♻ Allow 16-bit and 32-bit reads in ByteReader

src/ssn/extractFile.ts

@@ -11,14 +11,14 @@ export default async function extractFile(file: ISsnFileEntry, dvArray: DataView
   const byteReader = new ByteReader(dvArray, file.diskNumberStart, file.offset);
 
   //Local file header signature must be 0x04034B50
-  if (byteReader.readByte() !== 0x50 || byteReader.readByte() !== 0x4B || byteReader.readByte() !== 0x03 || byteReader.readByte() !== 0x04) {
+  if (byteReader.readUint32() !== 0x04034B50) {
     throw new Error('Local file header had wrong magic');
   }
   //All fields in the local file header are copies of the central file header, so we can skip them.
   //FIXME: Maybe we should actually read these fields to verify that they are identical?
   byteReader.seek(22);
-  const localFilenameSize = byteReader.readByte() + (byteReader.readByte() << 8);
+  const localFilenameSize = byteReader.readUint16();
-  const localExtraSize = byteReader.readByte() + (byteReader.readByte() << 8);
+  const localExtraSize = byteReader.readUint16();
   byteReader.seek(localFilenameSize + localExtraSize);
 
   //Extract actual file contents

src/ssn/extractFileByteReader.ts

@@ -7,7 +7,8 @@ export default class ByteReader {
     this.dvIndex = startDvIndex;
     this.pos = offset;
   }
-  public readByte() {
+  /** Reads one byte and returns it. */
+  public readUint8() {
     const curByte = this.dvArray[this.dvIndex].getUint8(this.pos);
     this.pos += 1;
     if (this.pos >= this.dvArray[this.dvIndex].byteLength) {
@@ -17,18 +18,28 @@ export default class ByteReader {
     }
     return curByte;
   }
-  public seek(num: number) {
+  /** Reads two bytes as an unsigned 16-bit integer and returns it. */
-    this.pos += num;
+  public readUint16() {
+    return this.readUint8() | (this.readUint8() << 8);
+  }
+  /** Reads four bytes as an unsigned 32-bit integer and returns it. */
+  public readUint32() {
+    return (this.readUint8() | (this.readUint8() << 8) | (this.readUint8() << 16) | (this.readUint8() << 24)) >>> 0;
+  }
+  /** Seeks the given number of bytes forward, without reading the bytes. */
+  public seek(numBytes: number) {
+    this.pos += numBytes;
     if (this.pos >= this.dvArray[this.dvIndex].byteLength) {
       this.pos -= this.dvArray[this.dvIndex].byteLength;
       this.dvIndex += 1;
       if (this.dvIndex >= this.dvArray.length) { throw new Error('Tried to read beyond DataView boundary in extractFile'); }
     }
   }
+  /** Reads the given amount of bytes, and returns it as a DataView. */
   public extractDv(length: number) {
     const dv = new DataView(new ArrayBuffer(length));
     for (let i = 0; i < length; i += 1) {
-        dv.setUint8(i, this.readByte()); //TODO: refactor this so it is more optimized
+        dv.setUint8(i, this.readUint8()); //TODO: refactor this so it is more optimized
     }
     return dv;
   }