chore: import upstream snapshot with attribution

source/node.js

@@ -0,0 +1,104 @@
+
+import * as fs from 'fs';
+
+const node = {};
+
+node.FileStream = class {
+
+    constructor(file, start, length, mtime) {
+        this._file = file;
+        this._start = start;
+        this._length = length;
+        this._position = 0;
+        this._mtime = mtime;
+    }
+
+    get position() {
+        return this._position;
+    }
+
+    get length() {
+        return this._length;
+    }
+
+    stream(length) {
+        const stream = new node.FileStream(this._file, this._start + this._position, length, this._mtime);
+        this.skip(length);
+        return stream;
+    }
+
+    seek(position) {
+        this._position = position >= 0 ? position : this._length + position;
+        if (this._position > this._length || this._position < 0) {
+            throw new Error(`Expected ${this._position - this._length} more bytes. The file might be corrupted. Unexpected end of file.`);
+        }
+    }
+
+    skip(offset) {
+        this._position += offset;
+        if (this._position > this._length || this._position < 0) {
+            throw new Error(`Expected ${this._position - this._length} more bytes. The file might be corrupted. Unexpected end of file.`);
+        }
+    }
+
+    peek(length) {
+        length = length === undefined ? this._length - this._position : length;
+        if (length < 0x10000000) {
+            const position = this._fill(length);
+            this._position -= length;
+            return this._buffer.subarray(position, position + length);
+        }
+        const position = this._position;
+        this.skip(length);
+        this.seek(position);
+        const buffer = new Uint8Array(length);
+        this._read(buffer, position);
+        return buffer;
+    }
+
+    read(length) {
+        length = length === undefined ? this._length - this._position : length;
+        if (length < 0x10000000) {
+            const position = this._fill(length);
+            return this._buffer.slice(position, position + length);
+        }
+        const position = this._position;
+        this.skip(length);
+        const buffer = new Uint8Array(length);
+        this._read(buffer, position);
+        return buffer;
+    }
+
+    _fill(length) {
+        if (this._position + length > this._length) {
+            const offset = this._position + length - this._length;
+            throw new Error(`Expected ${offset} more bytes. The file might be corrupted. Unexpected end of file.`);
+        }
+        if (!this._buffer || this._position < this._offset || this._position + length > this._offset + this._buffer.length) {
+            this._offset = this._position;
+            const length = Math.min(0x10000000, this._length - this._offset);
+            if (!this._buffer || length !== this._buffer.length) {
+                this._buffer = new Uint8Array(length);
+            }
+            this._read(this._buffer, this._offset);
+        }
+        const position = this._position;
+        this._position += length;
+        return position - this._offset;
+    }
+
+    _read(buffer, offset) {
+        const descriptor = fs.openSync(this._file, 'r');
+        const stat = fs.statSync(this._file);
+        if (stat.mtimeMs !== this._mtime) {
+            throw new Error(`File '${this._file}' last modified time changed.`);
+        }
+        try {
+            fs.readSync(descriptor, buffer, 0, buffer.length, offset + this._start);
+        } finally {
+            fs.closeSync(descriptor);
+        }
+    }
+};
+
+export const FileStream = node.FileStream;