export function getShardedVolume(baseUrls: string[], path: string) {
  let fullKey = stableStringify({'baseUrls': baseUrls, 'path': path});
  let existingResult = existingVolumes.get(fullKey);
  if (existingResult !== undefined) {
    return existingResult;
  }
  let promise = sendHttpRequest(openShardedHttpRequest(baseUrls, path + '/info'), 'json')
                    .then(response => new MultiscaleVolumeChunkSource(baseUrls, path, response));
  existingVolumes.set(fullKey, promise);
  return promise;
}

 .map(spec => {
   let path = `${this.path}/${scaleInfo.key}`;
   let cacheKey = stableStringify({
     'spec': spec,
     'baseUrls': this.baseUrls,
     'path': path,
     'encoding': scaleInfo.encoding
   });
   return chunkManager.getChunkSource(
       VolumeChunkSource, cacheKey,
       () => new VolumeChunkSource(
           chunkManager, spec, this.baseUrls, path, scaleInfo.encoding));
 });

export function getShardedVolume(hostnames: string[], path: string) {
  let match = path.match(pathPattern);
  if (match === null) {
    throw new Error(`Invalid volume path ${JSON.stringify(path)}`);
  }
  // Warning: If additional arguments are added, fullKey should be updated as well.
  let fullKey = stableStringify({'hostnames': hostnames, 'path': path});
  let existingResult = existingVolumes.get(fullKey);
  if (existingResult !== undefined) {
    return existingResult;
  }
  let key = match[1];
  let channel = match[2];
  let promise =
      getVolumeInfo(hostnames, key)
    .then(response => new MultiscaleVolumeChunkSource(hostnames, key, response, channel));
  existingVolumes.set(fullKey, promise);
  return promise;
}

 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;
 }

 static get(chunkManager: ChunkManager, spec: VolumeChunkSpecification, parameters: Parameters) {
   return chunkManager.getChunkSource(
       this, stableStringify({parameters, spec: spec.toObject()}),
       () => new this(chunkManager, spec, parameters));
 }