build Blob on the fly

lib/core/io.js

@@ -190,22 +190,40 @@ class BlobWriter extends Writer {
 	constructor(contentType) {
 		super();
 		this.contentType = contentType;
-		this.arrayBuffers = [];
+		this.arrayBuffersMaxlength = 8;
+		initArrayBuffers(this);
 	}
 
 	async writeUint8Array(array) {
 		super.writeUint8Array(array);
+		if (this.arrayBuffers.length == this.arrayBuffersMaxlength) {
+			flushArrayBuffers(this);
+		}
 		this.arrayBuffers.push(array.buffer);
 	}
 
 	getData() {
 		if (!this.blob) {
-			this.blob = new Blob(this.arrayBuffers, { type: this.contentType });
+			if (this.arrayBuffers.length) {
+				flushArrayBuffers(this);
+			}
+			this.blob = this.pendingBlob;
+			initArrayBuffers(this);
 		}
 		return this.blob;
 	}
 }
 
+function initArrayBuffers(blobWriter) {
+	blobWriter.pendingBlob = new Blob([], { type: blobWriter.contentType });
+	blobWriter.arrayBuffers = [];
+}
+
+function flushArrayBuffers(blobWriter) {
+	blobWriter.pendingBlob = new Blob([blobWriter.pendingBlob, ...blobWriter.arrayBuffers], { type: blobWriter.contentType });
+	blobWriter.arrayBuffers = [];
+}
+
 class WritableStreamWriter extends Writer {
 	constructor(writableStream) {
 		super();