async next(length? : number) {
   if(length === undefined){
     const result = await super.next();
     this.temp[0] = result;
     this.sha.update(this.temp);
     return result;
   }else{
     const result = await super.next(length);
     return this.sha.update(result);
   }
 }

 async nextInt32() : Promise<number> {
   const buffer = await super.next(4);
   this.sha.update(buffer);
   let result = 0;
   for(let i=0; i<4; i++){
     result = (result << 8) | buffer[i];
   }
   return result;
 }

 digest(){
   const result = this.sha.digest();
   this.sha = sha1();
   return result;
 }

 rewind(length : number){
   if(this.tempChunk) this.sha.update(this.tempChunk.subarray(0, this.tempChunk.length - length));
   this.tempChunk = undefined;
   super.rewind(length);
 }

 async chunk() {
   if(this.tempChunk) this.sha.update(this.tempChunk);
   this.tempChunk = await super.chunk();
   return this.tempChunk;
 }