dockerfile argument in images.build() is defaulting to HTTP, not file source

Summary

When trying to build a Dockerfile from local file system while running in pytest, images.build() fails for HTTP 404. Issue is not present in 3.0.1

System Info

• Python 3.6.3
• pytest-3.4.1
• docker-py: 3.1.0
• docker: 17.12.0-ce
• OS: macOs 10.13.3

Code snippet works under 3.0.1 but not 3.1.0

Reproduction

Code

run as a pytest test.

from os import path
import docker

HERE = path.abspath(path.dirname(__file__))
ROOT = path.dirname(HERE)
CLIENT = docker.from_env(timeout=1)

def test_build_image():
    image, log = CLIENT.images.build(
        buildargs={'PROJECT_SOURCE': '/opt/PROJECT_NAME/'},
        dockerfile=path.join(HERE, 'Dockerfile'),
        path=ROOT,
        nocache=True
    )

Traceback

pytest output:

self = <docker.api.client.APIClient object at 0x10d34de10>, response = <Response [500]>

    def _raise_for_status(self, response):
        """Raises stored :class:`APIError`, if one occurred."""
        try:
>           response.raise_for_status()

venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/api/client.py:223: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <Response [500]>

    def raise_for_status(self):
        """Raises stored :class:`HTTPError`, if one occurred."""
    
        http_error_msg = ''
        if isinstance(self.reason, bytes):
            # We attempt to decode utf-8 first because some servers
            # choose to localize their reason strings. If the string
            # isn't utf-8, we fall back to iso-8859-1 for all other
            # encodings. (See PR #3538)
            try:
                reason = self.reason.decode('utf-8')
            except UnicodeDecodeError:
                reason = self.reason.decode('iso-8859-1')
        else:
            reason = self.reason
    
        if 400 <= self.status_code < 500:
            http_error_msg = u'%s Client Error: %s for url: %s' % (self.status_code, reason, self.url)
    
        elif 500 <= self.status_code < 600:
            http_error_msg = u'%s Server Error: %s for url: %s' % (self.status_code, reason, self.url)
    
        if http_error_msg:
>           raise HTTPError(http_error_msg, response=self)
E           requests.exceptions.HTTPError: 500 Server Error: Internal Server Error for url: http+docker://localunixsocket/v1.35/build?q=False&nocache=True&rm=False&forcerm=False&pull=False&dockerfile=%2FUsers%2Fjpurcell%2FCrowdstrike%2Fsensor%2FTest%2Fcookiecutters%2FDEMO_FlaskCookiecutter%2Ftests%2FDockerfile&buildargs=%7B%22PROJECT_SOURCE%22%3A+%22%2Fopt%2Fcrowdstrike%2FDEMO_FlaskCookiecutter%2Fsource%2F%22%7D

venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/requests/models.py:935: HTTPError

During handling of the above exception, another exception occurred:

    def test_build_image():
        image, log = CLIENT.images.build(
            buildargs={'PROJECT_SOURCE': '/opt/crowdstrike/DEMO_FlaskCookiecutter/source/'},
            dockerfile=path.join(HERE, 'Dockerfile'),
            path=HERE,
>           nocache=True
        )

tests/test_integration.py:32: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/models/images.py:187: in build
    for chunk in internal_stream:
venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/utils/json_stream.py:66: in split_buffer
    for data in stream_as_text(stream):
venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/utils/json_stream.py:22: in stream_as_text
    for data in stream:
venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/api/client.py:314: in _stream_helper
    yield self._result(response, json=decode)
venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/api/client.py:229: in _result
    self._raise_for_status(response)
venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/api/client.py:225: in _raise_for_status
    raise create_api_error_from_http_exception(e)

tests/helpers.py:76: in start_docker
    nocache=True,
venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/models/images.py:187: in build
    for chunk in internal_stream:
venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/utils/json_stream.py:66: in split_buffer
    for data in stream_as_text(stream):
venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/utils/json_stream.py:22: in stream_as_text
    for data in stream:
venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/api/client.py:314: in _stream_helper
    yield self._result(response, json=decode)
venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/api/client.py:229: in _result
    self._raise_for_status(response)
venv_DEMO_FlaskCookiecutter/lib/python3.6/site-packages/docker/api/client.py:225: in _raise_for_status
    raise create_api_error_from_http_exception(e)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Code works OK in REPL, but not in pytest. Works in both on 3.0.1

Start at the images.build() entry point shown in docker/models/images.py and compare the pytest call in tests/test_integration.py with the REPL behavior; inspect the request path in the traceback and the related call in tests/helpers.py. Reproduce with the listed Docker and Python versions, then verify that building a local Dockerfile under pytest uses the file source correctly.