jspg masking system installed

GEMINI.md

@@ -31,6 +31,17 @@ Loads and compiles the entire schema registry into the session's memory, atomica
     *   Compiles schemas into validators.
 *   **Returns**: `{"response": "success"}` or an error object.
 
+### `mask_json_schema(schema_id text, instance jsonb) -> jsonb`
+
+Validates a JSON instance and returns a new JSON object with unknown properties removed (pruned) based on the schema.
+
+*   **Inputs**:
+    *   `schema_id`: The `$id` of the schema to mask against.
+    *   `instance`: The JSON data to mask.
+*   **Returns**:
+    *   On success: A `Drop` containing the **masked data**.
+    *   On failure: A `Drop` containing validation errors.
+
 ### `validate_json_schema(schema_id text, instance jsonb) -> jsonb`
 
 Validates a JSON instance against a pre-compiled schema.
@@ -83,6 +94,16 @@ JSPG enforces a "Secure by Default" philosophy. All schemas are treated as if `u
 ### 4. Format Leniency for Empty Strings
 To simplify frontend form logic, the format validators for `uuid`, `date-time`, and `email` explicitly allow empty strings (`""`). This treats an empty string as "present but unset" rather than "invalid format".
 
+### 5. Masking (Constructive Validation)
+JSPG supports a "Constructive Validation" mode via `mask_json_schema`. This is designed for high-performance API responses where the schema dictates the exact shape of the returned data.
+
+*   **Mechanism**: The validator traverses the instance against the schema.
+*   **Valid Fields**: Kept in the output.
+*   **Unknown/Extra Fields**: Silently removed (pruned) if `extensible: false` (default).
+*   **Invalid Fields**: Still trigger standard validation errors.
+
+This allows the database to return "raw" joined rows (e.g. `SELECT * FROM person JOIN organization ...`) and have JSPG automatically shape the result into the expected API response, removing any internal or unrelated columns not defined in the schema.
+
 ## 🏗️ Architecture
 
 The extension is written in Rust using `pgrx` and structures its schema parser to mirror the Punc Generator's design:

src/drop.rs

@@ -3,59 +3,66 @@ use serde_json::Value;
 
 #[derive(Debug, Serialize, Deserialize, Clone)]
 pub struct Drop {
-    // We don't need id, frequency, etc. for the validation result specifically,
-    // as they are added by the SQL wrapper. We just need to conform to the structure.
-    // The user said "Validator::validate always needs to return this drop type".
-    // So we should match it as closely as possible.
+  // We don't need id, frequency, etc. for the validation result specifically,
+  // as they are added by the SQL wrapper. We just need to conform to the structure.
+  // The user said "Validator::validate always needs to return this drop type".
+  // So we should match it as closely as possible.
+  #[serde(rename = "type")]
+  pub type_: String, // "drop"
 
-    #[serde(rename = "type")]
-    pub type_: String, // "drop"
+  #[serde(skip_serializing_if = "Option::is_none")]
+  pub response: Option<Value>,
 
-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub response: Option<Value>,
-    
-    #[serde(default)]
-    pub errors: Vec<Error>,
+  #[serde(default)]
+  pub errors: Vec<Error>,
 }
 
 impl Drop {
-    pub fn new() -> Self {
-        Self {
-            type_: "drop".to_string(),
-            response: None,
-            errors: vec![],
-        }
+  pub fn new() -> Self {
+    Self {
+      type_: "drop".to_string(),
+      response: None,
+      errors: vec![],
     }
+  }
 
-    pub fn success() -> Self {
-        Self {
-            type_: "drop".to_string(),
-            response: Some(serde_json::json!({ "result": "success" })), // Or appropriate success response
-            errors: vec![],
-        }
+  pub fn success() -> Self {
+    Self {
+      type_: "drop".to_string(),
+      response: Some(serde_json::json!({ "result": "success" })), // Or appropriate success response
+      errors: vec![],
     }
+  }
 
-    pub fn with_errors(errors: Vec<Error>) -> Self {
-        Self {
-            type_: "drop".to_string(),
-            response: None,
-            errors,
-        }
+  pub fn success_with_val(val: Value) -> Self {
+    Self {
+      type_: "drop".to_string(),
+      response: Some(val),
+      errors: vec![],
     }
+  }
+
+  pub fn with_errors(errors: Vec<Error>) -> Self {
+    Self {
+      type_: "drop".to_string(),
+      response: None,
+      errors,
+    }
+  }
 }
 
 #[derive(Debug, Serialize, Deserialize, Clone)]
 pub struct Error {
-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub punc: Option<String>,
-    pub code: String,
-    pub message: String,
-    pub details: ErrorDetails,
+  #[serde(skip_serializing_if = "Option::is_none")]
+  pub punc: Option<String>,
+  pub code: String,
+  pub message: String,
+  pub details: ErrorDetails,
 }
 
 #[derive(Debug, Serialize, Deserialize, Clone)]
 pub struct ErrorDetails {
-    pub path: String,
-    // Extensions can be added here (package, cause, etc)
-    // For now, validator only provides path
+  pub path: String,
+  // Extensions can be added here (package, cause, etc)
+  // For now, validator only provides path
 }

src/lib.rs

@@ -110,6 +110,65 @@ fn cache_json_schemas(enums: JsonB, types: JsonB, puncs: JsonB) -> JsonB {
   JsonB(json!({ "response": "success" }))
 }
 
+#[pg_extern(strict, parallel_safe)]
+fn mask_json_schema(schema_id: &str, instance: JsonB) -> JsonB {
+  // 1. Acquire Snapshot
+  let validator_arc = {
+    let lock = GLOBAL_VALIDATOR.read().unwrap();
+    lock.clone()
+  };
+
+  // 2. Validate (Lock-Free)
+  if let Some(validator) = validator_arc {
+    // We need a mutable copy of the value to mask it
+    let mut mutable_instance = instance.0.clone();
+
+    match validator.mask(schema_id, &mut mutable_instance) {
+      Ok(result) => {
+        // If valid, return the MASKED instance
+        if result.is_valid() {
+          let drop = crate::drop::Drop::success_with_val(mutable_instance);
+          JsonB(serde_json::to_value(drop).unwrap())
+        } else {
+          // If invalid, return errors (Schema Validation Errors)
+          let errors: Vec<crate::drop::Error> = result
+            .errors
+            .into_iter()
+            .map(|e| crate::drop::Error {
+              punc: None,
+              code: e.code,
+              message: e.message,
+              details: crate::drop::ErrorDetails { path: e.path },
+            })
+            .collect();
+          let drop = crate::drop::Drop::with_errors(errors);
+          JsonB(serde_json::to_value(drop).unwrap())
+        }
+      }
+      Err(e) => {
+        // Schema Not Found or other fatal error
+        let error = crate::drop::Error {
+          punc: None,
+          code: e.code,
+          message: e.message,
+          details: crate::drop::ErrorDetails { path: e.path },
+        };
+        let drop = crate::drop::Drop::with_errors(vec![error]);
+        JsonB(serde_json::to_value(drop).unwrap())
+      }
+    }
+  } else {
+    JsonB(json!({
+        "punc": null,
+        "errors": [{
+            "code": "VALIDATOR_NOT_INITIALIZED",
+            "message": "JSON Schemas have not been cached yet. Run cache_json_schemas()",
+            "details": { "path": "" }
+        }]
+    }))
+  }
+}
+
 #[pg_extern(strict, parallel_safe)]
 fn validate_json_schema(schema_id: &str, instance: JsonB) -> JsonB {
   // 1. Acquire Snapshot
@@ -120,8 +179,37 @@ fn validate_json_schema(schema_id: &str, instance: JsonB) -> JsonB {
 
