Packages/Yum.py: Fix dependency resolution logic

This commit helps the internal YUM resolver to choose the latest version
of a package to generate dependencies. Previously, we were simply
iterating through the file so that the last instance listed always won
(even if that instance was an older version with differing
dependencies).

Signed-off-by: Sol Jerome <sol.jerome@gmail.com>

1 files changed, 101 insertions, 2 deletions

diff --git a/src/lib/Bcfg2/Server/Plugins/Packages/Yum.py b/src/lib/Bcfg2/Server/Plugins/Packages/Yum.py
index 20b0e103d..789df79d5 100644
--- a/src/lib/Bcfg2/Server/Plugins/Packages/Yum.py
+++ b/src/lib/Bcfg2/Server/Plugins/Packages/Yum.py
@@ -1169,6 +1169,94 @@ class YumSource(Source):
                 self.file_to_arch[self.escape_url(fullurl)] = arch
         return urls
 
+    # pylint: disable=R0911,R0912
+    # disabling the pylint errors above because we are interesting in
+    # replicating the flow of the RPM code.
+    def _compare_rpm_versions(self, str1, str2):
+        """ Compare RPM versions.
+
+        This is an attempt to reimplement RPM's rpmvercmp method in python.
+
+        :param str1: package 1 version string
+        :param str2: package 2 version string
+        :return: 1 - str1 is newer than str2
+                 0 - str1 and str2 are the same version
+                -1 - str2 is newer than str1"""
+        if str1 == str2:
+            return 0
+
+        front_strip_re = re.compile('^[^A-Za-z0-9~]+')
+        risdigit = re.compile('(^[0-9]+)')
+        risalpha = re.compile('(^[A-Za-z])')
+        lzeroes = re.compile('^0+')
+
+        while len(str1) > 0 or len(str2) > 0:
+            str1 = front_strip_re.sub('', str1)
+            str2 = front_strip_re.sub('', str2)
+
+            if len(str1) == 0 or len(str2) == 0:
+                break
+
+            # handle the tilde separator
+            if str1[0] == '~' and str2[0] == '~':
+                str1 = str1[1:]
+                str2 = str2[1:]
+            elif str1[0] == '~':
+                return -1
+            elif str2[0] == '~':
+                return 1
+
+            # grab continuous segments from each string
+            isnum = False
+            if risdigit.match(str1):
+                segment1 = risdigit.split(str1)[1]
+                str1 = risdigit.split(str1)[2]
+                if risdigit.match(str2):
+                    segment2 = risdigit.split(str2)[1]
+                    str2 = risdigit.split(str2)[2]
+                else:
+                    segment2 = ''
+                isnum = True
+            else:
+                segment1 = risalpha.split(str1)[1]
+                str1 = risalpha.split(str1)[2]
+                if risalpha.match(str2):
+                    segment2 = risalpha.split(str2)[1]
+                    str2 = risalpha.split(str2)[2]
+                else:
+                    segment2 = ''
+
+            # numeric segments are always newer than alpha segments
+            if len(segment2) == 0:
+                if isnum:
+                    return 1
+                return -1
+
+            if isnum:
+                # discard leading zeroes
+                segment1 = lzeroes.sub('', segment1)
+                segment2 = lzeroes.sub('', segment2)
+                # higher number has more digits
+                if len(segment1) > len(segment2):
+                    return 1
+                elif len(segment2) > len(segment1):
+                    return -1
+            # do a simple string comparison
+            if segment1 > segment2:
+                return 1
+            elif segment2 > segment1:
+                return -1
+
+        # if one of the strings is empty, the version of the longer
+        # string is higher
+        if len(str1) > len(str2):
+            return 1
+        elif len(str2) > len(str1):
+            return -1
+        else:
+            return 0
+    # pylint: enable=R0911,R0912
+
     @Bcfg2.Server.Plugin.track_statistics()
     def read_files(self):
         """ When using the builtin yum parser, read and parse locally
@@ -1237,13 +1325,24 @@ class YumSource(Source):
         if arch not in self.packages:
             self.packages[arch] = set()
         if arch not in self.deps:
-            self.deps[arch] = dict()
+            self.deps[arch] = {}
         if arch not in self.provides:
-            self.provides[arch] = dict()
+            self.provides[arch] = {}
+        versionmap = {}
         for pkg in data.getchildren():
             if not pkg.tag.endswith('package'):
                 continue
             pkgname = pkg.find(XP + 'name').text
+            vtag = pkg.find(XP + 'version')
+            version = "%s%s-%s" % (vtag.get('epoch'), vtag.get('ver'),
+                                   vtag.get('rel'))
+            if pkgname in self.packages[arch]:
+                # skip if version older than a previous version
+                if self._compare_rpm_versions(version,
+                                              versionmap[pkgname]) < 0:
+                    continue
+
+            versionmap[pkgname] = version
             self.packages[arch].add(pkgname)
 
             pdata = pkg.find(XP + 'format')