Caller is moved into its own repo
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# Caller
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Package caller is used to dynamically call functions with data unmarshalled
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into the functions' first argument. Its main purpose is to hide common
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unmarshalling code from each function implementation thus reducing
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boilerplate and making package interaction code sexier.
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[Documentation](https://godoc.org/github.com/localhots/shezmu/caller)
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Caller abstracts away the process of unmarshaling data before processing.
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```go
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type PriceUpdate struct {
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Product string `json:"product"`
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Amount float32 `json:"amount"`
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}
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func PriceUpdatePrinter(p PriceUpdate) {
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log.Printf("Price for %q is now $%.2f", p.Product, p.Amount)
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}
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// Error handling is skipped for clarity
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func main() {
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printer, _ := caller.New(PriceUpdatePrinter)
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_ = printer.Call([]byte(`{"product": "Paperclip", "amount": 0.01}`))
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}
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```
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@ -1,84 +0,0 @@
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// Package caller is used to dynamically call functions with data unmarshalled
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// into the functions' first argument. Its main purpose is to hide common
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// unmarshalling code from each function implementation thus reducing
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// boilerplate and making package interaction code sexier.
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package caller
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import (
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"encoding/json"
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"errors"
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"reflect"
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)
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// Caller wraps a function and makes it ready to be dynamically called.
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type Caller struct {
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// Unmarshaller is a BYOB unmarshaller function. By default it uses JSON.
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Unmarshaller func(data []byte, v interface{}) error
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fun reflect.Value
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argtyp reflect.Type
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}
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var (
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// ErrInvalidFunctionType is an error that is returned by the New function
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// when its argument is not a function.
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ErrInvalidFunctionType = errors.New("argument must be function")
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// ErrInvalidFunctionInArguments is an error that is returned by the New
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// function when its argument-function has a number of input arguments other
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// than 1.
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ErrInvalidFunctionInArguments = errors.New("function must have only one input argument")
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// ErrInvalidFunctionOutArguments is an error that is returned by the New
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// function when its argument-function returs any values.
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ErrInvalidFunctionOutArguments = errors.New("function must not have output arguments")
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)
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// New creates a new Caller instance using the function given as an argument.
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// It returns the Caller instance and an error if something is wrong with the
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// argument-function.
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func New(fun interface{}) (c *Caller, err error) {
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fval := reflect.ValueOf(fun)
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ftyp := reflect.TypeOf(fun)
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if ftyp.Kind() != reflect.Func {
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return nil, ErrInvalidFunctionType
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}
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if ftyp.NumIn() != 1 {
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return nil, ErrInvalidFunctionInArguments
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}
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if ftyp.NumOut() != 0 {
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return nil, ErrInvalidFunctionOutArguments
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}
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c = &Caller{
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Unmarshaller: json.Unmarshal,
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fun: fval,
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argtyp: ftyp.In(0),
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}
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return c, nil
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}
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// Call creates an instance of the Caller function's argument type, unmarshalls
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// the payload into it and dynamically calls the Caller function with this
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// instance.
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func (c *Caller) Call(data []byte) error {
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val, err := c.unmarshal(data)
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if err != nil {
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return err
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}
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c.makeDynamicCall(val)
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return nil
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}
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func (c *Caller) unmarshal(data []byte) (val reflect.Value, err error) {
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val = c.newValue()
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err = c.Unmarshaller(data, val.Interface())
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return
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}
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func (c *Caller) makeDynamicCall(val reflect.Value) {
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c.fun.Call([]reflect.Value{val.Elem()})
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}
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func (c *Caller) newValue() reflect.Value {
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return reflect.New(c.argtyp)
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}
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@ -1,202 +0,0 @@
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package caller
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import (
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"encoding/json"
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"fmt"
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"io/ioutil"
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"os"
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"testing"
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)
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//
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// Testing targets
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//
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type testMessage struct {
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Body string `json:"body"`
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}
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const testPayload = `{"body":"Success!"}`
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func testFun(m testMessage) {
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fmt.Print(m.Body)
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}
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func testFunSilent(_ testMessage) {}
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//
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// Tests
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//
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func TestNewCallerSuccess(t *testing.T) {
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c, err := New(testFun)
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if err != nil {
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t.Errorf("Expected no error, got: %v", err)
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}
