Merge master into breakout_swarm

Signed-off-by: Alex Ellis <alexellis2@gmail.com>

gateway/vendor/github.com/docker/distribution/configuration/parser.go

@@ -0,0 +1,283 @@
+package configuration
+
+import (
+	"fmt"
+	"os"
+	"reflect"
+	"sort"
+	"strconv"
+	"strings"
+
+	"github.com/Sirupsen/logrus"
+	"gopkg.in/yaml.v2"
+)
+
+// Version is a major/minor version pair of the form Major.Minor
+// Major version upgrades indicate structure or type changes
+// Minor version upgrades should be strictly additive
+type Version string
+
+// MajorMinorVersion constructs a Version from its Major and Minor components
+func MajorMinorVersion(major, minor uint) Version {
+	return Version(fmt.Sprintf("%d.%d", major, minor))
+}
+
+func (version Version) major() (uint, error) {
+	majorPart := strings.Split(string(version), ".")[0]
+	major, err := strconv.ParseUint(majorPart, 10, 0)
+	return uint(major), err
+}
+
+// Major returns the major version portion of a Version
+func (version Version) Major() uint {
+	major, _ := version.major()
+	return major
+}
+
+func (version Version) minor() (uint, error) {
+	minorPart := strings.Split(string(version), ".")[1]
+	minor, err := strconv.ParseUint(minorPart, 10, 0)
+	return uint(minor), err
+}
+
+// Minor returns the minor version portion of a Version
+func (version Version) Minor() uint {
+	minor, _ := version.minor()
+	return minor
+}
+
+// VersionedParseInfo defines how a specific version of a configuration should
+// be parsed into the current version
+type VersionedParseInfo struct {
+	// Version is the version which this parsing information relates to
+	Version Version
+	// ParseAs defines the type which a configuration file of this version
+	// should be parsed into
+	ParseAs reflect.Type
+	// ConversionFunc defines a method for converting the parsed configuration
+	// (of type ParseAs) into the current configuration version
+	// Note: this method signature is very unclear with the absence of generics
+	ConversionFunc func(interface{}) (interface{}, error)
+}
+
+type envVar struct {
+	name  string
+	value string
+}
+
+type envVars []envVar
+
+func (a envVars) Len() int           { return len(a) }
+func (a envVars) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a envVars) Less(i, j int) bool { return a[i].name < a[j].name }
+
+// Parser can be used to parse a configuration file and environment of a defined
+// version into a unified output structure
+type Parser struct {
+	prefix  string
+	mapping map[Version]VersionedParseInfo
+	env     envVars
+}
+
+// NewParser returns a *Parser with the given environment prefix which handles
+// versioned configurations which match the given parseInfos
+func NewParser(prefix string, parseInfos []VersionedParseInfo) *Parser {
+	p := Parser{prefix: prefix, mapping: make(map[Version]VersionedParseInfo)}
+
+	for _, parseInfo := range parseInfos {
+		p.mapping[parseInfo.Version] = parseInfo
+	}
+
+	for _, env := range os.Environ() {
+		envParts := strings.SplitN(env, "=", 2)
+		p.env = append(p.env, envVar{envParts[0], envParts[1]})
+	}
+
+	// We must sort the environment variables lexically by name so that
+	// more specific variables are applied before less specific ones
+	// (i.e. REGISTRY_STORAGE before
+	// REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY). This sucks, but it's a
+	// lot simpler and easier to get right than unmarshalling map entries
+	// into temporaries and merging with the existing entry.
+	sort.Sort(p.env)
+
+	return &p
+}
+
+// Parse reads in the given []byte and environment and writes the resulting
+// configuration into the input v
+//
+// Environment variables may be used to override configuration parameters other
+// than version, following the scheme below:
+// v.Abc may be replaced by the value of PREFIX_ABC,
+// v.Abc.Xyz may be replaced by the value of PREFIX_ABC_XYZ, and so forth
+func (p *Parser) Parse(in []byte, v interface{}) error {
+	var versionedStruct struct {
+		Version Version
+	}
+
+	if err := yaml.Unmarshal(in, &versionedStruct); err != nil {
+		return err
+	}
+
+	parseInfo, ok := p.mapping[versionedStruct.Version]
+	if !ok {
+		return fmt.Errorf("Unsupported version: %q", versionedStruct.Version)
+	}
+
+	parseAs := reflect.New(parseInfo.ParseAs)
+	err := yaml.Unmarshal(in, parseAs.Interface())
