api: rewrite conflict detection in iterators

Cargo.lock

@@ -240,6 +240,12 @@ dependencies = [
  "regex 0.2.11",
 ]
 
+[[package]]
+name = "either"
+version = "1.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bb1f6b1ce1c140482ea30ddd3335fc0024ac7ee112895426e0a629a6c20adfe3"
+
 [[package]]
 name = "fake-simd"
 version = "0.1.2"
@@ -412,6 +418,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "itertools"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f56a2d0bc861f9165be4eb3442afd3c236d8a98afd426f65d92324ae1091a484"
+dependencies = [
+ "either",
+]
+
 [[package]]
 name = "itoa"
 version = "0.4.5"
@@ -1079,6 +1094,7 @@ dependencies = [
  "diesel",
  "diesel_migrations",
  "dotenv",
+ "itertools",
  "lazy_static",
  "regex 1.3.4",
  "rocket",

Cargo.toml

@@ -17,4 +17,5 @@ scrypt = "0.2.0"
 uuid = { version = "0.8", features = ["v4"] }
 chrono = "0.4"
 serde_json = "1.0"
-regex = "1"
+regex = "1"
+itertools = "0.8"

src/api.rs

@@ -2,6 +2,7 @@ use crate::DbConn;
 use crate::user;
 use crate::item;
 use crate::lock::UserLock;
+use itertools::{Itertools, Either};
 use rocket::State;
 use rocket::http::Status;
 use rocket::response::status::Custom;
@@ -258,42 +259,41 @@ fn items_sync(
         }
     }
 
-    // Then, update all items sent by client
-    let mut last_id: i64 = -1;
-    for mut it in inner_params.items.into_iter() {
-        // Handle conflicts 
-        // Anything that we just retrieved but need to save immediately
-        // is potentially a conflict
-        // TODO: how do we handle this when the sync needs multiple requests
-        //   to finish?
-        let mut conflicted = false;
-        for y in resp.retrieved_items.iter() {
-            if it.uuid == y.uuid {
-                conflicted = true;
-                // We assume enc_item_key identifies an "item"
-                if it.enc_item_key == y.enc_item_key {
-                    // A sync conflict
-                    resp.conflicts.push(SyncConflict {
-                        conf_type: "sync_conflict".to_string(),
-                        server_item: Some(y.clone()),
-                        unsaved_item: None
-                    });
-                } else {
-                    // A UUID conflict (unlikely)
-                    resp.conflicts.push(SyncConflict {
-                        conf_type: "uuid_conflict".to_string(),
-                        server_item: None,
-                        unsaved_item: Some(it.clone())
-                    })
-                }
+    // Detect conflicts between client items and server items
+    let (items_conflicted, items_to_save): (Vec<_>, Vec<_>) =
+        inner_params.items.into_iter().partition_map(|client_item| {
+            let conflict: Vec<_> = resp.retrieved_items.iter()
+                .filter(|server_item| client_item.uuid == server_item.uuid)
+                .collect();
+            if !conflict.is_empty() {
+                Either::Left((client_item, conflict[0].clone()))
+            } else {
+                Either::Right(client_item)
+            }
+        });
+
+    // Convert conflicts into the format our client wants
+    resp.conflicts = items_conflicted.into_iter().map(|(client_item, server_item)| {
+        // We assume enc_item_key "identifies" an "item"
+        if client_item.enc_item_key == server_item.enc_item_key {
+            SyncConflict {
+                conf_type: "sync_conflict".to_string(),
+                server_item: Some(server_item),
+                unsaved_item: None
+            }
+        } else {
+            // A UUID conflict (unlikely)
+            SyncConflict {
+                conf_type: "uuid_conflict".to_string(),
+                server_item: None,
+                unsaved_item: Some(client_item)
             }
         }
+    }).collect();
 
-        // do not save conflicted items
-        if conflicted {
-            continue;
-        }
-
+    // Then, update all items sent by client
+    let mut last_id: i64 = -1;
+    for mut it in items_to_save.into_iter() {
         // Always update updated_at for all items on server
         it.updated_at = 
             Some(chrono::Utc::now().to_rfc3339_opts(chrono::SecondsFormat::Millis, true));