feat: agent parses /etc/os-release for distro identification

agent/internal/packages/osrelease.go

@@ -0,0 +1,63 @@
+package packages
+
+import (
+	"bufio"
+	"errors"
+	"io"
+	"os"
+	"runtime"
+	"strings"
+)
+
+// OSRelease identifies the distribution well enough to select an advisory
+// feed. VersionID is not optional: Ubuntu 22.04 and 24.04 publish different
+// fixed versions for the same CVE.
+type OSRelease struct {
+	Family    string
+	VersionID string
+	Arch      string
+}
+
+// ParseOSRelease reads the os-release format: KEY=value, one per line, with
+// values optionally quoted, and # comments.
+//
+// The quote stripping handles both ID=ubuntu and ID="rocky", which real
+// distributions both emit.
+func ParseOSRelease(r io.Reader) (OSRelease, error) {
+	out := OSRelease{Arch: runtime.GOARCH}
+	sc := bufio.NewScanner(r)
+	for sc.Scan() {
+		line := strings.TrimSpace(sc.Text())
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+		key, val, ok := strings.Cut(line, "=")
+		if !ok {
+			continue
+		}
+		val = strings.Trim(strings.TrimSpace(val), `"'`)
+		switch strings.TrimSpace(key) {
+		case "ID":
+			out.Family = strings.ToLower(val)
+		case "VERSION_ID":
+			out.VersionID = val
+		}
+	}
+	if err := sc.Err(); err != nil {
+		return OSRelease{}, err
+	}
+	if out.Family == "" {
+		return OSRelease{}, errors.New("os-release has no ID")
+	}
+	return out, nil
+}
+
+// DetectOS reads /etc/os-release.
+func DetectOS() (OSRelease, error) {
+	f, err := os.Open("/etc/os-release")
+	if err != nil {
+		return OSRelease{}, err
+	}
+	defer f.Close()
+	return ParseOSRelease(f)
+}