It's timeout while return a response with a large dictionary

[lanlanlaura]

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• I already checked if it is not related to FastAPI but to Swagger UI.
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Example Code

from fastapi import FastAPI
import os

path = os.path.dirname(__file__)
file_path = os.path.join(path, "test.json")
file = json.load(open(file_path, 'r', encoding='utf-8'))

app = FastAPI()
@app.get("/read")
def read_dic():
    return file

Description

The test.json file size is around 2M, I convert it to dictionary, It's timeout, while FastAPI return a response. Thank you very much for your help.

Operating System

Windows

Operating System Details

No response

FastAPI Version

0.110.1

Pydantic Version

2.6.4

Python Version

3.8.10

Additional Context

No response

[AIdjis]

Hi , i found the solution to your problem, first you need to install orjson because it load the josn file much faster compered to json.
1- install orjson:

 pip install orjson 

2- use this code :

from fastapi import FastAPI
import os
import json
import orjson

@app.get("/read-json")
async def read_json_file():
    path = os.path.dirname(__file__)
    file_path = os.path.join(path, "file.json")
    with open(file_path, 'rb') as file:
        content = file.read()
        data = dict(orjson.loads(content))
        return data

Then send the request to the endpoint using Postman. I have already tried it with a file larger than 2MB, and the response was very quick.
I hope I answered your question.

[lanlanlaura]

Hi, Djemmal Islam,
Many thanks for your answer. I try this code and go to "http://127.0.0.1:8001/docs" to return data, as the data is huge, the page is block and I need to wait around 1min to get the data. I'm a beginner of FastAPI, This is truly a very tricky question for me. Do you have a suggestion for it? Thank you again.

[YuriiMotov]

Try removing async:
def read_json_file(): instead of async def read_json_file():

The code of this endpoint is sync and if the file is big it will block event loop

[PhysicallyActive]

I tried it out using both Swagger and Curl (and also the two different implementations), and I'm fairly sure the issue lies with Swagger.
That might be why it works for @AIdjis (since Postman was used for the verification).

If you try to curl your endpoint:

curl -X GET http://127.0.0.1:8001/read-json -H "content-type: application/json" > tmp.json

and compare the result, they're identical.

[jgould22]

The problem is you are using swagger and when it gets a response back it applies syntax highlighting and other processing to the 2mb of json which can take a lot of time in a browser.

https://fastapi.tiangolo.com/ru/how-to/configure-swagger-ui/#disable-syntax-highlighting

[lanlanlaura]

Many thanks, all of you. I know why the problem comes up. Thank you again for your help!