Preserve partial DataView offsets and lengths

cjs/deserialize.js

@@ -88,8 +88,9 @@ const deserializer = ($, _) => {
       case 'ArrayBuffer':
         return as(new Uint8Array(value).buffer, value);
       case 'DataView': {
-        const { buffer } = new Uint8Array(value);
-        return as(new DataView(buffer), value);
+        const {buffer, byteOffset, byteLength} = Array.isArray(value) ?
+          {buffer: value, byteOffset: 0, byteLength: value.length} : value;
+        return as(new DataView(new Uint8Array(buffer).buffer, byteOffset, byteLength), value);
       }
       case '-0': return -0;
     }

cjs/serialize.js

@@ -85,7 +85,10 @@ const serializer = (strict, json, $, _) => {
         if (type) {
           let spread = value;
           if (type === 'DataView') {
-            spread = new Uint8Array(value.buffer);
+            const {buffer, byteOffset, byteLength} = value;
+            return as([type, {
+              buffer: [...new Uint8Array(buffer)], byteOffset, byteLength
+            }], value);
           }
           else if (type === 'ArrayBuffer') {
             spread = new Uint8Array(value);

esm/deserialize.js

@@ -90,8 +90,9 @@ const deserializer = ($, _) => {
       case 'ArrayBuffer':
         return as(new Uint8Array(value).buffer, value);
       case 'DataView': {
-        const { buffer } = new Uint8Array(value);
-        return as(new DataView(buffer), value);
+        const {buffer, byteOffset, byteLength} = Array.isArray(value) ?
+          {buffer: value, byteOffset: 0, byteLength: value.length} : value;
+        return as(new DataView(new Uint8Array(buffer).buffer, byteOffset, byteLength), value);
       }
       case '-0': return -0;
     }

esm/serialize.js

@@ -87,7 +87,10 @@ const serializer = (strict, json, $, _) => {
         if (type) {
           let spread = value;
           if (type === 'DataView') {
-            spread = new Uint8Array(value.buffer);
+            const {buffer, byteOffset, byteLength} = value;
+            return as([type, {
+              buffer: [...new Uint8Array(buffer)], byteOffset, byteLength
+            }], value);
           }
           else if (type === 'ArrayBuffer') {
             spread = new Uint8Array(value);

test/index.js

@@ -8,6 +8,55 @@ const assert = (expected, result, message = '') => {
   }
 };
 
+{
+  const buffer = new Uint8Array([10, 20, 30, 40]).buffer;
+  for (const [offset, length] of [[0, 2], [1, 2], [2, 2], [3, 0], [4, 0], [0, 0], [0, 4]]) {
+    const original = new DataView(buffer, offset, length);
+    const [record] = serialize(original);
+    assert(record.length, 2, 'keeps the type/value pair contract');
+    assert(JSON.stringify(record), JSON.stringify(['DataView', {
+      buffer: [10, 20, 30, 40], byteOffset: offset, byteLength: length
+    }]), 'uses named DataView fields for every view');
+    const native = typeof globalThis.structuredClone === 'function' ?
+      globalThis.structuredClone(original) : original;
+    for (const result of [
+      deserialize(serialize(original)),
+      deserialize(JSON.parse(JSON.stringify(serialize(original)))),
+      parse(stringify(original)),
+      structuredClone(original, {lossy: true})
+    ]) {
+      assert(result instanceof DataView, true);
+      assert(result.byteOffset, native.byteOffset, 'preserves DataView byteOffset');
+      assert(result.byteLength, native.byteLength, 'preserves DataView byteLength');
+      assert(result.buffer.byteLength, native.buffer.byteLength);
+      assert([...new Uint8Array(result.buffer)].join(','), [...new Uint8Array(native.buffer)].join(','));
+      for (let i = 0; i < length; i++)
+        assert(result.getUint8(i), native.getUint8(i));
+      let outOfBounds = false;
+      try {
+        result.getUint8(length);
+      }
+      catch (error) {
+        outOfBounds = error instanceof RangeError;
+      }
+      assert(outOfBounds, true, 'keeps reads outside the DataView out of bounds');
+      if (length) {
+        result.setUint8(0, 255);
+        assert(original.getUint8(0), native.getUint8(0), 'does not share the source buffer');
+      }
+    }
+  }
+  for (const bytes of [[], [10, 20, 30, 40]]) {
+    const legacy = deserialize([['DataView', bytes]]);
+    assert(legacy.byteOffset, 0);
+    assert(legacy.byteLength, bytes.length);
+    assert([...new Uint8Array(legacy.buffer)].join(','), bytes.join(','));
+  }
+  const empty = deserialize(serialize(new DataView(new ArrayBuffer(0))));
+  assert(empty.byteOffset, 0);
+  assert(empty.byteLength, 0);
+}
+
 // @see https://github.com/ungap/structured-clone/issues/4
 const withUndefined = stringify({foo: 'test', bar: undefined, foobar: null});
 assert(withUndefined, '[[2,[[1,2],[3,4],[5,6]]],[0,"foo"],[0,"test"],[0,"bar"],[-1],[0,"foobar"],[0,null]]');
@@ -66,7 +115,7 @@ function test(firstRun = false) {
   console.timeEnd('serialized in');
 
