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Precompute decode hooks for performance reason #324

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Precompute decode hooks for performance reason #324

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f4f8905
Precompute decode hooks for performance reason
Apr 14, 2023
cd2091e
Also precompute hook in decoder
Apr 14, 2023
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40 changes: 36 additions & 4 deletions decode_hooks.go
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Expand Up @@ -35,6 +35,30 @@ func typedDecodeHook(h DecodeHookFunc) DecodeHookFunc {
return nil
}

// cachedDecodeHook takes a raw DecodeHookFunc (an interface{}) and turns
// it into a closure to be used directly
// if the type fails to convert we return a closure always erroring to keep the previous behaviour
func cachedDecodeHook(raw DecodeHookFunc) func(from reflect.Value, to reflect.Value) (interface{}, error) {
switch f := typedDecodeHook(raw).(type) {
case DecodeHookFuncType:
return func(from reflect.Value, to reflect.Value) (interface{}, error) {
return f(from.Type(), to.Type(), from.Interface())
}
case DecodeHookFuncKind:
return func(from reflect.Value, to reflect.Value) (interface{}, error) {
return f(from.Kind(), to.Kind(), from.Interface())
}
case DecodeHookFuncValue:
return func(from reflect.Value, to reflect.Value) (interface{}, error) {
return f(from, to)
}
default:
return func(from reflect.Value, to reflect.Value) (interface{}, error) {
return nil, errors.New("invalid decode hook signature")
}
}
}

// DecodeHookExec executes the given decode hook. This should be used
// since it'll naturally degrade to the older backwards compatible DecodeHookFunc
// that took reflect.Kind instead of reflect.Type.
Expand All @@ -60,13 +84,17 @@ func DecodeHookExec(
// The composed funcs are called in order, with the result of the
// previous transformation.
func ComposeDecodeHookFunc(fs ...DecodeHookFunc) DecodeHookFunc {
cached := make([]func(from reflect.Value, to reflect.Value) (interface{}, error), 0, len(fs))
for _, f := range fs {
cached = append(cached, cachedDecodeHook(f))
}
return func(f reflect.Value, t reflect.Value) (interface{}, error) {
var err error
data := f.Interface()

newFrom := f
for _, f1 := range fs {
data, err = DecodeHookExec(f1, newFrom, t)
for _, c := range cached {
data, err = c(newFrom, t)
if err != nil {
return nil, err
}
Expand All @@ -80,13 +108,17 @@ func ComposeDecodeHookFunc(fs ...DecodeHookFunc) DecodeHookFunc {
// OrComposeDecodeHookFunc executes all input hook functions until one of them returns no error. In that case its value is returned.
// If all hooks return an error, OrComposeDecodeHookFunc returns an error concatenating all error messages.
func OrComposeDecodeHookFunc(ff ...DecodeHookFunc) DecodeHookFunc {
cached := make([]func(from reflect.Value, to reflect.Value) (interface{}, error), 0, len(ff))
for _, f := range ff {
cached = append(cached, cachedDecodeHook(f))
}
return func(a, b reflect.Value) (interface{}, error) {
var allErrs string
var out interface{}
var err error

