Claude's random GIF generator, based only on the GIF89a spec

gengif_spec.py

from typing import BinaryIO
import random
import struct

def generate_random_input(out: BinaryIO):
    # Generate Header
    out.write(b'GIF89a')  # GIF signature and version

    # Generate Logical Screen Descriptor
    screen_width = random.randint(1, 65535)
    screen_height = random.randint(1, 65535)
    packed_fields = random.randint(0, 255)
    background_color_index = random.randint(0, 255)
    pixel_aspect_ratio = random.randint(0, 255)
    out.write(struct.pack('<HHBBB', screen_width, screen_height, packed_fields,
                          background_color_index, pixel_aspect_ratio))

    # Generate Global Color Table (optional)
    if packed_fields & 0x80:
        color_table_size = 2 ** ((packed_fields & 0x07) + 1)
        for _ in range(color_table_size):
            red = random.randint(0, 255)
            green = random.randint(0, 255)
            blue = random.randint(0, 255)
            out.write(struct.pack('BBB', red, green, blue))

    # Generate Image Descriptor and Image Data (optional, multiple)
    for _ in range(random.randint(0, 5)):
        # Generate Image Descriptor
        left = random.randint(0, screen_width - 1)
        top = random.randint(0, screen_height - 1)
        width = random.randint(1, screen_width - left)
        height = random.randint(1, screen_height - top)
        packed_fields = random.randint(0, 255)
        out.write(struct.pack('<BHHHHB', 0x2C, left, top, width, height, packed_fields))

        # Generate Local Color Table (optional)
        if packed_fields & 0x80:
            color_table_size = 2 ** ((packed_fields & 0x07) + 1)
            for _ in range(color_table_size):
                red = random.randint(0, 255)
                green = random.randint(0, 255)
                blue = random.randint(0, 255)
                out.write(struct.pack('BBB', red, green, blue))

        # Generate Image Data
        lzw_minimum_code_size = random.randint(2, 8)
        out.write(struct.pack('B', lzw_minimum_code_size))
        data_block_size = random.randint(1, 255)
        out.write(struct.pack('B', data_block_size))
        out.write(bytes(random.randint(0, 255) for _ in range(data_block_size)))
        out.write(b'\x00')  # Block Terminator

    # Generate Extensions (optional, multiple)
    for _ in range(random.randint(0, 5)):
        extension_label = random.choice([0xF9, 0xFE, 0x01, 0xFF])
        out.write(struct.pack('BB', 0x21, extension_label))

        if extension_label == 0xF9:  # Graphic Control Extension
            packed_fields = random.randint(0, 255)
            delay_time = random.randint(0, 65535)
            transparent_color_index = random.randint(0, 255)
            out.write(struct.pack('<BBHBB', 4, packed_fields, delay_time,
                                  transparent_color_index, 0))

        elif extension_label == 0xFE:  # Comment Extension
            comment_data = b''.join(bytes([random.randint(1, 255)]) +
                                    bytes(random.randint(0, 255) for _ in range(random.randint(1, 255)))
                                    for _ in range(random.randint(1, 5)))
            out.write(comment_data)
            out.write(b'\x00')  # Block Terminator

        elif extension_label == 0x01:  # Plain Text Extension
            text_grid_left = random.randint(0, screen_width - 1)
            text_grid_top = random.randint(0, screen_height - 1)
            text_grid_width = random.randint(1, screen_width - text_grid_left)
            text_grid_height = random.randint(1, screen_height - text_grid_top)
            character_cell_width = random.randint(1, 255)
            character_cell_height = random.randint(1, 255)
            text_foreground_color_index = random.randint(0, 255)
            text_background_color_index = random.randint(0, 255)
            out.write(struct.pack('<BHHHHBBBB', 12, text_grid_left, text_grid_top,
                                  text_grid_width, text_grid_height,
                                  character_cell_width, character_cell_height,
                                  text_foreground_color_index, text_background_color_index))
            plain_text_data = b''.join(bytes([random.randint(1, 255)]) +
                                       bytes(random.randint(0, 255) for _ in range(random.randint(1, 255)))
                                       for _ in range(random.randint(1, 5)))
            out.write(plain_text_data)
            out.write(b'\x00')  # Block Terminator

        elif extension_label == 0xFF:  # Application Extension
            application_identifier = bytes(random.randint(32, 255) for _ in range(8))
            application_authentication_code = bytes(random.randint(0, 255) for _ in range(3))
            out.write(struct.pack('<B8s3s', 11, application_identifier, application_authentication_code))
            application_data = b''.join(bytes([random.randint(1, 255)]) +
                                        bytes(random.randint(0, 255) for _ in range(random.randint(1, 255)))
                                        for _ in range(random.randint(1, 5)))
            out.write(application_data)
            out.write(b'\x00')  # Block Terminator

    # Generate Trailer
    out.write(b'\x3B')  # GIF Trailer

import sys
for f in sys.argv[1:]:
    with open(f,'wb') as of:
        generate_random_input(of)
    print(f)