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Caller is moved into its own repo

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Gregory Eremin 2016-07-26 21:59:27 +02:00
parent 98b341ec02
commit 8c73487c08
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27
caller/README.md
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# Caller
Package caller is used to dynamically call functions with data unmarshalled
into the functions' first argument. Its main purpose is to hide common
unmarshalling code from each function implementation thus reducing
boilerplate and making package interaction code sexier.
[Documentation](https://godoc.org/github.com/localhots/shezmu/caller)
Caller abstracts away the process of unmarshaling data before processing.
```go
type PriceUpdate struct {
Product string `json:"product"`
Amount float32 `json:"amount"`
}
func PriceUpdatePrinter(p PriceUpdate) {
log.Printf("Price for %q is now $%.2f", p.Product, p.Amount)
}
// Error handling is skipped for clarity
func main() {
printer, _ := caller.New(PriceUpdatePrinter)
_ = printer.Call([]byte(`{"product": "Paperclip", "amount": 0.01}`))
}
```

84
caller/caller.go
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// Package caller is used to dynamically call functions with data unmarshalled
// into the functions' first argument. Its main purpose is to hide common
// unmarshalling code from each function implementation thus reducing
// boilerplate and making package interaction code sexier.
package caller
import (
"encoding/json"
"errors"
"reflect"
)
// Caller wraps a function and makes it ready to be dynamically called.
type Caller struct {
// Unmarshaller is a BYOB unmarshaller function. By default it uses JSON.
Unmarshaller func(data []byte, v interface{}) error
fun reflect.Value
argtyp reflect.Type
}
var (
// ErrInvalidFunctionType is an error that is returned by the New function
// when its argument is not a function.
ErrInvalidFunctionType = errors.New("argument must be function")
// ErrInvalidFunctionInArguments is an error that is returned by the New
// function when its argument-function has a number of input arguments other
// than 1.
ErrInvalidFunctionInArguments = errors.New("function must have only one input argument")
// ErrInvalidFunctionOutArguments is an error that is returned by the New
// function when its argument-function returs any values.
ErrInvalidFunctionOutArguments = errors.New("function must not have output arguments")
)
// New creates a new Caller instance using the function given as an argument.
// It returns the Caller instance and an error if something is wrong with the
// argument-function.
func New(fun interface{}) (c *Caller, err error) {
fval := reflect.ValueOf(fun)
ftyp := reflect.TypeOf(fun)
if ftyp.Kind() != reflect.Func {
return nil, ErrInvalidFunctionType
}
if ftyp.NumIn() != 1 {
return nil, ErrInvalidFunctionInArguments
}
if ftyp.NumOut() != 0 {
return nil, ErrInvalidFunctionOutArguments
}
c = &Caller{
Unmarshaller: json.Unmarshal,
fun: fval,
argtyp: ftyp.In(0),
}
return c, nil
}
// Call creates an instance of the Caller function's argument type, unmarshalls
// the payload into it and dynamically calls the Caller function with this
// instance.
func (c *Caller) Call(data []byte) error {
val, err := c.unmarshal(data)
if err != nil {
return err
}
c.makeDynamicCall(val)
return nil
}
func (c *Caller) unmarshal(data []byte) (val reflect.Value, err error) {
val = c.newValue()
err = c.Unmarshaller(data, val.Interface())
return
}
func (c *Caller) makeDynamicCall(val reflect.Value) {
c.fun.Call([]reflect.Value{val.Elem()})
}
func (c *Caller) newValue() reflect.Value {
return reflect.New(c.argtyp)
}

