A generic mechanism for supporting new types (#23)

Author: hujun-open

.github/workflows/test.yml

@@ -1,6 +1,7 @@
 name: Test
 
 on:
+  workflow_dispatch:
   push:
     branches: [ master ]
   pull_request:
@@ -16,7 +17,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v4
       with:
-        go-version: '1.16'
+        go-version: '1.19'
 
     - name: Test
       run: go test -v ./...

README.md

@@ -29,7 +29,12 @@ import "github.com/itzg/go-flagsfiller"
 - Beyond the standard types supported by flag.FlagSet also includes support for:
     - `[]string` where repetition of the argument appends to the slice and/or an argument value can contain a comma-separated list of values. For example: `--arg one --arg two,three`
     - `map[string]string` where each entry is a `key=value` and/or repetition of the arguments adds to the map or multiple entries can be comma-separated in a single argument value. For example: `--arg k1=v1 --arg k2=v2,k3=v3`
+	- `time.Time` parse via time.Parse(), with tag `layout` specify the layout string, default is "2006-01-02 15:04:05"
+	- `net.IP` parse via net.ParseIP()
+	- `net.IPNet` parse via net.ParseCIDR()
+	- `net.HardwareAddr` parse via net.ParseMAC()
 - Optionally set flag values from environment variables. Similar to flag names, environment variable names are derived automatically from the field names
+- New types could be supported via user code, via `RegisterSimpleType(ConvertFunc)`, check [time.go](time.go) and [net.go](net.go) to see how it works
 
 ## Quick example
 

flagset.go

@@ -55,13 +55,8 @@ func (f *FlagSetFiller) Fill(flagSet *flag.FlagSet, from interface{}) error {
 	}
 }
 
-// this is a list of supported struct, like time.Time, that walkFields() won't walk into,
-// the key is the is string returned by the getTypeName(<struct_type>),
-// each supported struct need to be added in this map in init()
-var supportedStructList = make(map[string]struct{})
-
 func isSupportedStruct(name string) bool {
-	_, ok := supportedStructList[name]
+	_, ok := extendedTypes[name]
 	return ok
 }
 
@@ -181,20 +176,13 @@ func (f *FlagSetFiller) processField(flagSet *flag.FlagSet, fieldRef interface{}
 		renamed = f.options.renameLongName(name)
 	}
 	typeName := getTypeName(t)
-	switch {
-	//check the typeName
-	case typeName == "net.IP":
-		f.processIP(fieldRef, hasDefaultTag, tagDefault, flagSet, renamed, usage, aliases)
-	case typeName == "net.IPNet":
-		f.processIPNet(fieldRef, hasDefaultTag, tagDefault, flagSet, renamed, usage, aliases)
-	case typeName == "net.HardwareAddr":
-		f.processMAC(fieldRef, hasDefaultTag, tagDefault, flagSet, renamed, usage, aliases)
-
-	case typeName == "time.Time":
-		layoutStr, _ := tag.Lookup("layout")
-		f.processTime(fieldRef, hasDefaultTag, tagDefault, flagSet, renamed, usage, aliases, layoutStr)
-	//end of check typeName
 
+	// go through all supported structs
+	if handler, ok := extendedTypes[typeName]; ok {
+		err = handler(tag, fieldRef, hasDefaultTag, tagDefault, flagSet, renamed, usage, aliases)
+	}
+
+	switch {
 	case t.Kind() == reflect.String:
 		f.processString(fieldRef, hasDefaultTag, tagDefault, flagSet, renamed, usage, aliases)
 

