Motoserver multipart upload failure

[vdytyniak-exos]

There is the code I am running to save the file using multipart upload:

import boto3
from boto3.s3.transfer import TransferConfig

s3 = boto3.client('s3')
s3.create_bucket(Bucket='test')
s3.upload_fileobj(
    io.BytesIO(b'123'),
    'test',
    'ns/id=A%20B/9d985da515104b58adcf01acf79f6892-0.raw',
    Config=TransferConfig(multipart_threshold=1),
)

Client error:

botocore.errorfactory.NoSuchKey: An error occurred (NoSuchKey) when calling the CompleteMultipartUpload operation: The specified key does not exist.

Motoserver logs(404 for POST request):

2023-05-03 11:44:47 172.17.0.1 - - [03/May/2023 08:44:47] "PUT /test HTTP/1.1" 200 -
2023-05-03 11:44:47 172.17.0.1 - - [03/May/2023 08:44:47] "POST /test/ns/id%3DA%2520B/9d985da515104b58adcf01acf79f6892-0.raw?uploads HTTP/1.1" 200 -
2023-05-03 11:44:47 172.17.0.1 - - [03/May/2023 08:44:47] "PUT /test/ns/id%3DA%2520B/9d985da515104b58adcf01acf79f6892-0.raw?uploadId=XBHMvHpDsU8xlBSIhfRZetKf0Vum7iUWzdL7eVsgxpsVTZlDchbejBsCQ&partNumber=1 HTTP/1.1" 200 -
2023-05-03 11:44:47 172.17.0.1 - - [03/May/2023 08:44:47] "POST /test/ns/id%3DA%2520B/9d985da515104b58adcf01acf79f6892-0.raw?uploadId=XBHMvHpDsU8xlBSIhfRZetKf0Vum7iUWzdL7eVsgxpsVTZlDchbejBsCQ HTTP/1.1" 404 -

It works fine if you don't use A%20B, but just AB for example:

import boto3
from boto3.s3.transfer import TransferConfig

s3 = boto3.client('s3')
s3.create_bucket(Bucket='test')
s3.upload_fileobj(
    io.BytesIO(b'123'),
    'test',
    'ns/id=AB/9d985da515104b58adcf01acf79f6892-0.raw',
    Config=TransferConfig(multipart_threshold=1),
)

Could you please explain what is wrong with that path?

[vdytyniak-exos]

Created PR: #6287.