   // 2. Validate (Lock-Free)
   if let Some(validator) = validator_arc {
-    let drop = validator.validate(schema_id, &instance.0);
-    JsonB(serde_json::to_value(drop).unwrap())
+    match validator.validate(schema_id, &instance.0) {
+      Ok(result) => {
+        if result.is_valid() {
+          let drop = crate::drop::Drop::success();
+          JsonB(serde_json::to_value(drop).unwrap())
+        } else {
+          let errors: Vec<crate::drop::Error> = result
+            .errors
+            .into_iter()
+            .map(|e| crate::drop::Error {
+              punc: None,
+              code: e.code,
+              message: e.message,
+              details: crate::drop::ErrorDetails { path: e.path },
+            })
+            .collect();
+          let drop = crate::drop::Drop::with_errors(errors);
+          JsonB(serde_json::to_value(drop).unwrap())
+        }
+      }
+      Err(e) => {
+        let error = crate::drop::Error {
+          punc: None,
+          code: e.code,
+          message: e.message,
+          details: crate::drop::ErrorDetails { path: e.path },
+        };
+        let drop = crate::drop::Drop::with_errors(vec![error]);
+        JsonB(serde_json::to_value(drop).unwrap())
+      }
+    }
   } else {
     JsonB(json!({
         "punc": null,
@@ -136,34 +224,11 @@ fn validate_json_schema(schema_id: &str, instance: JsonB) -> JsonB {
 
 #[pg_extern(strict, parallel_safe)]
 fn json_schema_cached(schema_id: &str) -> bool {
-  // Acquire Snapshot for safe read
   if let Some(validator) = GLOBAL_VALIDATOR.read().unwrap().as_ref() {
-    // We can expose a get/contains method on Validator or peek inside
-    // Since Validator owns Registry, we need a method there or hack it
-    // Let's assume Validator exposes a minimal check or we just check validity of that schema?
-    // Actually, registry access is private inside Validator now.
-    // We should add `has_schema` to Validator.
-    // For now, let's just cheat: Validate against it, if schema not found error, return false.
-    // Or better: Add `has_schema` to Validator.
-    // Let's do that in a follow up if needed, but for now we need a way.
-    // I'll add `has_schema` to Validator via a quick task or assume it exists?
-    // No, I just overwrote Validator without it.
-    // Better Logic: Try to validate "null" against it?
-    // No, simpler: Update Validator to expose has_schema.
-    // But I cannot call replace_validator now.
-    // Wait, I can try to access the public underlying registry if I expose it?
-    // Validator struct: `pub struct Validator { registry: Registry }`?
-    // No, keeping it opaque is better.
-    // Let's execute validate and check if error code is SCHEMA_NOT_FOUND.
-    let drop = validator.validate(schema_id, &serde_json::Value::Null); // Minimal payload
-    if !drop.errors.is_empty() {
-      for e in drop.errors {
-        if e.code == "SCHEMA_NOT_FOUND" {
-          return false;
-        }
-      }
+    match validator.validate(schema_id, &serde_json::Value::Null) {
+      Err(e) if e.code == "SCHEMA_NOT_FOUND" => false,
+      _ => true,
     }
-    true
   } else {
     false
   }
@@ -178,13 +243,8 @@ fn clear_json_schemas() -> JsonB {
 
 #[pg_extern(strict, parallel_safe)]
 fn show_json_schemas() -> JsonB {
-  // Use _validator to suppress warning
   if let Some(_validator) = GLOBAL_VALIDATOR.read().unwrap().as_ref() {
-    // Debug dump
-    // We need Validator to expose len() or debug info?
-    // Or just return success for now as in original code.
     JsonB(json!({ "response": "success", "status": "active" }))
-    // Ideally: validator.registry_len()
   } else {
     JsonB(json!({ "response": "success", "status": "empty" }))
   }

src/tests.rs

@@ -1097,6 +1097,30 @@ fn test_pattern_1() {
     crate::util::run_test_file_at_index(&path, 1).unwrap();
 }
 
+#[pg_test]
+fn test_masking_0() {
+    let path = format!("{}/tests/fixtures/masking.json", env!("CARGO_MANIFEST_DIR"));
+    crate::util::run_test_file_at_index(&path, 0).unwrap();
+}
+
+#[pg_test]
+fn test_masking_1() {
+    let path = format!("{}/tests/fixtures/masking.json", env!("CARGO_MANIFEST_DIR"));
+    crate::util::run_test_file_at_index(&path, 1).unwrap();
+}
+
+#[pg_test]
+fn test_masking_2() {
+    let path = format!("{}/tests/fixtures/masking.json", env!("CARGO_MANIFEST_DIR"));
+    crate::util::run_test_file_at_index(&path, 2).unwrap();
+}
+
+#[pg_test]
+fn test_masking_3() {
+    let path = format!("{}/tests/fixtures/masking.json", env!("CARGO_MANIFEST_DIR"));
+    crate::util::run_test_file_at_index(&path, 3).unwrap();
+}
+
 #[pg_test]
 fn test_max_properties_0() {
     let path = format!("{}/tests/fixtures/maxProperties.json", env!("CARGO_MANIFEST_DIR"));

src/util.rs

@@ -183,15 +183,51 @@ pub fn run_test_file_at_index(path: &str, index: usize) -> Result<(), String> {
     if let Some(sid) = schema_id {
       let result = validator.validate(&sid, &test.data);
 
