rpm: add common version comparison function

Signed-off-by: Hank Donnay <hdonnay@redhat.com>
Change-Id: I5f1f740f42b9ef6a8184a73873dbed56aebb5f6d

Author: hdonnay

internal/rpm/matcher.go

@@ -0,0 +1,49 @@
+package rpm
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/quay/claircore"
+	"github.com/quay/claircore/internal/rpmver"
+)
+
+// MatchVulnerable is a function implementing "driver.Matcher.Vulnerable"
+// in a common way.
+//
+// Given a package version "P" and vulnerability "V":
+//
+//   - If a fixed version "F" is specified in "V", "P < F" is reported.
+//   - If a package version "F" is specified in "V", "P <= F" is reported.
+//   - If no version is provided in "V", this function compares against an
+//     "infinite" version.
+//
+// In addition to this version comparison, the architectures are compared.
+func MatchVulnerable(ctx context.Context, rec *claircore.IndexRecord, vuln *claircore.Vulnerability) (bool, error) {
+	p, err := rpmver.Parse(rec.Package.Version)
+	if err != nil {
+		return false, fmt.Errorf("rpm: unable to parse package version %q: %w",
+			rec.Package.Version, err)
+	}
+
+	var v rpmver.Version
+	cmp := isLTE
+	switch {
+	case vuln.FixedInVersion != "":
+		v, err = rpmver.Parse(vuln.FixedInVersion)
+		cmp = isLT
+	case vuln.Package.Version != "":
+		v, err = rpmver.Parse(vuln.Package.Version)
+	default:
+		v, err = rpmver.Parse("65535:65535-65535")
+	}
+	if err != nil {
+		return false, fmt.Errorf("rpm: unable to parse vulnerability version %q: %w",
+			rec.Package.Version, err)
+	}
+
+	return cmp(rpmver.Compare(&p, &v)) && vuln.ArchOperation.Cmp(rec.Package.Arch, vuln.Package.Arch), nil
+}
+
+func isLTE(cmp int) bool { return cmp != 1 }
+func isLT(cmp int) bool  { return cmp == -1 }