generate_presigned_url not working with complete_multipart_upload

Hello, I am trying to generate a presigned URL for complete_multipart_upload, but I’m getting this error when running my code:

Traceback (most recent call last):
  File "/dev-env/test/chalicelib/rmodel.py", line 280, in __call__
    return funct(*args, **kwargs)
  File "/dev-env/test/chalicelib/upload.py", line 201, in create_complete_upload
    'MultipartUpload': upload})
  File "/dev-env/venv/lib/python3.7/site-packages/botocore/signers.py", line 595, in generate_presigned_url
    operation_name=operation_name)
  File "/dev-env/venv/lib/python3.7/site-packages/botocore/signers.py", line 268, in generate_presigned_url
    'presign-url', expires_in, signing_name)
  File "/dev-env/venv/lib/python3.7/site-packages/botocore/signers.py", line 157, in sign
    auth.add_auth(request)
  File "/dev-env/venv/lib/python3.7/site-packages/botocore/auth.py", line 362, in add_auth
    self._modify_request_before_signing(request)
  File "/dev-env/venv/lib/python3.7/site-packages/botocore/auth.py", line 525, in _modify_request_before_signing
    query_dict.update(self._get_body_as_dict(request))
  File "/dev-env/venv/lib/python3.7/site-packages/botocore/auth.py", line 550, in _get_body_as_dict
    data = json.loads(data.decode('utf-8'))
  File "/dev-env/Packages/miniconda3/lib/python3.7/json/__init__.py", line 348, in loads
    return _default_decoder.decode(s)
  File "/dev-env/Packages/miniconda3/lib/python3.7/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/dev-env/Packages/miniconda3/lib/python3.7/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

This is the code:

s3_client = boto3.client('s3')
signed_url = s3_client.generate_presigned_url('complete_multipart_upload',
    ExpiresIn=3600,
    HttpMethod='POST',
    Params={
        'Bucket': _BUCKET,
        'Key': key,
        'UploadId': upload_id,
        'MultipartUpload': upload})

If I call s3_client.complete_multipart_upload with the same arguments specified in Params, then the operation completes without issues. From the error it looks like AWS is returning an unexpected response message to boto.

The boto3 version is 1.10.2

Thank you,

[kdaily]

Hi @Caian, I can reproduce this issue. Thanks for your debugging thus far. Marking as a bug and will investigate further.

[alonbl]

Reproduction does not need any credentials or actual objects, but simple invocation.

import boto3
from botocore.client import Config

s3 = boto3.client(
    's3',
    region_name="us-east-1",
    config=Config(signature_version="s3v4"),
)

signed_url = s3.generate_presigned_url(
    ClientMethod ='complete_multipart_upload',
    Params = {
       'Bucket': "bucket1",
       'UploadId': "id1",
       'Key': "key1",
       'UploadId': "id1",
       'MultipartUpload': {'Parts': []},
    }
)

Traceback (most recent call last):
  File "/home/alonbl/exodigo/alonbl-misc/aws-example/a.py", line 10, in <module>
    signed_url = s3.generate_presigned_url(
  File "/home/alonbl/exodigo/alonbl-misc/aws-example/x1/lib/python3.10/site-packages/botocore/signers.py", line 661, in generate_presigned_url
    return request_signer.generate_presigned_url(
  File "/home/alonbl/exodigo/alonbl-misc/aws-example/x1/lib/python3.10/site-packages/botocore/signers.py", line 312, in generate_presigned_url
    self.sign(
  File "/home/alonbl/exodigo/alonbl-misc/aws-example/x1/lib/python3.10/site-packages/botocore/signers.py", line 187, in sign
    auth.add_auth(request)
  File "/home/alonbl/exodigo/alonbl-misc/aws-example/x1/lib/python3.10/site-packages/botocore/auth.py", line 412, in add_auth
    self._modify_request_before_signing(request)
  File "/home/alonbl/exodigo/alonbl-misc/aws-example/x1/lib/python3.10/site-packages/botocore/auth.py", line 576, in _modify_request_before_signing
    query_dict.update(_get_body_as_dict(request))
  File "/home/alonbl/exodigo/alonbl-misc/aws-example/x1/lib/python3.10/site-packages/botocore/auth.py", line 96, in _get_body_as_dict
    data = json.loads(data.decode('utf-8'))
  File "/usr/lib/python3.10/json/__init__.py", line 346, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.10/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.10/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)