-      if !result.errors.is_empty() != !test.valid {
-        failures.push(format!(
-          "[{}] Test '{}' failed. Expected: {}, Got: {}. Errors: {:?}",
-          group.description,
-          test.description,
-          test.valid,
-          !result.errors.is_empty(), // "Got Invalid?"
-          result.errors
-        ));
+      let (got_valid, _errors) = match &result {
+        Ok(res) => (res.is_valid(), &res.errors),
+        Err(_e) => {
+          // If we encounter an execution error (e.g. Schema Not Found),
+          // we treat it as a test failure.
+          (false, &vec![])
+        }
+      };
+
+      if let Some(expected) = &test.expected {
+        // Masking Test
+        let mut data_for_mask = test.data.clone();
+        match validator.mask(&sid, &mut data_for_mask) {
+          Ok(_) => {
+            if !equals(&data_for_mask, expected) {
+              let msg = format!(
+                "Masking Test '{}' failed.\nExpected: {:?}\nGot: {:?}",
+                test.description, expected, data_for_mask
+              );
+              eprintln!("{}", msg);
+              failures.push(msg);
+            }
+          }
+          Err(e) => {
+            let msg = format!(
+              "Masking Test '{}' failed with execution error: {:?}",
+              test.description, e
+            );
+            eprintln!("{}", msg);
+            failures.push(msg);
+          }
+        }
+      } else {
+        // Standard Validation Test
+        if got_valid != test.valid {
+          let error_msg = match &result {
+            Ok(res) => format!("{:?}", res.errors),
+            Err(e) => format!("Execution Error: {:?}", e),
+          };
+
+          failures.push(format!(
+            "[{}] Test '{}' failed. Expected: {}, Got: {}. Errors: {}",
+            group.description, test.description, test.valid, got_valid, error_msg
+          ));
+        }
       }
     } else {
       failures.push(format!(
@@ -310,28 +346,47 @@ pub fn run_test_file(path: &str) -> Result<(), String> {
       // Use explicit schema_id from test, or default to unique_id
       let schema_id = test.schema_id.as_deref().unwrap_or(&unique_id).to_string();
 
-      let drop = validator.validate(&schema_id, &test.data);
+      let result = validator.validate(&schema_id, &test.data);
 
       if test.valid {
-        if !drop.errors.is_empty() {
-          let msg = format!(
-            "Test failed (expected valid): {}\nSchema: {:?}\nData: {:?}\nErrors: {:?}",
-            test.description,
-            group.schema, // We might need to find the actual schema used if schema_id is custom
-            test.data,
-            drop.errors
-          );
-          eprintln!("{}", msg);
-          failures.push(msg);
+        match result {
+          Ok(res) => {
+            if !res.is_valid() {
+              let msg = format!(
+                "Test failed (expected valid): {}\nSchema: {:?}\nData: {:?}\nErrors: {:?}",
+                test.description,
+                group.schema, // We might need to find the actual schema used if schema_id is custom
+                test.data,
+                res.errors
+              );
+              eprintln!("{}", msg);
+              failures.push(msg);
+            }
+          }
+          Err(e) => {
+            let msg = format!(
+              "Test failed (expected valid) but got execution error: {}\nSchema: {:?}\nData: {:?}\nError: {:?}",
+              test.description, group.schema, test.data, e
+            );
+            eprintln!("{}", msg);
+            failures.push(msg);
+          }
         }
       } else {
-        if drop.errors.is_empty() {
-          let msg = format!(
-            "Test failed (expected invalid): {}\nSchema: {:?}\nData: {:?}\nErrors: (Empty)",
-            test.description, group.schema, test.data
-          );
-          println!("{}", msg);
-          failures.push(msg);
+        match result {
+          Ok(res) => {
+            if res.is_valid() {
+              let msg = format!(
+                "Test failed (expected invalid): {}\nSchema: {:?}\nData: {:?}",
+                test.description, group.schema, test.data
+              );
+              eprintln!("{}", msg);
+              failures.push(msg);
+            }
+          }
+          Err(_) => {
+            // Expected invalid, got error (which implies invalid/failure), so this is PASS.
+          }
         }
       }
     }

src/validator.rs

@@ -6,7 +6,7 @@ use regex::Regex;
 use serde_json::Value;
 use std::collections::HashSet;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, serde::Serialize)]
 pub struct ValidationError {
   pub code: String,
   pub message: String,
@@ -18,10 +18,12 @@ pub enum ResolvedRef<'a> {
   Global(&'a Schema, &'a Schema),
 }
 
-#[derive(Debug, Default, Clone)]
+#[derive(Debug, Default, Clone, serde::Serialize)]
 pub struct ValidationResult {
   pub errors: Vec<ValidationError>,
+  #[serde(skip)]
   pub evaluated_keys: HashSet<String>,
+  #[serde(skip)]
   pub evaluated_indices: HashSet<usize>,
 }
 
@@ -41,7 +43,110 @@ impl ValidationResult {
   }
 }
 
-pub struct ValidationContext<'a> {
+use std::ptr::NonNull;
+
+pub trait ValidationInstance<'a>: Copy + Clone {
+  fn as_value(&self) -> &'a Value;
+  fn child_at_key(&self, key: &str) -> Option<Self>;
+  fn child_at_index(&self, idx: usize) -> Option<Self>;
+  fn prune_object(&self, _keys: &HashSet<String>) {}
+  fn prune_array(&self, _indices: &HashSet<usize>) {}
+}
+
+#[derive(Clone, Copy)]
+pub struct ReadOnlyInstance<'a>(pub &'a Value);
+
+impl<'a> ValidationInstance<'a> for ReadOnlyInstance<'a> {
+  fn as_value(&self) -> &'a Value {
+    self.0
+  }
+
+  fn child_at_key(&self, key: &str) -> Option<Self> {
+    self.0.get(key).map(ReadOnlyInstance)
+  }
+
+  fn child_at_index(&self, idx: usize) -> Option<Self> {
+    self.0.get(idx).map(ReadOnlyInstance)
+  }
+}
+
+#[derive(Clone, Copy)]
+pub struct MutableInstance {
+  ptr: NonNull<Value>,
+}
+
+impl MutableInstance {
+  pub fn new(val: &mut Value) -> Self {
+    Self {
+      ptr: NonNull::from(val),
+    }
+  }
+}
+
+impl<'a> ValidationInstance<'a> for MutableInstance {
+  fn as_value(&self) -> &'a Value {
+    unsafe { self.ptr.as_ref() }
+  }
+
+  fn child_at_key(&self, key: &str) -> Option<Self> {
+    unsafe {
+      if let Some(obj) = self.ptr.as_ref().as_object() {
+        // We use as_ref() to check existence (safe read).
+        if obj.contains_key(key) {
+          // Now we need mutable pointer to child.
+          // Since we have *mut parent, and we know key exists...
+          // casting *mut Value -> &mut Value -> get_mut -> *mut Value
+          // This is safe because we are single threaded and not holding other refs across this call.
+          let parent_mut = &mut *self.ptr.as_ptr();
+          if let Some(child_val) = parent_mut.get_mut(key) {
+            return Some(MutableInstance::new(child_val));
+          }
+        }
+      }
+      None
+    }
+  }
+
+  fn child_at_index(&self, idx: usize) -> Option<Self> {
+    unsafe {
+      if let Some(arr) = self.ptr.as_ref().as_array() {
+        if idx < arr.len() {
+          let parent_mut = &mut *self.ptr.as_ptr();
+          if let Some(child_val) = parent_mut.get_mut(idx) {
+            return Some(MutableInstance::new(child_val));
+          }
+        }
+      }
+      None
+    }
+  }
+
+  fn prune_object(&self, keys: &HashSet<String>) {
+    unsafe {
+      // We must re-acquire mutable reference from pointer
+      let val_mut = &mut *self.ptr.as_ptr();
+      if let Some(obj) = val_mut.as_object_mut() {
+        obj.retain(|k, _| keys.contains(k));
+      }
+    }
+  }
+
+  fn prune_array(&self, indices: &HashSet<usize>) {
+    unsafe {
+      let val_mut = &mut *self.ptr.as_ptr();
+      if let Some(arr) = val_mut.as_array_mut() {
+        let mut i = 0;
+        arr.retain(|_| {
+          let keep = indices.contains(&i);
+          i += 1;
+          keep
+        });
+      }
+    }
+  }
+}
+
+pub struct ValidationContext<'a, I: ValidationInstance<'a>> {
   // 1. Global (The Library) - now passed as reference
   pub registry: &'a Registry,
   pub root: &'a Schema,
@@ -50,12 +155,12 @@ pub struct ValidationContext<'a> {
   pub schema: &'a Schema,
 
