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Add retry logic to snap-tool to make downloads more resilient
LP: #1837871
This commit is contained in:
Tobias Koch
parent
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commit
e00b7fa1dc
8
debian/changelog
vendored
8
debian/changelog
vendored
@ -1,3 +1,11 @@
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livecd-rootfs (2.578.7) disco; urgency=medium
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[ Tobias Koch ]
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* Add retry logic to snap-tool to make downloads more resilient.
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(LP: #1837871)
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-- Tobias Koch <tobias.koch@canonical.com> Mon, 26 Aug 2019 13:36:36 +0200
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livecd-rootfs (2.578.6) disco; urgency=medium
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[ Tobias Koch ]
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222
snap-tool
222
snap-tool
@ -28,6 +28,7 @@ import re
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import shutil
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import subprocess
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import sys
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import time
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import urllib.error
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import urllib.request
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@ -50,6 +51,178 @@ class SnapAssertionError(SnapError):
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pass
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class ExpBackoffHTTPClient:
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"""This class is an abstraction layer on top of urllib with additional
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retry logic for more reliable downloads."""
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class Request:
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"""This is a convenience wrapper around urllib.request."""
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def __init__(self, request, do_retry, base_interval, num_tries):
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"""
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:param request:
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An urllib.request.Request instance.
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:param do_retry:
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Whether to enable the exponential backoff and retry logic.
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:param base_interval:
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The initial interval to sleep after a failed attempt.
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:param num_tries:
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How many attempts to make.
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"""
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self._request = request
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self._do_retry = do_retry
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self._base_interval = base_interval
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self._num_tries = num_tries
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self._response = None
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def open(self):
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"""Open the connection."""
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if not self._response:
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self._response = self._retry_urlopen()
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def close(self):
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"""Close the connection."""
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if self._response:
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self._response.close()
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self._response = None
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def data(self):
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"""Return the raw response body."""
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with self:
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return self.read()
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def json(self):
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"""Return the deserialized response body interpreted as JSON."""
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return json.loads(self.data(), encoding="utf-8")
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def text(self):
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"""Return the response body as a unicode string."""
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encoding = "utf-8"
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with self:
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content_type = self._response.getheader("Content-Type", "")
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if content_type == "application/json":
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encoding = "utf-8"
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else:
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m = re.match(r"text/\S+;\s*charset=(?P<charset>\S+)",
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content_type)
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if m:
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encoding=m.group("charset")
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return self.read().decode(encoding)
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def read(self, size=None):
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"""Read size bytes from the response. If size if not set, the
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complete response body is read in."""
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return self._response.read(size)
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def __enter__(self):
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"""Make this class a context manager."""
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self.open()
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return self
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def __exit__(self, type, value, traceback):
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"""Make this class a context manager."""
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self.close()
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def _retry_urlopen(self):
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"""Try to open the HTTP connection as many times as configured
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through the constructor. Every time an error occurs, double the
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time to wait until the next attempt."""
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for attempt in range(self._num_tries):
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try:
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return urllib.request.urlopen(self._request)
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except Exception as e:
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if isinstance(e, urllib.error.HTTPError) and e.code < 500:
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raise
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if attempt >= self._num_tries - 1:
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raise
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sys.stderr.write(
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"WARNING: failed to open URL '{}': {}\n"
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.format(self._request.full_url, str(e))
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)
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else:
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break
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sleep_interval = self._base_interval * 2**attempt
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sys.stderr.write(
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"Retrying HTTP request in {} seconds...\n"
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.format(sleep_interval)
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)
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time.sleep(sleep_interval)
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def __init__(self, do_retry=True, base_interval=2, num_tries=8):
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"""
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:param do_retry:
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Whether to enable the retry logic.
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:param base_interval:
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The initial interval to sleep after a failed attempt.
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:param num_tries:
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How many attempts to make.
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"""
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self._do_retry = do_retry
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self._base_interval = base_interval
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self._num_tries = num_tries if do_retry else 1
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def get(self, url, headers=None):
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"""Create a GET request that can be used to retrieve the resource
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at the given URL.
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:param url:
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An HTTP URL.
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:param headers:
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A dictionary of extra headers to send along.
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:return:
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An ExpBackoffHTTPClient.Request instance.