general.go

@@ -0,0 +1,51 @@
+package flagsfiller
+
+/*
+The code in this file could be opened up in future if more complex implementation is needed
+*/
+
+import (
+	"flag"
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+// this is a list of addtional supported types(include struct), like time.Time, that walkFields() won't walk into,
+// the key is the is string returned by the getTypeName(<type>),
+// each supported type need to be added in this map in init()
+var extendedTypes = make(map[string]handlerFunc)
+
+type handlerFunc func(tag reflect.StructTag, fieldRef interface{},
+	hasDefaultTag bool, tagDefault string,
+	flagSet *flag.FlagSet, renamed string,
+	usage string, aliases string) error
+
+type flagVal[T any] interface {
+	flag.Value
+	StrConverter(string) (T, error)
+	SetRef(*T)
+}
+
+func processGeneral[T any](fieldRef interface{}, val flagVal[T],
+	hasDefaultTag bool, tagDefault string,
+	flagSet *flag.FlagSet, renamed string,
+	usage string, aliases string) (err error) {
+
+	casted := fieldRef.(*T)
+	if hasDefaultTag {
+		*casted, err = val.StrConverter(tagDefault)
+		if err != nil {
+			return fmt.Errorf("failed to parse default into %T: %w", *new(T), err)
+		}
+	}
+	val.SetRef(casted)
+	flagSet.Var(val, renamed, usage)
+	if aliases != "" {
+		for _, alias := range strings.Split(aliases, ",") {
+			flagSet.Var(val, alias, usage)
+		}
+	}
+	return nil
+
+}

go.mod

@@ -1,6 +1,6 @@
 module github.com/itzg/go-flagsfiller
 
-go 1.16
+go 1.19
 
 require (
 	github.com/iancoleman/strcase v0.2.0

mac.go

@@ -1,123 +1,33 @@
 package flagsfiller
 
 import (
-	"flag"
 	"fmt"
 	"net"
-	"strings"
+	"reflect"
 )
 
 func init() {
-	supportedStructList["net.IPNet"] = struct{}{}
+	RegisterSimpleType(ipConverter)
+	RegisterSimpleType(ipnetConverter)
+	RegisterSimpleType(macConverter)
 }
 
-type ipValue struct {
-	addr *net.IP
-}
-
-func (v *ipValue) String() string {
-	if v.addr == nil {
-		return fmt.Sprint(nil)
-	}
-	return v.addr.String()
-}
-
-func (v *ipValue) Set(s string) error {
-	*v.addr = net.ParseIP(s)
-	if *v.addr == nil {
-		return fmt.Errorf("invalid ip addr %v", s)
-	}
-	return nil
-}
-
-func (f *FlagSetFiller) processIP(fieldRef interface{}, hasDefaultTag bool, tagDefault string, flagSet *flag.FlagSet, renamed string, usage string, aliases string) (err error) {
-	casted, ok := fieldRef.(*net.IP)
-	if !ok {
-		return f.processCustom(
-			fieldRef,
-			func(s string) (interface{}, error) {
-				value := net.ParseIP(s)
-				if value == nil {
-					return nil, fmt.Errorf("invalid IP address %s", s)
-				}
-				return value, nil
-			},
-			hasDefaultTag,
-			tagDefault,
-			flagSet,
-			renamed,
-			usage,
-			aliases,
-		)
-	}
-
-	if hasDefaultTag {
-		*casted = net.ParseIP(tagDefault)
-		if *casted == nil {
-			return fmt.Errorf("failed to parse default into net.IP: %s", tagDefault)
-		}
+func ipConverter(s string, tag reflect.StructTag) (net.IP, error) {
+	addr := net.ParseIP(s)
+	if addr == nil {
+		return nil, fmt.Errorf("%s is not a valid IP address", s)
 	}
-	flagSet.Var(&ipValue{casted}, renamed, usage)
-	if aliases != "" {
-		for _, alias := range strings.Split(aliases, ",") {
-			flagSet.Var(&ipValue{casted}, alias, usage)
-		}
-	}
-	return nil
-}
-
-type ipnetValue struct {
-	prefix *net.IPNet
-}
-
-func (v *ipnetValue) String() string {
-	if v.prefix == nil {
-		return fmt.Sprint(nil)
-	}
-	return v.prefix.String()
+	return addr, nil
 }
 