   // 3. The Data (The Instance)
-  pub current: &'a Value,
+  pub instance: I,
 
   // 4. State
-  pub path: &'a str,
+  pub path: String,
   pub depth: usize,
-  pub scope: &'a [String],
+  pub scope: Vec<String>, // OWNED to avoid lifetime hell
 
   // 5. Config
   pub overrides: HashSet<String>, // Keywords explicitly defined by callers that I should skip (Inherited Mask)
@@ -63,13 +168,13 @@ pub struct ValidationContext<'a> {
   pub reporter: bool, // If true, we only report evaluated keys, don't enforce strictness
 }
 
-impl<'a> ValidationContext<'a> {
+impl<'a, I: ValidationInstance<'a>> ValidationContext<'a, I> {
   pub fn new(
     registry: &'a Registry,
     root: &'a Schema,
     schema: &'a Schema,
-    current: &'a Value,
-    scope: &'a [String],
+    instance: I,
+    scope: Vec<String>,
     overrides: HashSet<String>,
     extensible: bool,
     reporter: bool,
@@ -79,8 +184,8 @@ impl<'a> ValidationContext<'a> {
       registry,
       root,
       schema,
-      current,
-      path: "",
+      instance,
+      path: String::new(),
       depth: 0,
       scope,
       overrides,
@@ -92,9 +197,9 @@ impl<'a> ValidationContext<'a> {
   pub fn derive(
     &self,
     schema: &'a Schema,
-    current: &'a Value,
-    path: &'a str,
-    scope: &'a [String],
+    instance: I, // We take I directly (it is Copy)
+    path: &str,
+    scope: Vec<String>,
     overrides: HashSet<String>,
     extensible: bool,
     reporter: bool,
@@ -105,8 +210,8 @@ impl<'a> ValidationContext<'a> {
       registry: self.registry,
       root: self.root,
       schema,
-      current,
-      path,
+      instance,
+      path: path.to_string(),
       depth: self.depth + 1,
       scope,
       overrides,
@@ -119,9 +224,9 @@ impl<'a> ValidationContext<'a> {
   pub fn derive_for_schema(&self, schema: &'a Schema, reporter: bool) -> Self {
     self.derive(
       schema,
-      self.current,
-      self.path,
-      self.scope,
+      self.instance, // Copy
+      &self.path,
+      self.scope.clone(),
       HashSet::new(), // Reset overrides for composition/branching (Strict Intersection)
       self.extensible, // Inherited extensibility doesn't change for same-level schema switch
       reporter,
@@ -132,8 +237,7 @@ impl<'a> ValidationContext<'a> {
 
   pub fn validate(&self) -> Result<ValidationResult, ValidationError> {
     // Check if we need to update scope due to ID
-    let mut effective_scope = self.scope;
-    let mut new_scope_buf: Vec<String>;
+    let mut effective_scope = self.scope.clone();
 
     if let Some(id) = &self.schema.obj.id {
       let current_base = self.scope.last().map(|s| s.as_str()).unwrap_or("");
@@ -146,18 +250,15 @@ impl<'a> ValidationContext<'a> {
         }
       }
 
-      new_scope_buf = self.scope.to_vec();
-      new_scope_buf.push(new_base);
-      effective_scope = &new_scope_buf;
-    }
+      effective_scope.push(new_base);
 
-    if effective_scope.len() != self.scope.len() {
+      // If scope changed, we create a shadow context to use the new scope
       let shadow = ValidationContext {
         registry: self.registry,
         root: self.root,
         schema: self.schema,
-        current: self.current,
-        path: self.path,
+        instance: self.instance,
+        path: self.path.clone(),
         depth: self.depth,
         scope: effective_scope,
         overrides: self.overrides.clone(),
@@ -167,6 +268,7 @@ impl<'a> ValidationContext<'a> {
       return shadow.validate_scoped();
     }
 
+    // If no ID change, proceed
     self.validate_scoped()
   }
 
@@ -193,15 +295,7 @@ impl<'a> ValidationContext<'a> {
     // --- Helpers Groups ---
 
     if let Some(ref_res) = self.validate_refs()? {
-      // eprintln!(
-      //   "DEBUG: validate_refs returned {} errors",
-      //   ref_res.errors.len()
-      // );
       result.merge(ref_res);
-      // eprintln!(
-      //   "DEBUG: result has {} errors after refs merge",
-      //   result.errors.len()
-      // );
     }
 
     // 2. Core
@@ -230,9 +324,10 @@ impl<'a> ValidationContext<'a> {
 
     // If extensible, mark all as evaluated so strictness checks pass and parents don't complain
     if self.extensible {
-      if let Some(obj) = self.current.as_object() {
+      let current = self.instance.as_value();
+      if let Some(obj) = current.as_object() {
         result.evaluated_keys.extend(obj.keys().cloned());
-      } else if let Some(arr) = self.current.as_array() {
+      } else if let Some(arr) = current.as_array() {
         result.evaluated_indices.extend(0..arr.len());
       }
     }
@@ -250,8 +345,10 @@ impl<'a> ValidationContext<'a> {
     let mut handled = false;
 
