Add support for parallel scan to Alternator API

src/scripting/alternator/functions.rs

@@ -1149,6 +1149,8 @@ pub async fn query(
 ///   - `limit`: The maximum number of items to evaluate (optional).
 ///   - `validation`: An optional item count validation. Look at [extract_validation_args] for details.
 ///   - `with_result`: If true, the scan result is returned (default: false).
+///   - `segment`: The segment to scan (optional).
+///   - `total_segments`: The total number of segments (optional).
 #[rune::function(instance)]
 pub async fn scan(
     ctx: Ref<Context>,
@@ -1171,9 +1173,33 @@ pub async fn scan(
             LIMIT_KEY,
             VALIDATION_KEY,
             WITH_RESULT_KEY,
+            SEGMENT_KEY,
+            TOTAL_SEGMENTS_KEY,
         ],
     )?;
 
+    if let Some(v) = params.get(SEGMENT_KEY) {
+        if let Ok(i) = v.as_signed() {
+            builder = builder.segment(match i32::try_from(i) {
+                Ok(val) => val,
+                Err(_) => return bad_input(format!("'{}' is out of range", SEGMENT_KEY)),
+            });
+        } else {
+            return bad_input(format!("'{}' must be an integer", SEGMENT_KEY));
+        }
+    }
+
+    if let Some(v) = params.get(TOTAL_SEGMENTS_KEY) {
+        if let Ok(i) = v.as_signed() {
+            builder = builder.total_segments(match i32::try_from(i) {
+                Ok(val) => val,
+                Err(_) => return bad_input(format!("'{}' is out of range", TOTAL_SEGMENTS_KEY)),
+            });
+        } else {
+            return bad_input(format!("'{}' must be an integer", TOTAL_SEGMENTS_KEY));
+        }
+    }
+
     if let Some(v) = params.get(FILTER_EXPRESSION_KEY) {
         if let Ok(s) = v.borrow_ref::<rune::alloc::String>() {
             builder = builder.filter_expression(s.as_str().to_string());

src/scripting/alternator/types.rs

@@ -22,6 +22,8 @@ pub const PROJECTION_EXPRESSION_KEY: &str = "projection_expression";
 pub const UPDATE_EXPRESSION_KEY: &str = "update";
 pub const QUERY_EXPRESSION_KEY: &str = "query";
 pub const FILTER_EXPRESSION_KEY: &str = "filter";
+pub const SEGMENT_KEY: &str = "segment";
+pub const TOTAL_SEGMENTS_KEY: &str = "total_segments";
 
 fn alternator_set_to_rune<I, T, F>(key: &str, iter: I, wrapper: F) -> Result<Value, AlternatorError>
 where

workloads/alternator/api_demo.rn

@@ -122,6 +122,16 @@ pub async fn run(db, i) {
         }
     }).await?;
 
+    // SCAN with segments
+    db.scan(TABLE, #{
+        filter: "age > :min_age",
+        "attribute_values": #{
+            ":min_age": 18
+        },
+        "segment": 1,
+        "total_segments": 5
+    }).await?;
+
     // DELETE Item
     db.delete(TABLE, key, ()).await?;
 }

workloads/alternator/invalid_params.rn

@@ -152,6 +152,24 @@ pub async fn run(db, i) {
         filter: 123
     }).await, "scan", "filter");
 
+    // Scan: segment must be integer and within range
+    assert_bad_param(db.scan(TABLE, #{
+        segment: "1"
+    }).await, "scan", "segment");
+
+    assert_bad_param(db.scan(TABLE, #{
+        segment: 1099511627776
+    }).await, "scan", "segment is out of range");
+
+    // Scan: total_segments must be integer and within range
+    assert_bad_param(db.scan(TABLE, #{
+        total_segments: "5"
+    }).await, "scan", "total_segments");
+
+    assert_bad_param(db.scan(TABLE, #{
+        total_segments: 1099511627776
+    }).await, "scan", "total_segments is out of range");
+
     // Create Table: primary_key must be object or string
     assert_bad_param(db.create_table("fail_table", #{
         primary_key: 123