-func (v *ipnetValue) Set(s string) error {
-	_, pr, err := net.ParseCIDR(s)
+func ipnetConverter(s string, tag reflect.StructTag) (net.IPNet, error) {
+	_, prefix, err := net.ParseCIDR(s)
 	if err != nil {
-		return fmt.Errorf("invalid ip prefix %v", s)
+		return net.IPNet{}, err
 	}
-	*v.prefix = *pr
-	return nil
+	return *prefix, nil
 }
 
-func (f *FlagSetFiller) processIPNet(fieldRef interface{}, hasDefaultTag bool, tagDefault string, flagSet *flag.FlagSet, renamed string, usage string, aliases string) (err error) {
-	casted, ok := fieldRef.(*net.IPNet)
-	if !ok {
-		return f.processCustom(
-			fieldRef,
-			func(s string) (interface{}, error) {
-				_, value, err := net.ParseCIDR(s)
-				if err != nil {
-					return nil, fmt.Errorf("invalid IP prefix %s, %w", s, err)
-				}
-				return *value, nil
-			},
-			hasDefaultTag,
-			tagDefault,
-			flagSet,
-			renamed,
-			usage,
-			aliases,
-		)
-	}
-
-	if hasDefaultTag {
-		_, casted, err = net.ParseCIDR(tagDefault)
-		if err != nil {
-			return fmt.Errorf("failed to parse default into net.IPNet: %s, %w", tagDefault, err)
-		}
-	}
-	flagSet.Var(&ipnetValue{casted}, renamed, usage)
-	if aliases != "" {
-		for _, alias := range strings.Split(aliases, ",") {
-			flagSet.Var(&ipnetValue{casted}, alias, usage)
-		}
-	}
-	return nil
+func macConverter(s string, tag reflect.StructTag) (net.HardwareAddr, error) {
+	return net.ParseMAC(s)
 }

net.go

@@ -0,0 +1,61 @@
+package flagsfiller
+
+import (
+	"flag"
+	"fmt"
+	"reflect"
+)
+
+// RegisterSimpleType register a new type,
+// should be called in init(),
+// see time.go and net.go for implementation examples
+func RegisterSimpleType[T any](c ConvertFunc[T]) {
+	base := simpleType[T]{converter: c}
+	extendedTypes[getTypeName(reflect.TypeOf(*new(T)))] = base.Process
+}
+
+// ConvertFunc is a function convert string s into a specific type T, the tag is the struct field tag, as addtional input.
+// see time.go and net.go for implementation examples
+type ConvertFunc[T any] func(s string, tag reflect.StructTag) (T, error)
+
+type simpleType[T any] struct {
+	val       *T
+	tags      reflect.StructTag
+	converter ConvertFunc[T]
+}
+
+func newSimpleType[T any](c ConvertFunc[T], tag reflect.StructTag) simpleType[T] {
+	return simpleType[T]{val: new(T), converter: c, tags: tag}
+}
+
+func (v *simpleType[T]) String() string {
+	if v.val == nil {
+		return fmt.Sprint(nil)
+	}
+	return fmt.Sprintf("%v", *v.val)
+}
+
+func (v *simpleType[T]) StrConverter(s string) (T, error) {
+	return v.converter(s, v.tags)
+}
+
+func (v *simpleType[T]) Set(s string) error {
+	var err error
+	*v.val, err = v.converter(s, v.tags)
+	if err != nil {
+		return fmt.Errorf("failed to parse %s into %T, %w", s, *(new(T)), err)
+	}
+	return nil
+}
+
+func (v *simpleType[T]) SetRef(t *T) {
+	v.val = t
+}
+
+func (v *simpleType[T]) Process(tag reflect.StructTag, fieldRef interface{},
+	hasDefaultTag bool, tagDefault string,
+	flagSet *flag.FlagSet, renamed string,
+	usage string, aliases string) error {
+	val := newSimpleType(v.converter, tag)
+	return processGeneral[T](fieldRef, &val, hasDefaultTag, tagDefault, flagSet, renamed, usage, aliases)
+}