     // Scope is already effective due to validate() wrapper!
-    let effective_scope = self.scope;
+    // self.scope is Vec<String>
+    let effective_scope = &self.scope;
     let current_base_resolved = effective_scope.last().map(|s| s.as_str()).unwrap_or("");
+    // Removed unused current binding
 
     // $ref
     if let Some(ref ref_string) = self.schema.ref_string {
@@ -266,9 +363,9 @@ impl<'a> ValidationContext<'a> {
 
         let derived = self.derive(
           self.root,
-          self.current,
-          self.path,
-          effective_scope,
+          self.instance, // Copy
+          &self.path,
+          effective_scope.clone(),
           new_overrides,
           self.extensible,
           self.reporter, // Inherit so efficient composition (allOf) works, but property refs stay strict
@@ -290,17 +387,16 @@ impl<'a> ValidationContext<'a> {
             &matched_key
           };
 
-          let mut new_scope_buffer: Vec<String>;
           let scope_to_pass = if target_schema.obj.id.is_none() {
             if !resource_base.is_empty() && resource_base != current_base_resolved {
-              new_scope_buffer = effective_scope.to_vec();
-              new_scope_buffer.push(resource_base.to_string());
-              &new_scope_buffer
+              let mut new_scope = effective_scope.clone();
+              new_scope.push(resource_base.to_string());
+              new_scope
             } else {
-              effective_scope
+              effective_scope.clone()
             }
           } else {
-            effective_scope
+            effective_scope.clone()
           };
 
           // Calculate new overrides (Masking)
@@ -313,7 +409,7 @@ impl<'a> ValidationContext<'a> {
             self.registry,
             target_root,
             target_schema,
-            self.current,
+            self.instance, // Copy
             scope_to_pass,
             new_overrides,
             false,         // Reset extensibility for $ref (Default Strict)
@@ -321,7 +417,7 @@ impl<'a> ValidationContext<'a> {
           );
           // Manually set path/depth to continue trace
           let mut manual_ctx = target_ctx;
-          manual_ctx.path = self.path;
+          manual_ctx.path = self.path.clone();
           manual_ctx.depth = self.depth + 1;
 
           let target_res = manual_ctx.validate()?;
@@ -432,18 +528,17 @@ impl<'a> ValidationContext<'a> {
           &matched_key
         };
 
-        let mut new_scope_buffer: Vec<String>;
         let scope_to_pass = if let Some(ref tid) = target_schema.obj.id {
-          new_scope_buffer = effective_scope.to_vec();
-          new_scope_buffer.push(tid.clone());
-          &new_scope_buffer
+          let mut new_scope = effective_scope.clone();
+          new_scope.push(tid.clone());
+          new_scope
         } else {
           if !resource_base.is_empty() && resource_base != current_base_resolved {
-            new_scope_buffer = effective_scope.to_vec();
-            new_scope_buffer.push(resource_base.to_string());
-            &new_scope_buffer
+            let mut new_scope = effective_scope.clone();
+            new_scope.push(resource_base.to_string());
+            new_scope
           } else {
-            effective_scope
+            effective_scope.clone()
           }
         };
 
@@ -457,14 +552,14 @@ impl<'a> ValidationContext<'a> {
           self.registry,
           target_root,
           target_schema,
-          self.current,
+          self.instance, // Copy
           scope_to_pass,
           new_overrides,
           false,
           self.reporter, // Propagate reporter
         );
         let mut manual_ctx = target_ctx;
-        manual_ctx.path = self.path;
+        manual_ctx.path = self.path.clone();
         manual_ctx.depth = self.depth + 1;
         // manual_ctx.reporter = true;
 
@@ -482,11 +577,12 @@ impl<'a> ValidationContext<'a> {
   }
 
   fn validate_core(&self, result: &mut ValidationResult) {
+    let current = self.instance.as_value();
     // Type
     if let Some(ref type_) = self.schema.type_ {
       match type_ {
         crate::schema::SchemaTypeOrArray::Single(t) => {
-          if !Validator::check_type(t, self.current) {
+          if !Validator::check_type(t, current) {
             result.errors.push(ValidationError {
               code: "INVALID_TYPE".to_string(),
               message: format!("Expected type '{}'", t),
@@ -497,7 +593,7 @@ impl<'a> ValidationContext<'a> {
         crate::schema::SchemaTypeOrArray::Multiple(types) => {
           let mut valid = false;
           for t in types {
-            if Validator::check_type(t, self.current) {
+            if Validator::check_type(t, current) {
               valid = true;
               break;
             }
@@ -515,16 +611,16 @@ impl<'a> ValidationContext<'a> {
 
     // Const
     if let Some(ref const_val) = self.schema.const_ {
-      if !crate::util::equals(self.current, const_val) {
+      if !crate::util::equals(current, const_val) {
         result.errors.push(ValidationError {
           code: "CONST_VIOLATED".to_string(),
           message: "Value does not match const".to_string(),
           path: self.path.to_string(),
         });
       } else {
-        if let Some(obj) = self.current.as_object() {
+        if let Some(obj) = current.as_object() {
           result.evaluated_keys.extend(obj.keys().cloned());
-        } else if let Some(arr) = self.current.as_array() {
+        } else if let Some(arr) = current.as_array() {
           result.evaluated_indices.extend(0..arr.len());
         }
       }
@@ -534,7 +630,7 @@ impl<'a> ValidationContext<'a> {
     if let Some(ref enum_vals) = self.schema.enum_ {
       let mut found = false;
       for val in enum_vals {
-        if crate::util::equals(self.current, val) {
+        if crate::util::equals(current, val) {
           found = true;
           break;
         }
@@ -546,9 +642,9 @@ impl<'a> ValidationContext<'a> {
           path: self.path.to_string(),
         });
       } else {
-        if let Some(obj) = self.current.as_object() {
+        if let Some(obj) = current.as_object() {
           result.evaluated_keys.extend(obj.keys().cloned());
-        } else if let Some(arr) = self.current.as_array() {
+        } else if let Some(arr) = current.as_array() {
           result.evaluated_indices.extend(0..arr.len());
         }
       }
@@ -556,7 +652,8 @@ impl<'a> ValidationContext<'a> {
   }
 
   fn validate_numeric(&self, result: &mut ValidationResult) {
-    if let Some(num) = self.current.as_f64() {
+    let current = self.instance.as_value();
+    if let Some(num) = current.as_f64() {
       if let Some(min) = self.schema.minimum {
         if num < min {
           result.errors.push(ValidationError {
@@ -607,7 +704,8 @@ impl<'a> ValidationContext<'a> {
   }
 
