_site.py: Add check_bwrap_version() function

Lazily parse the version of bwrap the first time the function is called.
On subsequent calls, used cached version info.

See: #373

1 files changed, 49 insertions, 0 deletions

diff --git a/buildstream/_site.py b/buildstream/_site.py
index 622839511..f4780ef3d 100644
--- a/buildstream/_site.py
+++ b/buildstream/_site.py
@@ -19,6 +19,8 @@
 #        Tristan Van Berkom <tristan.vanberkom@codethink.co.uk>
 
 import os
+import shutil
+import subprocess
 
 #
 # Private module declaring some info about where the buildstream
@@ -45,3 +47,50 @@ build_all_template = os.path.join(root, 'data', 'build-all.sh.in')
 
 # Module building script template
 build_module_template = os.path.join(root, 'data', 'build-module.sh.in')
+
+# Cached bwrap version
+_bwrap_major = None
+_bwrap_minor = None
+_bwrap_patch = None
+
+
+# check_bwrap_version()
+#
+# Checks the version of installed bwrap against the requested version
+#
+# Args:
+#    major (int): The required major version
+#    minor (int): The required minor version
+#    patch (int): The required patch level
+#
+# Returns:
+#    (bool): Whether installed bwrap meets the requirements
+#
+def check_bwrap_version(major, minor, patch):
+    # pylint: disable=global-statement
+
+    global _bwrap_major
+    global _bwrap_minor
+    global _bwrap_patch
+
+    # Parse bwrap version and save into cache, if not already cached
+    if _bwrap_major is None:
+        bwrap_path = shutil.which('bwrap')
+        if not bwrap_path:
+            return False
+        cmd = [bwrap_path, "--version"]
+        version = str(subprocess.check_output(cmd).split()[1], "utf-8")
+        _bwrap_major, _bwrap_minor, _bwrap_patch = map(int, version.split("."))
+
+    # Check whether the installed version meets the requirements
+    if _bwrap_major > major:
+        return True
+    elif _bwrap_major < major:
+        return False
+    else:
+        if _bwrap_minor > minor:
+            return True
+        elif _bwrap_minor < minor:
+            return False
+        else:
+            return _bwrap_patch >= patch