ResponseWithQrBot — Telegram In-Memory QR Code Generator

Generate sharp 512x512 QR code PNGs from URLs and text strings directly inside Telegram chats via @responseWithQrBot.

Technical Architecture: Reverse-Engineering @responseWithQrBot​

I structured @responseWithQrBot around an event-driven pipeline that decouples Telegram Bot API webhook dispatching (responsewithqrbot/handlers.py) from matrix synthesis (responsewithqrbot/core.py). Every QR code is constructed in RAM using python-qrcode and Pillow (PIL) and streamed directly to Telegram via io.BytesIO.

+------------------+         +--------------------------+         +------------------------+
| Telegram Server  |  -----> | Handler & Auth Layer     |  -----> | Core QR Engine         |
| (Webhook/Update) |         | (handlers.py)            |         | (core.py)              |
+------------------+         +--------------------------+         +------------------------+
                                          |                                   |
                                          v                                   v
                                [Length & Auth Checks]                [In-Memory BytesIO PNG]

1. In-Memory QR Matrix Synthesis & Box Resampling​

Standard image resampling filters (such as bilinear or bicubic) introduce anti-aliased gray pixels along module boundaries when scaling QR matrices. In responsewithqrbot/core.py, the rendered matrix is resized to 512x512 pixels using Image.Resampling.BOX to preserve hard pixel edges:

import qrcode
import io
import logging
from settings import settings
from PIL import Image
from typing import Optional

logger = logging.getLogger(__name__)

def generate_qrcode(message: str) -> Optional[io.BytesIO]:
    try:
        qr = qrcode.QRCode(
            version=1,
            error_correction=qrcode.constants.ERROR_CORRECT_L,
            box_size=10,
            border=4,
        )
        qr.add_data(message)
        qr.make(fit=True)
        img = qr.make_image(fill_color="black", back_color="white")

        target_size = (
            int(settings.RESPONSEWITHQRBOT_IMAGE_BOX_SIZE),
            int(settings.RESPONSEWITHQRBOT_IMAGE_BOX_SIZE),
        )
        img = img.resize(target_size, Image.Resampling.BOX)

        buffer = io.BytesIO()
        img.save(buffer, format="PNG")
        buffer.seek(0)

        return buffer

    except Exception as e:
        logger.error(f"Error generating QR code: {e}")
        return None

2. Payload Validation & Handler Registration​

Before invoking generate_qrcode(), responsewithqrbot/handlers.py validates that incoming text messages do not exceed 256 characters (RESPONSEWITHQRBOT_TEXT_LENGTH), preventing dense, high-version QR matrices that are difficult for phone cameras to scan off a small chat thumbnail:

def parse_update_message(update) -> Optional[str]:
    if not update.message.text:
        return None
    if len(update.message.text) > int(settings.RESPONSEWITHQRBOT_TEXT_LENGTH):
        return None
    return update.message.text

def register_responsewithqrbot_handlers(dispatcher):
    dispatcher.add_handler(CommandHandler('start', handle_start_message))
    dispatcher.add_handler(MessageHandler(Filters.text, handle_message))
    dispatcher.add_handler(ChatMemberHandler(user_left, ChatMemberHandler.MY_CHAT_MEMBER))

QR Synthesis Specifications​

Stateless Processing & Privacy Guarantees​

• Zero Disk I/O: QR images are synthesized inside io.BytesIO memory buffers and garbage-collected immediately after Telegram API upload.
• Instant Browser Alternative: For client-side SVG/Canvas QR generation with custom foreground/background colors, use the browser-based QR Code Generator.

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