initial take on distro identification

Signed-off-by: Alfredo Deza <adeza@anchore.com>

imgbom/distro/identify.go

@@ -1,11 +1,104 @@
 package distro
 
 import (
+	"regexp"
+	"strings"
+
+	"github.com/anchore/imgbom/internal/log"
+	"github.com/anchore/stereoscope/pkg/file"
 	"github.com/anchore/stereoscope/pkg/image"
 )
 
-func Identify(img *image.Image) (Distro, error) {
+// returns a distro or nil
+type parseFunc func(string) *Distro
+
+// Identify parses distro-specific files to determine distro metadata like version and release
+func Identify(img *image.Image) *Distro {
 	// TODO: implement me based off of https://github.com/anchore/anchore-engine/blob/78b23d7e8f007005c070673405b5e23730a660e0/anchore_engine/analyzers/utils.py#L131
 
-	return NewDistro(UnknownDistro, "0.0.0")
+	identityFiles := map[file.Path]parseFunc{
+		"/etc/os-release": parseOsRelease,
+		// Debian and Debian-based distros have the same contents linked from this path
+		"/usr/lib/os-release": parseOsRelease,
+		// TODO: change this to /bin/busybox when stereoscope deals with hardlinks
+		"/bin/[": parseBusyBox,
+	}
+
+	for path, fn := range identityFiles {
+
+		contents, err := img.FileContentsFromSquash(path)
+
+		if err != nil {
+			log.Errorf("unable to get contents from %s: %s", path, err)
+			continue
+		}
+
+		if contents == "" {
+			log.Debugf("no contents in file, skipping: %s", path)
+			continue
+		}
+		distro := fn(contents)
+
+		if distro == nil {
+			continue
+		}
+
+		return distro
+
+	}
+	// TODO: is it useful to know partially detected distros? where the ID is known but not the version (and viceversa?)
+	return nil
+}
+
+func assembleDistro(name, version string) *Distro {
+	distroType, ok := Mappings[name]
+
+	// Both distro and version must be present
+	if len(name) == 0 || len(version) == 0 {
+		return nil
+	}
+
+	if ok {
+		distro, err := NewDistro(distroType, version)
+		if err != nil {
+			return nil
+		}
+		return &distro
+	}
+
+	return nil
+}
+
+func parseOsRelease(contents string) *Distro {
+	id, vers := "", ""
+	for _, line := range strings.Split(contents, "\n") {
+
+		parts := strings.Split(line, "=")
+		prefix := parts[0]
+		value := strings.ReplaceAll(parts[len(parts)-1], `"`, "")
+
+		switch prefix {
+		case "ID":
+			id = value
+		case "VERSION_ID":
+			vers = value
+		}
+	}
+
+	return assembleDistro(id, vers)
+}
+
+var busyboxVersionMatcher = regexp.MustCompile(`BusyBox v[\d\.]+`)
+
+func parseBusyBox(contents string) *Distro {
+	matches := busyboxVersionMatcher.FindAllString(contents, -1)
+	for _, match := range matches {
+		parts := strings.Split(match, " ")
+		version := strings.ReplaceAll(parts[1], "v", "")
+		distro := assembleDistro("busybox", version)
+		if distro != nil {
+			return distro
+		}
+	}
+	return nil
 }