datastream

src/utils/datastream.ts

@@ -0,0 +1,225 @@
+/* eslint-disable max-classes-per-file */
+
+/**
+ * Byte lengths for primitive types.
+ */
+const SHORT_BYTES = 2;
+const INT_BYTES = 4;
+const LONG_BYTES = 8;
+
+/**
+ * EOF error thrown by DataInputStream.
+ */
+class DataInputStreamEOFError extends Error {
+    bufLen: number;
+
+    requiredLen: number;
+
+    /**
+     * @param bufLen The length of the buffer.
+     * @param requiredLen The required length of the buffer (i.e. what was needed for
+     * a successful read).
+     * @param message
+     */
+    constructor (bufLen: number, requiredLen: number, message: string = "") {
+        let formattedMessage = `[bufLen=${bufLen}, requiredLen=${requiredLen}]`;
+        if ("" !== message) {
+            formattedMessage += ` ${message}`;
+        }
+        super(formattedMessage);
+        this.name = "DataInputStreamEOFError";
+        this.bufLen = bufLen;
+        this.requiredLen = requiredLen;
+    }
+}
+
+/**
+ * Decodes primitive types from a byte stream (similar to Java's DataInputStream class).
+ */
+class DataInputStream {
+    #dataView: DataView;
+
+    #isLittleEndian: boolean;
+
+    #byteIdx: number;
+
+    /**
+     * @param arrayBuffer Underlying array buffer.
+     * @param isLittleEndian Byte endianness.
+     */
+    constructor (arrayBuffer: ArrayBufferLike, isLittleEndian: boolean = false) {
+        this.#dataView = new DataView(arrayBuffer);
+        this.#isLittleEndian = isLittleEndian;
+        this.#byteIdx = 0;
+    }
+
+    /**
+     * Seeks to the given index.
+     *
+     * @param idx
+     * @throws {Error} If encounter EOF while seeking.
+     */
+    seek (idx: number): void {
+        if (idx > this.#dataView.byteLength) {
+            this.#byteIdx = this.#dataView.byteLength;
+            throw new DataInputStreamEOFError(this.#dataView.byteLength, idx);
+        }
+        this.#byteIdx = idx;
+    }
+
+    /**
+     * Returns the current read offset in the stream.
+     *
+     * @return
+     */
+    getPos (): number {
+        return this.#byteIdx;
+    }
+
+    /**
+     * Reads the specified amount of data.
+     *
+     * @param length
+     * @return
+     * @throws {Error} If encounter EOF while reading.
+     */
+    readFully (length: number): Uint8Array {
+        const requiredLen: number = this.#byteIdx + length;
+        if (this.#dataView.byteLength < requiredLen) {
+            this.#byteIdx = this.#dataView.byteLength;
+            throw new DataInputStreamEOFError(this.#dataView.byteLength, requiredLen);
+        }
+
+        const val: Uint8Array = new Uint8Array(this.#dataView.buffer, this.#byteIdx, length);
+        this.#byteIdx += length;
+
+        return val;
+    }
+
+    /**
+     * Reads an unsigned byte.
+     *
+     * @return
+     * @throws {Error} If encounter EOF while reading.
+     */
+    readUnsignedByte (): number {
+        const requiredLen: number = this.#byteIdx + 1;
+        if (this.#dataView.byteLength < requiredLen) {
+            this.#byteIdx = this.#dataView.byteLength;
+            throw new DataInputStreamEOFError(this.#dataView.byteLength, requiredLen);
+        }
+
+        return this.#dataView.getUint8(this.#byteIdx++);
+    }
+
+    /**
+     * Reads a signed byte
+     *
+     * @return
+     * @throws {Error} If encounter EOF while reading.
+     */
+    readSignedByte (): number {
+        const requiredLen: number = this.#byteIdx + 1;
+        if (this.#dataView.byteLength < requiredLen) {
+            this.#byteIdx = this.#dataView.byteLength;
+            throw new DataInputStreamEOFError(this.#dataView.byteLength, requiredLen);
+        }
+
+        return this.#dataView.getInt8(this.#byteIdx++);
+    }
+
+    /**
+     * Reads an unsigned short
+     *
+     * @return
+     * @throws {Error} If encounter EOF while reading.
+     */
+    readUnsignedShort (): number {
+        const requiredLen: number = this.#byteIdx + SHORT_BYTES;
+        if (this.#dataView.byteLength < requiredLen) {
+            this.#byteIdx = this.#dataView.byteLength;
+            throw new DataInputStreamEOFError(this.#dataView.byteLength, requiredLen);
+        }
+        const val: number = this.#dataView.getUint16(this.#byteIdx, this.#isLittleEndian);
+        this.#byteIdx += SHORT_BYTES;
+
+        return val;
+    }
+
+    /**
+     * Reads a signed short
+     *
+     * @return
+     * @throws {Error} If encounter EOF while reading.
+     */
+    readSignedShort (): number {
+        const requiredLen: number = this.#byteIdx + SHORT_BYTES;
+        if (this.#dataView.byteLength < requiredLen) {
+            this.#byteIdx = this.#dataView.byteLength;
+            throw new DataInputStreamEOFError(this.#dataView.byteLength, requiredLen);
+        }
+        const val: number = this.#dataView.getInt16(this.#byteIdx, this.#isLittleEndian);
+        this.#byteIdx += SHORT_BYTES;
+
+        return val;
+    }
+
+    /**
+     * Reads an int.
+     *
+     * @return
+     * @throws {Error} If encounter EOF while reading.
+     */
+    readInt (): number {
+        const requiredLen: number = this.#byteIdx + INT_BYTES;
+        if (this.#dataView.byteLength < requiredLen) {
+            this.#byteIdx = this.#dataView.byteLength;
+            throw new DataInputStreamEOFError(this.#dataView.byteLength, requiredLen);
+        }
+        const val: number = this.#dataView.getInt32(this.#byteIdx, this.#isLittleEndian);
+        this.#byteIdx += INT_BYTES;
+
+        return val;
+    }
+
+    /**
+     * Reads a signed long int (64 bit).
+     *
+     * @return
+     * @throws {Error} If encounter EOF while reading.
+     */
+    readSignedLong (): bigint {
+        const requiredLen = this.#byteIdx + LONG_BYTES;
+        if (this.#dataView.byteLength < requiredLen) {
+            this.#byteIdx = this.#dataView.byteLength;
+            throw new DataInputStreamEOFError(this.#dataView.byteLength, requiredLen);
+        }
+        const val: bigint = this.#dataView.getBigInt64(this.#byteIdx, this.#isLittleEndian);
+        this.#byteIdx += LONG_BYTES;
+
+        return val;
+    }
+
+    /**
+     * Reads an unsigned long int (64 bit).
+     *
+     * @return
+     * @throws {Error} If encounter EOF while reading.
+     */
+    readUnsignedLong (): bigint {
+        const requiredLen = this.#byteIdx + LONG_BYTES;
+        if (this.#dataView.byteLength < requiredLen) {
+            this.#byteIdx = this.#dataView.byteLength;
+            throw new DataInputStreamEOFError(this.#dataView.byteLength, requiredLen);
+        }
+        const val: bigint = this.#dataView.getBigUint64(this.#byteIdx, this.#isLittleEndian);
+        this.#byteIdx += LONG_BYTES;
+
+        return val;
+    }
+}
+
+export {
+    DataInputStream,
+    DataInputStreamEOFError,
+};