   assert(JSON.stringify(serialized), [
-    `[[2,[[1,2],[3,4],[5,6],[7,8],[9,10],[11,12],[13,14],[15,16],[17,18],[19,20],[21,22],[24,25],[27,28],[29,30],[31,32],[33,34],[35,36],[37,38],[39,40]]],[0,"arr"],[1,[0,0,0]],[0,"bigint"],[8,"1"],[0,"boolean"],[0,true],[0,"number"],[0,123],[0,"string"],[0,""],[0,"undefined"],[-1],[0,"null"],[0,null],[0,"buffer"],["ArrayBuffer",[0,1,2,3,4,5,6,7]],[0,"dataview"],["DataView",[0,1,2,3,4,5,6,7]],[0,"int"],["Uint32Array",[1,2,3]],[0,"map"],[5,[[23,8]]],[0,"a"],[0,"set"],[6,[23,26]],[0,"b"],[0,"Bool"],["Boolean",false],[0,"Num"],["Number",0],[0,"Str"],["String",""],[0,"re"],[4,{"source":"test","flags":"gim"}],[0,"error"],[7,{"name":"Error","message":"test"}],[0,"BI"],["BigInt","1"],[0,"date"],[3,"${date.toISOString()}"]]`
+    `[[2,[[1,2],[3,4],[5,6],[7,8],[9,10],[11,12],[13,14],[15,16],[17,18],[19,20],[21,22],[24,25],[27,28],[29,30],[31,32],[33,34],[35,36],[37,38],[39,40]]],[0,"arr"],[1,[0,0,0]],[0,"bigint"],[8,"1"],[0,"boolean"],[0,true],[0,"number"],[0,123],[0,"string"],[0,""],[0,"undefined"],[-1],[0,"null"],[0,null],[0,"buffer"],["ArrayBuffer",[0,1,2,3,4,5,6,7]],[0,"dataview"],["DataView",{"buffer":[0,1,2,3,4,5,6,7],"byteOffset":0,"byteLength":8}],[0,"int"],["Uint32Array",[1,2,3]],[0,"map"],[5,[[23,8]]],[0,"a"],[0,"set"],[6,[23,26]],[0,"b"],[0,"Bool"],["Boolean",false],[0,"Num"],["Number",0],[0,"Str"],["String",""],[0,"re"],[4,{"source":"test","flags":"gim"}],[0,"error"],[7,{"name":"Error","message":"test"}],[0,"BI"],["BigInt","1"],[0,"date"],[3,"${date.toISOString()}"]]`
   ].join(','));
 
   // firstRun && console.log(serialized);