for _, f := range ff {
out, err = DecodeHookExec(f, a, b)
for _, c := range cached {
out, err = c(a, b)
if err != nil {
allErrs += err.Error() + "\n"
continue
Expand Down
126 changes: 65 additions & 61 deletions mapstructure.go
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Expand Up @@ -9,84 +9,84 @@
//
// The simplest function to start with is Decode.
//
// Field Tags
// # Field Tags
//
// When decoding to a struct, mapstructure will use the field name by
// default to perform the mapping. For example, if a struct has a field
// "Username" then mapstructure will look for a key in the source value
// of "username" (case insensitive).
//
// type User struct {
// Username string
// }
// type User struct {
// Username string
// }
//
// You can change the behavior of mapstructure by using struct tags.
// The default struct tag that mapstructure looks for is "mapstructure"
// but you can customize it using DecoderConfig.
//
// Renaming Fields
// # Renaming Fields
//
// To rename the key that mapstructure looks for, use the "mapstructure"
// tag and set a value directly. For example, to change the "username" example
// above to "user":
//
// type User struct {
// Username string `mapstructure:"user"`
// }
// type User struct {
// Username string `mapstructure:"user"`
// }
//
// Embedded Structs and Squashing
// # Embedded Structs and Squashing
//
// Embedded structs are treated as if they're another field with that name.
// By default, the two structs below are equivalent when decoding with
// mapstructure:
//
// type Person struct {
// Name string
// }
// type Person struct {
// Name string
// }
//
// type Friend struct {
// Person
// }
// type Friend struct {
// Person
// }
//
// type Friend struct {
// Person Person
// }
// type Friend struct {
// Person Person
// }
//
// This would require an input that looks like below:
//
// map[string]interface{}{
// "person": map[string]interface{}{"name": "alice"},
// }
// map[string]interface{}{
// "person": map[string]interface{}{"name": "alice"},
// }
//
// If your "person" value is NOT nested, then you can append ",squash" to
// your tag value and mapstructure will treat it as if the embedded struct
// were part of the struct directly. Example:
//
// type Friend struct {
// Person `mapstructure:",squash"`
// }
// type Friend struct {
// Person `mapstructure:",squash"`
// }
//
// Now the following input would be accepted:
//
// map[string]interface{}{
// "name": "alice",
// }
// map[string]interface{}{
// "name": "alice",
// }
//
// When decoding from a struct to a map, the squash tag squashes the struct
// fields into a single map. Using the example structs from above:
//
// Friend{Person: Person{Name: "alice"}}
// Friend{Person: Person{Name: "alice"}}
//
// Will be decoded into a map:
//
// map[string]interface{}{
// "name": "alice",
// }
// map[string]interface{}{
// "name": "alice",
// }
//
// DecoderConfig has a field that changes the behavior of mapstructure
// to always squash embedded structs.
//
// Remainder Values
// # Remainder Values
//
// If there are any unmapped keys in the source value, mapstructure by
// default will silently ignore them. You can error by setting ErrorUnused
Expand All @@ -98,20 +98,20 @@
// probably be a "map[string]interface{}" or "map[interface{}]interface{}".
// See example below:
//
// type Friend struct {
// Name string
// Other map[string]interface{} `mapstructure:",remain"`
// }
// type Friend struct {
// Name string
// Other map[string]interface{} `mapstructure:",remain"`
// }
//
// Given the input below, Other would be populated with the other
// values that weren't used (everything but "name"):
//
// map[string]interface{}{
// "name": "bob",
// "address": "123 Maple St.",
// }
// map[string]interface{}{
// "name": "bob",
// "address": "123 Maple St.",
// }
//
// Omit Empty Values
// # Omit Empty Values
//
// When decoding from a struct to any other value, you may use the
// ",omitempty" suffix on your tag to omit that value if it equates to
Expand All @@ -122,37 +122,37 @@
// field value is zero and a numeric type, the field is empty, and it won't
// be encoded into the destination type.
//
// type Source struct {
// Age int `mapstructure:",omitempty"`
// }
// type Source struct {
// Age int `mapstructure:",omitempty"`
// }
//
// Unexported fields
// # Unexported fields
//
// Since unexported (private) struct fields cannot be set outside the package
// where they are defined, the decoder will simply skip them.
//
// For this output type definition:
//
// type Exported struct {
// private string // this unexported field will be skipped
// Public string
// }
// type Exported struct {
// private string // this unexported field will be skipped
// Public string
// }
//
// Using this map as input:
//
// map[string]interface{}{
// "private": "I will be ignored",
// "Public": "I made it through!",
// }
// map[string]interface{}{
// "private": "I will be ignored",
// "Public": "I made it through!",
// }
//
// The following struct will be decoded:
//
// type Exported struct {
// private: "" // field is left with an empty string (zero value)
// Public: "I made it through!"
// }
// type Exported struct {
// private: "" // field is left with an empty string (zero value)
// Public: "I made it through!"
// }
//
// Other Configuration
// # Other Configuration
//
// mapstructure is highly configurable. See the DecoderConfig struct
// for other features and options that are supported.
Expand Down Expand Up @@ -282,7 +282,8 @@ type DecoderConfig struct {
// structure. The top-level Decode method is just a convenience that sets
// up the most basic Decoder.
type Decoder struct {
config *DecoderConfig
config *DecoderConfig
cachedDecodeHook func(from reflect.Value, to reflect.Value) (interface{}, error)
}

// Metadata contains information about decoding a structure that
Expand Down Expand Up @@ -407,6 +408,9 @@ func NewDecoder(config *DecoderConfig) (*Decoder, error) {
result := &Decoder{
config: config,
}
if config.DecodeHook != nil {
result.cachedDecodeHook = cachedDecodeHook(config.DecodeHook)
}

return result, nil
}
Expand Down Expand Up @@ -453,10 +457,10 @@ func (d *Decoder) decode(name string, input interface{}, outVal reflect.Value) e
return nil
}

if d.config.DecodeHook != nil {
if d.cachedDecodeHook != nil {
// We have a DecodeHook, so let's pre-process the input.
var err error
input, err = DecodeHookExec(d.config.DecodeHook, inputVal, outVal)
input, err = d.cachedDecodeHook(inputVal, outVal)
if err != nil {
return fmt.Errorf("error decoding '%s': %w", name, err)
}
Expand Down