Using Conan with Python3 on Travis-CI - c++

Question

I have a C++ project that uses Travis-CI and Conan. My Linux build on Travis-CI is failing when it attempts to download libcurl:
libcurl/7.61.1#bincrafters/stable: Building your package in /home/travis/.conan/data/libcurl/7.61.1/bincrafters/stable/build/b6dbf799dd7e6d1c740e159bea361666320a3db8
libcurl/7.61.1#bincrafters/stable: Configuring sources in /home/travis/.conan/data/libcurl/7.61.1/bincrafters/stable/source
/usr/local/lib/python2.7/dist-packages/urllib3/util/ssl_.py:150: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/advanced-usage.html#ssl-warnings
InsecurePlatformWarning
ERROR: Error downloading file https://curl.haxx.se/download/curl-7.61.1.tar.gz: 'HTTPSConnectionPool(host='curl.haxx.se', port=443): Max retries exceeded with url: /download/curl-7.61.1.tar.gz (Caused by SSLError(CertificateError("hostname 'curl.haxx.se' doesn't match 'c.sni.fastly.net'",),))'
Waiting 5 seconds to retry...
/usr/local/lib/python2.7/dist-packages/urllib3/util/ssl_.py:150: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/advanced-usage.html#ssl-warnings
InsecurePlatformWarning
libcurl/7.61.1#bincrafters/stable: WARN: Trying to remove corrupted source folder
libcurl/7.61.1#bincrafters/stable: WARN: This can take a while for big packages
ERROR: libcurl/7.61.1#bincrafters/stable: Error in source() method, line 131
tools.get("https://curl.haxx.se/download/curl-%s.tar.gz" % self.version)
ConanException: Error downloading file https://curl.haxx.se/download/curl-7.61.1.tar.gz: 'HTTPSConnectionPool(host='curl.haxx.se', port=443): Max retries exceeded with url: /download/curl-7.61.1.tar.gz (Caused by SSLError(CertificateError("hostname 'curl.haxx.se' doesn't match 'c.sni.fastly.net'",),))'
The command "conan install .. --build missing" exited with 1.
Per the advise in the error, I have tried to get Travis to use Python3 to see if that would resolve the problem but I have had no luck. First I added python3 to my packages: like so:
matrix:
include:
- os: linux
dist: trusty
sudo: required
env:
- CC_COMPILER=gcc-7
- CXX_COMPILER=g++-7
- BUILD_TYPE=RelWithDebInfo
addons:
apt:
packages:
- python3
- gcc-7
- g++-7
sources:
- ubuntu-toolchain-r-test
But I received the same error as above. Then I tried alias'ing the command:
install:
- |
if [[ "${TRAVIS_OS_NAME}" == "linux" ]]; then
sudo pip install conan
alias python=python3
fi
Yet, I get the same results.
How can I get Travis-CI to use python3 for Conan? Or is there another way I can get my conan install command to work?
Thank you!

Answer 1

The default CI scripts generated with conan new pkg/version -s -cilg might help. They contain something like:
linux: &linux
os: linux
dist: xenial
sudo: required
language: python
python: "3.6"
services:
- docker
matrix:
include:
- <<: *linux
env: ...
install:
- chmod +x .travis/install.sh
- ./.travis/install.sh
And the install script:
pip install conan --upgrade
pip install conan_package_tools
conan user
So it is not declared as a package, but defined at the root level, and that seems to be enough to later use it with bare pip install.

Answer 2

Well if I am reading it correctly python3 is not the issue here. The error is:
CertificateError("hostname 'curl.haxx.se' doesn't match 'c.sni.fastly.net'",
So something fishy with ssl.
Python2 does produce insecure platform warning when using ssl / https but it's rarely the issue.
As for python3 on Travis - I personally couldn't get conan to work in CI with python3.
But basic steps are:
apt:
packages:
- python3
- python3-pip
...
To install conan using python3:
sudo pip3 install conan
Note that in your example install you called pip - which installs conan with python3 and it will run by python2 when called from command line despite the alias. The interpreter to use is actually in the conan script.