ReadRequest: Create structure for recording ResumeReadRequest

matter/src/data_model/core.rs

@@ -164,7 +164,7 @@ impl DataModel {
         attr_encoder: &mut AttrReadEncoder,
         attr_details: &mut AttrDetails,
         resume_from: &mut Option<GenericPath>,
-    ) -> Result<(), GenericPath> {
+    ) -> Result<(), Error> {
         let mut status = Ok(());
         let path = attr_encoder.path;
 
@@ -181,6 +181,8 @@ impl DataModel {
                 return Ok(());
             }
 
+            // The resume_from indicates that this is the next chunk of a previous Read Request. In such cases, we
+            // need to skip until we hit this path.
             if let Some(r) = resume_from {
                 // If resume_from is valid, and we haven't hit the resume_from yet, skip encoding
                 if r != path {
@@ -200,7 +202,8 @@ impl DataModel {
             Cluster::read_attribute(c, &mut access_req, attr_encoder, attr_details);
             if attr_encoder.is_buffer_full() {
                 // Buffer is full, next time resume from this attribute
-                status = Err(*path);
+                *resume_from = Some(*path);
+                status = Err(Error::NoSpace);
             }
             Ok(())
         });
@@ -295,6 +298,26 @@ impl objects::ChangeConsumer for DataModel {
     }
 }
 
+/// State to maintain when a Read Request needs to be resumed
+/// resumed - the next chunk of the read needs to be returned
+#[derive(Default)]
+pub struct ResumeReadReq {
+    /// The Read Request Attribute Path that caused chunking, and this is the path
+    /// that needs to be resumed.
+    ///
+    /// TODO: Ideally, the entire ReadRequest (with any subsequent AttrPaths) should also
+    /// be maintained. But for now, we just store the AttrPath that caused the overflow
+    /// and chunking. Hopefully, the other end requests any pending paths when it sees no
+    /// more chunks.
+    pending_path: GenericPath,
+
+    /// The Attribute that couldn't be encoded because our buffer got full. The next chunk
+    /// will start encoding from this attribute onwards.
+    /// Note that given wildcard reads, one PendingPath in the member above can generated
+    /// multiple encode paths. Hence this has to be maintained separately.
+    resume_encode: Option<GenericPath>,
+}
+
 impl InteractionConsumer for DataModel {
     fn consume_write_attr(
         &self,
@@ -320,49 +343,42 @@ impl InteractionConsumer for DataModel {
         trans: &mut Transaction,
         tw: &mut TLVWriter,
     ) -> Result<(), Error> {
+        let mut resume_read_req: ResumeReadReq = Default::default();
+
         let mut attr_encoder = AttrReadEncoder::new(tw);
         if let Some(filters) = &read_req.dataver_filters {
             attr_encoder.set_data_ver_filters(filters);
         }
 
-        let mut attr_details = AttrDetails {
-            // This will be updated internally
-            attr_id: 0,
-            // This will be updated internally
-            list_index: None,
-            // This will be updated internally
-            fab_idx: 0,
-            fab_filter: read_req.fabric_filtered,
-        };
-
         if let Some(attr_requests) = &read_req.attr_requests {
             let accessor = self.sess_to_accessor(trans.session);
+            let mut attr_details = AttrDetails::new(accessor.fab_idx, read_req.fabric_filtered);
             let node = self.node.read().unwrap();
             attr_encoder
                 .tw
                 .start_array(TagType::Context(msg::ReportDataTag::AttributeReports as u8))?;
 
             let mut result = Ok(());
-            let mut resume_from = None;
             for attr_path in attr_requests.iter() {
                 attr_encoder.set_path(attr_path.to_gp());
                 // Extract the attr_path fields into various structures
                 attr_details.list_index = attr_path.list_index;
-                attr_details.fab_idx = accessor.fab_idx;
                 result = DataModel::handle_read_attr_path(
                     &node,
                     &accessor,
                     &mut attr_encoder,
                     &mut attr_details,
-                    &mut resume_from,
+                    &mut resume_read_req.resume_encode,
                 );
                 if result.is_err() {
+                    resume_read_req.pending_path = attr_path.to_gp();
                     break;
                 }
             }
             tw.end_container()?;
-            if let Err(path) = result {
-                // If there was an error, make a note of this 'path' to resume for the next chunk
+            if result.is_err() {
+                // If there was an error, indicate chunking. The resume_read_req would have been
+                // already populated from in the loop above.
                 tw.bool(
                     TagType::Context(msg::ReportDataTag::MoreChunkedMsgs as u8),
                     true,
@@ -371,6 +387,7 @@ impl InteractionConsumer for DataModel {
                     TagType::Context(msg::ReportDataTag::SupressResponse as u8),
                     false,
                 )?;
+                // Don't complete the transaction
             } else {
                 tw.bool(
                     TagType::Context(msg::ReportDataTag::SupressResponse as u8),