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if c == nil {
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t.Error("Expected an instance of Caller, got nil")
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}
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}
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func TestNewCallerWithNonFunc(t *testing.T) {
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c, err := New(1)
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if err != ErrInvalidFunctionType {
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t.Errorf("Expected ErrInvalidFunctionType, got: %v", err)
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}
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if c != nil {
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t.Error("Expected nil, got an instance of Caller")
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}
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}
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func TestNewCallerWithFuncMultipleArgs(t *testing.T) {
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fun := func(a, b int) {}
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c, err := New(fun)
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if err != ErrInvalidFunctionInArguments {
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t.Errorf("Expected ErrInvalidFunctionInArguments, got: %v", err)
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}
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if c != nil {
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t.Error("Expected nil, got an instance of Caller")
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}
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}
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func TestNewCallerWithFuncReturnValue(t *testing.T) {
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fun := func(a int) int { return 0 }
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c, err := New(fun)
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if err != ErrInvalidFunctionOutArguments {
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t.Errorf("Expected ErrInvalidFunctionOutArguments, got: %v", err)
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}
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if c != nil {
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t.Error("Expected nil, got an instance of Caller")
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}
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}
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func TestCallSuccess(t *testing.T) {
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c, err := New(testFun)
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if err != nil {
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t.Fatal(err.Error())
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}
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out := captureStdoutAround(func() {
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if err := c.Call([]byte(testPayload)); err != nil {
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t.Fatal(err.Error())
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}
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})
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if string(out) != "Success!" {
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t.Errorf("Expected output to be %q, got %q", "Success!", out)
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}
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}
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func TestCallFalure(t *testing.T) {
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c, _ := New(testFunSilent)
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err := c.Call([]byte("{"))
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if err == nil {
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t.Error("Expected unmarshalling error, got nil")
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}
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}
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func TestUnmarshalSuccess(t *testing.T) {
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c, _ := New(testFunSilent)
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_, err := c.unmarshal([]byte(testPayload))
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if err != nil {
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t.Errorf("Expected no error, got: %v", err)
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}
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}
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func TestUnmarshalFailure(t *testing.T) {
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c, _ := New(testFunSilent)
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_, err := c.unmarshal([]byte("{"))
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if err == nil {
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t.Error("Expected unmarshalling error, got nil")
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}
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}
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func captureStdoutAround(f func()) []byte {
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origStdout := os.Stdout
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r, w, _ := os.Pipe()
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os.Stdout = w
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f()
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w.Close()
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out, err := ioutil.ReadAll(r)
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if err != nil {
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os.Stdout = origStdout
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panic(err)
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}
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r.Close()
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os.Stdout = origStdout
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return out
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}
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//
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// Benchmarks
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//
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func BenchmarkCaller(b *testing.B) {
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c, _ := New(testFunSilent)
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for i := 0; i < b.N; i++ {
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c.Call([]byte(testPayload))
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}
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}
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func BenchmarkNoCaller(b *testing.B) {
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for i := 0; i < b.N; i++ {
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var msg testMessage
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json.Unmarshal([]byte(testPayload), &msg)
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testFunSilent(msg)
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}
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}
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func BenchmarkDynamicNew(b *testing.B) {
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c, _ := New(testFunSilent)
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for i := 0; i < b.N; i++ {
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_ = c.newValue()
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}
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}
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func BenchmarkStaticNew(b *testing.B) {
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for i := 0; i < b.N; i++ {
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_ = testMessage{}
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}
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}
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func BenchmarkDynamicCall(b *testing.B) {
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c, _ := New(testFunSilent)
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val, _ := c.unmarshal([]byte(testPayload))
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for i := 0; i < b.N; i++ {
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c.makeDynamicCall(val)
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}
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}
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func BenchmarkStaticCall(b *testing.B) {
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var msg testMessage
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for i := 0; i < b.N; i++ {
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testFunSilent(msg)
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}
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}
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func BenchmarkUnmarshalIntoInterface(b *testing.B) {
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c, _ := New(testFunSilent)
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val := c.newValue()
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for i := 0; i < b.N; i++ {
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json.Unmarshal([]byte(testPayload), val.Interface())
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}
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}
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func BenchmarkUnmarshalIntoTypedValue(b *testing.B) {
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var msg testMessage
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for i := 0; i < b.N; i++ {
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json.Unmarshal([]byte(testPayload), &msg)
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}
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}
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