   fn validate_string(&self, result: &mut ValidationResult) {
-    if let Some(s) = self.current.as_str() {
+    let current = self.instance.as_value();
+    if let Some(s) = current.as_str() {
       if let Some(min) = self.schema.min_length {
         if (s.chars().count() as f64) < min {
           result.errors.push(ValidationError {
@@ -649,16 +747,17 @@ impl<'a> ValidationContext<'a> {
   }
 
   fn validate_format(&self, result: &mut ValidationResult) {
+    let current = self.instance.as_value();
     if let Some(ref compiled_fmt) = self.schema.compiled_format {
       match compiled_fmt {
         crate::compiler::CompiledFormat::Func(f) => {
-          let should = if let Some(s) = self.current.as_str() {
+          let should = if let Some(s) = current.as_str() {
             !s.is_empty()
           } else {
             true
           };
           if should {
-            if let Err(e) = f(self.current) {
+            if let Err(e) = f(current) {
               result.errors.push(ValidationError {
                 code: "FORMAT_MISMATCH".to_string(),
                 message: format!("Format error: {}", e),
@@ -668,7 +767,7 @@ impl<'a> ValidationContext<'a> {
           }
         }
         crate::compiler::CompiledFormat::Regex(re) => {
-          if let Some(s) = self.current.as_str() {
+          if let Some(s) = current.as_str() {
             if !re.is_match(s) {
               result.errors.push(ValidationError {
                 code: "FORMAT_MISMATCH".to_string(),
@@ -683,7 +782,8 @@ impl<'a> ValidationContext<'a> {
   }
 
   fn validate_object(&self, result: &mut ValidationResult) -> Result<(), ValidationError> {
-    if let Some(obj) = self.current.as_object() {
+    let current = self.instance.as_value();
+    if let Some(obj) = current.as_object() {
       // 1. Min Properties
       if let Some(min) = self.schema.min_properties {
         if (obj.len() as f64) < min {
@@ -739,9 +839,9 @@ impl<'a> ValidationContext<'a> {
             // Reporter = true (merges results).
             let derived = self.derive(
               sub_schema,
-              self.current,
-              self.path,
-              self.scope,
+              self.instance, // Copy
+              &self.path,
+              self.scope.clone(),
               HashSet::new(),
               self.extensible,
               false,
@@ -759,7 +859,7 @@ impl<'a> ValidationContext<'a> {
             continue;
           }
 
-          if let Some(val) = obj.get(key) {
+          if let Some(child_instance) = self.instance.child_at_key(key) {
             let new_path = format!("{}/{}", self.path, key);
 
             let is_ref = sub_schema.ref_string.is_some() || sub_schema.obj.dynamic_ref.is_some();
@@ -767,9 +867,9 @@ impl<'a> ValidationContext<'a> {
 
             let derived = self.derive(
               sub_schema,
-              val,
+              child_instance,
               &new_path,
-              self.scope,
+              self.scope.clone(),
               HashSet::new(),
               next_extensible,
               false,
@@ -783,31 +883,28 @@ impl<'a> ValidationContext<'a> {
 
       if let Some(ref compiled_pp) = self.schema.compiled_pattern_properties {
         for (compiled_re, sub_schema) in compiled_pp {
-          for (key, val) in obj {
+          for (key, _) in obj {
             if compiled_re.0.is_match(key) {
-              // Note: Pattern properties are not shadowed by property names in standard override logic typically,
-              // but if we supported masking pattern props, we'd check here. For now, assuming standard behavior + no masking.
+              // Note: Pattern properties need to derive child instance dynamically for each matching key
+              if let Some(child_instance) = self.instance.child_at_key(key) {
+                let new_path = format!("{}/{}", self.path, key);
+                let is_ref =
+                  sub_schema.ref_string.is_some() || sub_schema.obj.dynamic_ref.is_some();
+                let next_extensible = if is_ref { false } else { self.extensible };
 
-              let new_path = format!("{}/{}", self.path, key);
-              let is_ref = sub_schema.ref_string.is_some() || sub_schema.obj.dynamic_ref.is_some();
-              let next_extensible = if is_ref { false } else { self.extensible };
-
-              let derived = self.derive(
-                sub_schema,
-                val,
-                &new_path,
-                self.scope,
-                HashSet::new(),
-                next_extensible,
-                false,
-              );
-              let item_res = derived.validate()?;
-              // eprintln!(
-              //   "PPROP VALIDATE: path={} key={} keys={:?}",
-              //   self.path, key, item_res.evaluated_keys
-              // );
-              result.merge(item_res);
-              result.evaluated_keys.insert(key.clone());
+                let derived = self.derive(
+                  sub_schema,
+                  child_instance,
+                  &new_path,
+                  self.scope.clone(),
+                  HashSet::new(),
+                  next_extensible,
+                  false,
+                );
+                let item_res = derived.validate()?;
+                result.merge(item_res);
+                result.evaluated_keys.insert(key.clone());
+              }
             }
           }
         }
@@ -816,39 +913,44 @@ impl<'a> ValidationContext<'a> {
       // 7. Property Names
       if let Some(ref property_names) = self.schema.property_names {
         for key in obj.keys() {
-          let new_path = format!("{}/propertyNames/{}", self.path, key);
+          let _new_path = format!("{}/propertyNames/{}", self.path, key);
           let val_str = Value::String(key.clone());
 
-          // Validating the KEY as a STRING instance.
-          // New scope.
-          let derived = self.derive(
+          let ctx = ValidationContext::new(
+            self.registry,
+            self.root,
             property_names,
-            &val_str,
-            &new_path,
-            self.scope,
+            crate::validator::ReadOnlyInstance(&val_str),
+            self.scope.clone(),
             HashSet::new(),
             self.extensible,
-            false,
+            self.reporter,
           );
-          result.merge(derived.validate()?);
+
+          result.merge(ctx.validate()?);
         }
       }
+      // 7. Additional Properties (Strictness / Extensibility)
+      // Done via check_strictness at end OR explicit schema keyword.
+    }
+
+    // --- Pruning (Masking) ---
+    if !self.extensible {
+      self.instance.prune_object(&result.evaluated_keys);
     }
-    // 8. Strictness Check (Unevaluated Properties) - MOVED TO validate_scoped END
-    // Lines 843-856 removed to correct evaluation order.
-    // if !self.extensible && !self.reporter { ... }
 
