constructor (response: any) {
   if (typeof response !== 'object' || Array.isArray(response)) {
     throw new Error('Failed to parse volume metadata.');
   }
   this.resolution = parseFiniteVec(vec3.create(), response['resolution']);
   this.voxelOffset = parseIntVec(vec3.create(), response['voxel_offset']);
   this.size = parseIntVec(vec3.create(), response['size']);
   this.chunkSizes = parseArray(response['chunk_sizes'], x => parseFiniteVec(vec3.create(), x));
   if (this.chunkSizes.length === 0) {
     throw new Error('No chunk sizes specified.');
   }
   let encodingStr = response['encoding'];
   let encoding = serverChunkEncodings.get(encodingStr);
   if (encoding === undefined) {
     throw new Error(`Invalid chunk encoding: ${JSON.stringify(encodingStr)}`);
   }
   this.encoding = encoding;
   if (encoding === VolumeChunkEncoding.COMPRESSED_SEGMENTATION) {
     this.compressedSegmentationBlockSize = parseIntVec(vec3.create(), response['compressed_segmentation_block_size']);
   }
   this.key = response['key'];
   if (typeof this.key !== 'string') {
     throw new Error('No key specified.');
   }
 }

 getSources(chunkManager: ChunkManager) {
   let sources: VolumeChunkSource[][] = [];
   const {response, volumeType} = this;
   const datasetObject = response['dataset'];
   const encoding = volumeType === VolumeType.IMAGE ? 'jpeg' : 'npz';
   for (let resolution of Object.keys(datasetObject['neariso_imagesize'])) {
     let imageSize = parseIntVec(vec3.create(), datasetObject['neariso_imagesize'][resolution]);
     let voxelSize = parseFiniteVec(vec3.create(), datasetObject['neariso_voxelres'][resolution]);
     let alternatives: VolumeChunkSource[] = [];
     sources.push(alternatives);
     // The returned offset for downsampled resolutions can have non-integer components.  It
     // appears that the true offset is obtained by rounding up.
     let origLowerVoxelBound =
         parseFiniteVec(vec3.create(), datasetObject['neariso_offset'][resolution]);
     let lowerVoxelBound = vec3.create();
     let upperVoxelBound = vec3.create();
     for (let i = 0; i < 3; ++i) {
       let origLower = origLowerVoxelBound[i];
       lowerVoxelBound[i] = Math.ceil(origLower);
       upperVoxelBound[i] = Math.floor(origLower + imageSize[i]);
     }
     for (let spec of VolumeChunkSpecification.getDefaults({
            volumeType,
            voxelSize,
            dataType: this.dataType, lowerVoxelBound, upperVoxelBound
          })) {
       let cacheKey = stableStringify(
           {'spec': spec, key: this.key, channel: this.channel, resolution: resolution});
       alternatives.push(chunkManager.getChunkSource(
           VolumeChunkSource, cacheKey,
           () => new VolumeChunkSource(
               chunkManager, spec, this.hostnames, this.key, this.channel, resolution, encoding)));
     }
   }
   return sources;
 }

 verifyObjectProperty(obj, 'voxel_offset', x => parseIntVec(vec3.create(), x)),