Return SnapshotUrgency from AddVersion

taskchampion/src/server/local.rs

@@ -1,5 +1,6 @@
 use crate::server::{
-    AddVersionResult, GetVersionResult, HistorySegment, Server, VersionId, NIL_VERSION_ID,
+    AddVersionResult, GetVersionResult, HistorySegment, Server, SnapshotUrgency, VersionId,
+    NIL_VERSION_ID,
 };
 use crate::storage::sqlite::StoredUuid;
 use anyhow::Context;
@@ -116,14 +117,17 @@ impl Server for LocalServer {
         &mut self,
         parent_version_id: VersionId,
         history_segment: HistorySegment,
-    ) -> anyhow::Result<AddVersionResult> {
+    ) -> anyhow::Result<(AddVersionResult, SnapshotUrgency)> {
         // no client lookup
         // no signature validation
 
         // check the parent_version_id for linearity
         let latest_version_id = self.get_latest_version_id()?;
         if latest_version_id != NIL_VERSION_ID && parent_version_id != latest_version_id {
-            return Ok(AddVersionResult::ExpectedParentVersion(latest_version_id));
+            return Ok((
+                AddVersionResult::ExpectedParentVersion(latest_version_id),
+                SnapshotUrgency::None,
+            ));
         }
 
         // invent a new ID for this version
@@ -136,7 +140,7 @@ impl Server for LocalServer {
         })?;
         self.set_latest_version_id(version_id)?;
 
-        Ok(AddVersionResult::Ok(version_id))
+        Ok((AddVersionResult::Ok(version_id), SnapshotUrgency::None))
     }
 
     /// Get a vector of all versions after `since_version`
@@ -176,7 +180,7 @@ mod test {
         let tmp_dir = TempDir::new()?;
         let mut server = LocalServer::new(&tmp_dir.path())?;
         let history = b"1234".to_vec();
-        match server.add_version(NIL_VERSION_ID, history.clone())? {
+        match server.add_version(NIL_VERSION_ID, history.clone())?.0 {
             AddVersionResult::ExpectedParentVersion(_) => {
                 panic!("should have accepted the version")
             }
@@ -204,7 +208,7 @@ mod test {
         let parent_version_id = Uuid::new_v4() as VersionId;
 
         // This is OK because the server has no latest_version_id yet
-        match server.add_version(parent_version_id, history.clone())? {
+        match server.add_version(parent_version_id, history.clone())?.0 {
             AddVersionResult::ExpectedParentVersion(_) => {
                 panic!("should have accepted the version")
             }
@@ -232,14 +236,16 @@ mod test {
         let parent_version_id = Uuid::new_v4() as VersionId;
 
         // add a version
-        if let AddVersionResult::ExpectedParentVersion(_) =
+        if let (AddVersionResult::ExpectedParentVersion(_), SnapshotUrgency::None) =
             server.add_version(parent_version_id, history.clone())?
         {
             panic!("should have accepted the version")
         }
 
         // then add another, not based on that one
-        if let AddVersionResult::Ok(_) = server.add_version(parent_version_id, history.clone())? {
+        if let (AddVersionResult::Ok(_), SnapshotUrgency::None) =
+            server.add_version(parent_version_id, history.clone())?
+        {
             panic!("should not have accepted the version")
         }
 

taskchampion/src/server/remote/mod.rs

@@ -1,4 +1,6 @@
-use crate::server::{AddVersionResult, GetVersionResult, HistorySegment, Server, VersionId};
+use crate::server::{
+    AddVersionResult, GetVersionResult, HistorySegment, Server, SnapshotUrgency, VersionId,
+};
 use std::convert::TryInto;
 use std::time::Duration;
 use uuid::Uuid;
@@ -43,12 +45,24 @@ fn get_uuid_header(resp: &ureq::Response, name: &str) -> anyhow::Result<Uuid> {
     Ok(value)
 }
 
