Use the same python interpreter as yum when possiblessd/find-python

We rely on a system python installation with the correct python
libraries.  To improve the chances that the python interpreter we call
has the yum libary available, we use the same interpreter as yum uses.

Fixes #3143

2 files changed, 64 insertions, 2 deletions

diff --git a/lib/chef/provider/package/yum.rb b/lib/chef/provider/package/yum.rb
index 49c6f6beb5..b3d3d72844 100644
--- a/lib/chef/provider/package/yum.rb
+++ b/lib/chef/provider/package/yum.rb
@@ -19,6 +19,7 @@
 require 'chef/config'
 require 'chef/provider/package'
 require 'chef/mixin/shell_out'
+require 'chef/mixin/which'
 require 'chef/resource/package'
 require 'singleton'
 require 'chef/mixin/get_source_from_package'
@@ -647,6 +648,7 @@ class Chef
         # Cache for our installed and available packages, pulled in from yum-dump.py
         class YumCache
           include Chef::Mixin::Command
+          include Chef::Mixin::Which
           include Chef::Mixin::ShellOut
           include Singleton
 
@@ -713,7 +715,7 @@ class Chef
             status = nil
 
             begin
-              status = shell_out!("/usr/bin/python #{helper}#{opts}", :timeout => Chef::Config[:yum_timeout])
+              status = shell_out!("#{python_bin} #{helper}#{opts}", :timeout => Chef::Config[:yum_timeout])
               status.stdout.each_line do |line|
                 one_line = true
 
@@ -779,6 +781,32 @@ class Chef
             @next_refresh = :none
           end
 
+          def python_bin
+            yum_executable = which("yum")
+            if yum_executable && shabang?(yum_executable)
+              extract_interpreter(yum_executable)
+            else
+              Chef::Log.warn("Yum executable not found or doesn't start with #!. Using default python.")
+              "/usr/bin/python"
+            end
+          rescue StandardError => e
+            Chef::Log.warn("An error occured attempting to determine correct python executable. Using default.")
+            Chef::Log.debug(e)
+            "/usr/bin/python"
+          end
+
+          def extract_interpreter(file)
+            ::File.open(file, 'r', &:readline)[2..-1].chomp
+          end
+
+          def shabang?(file)
+            ::File.open(file, 'r') do |f|
+              f.read(2) == '#!'
+            end
+          rescue Errno::ENOENT
+            false
+          end
+
           def reload
             @next_refresh = :all
           end
diff --git a/spec/unit/provider/package/yum_spec.rb b/spec/unit/provider/package/yum_spec.rb
index 865dce23fa..8f4bde7f62 100644
--- a/spec/unit/provider/package/yum_spec.rb
+++ b/spec/unit/provider/package/yum_spec.rb
@@ -17,6 +17,7 @@
 #
 
 require 'spec_helper'
+require 'securerandom'
 
 describe Chef::Provider::Package::Yum do
   before(:each) do
@@ -1659,6 +1660,14 @@ describe Chef::Provider::Package::Yum::YumCache do
     end
   end
 
+  let(:yum_exe) {
+    StringIO.new("#!/usr/bin/python\n\naldsjfa\ldsajflkdsjf\lajsdfj")
+  }
+
+  let(:bin_exe) {
+    StringIO.new(SecureRandom.random_bytes)
+  }
+
   before(:each) do
     @stdin = double("STDIN", :nil_object => true)
     @stdout = double("STDOUT", :nil_object => true)
@@ -1704,12 +1713,19 @@ file: file://///etc/yum.repos.d/CentOS-Base.repo, line: 12
 'qeqwewe\n'
 EOF
     @status = double("Status", :exitstatus => 0, :stdin => @stdin, :stdout => @stdout_good, :stderr => @stderr)
-
     # new singleton each time
     Chef::Provider::Package::Yum::YumCache.reset_instance
     @yc = Chef::Provider::Package::Yum::YumCache.instance
     # load valid data
     allow(@yc).to receive(:shell_out!).and_return(@status)
+    allow_any_instance_of(described_class).to receive(:which).with("yum").and_return("/usr/bin/yum")
+    allow(::File).to receive(:open).with("/usr/bin/yum", "r") do |&block|
+      res = block.call(yum_exe)
+      # a bit of a hack. rewind this since it seem that no matter what
+      # I do, we get the same StringIO objects on multiple calls to
+      # ::File.open
+      yum_exe.rewind; res
+    end
   end
 
   describe "initialize" do
@@ -1726,6 +1742,24 @@ EOF
     end
   end
 
+  describe "python_bin" do
+    it "should return the default python if an error occurs" do
+      allow(::File).to receive(:open).with("/usr/bin/yum", "r").and_raise(StandardError)
+      expect(@yc.python_bin).to eq("/usr/bin/python")
+    end
+
+    it "should return the default python if the yum-executable doesn't start with #!" do
+      allow(::File).to receive(:open).with("/usr/bin/yum", "r") { |&b| r = b.call(bin_exe); bin_exe.rewind; r}
+      expect(@yc.python_bin).to eq("/usr/bin/python")
+    end
+
+    it "should return the interpreter for yum" do
+      other = StringIO.new("#!/usr/bin/super_python\n\nlasjdfdsaljf\nlasdjfs")
+      allow(::File).to receive(:open).with("/usr/bin/yum", "r") { |&b| r = b.call(other); other.rewind; r}
+      expect(@yc.python_bin).to eq("/usr/bin/super_python")
+    end
+  end
+
   describe "refresh" do
     it "should implicitly call yum-dump.py only once by default after being instantiated" do
       expect(@yc).to receive(:shell_out!).once