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"""
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return self._prepare_request(url, headers=headers)
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def post(self, url, data=None, json=None, headers=None):
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"""Create a POST request that can be used to submit data to the
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endpoint at the given URL."""
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return self._prepare_request(
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url, data=data, json_data=json, headers=headers
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)
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def _prepare_request(self, url, data=None, json_data=None, headers=None):
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"""Prepare a Request instance that can be used to retrieve data from
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and/or send data to the endpoint at the given URL.
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:param url:
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An HTTP URL.
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:param data:
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Raw binary data to send along in the request body.
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:param json_data:
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A Python data structure to be serialized and sent out in JSON
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format.
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:param headers:
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A dictionary of extra headers to send along.
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:return:
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An ExpBackoffHTTPClient.Request instance.
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"""
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if data is not None and json_data is not None:
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raise ValueError(
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"Parameters 'data' and 'json_data' are mutually exclusive."
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)
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if json_data:
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data = json.dumps(json_data, ensure_ascii=False)
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if headers is None:
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headers = {}
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headers["Content-Type"] = "application/json"
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if isinstance(data, str):
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data = data.encode("utf-8")
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return ExpBackoffHTTPClient.Request(
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urllib.request.Request(url, data=data, headers=headers or {}),
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self._do_retry,
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self._base_interval,
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self._num_tries
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)
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class Snap:
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"""This class provides methods to retrieve information about a snap and
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download it together with its assertions."""
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@ -115,13 +288,17 @@ class Snap:
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"Snap-CDN": "none",
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})
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request = urllib.request.Request(snap_download_url, headers=headers)
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if not skip_snap_download:
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with urllib.request.urlopen(request) as response, \
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open(snap_filename, "wb+") as fp:
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http_client = ExpBackoffHTTPClient()
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response = http_client.get(snap_download_url, headers=headers)
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with response, open(snap_filename, "wb+") as fp:
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shutil.copyfileobj(response, fp)
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if os.path.getsize(snap_filename) != snap_byte_size:
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raise SnapError(
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"The downloaded snap does not have the expected size."
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)
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if not download_assertions:
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return
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@ -193,16 +370,20 @@ class Snap:
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elif self._cohort_key:
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data["actions"][0]["cohort-key"] = self._cohort_key
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request_json = json.dumps(data, ensure_ascii=False).encode("utf-8")
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try:
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response_dict = self._do_snapcraft_request(path, data=request_json)
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response_dict = self._do_snapcraft_request(path, json_data=data)
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except SnapCraftError as e:
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raise SnapError("failed to get details for '{}': {}"
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.format(self._name, str(e)))
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snap_data = response_dict["results"][0]
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if snap_data.get("result") == "error":
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raise SnapError(
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"failed to get details for '{}': {}"
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.format(self._name, snap_data.get("error", {}).get("message"))
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)
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# Have "base" initialized to something meaningful.
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if self.is_core_snap():
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snap_data["snap"]["base"] = ""
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@ -296,40 +477,29 @@ class Snap:
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"Accept": "application/x.ubuntu.assertion",
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}
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request = urllib.request.Request(url, headers=headers)
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http_client = ExpBackoffHTTPClient()
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try:
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with urllib.request.urlopen(request) as response:
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body = response.read()
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with http_client.get(url, headers=headers) as response:
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return response.text()
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except urllib.error.HTTPError as e:
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raise SnapAssertionError(str(e))
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return body.decode("utf-8")
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def _do_snapcraft_request(self, path, data=None):
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def _do_snapcraft_request(self, path, json_data=None):
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url = self._snapcraft_url + "/" + path
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headers = {
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"Snap-Device-Series": str(self._series),
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"Snap-Device-Architecture": self._arch,
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"Content-Type": "application/json",
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}
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request = urllib.request.Request(url, data=data, headers=headers)
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http_client = ExpBackoffHTTPClient()
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try:
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with urllib.request.urlopen(request) as response:
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body = response.read()
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response = http_client.post(url, json=json_data, headers=headers)
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with response:
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return response.json()
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except urllib.error.HTTPError as e:
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raise SnapCraftError(str(e))
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try:
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response_data = json.loads(body, encoding="utf-8")
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except json.JSONDecodeError as e:
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raise SnapCraftError("failed to decode response body: " + str(e))
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return response_data
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class SnapCli:
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