+/// Read the X-Snapshot-Request header and return a SnapshotUrgency
+fn get_snapshot_urgency(resp: &ureq::Response) -> SnapshotUrgency {
+    match resp.header("X-Snapshot-Request") {
+        None => SnapshotUrgency::None,
+        Some(hdr) => match hdr {
+            "urgency=low" => SnapshotUrgency::Low,
+            "urgency=high" => SnapshotUrgency::High,
+            _ => SnapshotUrgency::None,
+        },
+    }
+}
+
 impl Server for RemoteServer {
     fn add_version(
         &mut self,
         parent_version_id: VersionId,
         history_segment: HistorySegment,
-    ) -> anyhow::Result<AddVersionResult> {
+    ) -> anyhow::Result<(AddVersionResult, SnapshotUrgency)> {
         let url = format!(
             "{}/v1/client/add-version/{}",
             self.origin, parent_version_id
@@ -70,11 +84,17 @@ impl Server for RemoteServer {
         {
             Ok(resp) => {
                 let version_id = get_uuid_header(&resp, "X-Version-Id")?;
-                Ok(AddVersionResult::Ok(version_id))
+                Ok((
+                    AddVersionResult::Ok(version_id),
+                    get_snapshot_urgency(&resp),
+                ))
             }
             Err(ureq::Error::Status(status, resp)) if status == 409 => {
                 let parent_version_id = get_uuid_header(&resp, "X-Parent-Version-Id")?;
-                Ok(AddVersionResult::ExpectedParentVersion(parent_version_id))
+                Ok((
+                    AddVersionResult::ExpectedParentVersion(parent_version_id),
+                    SnapshotUrgency::None,
+                ))
             }
             Err(err) => Err(err.into()),
         }

taskchampion/src/server/test.rs

@@ -1,5 +1,6 @@
 use crate::server::{
-    AddVersionResult, GetVersionResult, HistorySegment, Server, VersionId, NIL_VERSION_ID,
+    AddVersionResult, GetVersionResult, HistorySegment, Server, SnapshotUrgency, VersionId,
+    NIL_VERSION_ID,
 };
 use std::collections::HashMap;
 use uuid::Uuid;
@@ -33,15 +34,16 @@ impl Server for TestServer {
         &mut self,
         parent_version_id: VersionId,
         history_segment: HistorySegment,
-    ) -> anyhow::Result<AddVersionResult> {
+    ) -> anyhow::Result<(AddVersionResult, SnapshotUrgency)> {
         // no client lookup
         // no signature validation
 
         // check the parent_version_id for linearity
         if self.latest_version_id != NIL_VERSION_ID {
             if parent_version_id != self.latest_version_id {
-                return Ok(AddVersionResult::ExpectedParentVersion(
+                return Ok((
-                    self.latest_version_id,
+                    AddVersionResult::ExpectedParentVersion(self.latest_version_id),
+                    SnapshotUrgency::None,
                 ));
             }
         }
@@ -59,7 +61,7 @@ impl Server for TestServer {
         );
         self.latest_version_id = version_id;
 
-        Ok(AddVersionResult::Ok(version_id))
+        Ok((AddVersionResult::Ok(version_id), SnapshotUrgency::None))
     }
 
     /// Get a vector of all versions after `since_version`

taskchampion/src/server/types.rs

@@ -10,7 +10,7 @@ pub const NIL_VERSION_ID: VersionId = Uuid::nil();
 /// data is pre-encoded, and from the protocol level appears as a sequence of bytes.
 pub type HistorySegment = Vec<u8>;
 
-/// VersionAdd is the response type from [`crate::server::Server::add_version`].
+/// AddVersionResult is the response type from [`crate::server::Server::add_version`].
 #[derive(Debug, PartialEq)]
 pub enum AddVersionResult {
     /// OK, version added with the given ID
@@ -19,6 +19,17 @@ pub enum AddVersionResult {
     ExpectedParentVersion(VersionId),
 }
 
+/// SnapshotUrgency indicates how much the server would like this replica to send a snapshot.
+#[derive(PartialEq, Debug, Clone, Copy, Eq, PartialOrd, Ord)]
+pub enum SnapshotUrgency {
+    /// Don't need a snapshot right now.
+    None,
+    /// A snapshot would be good, but can wait for other replicas to provide it.
+    Low,
+    /// A snapshot is needed right now.
+    High,
+}
+
 /// A version as downloaded from the server
 #[derive(Debug, PartialEq)]
 pub enum GetVersionResult {
@@ -40,7 +51,7 @@ pub trait Server {
         &mut self,
         parent_version_id: VersionId,
         history_segment: HistorySegment,
-    ) -> anyhow::Result<AddVersionResult>;
+    ) -> anyhow::Result<(AddVersionResult, SnapshotUrgency)>;
 
     /// Get the version with the given parent VersionId
     fn get_child_version(

taskchampion/src/taskdb/sync.rs

@@ -57,7 +57,8 @@ pub(super) fn sync(server: &mut Box<dyn Server>, txn: &mut dyn StorageTxn) -> an
         let new_version = Version { operations };
         let history_segment = serde_json::to_string(&new_version).unwrap().into();
         info!("sending new version to server");
-        match server.add_version(base_version_id, history_segment)? {
+        let (res, _snapshot_urgency) = server.add_version(base_version_id, history_segment)?;
+        match res {
             AddVersionResult::Ok(new_version_id) => {
                 info!("version {:?} received by server", new_version_id);
                 txn.set_base_version(new_version_id)?;