Move GetRedHatRelease() and GetHostDistroName() to common package

The `distro` package is now used for distro definitions supported by
osbuild-composer, not for introspecting the Host system. Move
`GetRedHatRelease()` and `GetHostDistroName()` functions to the `common`
package.

internal/common/distro.go

@@ -0,0 +1,79 @@
+package common
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"strings"
+)
+
+func GetHostDistroName() (string, bool, bool, error) {
+	f, err := os.Open("/etc/os-release")
+	if err != nil {
+		return "", false, false, err
+	}
+	defer f.Close()
+	osrelease, err := readOSRelease(f)
+	if err != nil {
+		return "", false, false, err
+	}
+
+	isStream := osrelease["NAME"] == "CentOS Stream"
+
+	// NOTE: We only consider major releases up until rhel 8.4
+	version := strings.Split(osrelease["VERSION_ID"], ".")
+	name := osrelease["ID"] + "-" + version[0]
+	if osrelease["ID"] == "rhel" && ((version[0] == "8" && version[1] >= "4") || version[0] == "9") {
+		name = name + version[1]
+	}
+
+	// TODO: We should probably index these things by the full CPE
+	beta := strings.Contains(osrelease["CPE_NAME"], "beta")
+	return name, beta, isStream, nil
+}
+
+// GetRedHatRelease returns the content of /etc/redhat-release
+// without the trailing new-line.
+func GetRedHatRelease() (string, error) {
+	raw, err := ioutil.ReadFile("/etc/redhat-release")
+	if err != nil {
+		return "", fmt.Errorf("cannot read /etc/redhat-release: %v", err)
+	}
+
+	//Remove the trailing new-line.
+	redHatRelease := strings.TrimSpace(string(raw))
+
+	return redHatRelease, nil
+}
+
+func readOSRelease(r io.Reader) (map[string]string, error) {
+	osrelease := make(map[string]string)
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if len(line) == 0 {
+			continue
+		}
+
+		parts := strings.SplitN(line, "=", 2)
+		if len(parts) != 2 {
+			return nil, errors.New("readOSRelease: invalid input")
+		}
+
+		key := strings.TrimSpace(parts[0])
+		value := strings.TrimSpace(parts[1])
+		if value[0] == '"' {
+			if len(value) < 2 || value[len(value)-1] != '"' {
+				return nil, errors.New("readOSRelease: invalid input")
+			}
+			value = value[1 : len(value)-1]
+		}
+
+		osrelease[key] = value
+	}
+
+	return osrelease, nil
+}

internal/common/distro_test.go

@@ -0,0 +1,54 @@
+package common
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+)
+
+func TestOSRelease(t *testing.T) {
+	var cases = []struct {
+		Input     string
+		OSRelease map[string]string
+	}{
+		{
+			``,
+			map[string]string{},
+		},
+		{
+			`NAME=Fedora
+VERSION="30 (Workstation Edition)"
+ID=fedora
+VERSION_ID=30
+VERSION_CODENAME=""
+PLATFORM_ID="platform:f30"
+PRETTY_NAME="Fedora 30 (Workstation Edition)"
+VARIANT="Workstation Edition"
+VARIANT_ID=workstation`,
+			map[string]string{
+				"NAME":             "Fedora",
+				"VERSION":          "30 (Workstation Edition)",
+				"ID":               "fedora",
+				"VERSION_ID":       "30",
+				"VERSION_CODENAME": "",
+				"PLATFORM_ID":      "platform:f30",
+				"PRETTY_NAME":      "Fedora 30 (Workstation Edition)",
+				"VARIANT":          "Workstation Edition",
+				"VARIANT_ID":       "workstation",
+			},
+		},
+	}
+
+	for i, c := range cases {
+		r := strings.NewReader(c.Input)
+
+		osrelease, err := readOSRelease(r)
+		if err != nil {
+			t.Fatalf("%d: readOSRelease: %v", i, err)
+		}
+
+		if !reflect.DeepEqual(osrelease, c.OSRelease) {
+			t.Fatalf("%d: readOSRelease returned unexpected result: %#v", i, osrelease)
+		}
+	}
+}