     Ok(())
   }
 
   fn validate_array(&self, result: &mut ValidationResult) -> Result<(), ValidationError> {
-    if let Some(arr) = self.current.as_array() {
+    let current = self.instance.as_value();
+    if let Some(arr) = current.as_array() {
       // 1. Min/Max Items
       if let Some(min) = self.schema.min_items {
         if (arr.len() as f64) < min {
           result.errors.push(ValidationError {
             code: "MIN_ITEMS".to_string(),
-            message: format!("Length < min {}", min),
+            message: "Too few items".to_string(),
             path: self.path.to_string(),
           });
         }
@@ -857,26 +959,22 @@ impl<'a> ValidationContext<'a> {
         if (arr.len() as f64) > max {
           result.errors.push(ValidationError {
             code: "MAX_ITEMS".to_string(),
-            message: format!("Length > max {}", max),
+            message: "Too many items".to_string(),
             path: self.path.to_string(),
           });
         }
       }
+
       // 2. Unique Items
       if self.schema.unique_items.unwrap_or(false) {
-        let mut seen: Vec<&Value> = Vec::with_capacity(arr.len());
-        for (i, item) in arr.iter().enumerate() {
-          for seen_item in &seen {
-            if crate::util::equals(item, *seen_item) {
-              result.errors.push(ValidationError {
-                code: "UNIQUE_ITEMS".to_string(),
-                message: format!("Duplicate item at index {}", i),
-                path: format!("{}/{}", self.path, i),
-              });
-              break;
-            }
-          }
-          if !result.errors.is_empty() {
+        let mut seen: Vec<&Value> = Vec::new();
+        for item in arr {
+          if seen.contains(&item) {
+            result.errors.push(ValidationError {
+              code: "UNIQUE_ITEMS_VIOLATED".to_string(),
+              message: "Array has duplicate items".to_string(),
+              path: self.path.to_string(),
+            });
             break;
           }
           seen.push(item);
@@ -886,21 +984,25 @@ impl<'a> ValidationContext<'a> {
       // 3. Contains
       if let Some(ref contains_schema) = self.schema.contains {
         let mut _match_count = 0;
-        for (i, param) in arr.iter().enumerate() {
-          let derived = self.derive(
-            contains_schema,
-            param,
-            self.path,
-            self.scope,
-            HashSet::new(),
-            self.extensible,
-            false,
-          );
+        // self.instance.as_value() is &Value
+        // We iterate indices
+        for i in 0..arr.len() {
+          if let Some(child_instance) = self.instance.child_at_index(i) {
+            let derived = self.derive(
+              contains_schema,
+              child_instance,
+              &self.path,
+              self.scope.clone(),
+              HashSet::new(),
+              self.extensible,
+              false,
+            );
 
-          let check = derived.validate()?;
-          if check.is_valid() {
-            _match_count += 1;
-            result.evaluated_indices.insert(i);
+            let check = derived.validate()?;
+            if check.is_valid() {
+              _match_count += 1;
+              result.evaluated_indices.insert(i);
+            }
           }
         }
 
@@ -933,20 +1035,21 @@ impl<'a> ValidationContext<'a> {
         for (i, sub_schema) in prefix.iter().enumerate() {
           if i < len {
             let path = format!("{}/{}", self.path, i);
-
-            let derived = self.derive(
-              sub_schema,
-              &arr[i],
-              &path,
-              self.scope,
-              HashSet::new(),
-              self.extensible,
-              false,
-            );
-            let item_res = derived.validate()?;
-            result.merge(item_res);
-            result.evaluated_indices.insert(i);
-            validation_index += 1;
+            if let Some(child_instance) = self.instance.child_at_index(i) {
+              let derived = self.derive(
+                sub_schema,
+                child_instance,
+                &path,
+                self.scope.clone(),
+                HashSet::new(),
+                self.extensible,
+                false,
+              );
+              let item_res = derived.validate()?;
+              result.merge(item_res);
+              result.evaluated_indices.insert(i);
+              validation_index += 1;
+            }
           }
         }
       }
@@ -954,22 +1057,28 @@ impl<'a> ValidationContext<'a> {
       if let Some(ref items_schema) = self.schema.items {
         for i in validation_index..len {
           let path = format!("{}/{}", self.path, i);
-
-          let derived = self.derive(
-            items_schema,
-            &arr[i],
-            &path,
-            self.scope,
-            HashSet::new(),
-            self.extensible,
-            false,
-          );
-          let item_res = derived.validate()?;
-          result.merge(item_res);
-          result.evaluated_indices.insert(i);
+          if let Some(child_instance) = self.instance.child_at_index(i) {
+            let derived = self.derive(
+              items_schema,
+              child_instance,
+              &path,
+              self.scope.clone(),
+              HashSet::new(),
+              self.extensible,
+              false,
+            );
+            let item_res = derived.validate()?;
+            result.merge(item_res);
+            result.evaluated_indices.insert(i);
+          }
         }
       }
     }
+    // --- Pruning (Masking) ---
+    if !self.extensible {
+      self.instance.prune_array(&result.evaluated_indices);
+    }
+
     Ok(())
   }
 
@@ -1089,7 +1198,7 @@ impl<'a> ValidationContext<'a> {
     }
 
     // 1. Unevaluated Properties
-    if let Some(obj) = self.current.as_object() {
+    if let Some(obj) = self.instance.as_value().as_object() {
       for key in obj.keys() {
         if !result.evaluated_keys.contains(key) && !self.overrides.contains(key) {
           result.errors.push(ValidationError {
@@ -1102,7 +1211,7 @@ impl<'a> ValidationContext<'a> {
     }
 
     // 2. Unevaluated Items
-    if let Some(arr) = self.current.as_array() {
+    if let Some(arr) = self.instance.as_value().as_array() {
       for i in 0..arr.len() {
         if !result.evaluated_indices.contains(&i) {
           result.errors.push(ValidationError {
@@ -1267,65 +1376,58 @@ impl Validator {
     None
   }
 
-  pub fn validate(&self, schema_id: &str, instance: &Value) -> crate::drop::Drop {
-    let registry = &self.registry;
-    // Registry is owned, so we can access it directly. No mutex needed.
-    // However, Validator owns it, so we need &self to access.
-
-    if let Some(root) = registry.get(schema_id) {
-      let root_id = root.obj.id.clone().unwrap_or_default();
-      let scope = vec![root_id.clone()];
-
-      // Initial Context
+  pub fn validate(
+    &self,
+    schema_id: &str,
+    instance: &Value,
+  ) -> Result<ValidationResult, ValidationError> {
+    if let Some(schema) = self.registry.schemas.get(schema_id) {
       let ctx = ValidationContext::new(
-        registry,
-        &root,
-        &root,
-        instance,
-        &scope,
+        &self.registry,
+        schema,
+        schema,
+        ReadOnlyInstance(instance),
+        vec![],
         HashSet::new(),
+        false, // Default strictness (overridden by schema.extensible if present)
+        false,
+      );
+      ctx.validate()
+    } else {
+      Err(ValidationError {
+        code: "SCHEMA_NOT_FOUND".to_string(),
+        message: format!("Schema {} not found", schema_id),
+        path: "".to_string(),
+      })
+    }
+  }
+
+  pub fn mask(
+    &self,
+    schema_id: &str,
+    instance: &mut Value,
+  ) -> Result<ValidationResult, ValidationError> {
+    if let Some(schema) = self.registry.schemas.get(schema_id) {
+      let ctx = ValidationContext::new(
+        &self.registry,
+        schema,
+        schema,
+        MutableInstance::new(instance),
+        vec![],
+        HashSet::new(),
+        false, // Default strictness
         false,
-        false, // reporter = false (Default)
       );
 
