_unwrap(),
-            )
+            fastly::api::http_req::downstream_compliance_region()
         })
     }
 

lib/compute-at-edge-abi/compute-at-edge.witx

@@ -242,7 +242,14 @@
          (param $ja4_max_len (@witx usize))
          (param $nwritten_out (@witx pointer (@witx usize)))
          (result $err (expected (error $fastly_status)))
-     )
+    )
+
+    (@interface func (export "downstream_compliance_region")
+         (param $region_out (@witx pointer (@witx char8)))
+         (param $region_max_len (@witx usize))
+         (param $nwritten_out (@witx pointer (@witx usize)))
+         (result $err (expected (error $fastly_status)))
+    )
 
     (@interface func (export "new")
         (result $err (expected $request_handle (error $fastly_status)))

lib/src/component/http_req.rs

@@ -808,11 +808,8 @@ impl http_req::Host for Session {
         Err(Error::NotAvailable("Client TLS JA4 hash").into())
     }
 
-    async fn downstream_compliance_region(
-        &mut self,
-        _max_len: u64,
-    ) -> Result<Vec<u8>, types::Error> {
-        Err(Error::NotAvailable("Client TLS JA4 hash").into())
+    async fn downstream_compliance_region(&mut self) -> Result<Vec<u8>, types::Error> {
+        Ok(Vec::from(b"none"))
     }
 
     async fn original_header_names_get(

lib/src/wiggle_abi/req_impl.rs

@@ -300,6 +300,33 @@ impl FastlyHttpReq for Session {
         Err(Error::NotAvailable("Client TLS JA4 hash"))
     }
 
+    fn downstream_compliance_region(
+        &mut self,
+        memory: &mut GuestMemory<'_>,
+        // Must be a 16-byte array:
+        region_out: GuestPtr<u8>,
+        region_max_len: u32,
+        nwritten_out: GuestPtr<u32>,
+    ) -> Result<(), Error> {
+        const REGION_NONE: &[u8] = b"none";
+        const REGION_NONE_LEN: u32 = 4;
+
+        if region_max_len < REGION_NONE_LEN {
+            // Let the guest know how much we want to write.
+            memory.write(nwritten_out, REGION_NONE_LEN)?;
+
+            return Err(Error::BufferLengthError {
+                buf: "region_out",
+                len: "region_max_len",
+            });
+        }
+
+        memory.copy_from_slice(REGION_NONE, region_out.as_array(region_max_len))?;
+        memory.write(nwritten_out, REGION_NONE_LEN)?;
+
+        Ok(())
+    }
+
     fn framing_headers_mode_set(
         &mut self,
         _memory: &mut GuestMemory<'_>,

lib/wit/deps/fastly/compute.wit

@@ -323,7 +323,7 @@ interface http-req {
 
   downstream-tls-ja4: func(max-len: u64) -> result<list<u8>, error>;
 
-  downstream-compliance-region: func(max-len: u64) -> result<list<u8>, error>;
+  downstream-compliance-region: func() -> result<list<u8>, error>;
 
   new: func() -> result<request-handle, error>;