+	if err != nil {
+		return err
+	}
+
+	for _, envVar := range p.env {
+		pathStr := envVar.name
+		if strings.HasPrefix(pathStr, strings.ToUpper(p.prefix)+"_") {
+			path := strings.Split(pathStr, "_")
+
+			err = p.overwriteFields(parseAs, pathStr, path[1:], envVar.value)
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	c, err := parseInfo.ConversionFunc(parseAs.Interface())
+	if err != nil {
+		return err
+	}
+	reflect.ValueOf(v).Elem().Set(reflect.Indirect(reflect.ValueOf(c)))
+	return nil
+}
+
+// overwriteFields replaces configuration values with alternate values specified
+// through the environment. Precondition: an empty path slice must never be
+// passed in.
+func (p *Parser) overwriteFields(v reflect.Value, fullpath string, path []string, payload string) error {
+	for v.Kind() == reflect.Ptr {
+		if v.IsNil() {
+			panic("encountered nil pointer while handling environment variable " + fullpath)
+		}
+		v = reflect.Indirect(v)
+	}
+	switch v.Kind() {
+	case reflect.Struct:
+		return p.overwriteStruct(v, fullpath, path, payload)
+	case reflect.Map:
+		return p.overwriteMap(v, fullpath, path, payload)
+	case reflect.Interface:
+		if v.NumMethod() == 0 {
+			if !v.IsNil() {
+				return p.overwriteFields(v.Elem(), fullpath, path, payload)
+			}
+			// Interface was empty; create an implicit map
+			var template map[string]interface{}
+			wrappedV := reflect.MakeMap(reflect.TypeOf(template))
+			v.Set(wrappedV)
+			return p.overwriteMap(wrappedV, fullpath, path, payload)
+		}
+	}
+	return nil
+}
+
+func (p *Parser) overwriteStruct(v reflect.Value, fullpath string, path []string, payload string) error {
+	// Generate case-insensitive map of struct fields
+	byUpperCase := make(map[string]int)
+	for i := 0; i < v.NumField(); i++ {
+		sf := v.Type().Field(i)
+		upper := strings.ToUpper(sf.Name)
+		if _, present := byUpperCase[upper]; present {
+			panic(fmt.Sprintf("field name collision in configuration object: %s", sf.Name))
+		}
+		byUpperCase[upper] = i
+	}
+
+	fieldIndex, present := byUpperCase[path[0]]
+	if !present {
+		logrus.Warnf("Ignoring unrecognized environment variable %s", fullpath)
+		return nil
+	}
+	field := v.Field(fieldIndex)
+	sf := v.Type().Field(fieldIndex)
+
+	if len(path) == 1 {
+		// Env var specifies this field directly
+		fieldVal := reflect.New(sf.Type)
+		err := yaml.Unmarshal([]byte(payload), fieldVal.Interface())
+		if err != nil {
+			return err
+		}
+		field.Set(reflect.Indirect(fieldVal))
+		return nil
+	}
+
+	// If the field is nil, must create an object
+	switch sf.Type.Kind() {
+	case reflect.Map:
+		if field.IsNil() {
+			field.Set(reflect.MakeMap(sf.Type))
+		}
+	case reflect.Ptr:
+		if field.IsNil() {
+			field.Set(reflect.New(sf.Type))
+		}
+	}
+
+	err := p.overwriteFields(field, fullpath, path[1:], payload)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (p *Parser) overwriteMap(m reflect.Value, fullpath string, path []string, payload string) error {
+	if m.Type().Key().Kind() != reflect.String {
+		// non-string keys unsupported
+		logrus.Warnf("Ignoring environment variable %s involving map with non-string keys", fullpath)
+		return nil
+	}
+
+	if len(path) > 1 {
+		// If a matching key exists, get its value and continue the
+		// overwriting process.
+		for _, k := range m.MapKeys() {
+			if strings.ToUpper(k.String()) == path[0] {
+				mapValue := m.MapIndex(k)
+				// If the existing value is nil, we want to
+				// recreate it instead of using this value.
+				if (mapValue.Kind() == reflect.Ptr ||
+					mapValue.Kind() == reflect.Interface ||
+					mapValue.Kind() == reflect.Map) &&
+					mapValue.IsNil() {
+					break
+				}
+				return p.overwriteFields(mapValue, fullpath, path[1:], payload)
+			}
+		}
+	}
+
+	// (Re)create this key
+	var mapValue reflect.Value
+	if m.Type().Elem().Kind() == reflect.Map {
+		mapValue = reflect.MakeMap(m.Type().Elem())
+	} else {
+		mapValue = reflect.New(m.Type().Elem())
+	}
+	if len(path) > 1 {
+		err := p.overwriteFields(mapValue, fullpath, path[1:], payload)
+		if err != nil {
+			return err
+		}
+	} else {
+		err := yaml.Unmarshal([]byte(payload), mapValue.Interface())
+		if err != nil {
+			return err
+		}
+	}
+
+	m.SetMapIndex(reflect.ValueOf(strings.ToLower(path[0])), reflect.Indirect(mapValue))
+
+	return nil
+}