From af13996146f45f740104f79412b24276892bb913 Mon Sep 17 00:00:00 2001
From: Durran Jordan <durran@gmail.com>
Date: Wed, 12 Mar 2025 16:37:05 +0000
Subject: [PATCH] chore: design for bson options

---
 src/deserializer.ts        | 145 +++++++++++++++++++++++++++++++++++++
 src/parser/deserializer.ts |   5 ++
 2 files changed, 150 insertions(+)
 create mode 100644 src/deserializer.ts

diff --git a/src/deserializer.ts b/src/deserializer.ts
new file mode 100644
index 000000000..a748aeb82
--- /dev/null
+++ b/src/deserializer.ts
@@ -0,0 +1,145 @@
+import { type DeserializeOptions, Int32, type Document, BSONValue, BSONError } from './bson';
+import { BSON_DATA_INT, BSON_DATA_STRING } from './constants';
+import { type BSONElement, parseToElements } from './parser/on_demand/parse_to_elements';
+import { ByteUtils } from './utils/byte_utils';
+import { NumberUtils } from './utils/number_utils';
+
+/**
+ * Type for reviver functions.
+ */
+export type BSONReviver = (key: string, bytes: Uint8Array, element: BSONElement) => unknown;
+
+/**
+ * Deserializer interface.
+ */
+export interface BSONDeserializer {
+  deserialize(buffer: Uint8Array, reviver?: BSONReviver): Document;
+}
+
+// Reviver that returns Int32 boxed type.
+export const boxedInt32Reviver = (key: string, bytes: Uint8Array, element: BSONElement) => {
+  const [offset] = element;
+  return new Int32(NumberUtils.getInt32LE(bytes, offset));
+};
+
+// Reviver that returns numbers.
+export const nativeInt32Reviver = (key: string, bytes: Uint8Array, element: BSONElement) => {
+  const [offset] = element;
+  return NumberUtils.getInt32LE(bytes, offset);
+};
+
+// Reviver that returns strings.
+export const stringReviver = (key: string, bytes: Uint8Array, element: BSONElement) => {
+  return BSONString.fromElement(bytes, element).toNative();
+};
+
+// Reviver that returns strings or temporals based on the key.
+export const customStringReviver = (key: string, bytes: Uint8Array, element: BSONElement) => {
+  const value = BSONString.fromElement(bytes, element).toNative();
+  if (key === 'date') {
+    // Temporal not supported by Node.js at this time.
+    // return Temporal.PlainDate.from(value);
+    return value;
+  }
+  return value;
+};
+
+// Example boxed revivers map.
+export const BOXED_REVIVERS = new Map<number, BSONReviver>();
+BOXED_REVIVERS.set(BSON_DATA_INT, boxedInt32Reviver);
+BOXED_REVIVERS.set(BSON_DATA_STRING, stringReviver);
+Object.freeze(BOXED_REVIVERS);
+
+// Example native revivers map.
+export const NATIVE_REVIVERS = new Map<number, BSONReviver>();
+NATIVE_REVIVERS.set(BSON_DATA_INT, nativeInt32Reviver);
+NATIVE_REVIVERS.set(BSON_DATA_STRING, stringReviver);
+Object.freeze(NATIVE_REVIVERS);
+
+/**
+ * Deserialize the provided buffer.
+ * @param buffer - The buffer.
+ * @param reviver - The optional reviver.
+ */
+export function deserialize(buffer: Uint8Array, options?: DeserializeOptions): Document {
+  return new RevivingBSONDeserializer(options).deserialize(buffer);
+}
+
+export class MissingReviverError extends BSONError {
+  get name(): 'MissingReviverError' {
+    return 'MissingReviverError';
+  }
+}
+
+export class RevivingBSONDeserializer implements BSONDeserializer {
+  revivers: Map<number, BSONReviver>;
+
+  constructor(options?: DeserializeOptions) {
+    if (options?.reviverMap) {
+      this.revivers = options.reviverMap;
+    } else {
+      this.revivers = buildRevivers(options);
+    }
+  }
+
+  deserialize(buffer: Uint8Array): Document {
+    const document: Document = {};
+    // Go through the buffer and deserialize the elements to BSON boxed types.
+    // If a reviver map is provided, use that to deserialize each element,
+    // otherwise use the internal reviver for each type.
+    for (const element of parseToElements(buffer)) {
+      // For each of the BSONElements create the key, get the reviver for the specific type
+      // and call it with the key, the buffer, and the offset of the value in the buffer.
+      // Set the return value of the revivier on the document.
+      const [type, nameOffset, nameLength] = element;
+      const key = ByteUtils.toUTF8(buffer, nameOffset, nameOffset + nameLength, false);
+      const reviver = this.revivers.get(type);
+      if (!reviver) {
+        throw new MissingReviverError(`No reviver found for type ${type}.`);
+      }
+      document[key] = reviver(key, buffer, element);
+    }
+    return document;
+  }
+}
+
+// Build the reviver map based on the user provided BSON options.
+export function buildRevivers(options?: DeserializeOptions): Map<number, BSONReviver> {
+  const reviverMap = new Map(BOXED_REVIVERS);
+  // Example map population based on options.
+  if (options?.promoteValues) {
+    reviverMap.set(BSON_DATA_INT, nativeInt32Reviver);
+  }
+  return reviverMap;
+}
+
+export class BSONString extends BSONValue {
+  get _bsontype(): 'BSONString' {
+    return 'BSONString';
+  }
+
+  value: string;
+
+  constructor(value: string) {
+    super();
+    this.value = value;
+  }
+
+  static fromElement(bytes: Uint8Array, element: BSONElement): BSONString {
+    const [offset, length] = element;
+    return new BSONString(ByteUtils.toUTF8(bytes, offset, length, false));
+  }
+
+  toNative(): string {
+    return this.value;
+  }
+
+  inspect(): string {
+    return `new BSONString(${this.value})`;
+  }
+
+  /** @internal */
+  toExtendedJSON(): string {
+    return this.value;
+  }
+}
diff --git a/src/parser/deserializer.ts b/src/parser/deserializer.ts
index 97bdd6bf7..5eed7f757 100644
--- a/src/parser/deserializer.ts
+++ b/src/parser/deserializer.ts
@@ -4,6 +4,7 @@ import { Code } from '../code';
 import * as constants from '../constants';
 import { DBRef, type DBRefLike, isDBRefLike } from '../db_ref';
 import { Decimal128 } from '../decimal128';
+import { type BSONReviver } from '../deserializer';
 import { Double } from '../double';
 import { BSONError } from '../error';
 import { Int32 } from '../int_32';
@@ -77,6 +78,10 @@ export interface DeserializeOptions {
    * ```
    */
   validation?: { utf8: boolean | Record<string, true> | Record<string, false> };
+  /**
+   * A custom map of BSON revivers to override the defaults.
+   */
+  reviverMap?: Map<number, BSONReviver>;
 }
 
 // Internal long versions