loader-utils: Improved JSON parsding error messages

modules/gltf/src/lib/deprecated/gltf-parser.js

@@ -1,4 +1,5 @@
 import {TextDecoder, fetchFile} from '@loaders.gl/core';
+import {parseJSON} from '@loaders.gl/loader-utils';
 import {getFullUri} from '../gltf-utils/gltf-utils';
 import {getGLTFAccessors, getGLTFAccessor} from '../gltf-utils/gltf-attribute-utils';
 import {KHR_DRACO_MESH_COMPRESSION, UBER_POINT_CLOUD_EXTENSION} from '../gltf-constants';
@@ -53,7 +54,7 @@ export default class GLTFParser {
 
     // If string, try to parse as JSON
     if (typeof gltf === 'string') {
-      gltf = JSON.parse(gltf);
+      gltf = parseJSON(gltf);
     }
 
     if (gltf instanceof ArrayBuffer) {

modules/gltf/src/lib/parse-gltf.js

@@ -1,5 +1,6 @@
 /* eslint-disable camelcase, max-statements, no-restricted-globals */
 /* global TextDecoder */
+import {parseJSON} from '@loaders.gl/loader-utils';
 import assert from './utils/assert';
 import {getFullUri} from './gltf-utils/gltf-utils';
 import {decodeExtensions, decodeExtensionsSync} from './extensions/gltf-extensions';
@@ -73,7 +74,7 @@ function parseGLTFContainerSync(gltf, data, byteOffset, options) {
 
   if (typeof data === 'string') {
     // If string, try to parse as JSON
-    gltf.json = JSON.parse(data);
+    gltf.json = parseJSON(data);
   } else if (data instanceof ArrayBuffer) {
     // If still ArrayBuffer, parse as GLB container
     gltf._glb = {};

modules/loader-utils/src/index.js

@@ -2,14 +2,23 @@
 export {default as createWorker} from './worker-utils/create-worker';
 
 // MEMORY COPY UTILS
-export {padTo4Bytes, copyToArray, copyArrayBuffer} from './lib/memory-copy-utils';
+export {
+  padTo4Bytes,
+  copyToArray,
+  copyArrayBuffer,
+  getZeroOffsetArrayBuffer
+} from './lib/memory-copy-utils';
 export {copyPaddedArrayBufferToDataView, copyPaddedStringToDataView} from './lib/binary-copy-utils';
 export {
   padStringToByteAlignment,
   copyStringToDataView,
   copyBinaryToDataView
 } from './lib/encode-utils';
 
+export {getFirstCharacters, getMagicString} from './lib/get-first-characters';
+
+export {parseJSON} from './lib/parse-json';
+
 // MESH CATEGORY UTILS
 export {getMeshSize as _getMeshSize} from './categories/mesh/mesh-utils';
 

modules/loader-utils/src/lib/get-first-characters.js

@@ -0,0 +1,24 @@
+export function getFirstCharacters(data, length = 5) {
+  if (typeof data === 'string') {
+    return data.slice(0, length);
+  } else if (ArrayBuffer.isView(data)) {
+    // Typed Arrays can have offsets into underlying buffer
+    return getMagicString(data.buffer, data.byteOffset, length);
+  } else if (data instanceof ArrayBuffer) {
+    const byteOffset = 0;
+    return getMagicString(data, byteOffset, length);
+  }
+  return '';
+}
+
+export function getMagicString(arrayBuffer, byteOffset, length) {
+  if (arrayBuffer.byteLength <= byteOffset + length) {
+    return '';
+  }
+  const dataView = new DataView(arrayBuffer);
+  let magic = '';
+  for (let i = 0; i < length; i++) {
+    magic += String.fromCharCode(dataView.getUint8(byteOffset + i));
+  }
+  return magic;
+}

modules/loader-utils/src/lib/memory-copy-utils.js

@@ -2,6 +2,15 @@ export function padTo4Bytes(byteLength) {
   return (byteLength + 3) & ~3;
 }
 
+// Copy a view of an ArrayBuffer into new ArrayBuffer with byteOffset = 0
+export function getZeroOffsetArrayBuffer(arrayBuffer, byteOffset, byteLength) {
+  const subArray = byteLength
+    ? new Uint8Array(arrayBuffer).subarray(byteOffset, byteOffset + byteLength)
+    : new Uint8Array(arrayBuffer).subarray(byteOffset);
+  const arrayCopy = new Uint8Array(subArray);
+  return arrayCopy.buffer;
+}
+
 /* Creates a new Uint8Array based on two different ArrayBuffers
  * @private
  * @param {ArrayBuffers} buffer1 The first buffer.

modules/loader-utils/src/lib/parse-json.js

@@ -0,0 +1,10 @@
+import {getFirstCharacters} from './get-first-characters';
+
+// Minimal JSON parser with a meaningful error message
+export function parseJSON(string) {
+  try {
+    return JSON.parse(string);
+  } catch (_) {
+    throw new Error(`Failed to parse JSON from data starting with "${getFirstCharacters(string)}"`);
+  }
+}