-      match ctx.validate() {
-        Ok(result) => {
-          if result.is_valid() {
-            crate::drop::Drop::success()
-          } else {
-            let errors = result
-              .errors
-              .into_iter()
-              .map(|e| crate::drop::Error {
-                punc: None,
-                code: e.code,
-                message: e.message,
-                details: crate::drop::ErrorDetails { path: e.path },
-              })
-              .collect();
-            crate::drop::Drop::with_errors(errors)
-          }
-        }
-        Err(e) => {
-          let error = crate::drop::Error {
-            punc: None,
-            code: e.code,
-            message: e.message,
-            details: crate::drop::ErrorDetails { path: e.path },
-          };
-          crate::drop::Drop::with_errors(vec![error])
-        }
-      }
+      let res = ctx.validate()?;
+
+      Ok(res)
     } else {
-      let error = crate::drop::Error {
-        punc: None,
+      Err(ValidationError {
         code: "SCHEMA_NOT_FOUND".to_string(),
-        message: format!("Schema '{}' not found", schema_id),
-        details: crate::drop::ErrorDetails {
-          path: "".to_string(),
-        },
-      };
-      crate::drop::Drop::with_errors(vec![error])
+        message: format!("Schema {} not found", schema_id),
+        path: "".to_string(),
+      })
     }
   }
 }

tests/fixtures/masking.json

@@ -0,0 +1,171 @@
+[
+    {
+        "description": "Masking Properties",
+        "schema": {
+            "$id": "mask_properties",
+            "type": "object",
+            "properties": {
+                "foo": {
+                    "type": "string"
+                },
+                "bar": {
+                    "type": "integer"
+                }
+            },
+            "required": [
+                "foo"
+            ],
+            "extensible": false
+        },
+        "tests": [
+            {
+                "description": "Keep valid properties",
+                "data": {
+                    "foo": "a",
+                    "bar": 1
+                },
+                "valid": true,
+                "expected": {
+                    "foo": "a",
+                    "bar": 1
+                }
+            },
+            {
+                "description": "Remove unknown properties",
+                "data": {
+                    "foo": "a",
+                    "baz": true
+                },
+                "valid": true,
+                "expected": {
+                    "foo": "a"
+                }
+            },
+            {
+                "description": "Keep valid properties with unknown",
+                "data": {
+                    "foo": "a",
+                    "bar": 1,
+                    "baz": true
+                },
+                "valid": true,
+                "expected": {
+                    "foo": "a",
+                    "bar": 1
+                }
+            }
+        ]
+    },
+    {
+        "description": "Masking Nested Objects",
+        "schema": {
+            "$id": "mask_nested",
+            "type": "object",
+            "properties": {
+                "meta": {
+                    "type": "object",
+                    "properties": {
+                        "id": {
+                            "type": "integer"
+                        }
+                    },
+                    "extensible": false
+                }
+            },
+            "extensible": false
+        },
+        "tests": [
+            {
+                "description": "Mask nested object",
+                "data": {
+                    "meta": {
+                        "id": 1,
+                        "extra": "x"
+                    },
+                    "top_extra": "y"
+                },
+                "valid": true,
+                "expected": {
+                    "meta": {
+                        "id": 1
+                    }
+                }
+            }
+        ]
+    },
+    {
+        "description": "Masking Arrays",
+        "schema": {
+            "$id": "mask_arrays",
+            "type": "object",
+            "properties": {
+                "tags": {
+                    "type": "array",
+                    "items": {
+                        "type": "string"
+                    }
+                }
+            },
+            "extensible": false
+        },
+        "tests": [
+            {
+                "description": "Arrays are kept (items are valid)",
+                "data": {
+                    "tags": [
+                        "a",
+                        "b"
+                    ]
+                },
+                "valid": true,
+                "expected": {
+                    "tags": [
+                        "a",
+                        "b"
+                    ]
+                }
+            }
+        ]
+    },
+    {
+        "description": "Masking Tuple Arrays (prefixItems)",
+        "schema": {
+            "$id": "mask_tuple",
+            "type": "object",
+            "properties": {
+                "coord": {
+                    "type": "array",
+                    "prefixItems": [
+                        {
+                            "type": "number"
+                        },
+                        {
+                            "type": "number"
+                        }
+                    ]
+                }
+            },
+            "extensible": false
+        },
+        "tests": [
+            {
+                "description": "Extra tuple items removed",
+                "data": {
+                    "coord": [
+                        1,
+                        2,
+                        3,
+                        "extra"
+                    ]
+                },
+                "valid": true,
+                "expected": {
+                    "coord": [
+                        1,
+                        2
+                    ]
+                }
+            }
+        ]
+    }
+]

tests/tests.rs

@@ -1098,6 +1098,30 @@ fn test_pattern_1() {
     util::run_test_file_at_index(&path, 1).unwrap();
 }
 
+#[test]
+fn test_masking_0() {
+    let path = format!("{}/tests/fixtures/masking.json", env!("CARGO_MANIFEST_DIR"));
+    util::run_test_file_at_index(&path, 0).unwrap();
+}
+
+#[test]
+fn test_masking_1() {
+    let path = format!("{}/tests/fixtures/masking.json", env!("CARGO_MANIFEST_DIR"));
+    util::run_test_file_at_index(&path, 1).unwrap();
+}
+
+#[test]
+fn test_masking_2() {
+    let path = format!("{}/tests/fixtures/masking.json", env!("CARGO_MANIFEST_DIR"));
+    util::run_test_file_at_index(&path, 2).unwrap();
+}
+
+#[test]
+fn test_masking_3() {
+    let path = format!("{}/tests/fixtures/masking.json", env!("CARGO_MANIFEST_DIR"));
+    util::run_test_file_at_index(&path, 3).unwrap();
+}
+
 #[test]
 fn test_max_properties_0() {
     let path = format!("{}/tests/fixtures/maxProperties.json", env!("CARGO_MANIFEST_DIR"));