Question
I have the following FastAPI backend:
from fastapi import FastAPI
app = FastAPI
class Demo(BaseModel):
content: str = None
@app.post("/demo")
async def demoFunc(d:Demo):
return d.content
The issue is that when I send a request to this API with extra data like:
data = {"content":"some text here"}aaaa
or
data = {"content":"some text here"aaaaaa}
resp = requests.post(url, json=data)
it throws an error with status code 422 unprocessable entity
error with
Actual("some text here") and Extra("aaaaa") data in the return field in case
of data = {"content":"some text here"}aaaa
:
{
"detail": [
{
"loc": [
"body",
47
],
"msg": "Extra data: line 4 column 2 (char 47)",
"type": "value_error.jsondecode",
"ctx": {
"msg": "Extra data",
"doc": "{\n \"content\": \"some text here\"}aaaaa",
"pos": 47,
"lineno": 4,
"colno": 2
}
}
]
}
I tried to put the line app=FastAPI()
in a try-catch block, however, it
doesn't work. Is there any way I can handle this issue with own response
instead of the above mentioned auto response? Something like this:
{"error": {"message": "Invalid JSON body"},
"status": 0}
Answer
You are passing an invalid JSON, and hence, the server correctly responds with
the 422 Unprocessable Entity
error. Your test client shouldn't be able to
run at all, without throwing an invalid syntax
error. So, I'm guessing you
posted the request through the interactive autodocs provided by Swagger UI at
/docs
, and received the relevant 422 error.
If what you actually want is to handle the error, in order to customise the
error or something, you can override the request validation exception handler,
as described in the
[documentation](https://fastapi.tiangolo.com/tutorial/handling-
errors/#override-request-validation-exceptions) (have a look at this
discussion, as well as
this answer and this
answer that demonstrates how
to customise the RequestValidationError
for specific routes only).
Working Example:
from fastapi import FastAPI, Body, Request, status
from fastapi.encoders import jsonable_encoder
from fastapi.exceptions import RequestValidationError
from fastapi.responses import JSONResponse
from pydantic import BaseModel
app = FastAPI()
@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request: Request, exc: RequestValidationError):
return JSONResponse(
status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
content=jsonable_encoder({"detail": exc.errors(), # optionally include the errors
"body": exc.body,
"custom msg": {"Your error message"}}),
)
class Demo(BaseModel):
content: str = None
@app.post("/demo")
async def some_func(d: Demo):
return d.content
Or, you could also return a PlainTextResponse
with a custom message:
from fastapi.responses import PlainTextResponse
@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request, exc):
return PlainTextResponse(str(exc), status_code=422)