patchouli/lib/FWIF/FWIFDecodeStream.php

<?php
namespace FWIF;

class FWIFDecodeStream {
    private string $body;
    private int $length;
    private int $position = 0;

    public function __construct(string $body) {
        $this->body = $body;
        $this->length = strlen($body);
    }

    public function getLength(): int {
        return $this->length;
    }

    public function getPosition(): int {
        return $this->position;
    }

    public function stepBack(): void {
        $this->position = max(0, $this->position - 1);
    }

    public function readByte(): int {
        if($this->position + 1 >= $this->length)
            return FWIF::TRAILER;
        return ord($this->body[$this->position++]);
    }

    public function readChar(): string {
        return chr($this->readByte());
    }

    public function readString(int $length): string {
        // Bounds checks? What are those?
        $string = substr($this->body, $this->position, $length);
        $this->position += $length;
        return $string;
    }
}