202
caller/caller_test.go
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package caller
import (
"encoding/json"
"fmt"
"io/ioutil"
"os"
"testing"
)
//
// Testing targets
//
type testMessage struct {
Body string `json:"body"`
}
const testPayload = `{"body":"Success!"}`
func testFun(m testMessage) {
fmt.Print(m.Body)
}
func testFunSilent(_ testMessage) {}
//
// Tests
//
func TestNewCallerSuccess(t *testing.T) {
c, err := New(testFun)
if err != nil {
t.Errorf("Expected no error, got: %v", err)
}
if c == nil {
t.Error("Expected an instance of Caller, got nil")
}
}
func TestNewCallerWithNonFunc(t *testing.T) {
c, err := New(1)
if err != ErrInvalidFunctionType {
t.Errorf("Expected ErrInvalidFunctionType, got: %v", err)
}
if c != nil {
t.Error("Expected nil, got an instance of Caller")
}
}
func TestNewCallerWithFuncMultipleArgs(t *testing.T) {
fun := func(a, b int) {}
c, err := New(fun)
if err != ErrInvalidFunctionInArguments {
t.Errorf("Expected ErrInvalidFunctionInArguments, got: %v", err)
}
if c != nil {
t.Error("Expected nil, got an instance of Caller")
}
}
func TestNewCallerWithFuncReturnValue(t *testing.T) {
fun := func(a int) int { return 0 }
c, err := New(fun)
if err != ErrInvalidFunctionOutArguments {
t.Errorf("Expected ErrInvalidFunctionOutArguments, got: %v", err)
}
if c != nil {
t.Error("Expected nil, got an instance of Caller")
}
}
func TestCallSuccess(t *testing.T) {
c, err := New(testFun)
if err != nil {
t.Fatal(err.Error())
}
out := captureStdoutAround(func() {
if err := c.Call([]byte(testPayload)); err != nil {
t.Fatal(err.Error())
}
})
if string(out) != "Success!" {
t.Errorf("Expected output to be %q, got %q", "Success!", out)
}
}
func TestCallFalure(t *testing.T) {
c, _ := New(testFunSilent)
err := c.Call([]byte("{"))
if err == nil {
t.Error("Expected unmarshalling error, got nil")
}
}
func TestUnmarshalSuccess(t *testing.T) {
c, _ := New(testFunSilent)
_, err := c.unmarshal([]byte(testPayload))
if err != nil {
t.Errorf("Expected no error, got: %v", err)
}
}
func TestUnmarshalFailure(t *testing.T) {
c, _ := New(testFunSilent)
_, err := c.unmarshal([]byte("{"))
if err == nil {
t.Error("Expected unmarshalling error, got nil")
}
}
func captureStdoutAround(f func()) []byte {
origStdout := os.Stdout
r, w, _ := os.Pipe()
os.Stdout = w
f()
w.Close()
out, err := ioutil.ReadAll(r)
if err != nil {
os.Stdout = origStdout
panic(err)
}
r.Close()
os.Stdout = origStdout
return out
}
//
// Benchmarks
//
func BenchmarkCaller(b *testing.B) {
c, _ := New(testFunSilent)
for i := 0; i < b.N; i++ {
c.Call([]byte(testPayload))
}
}
func BenchmarkNoCaller(b *testing.B) {
for i := 0; i < b.N; i++ {
var msg testMessage
json.Unmarshal([]byte(testPayload), &msg)
testFunSilent(msg)
}
}
func BenchmarkDynamicNew(b *testing.B) {
c, _ := New(testFunSilent)
for i := 0; i < b.N; i++ {
_ = c.newValue()
}
}
func BenchmarkStaticNew(b *testing.B) {
for i := 0; i < b.N; i++ {
_ = testMessage{}
}
}
func BenchmarkDynamicCall(b *testing.B) {
c, _ := New(testFunSilent)
val, _ := c.unmarshal([]byte(testPayload))
for i := 0; i < b.N; i++ {
c.makeDynamicCall(val)
}
}
func BenchmarkStaticCall(b *testing.B) {
var msg testMessage
for i := 0; i < b.N; i++ {
testFunSilent(msg)
}
}
func BenchmarkUnmarshalIntoInterface(b *testing.B) {
c, _ := New(testFunSilent)
val := c.newValue()
for i := 0; i < b.N; i++ {
json.Unmarshal([]byte(testPayload), val.Interface())
}
}
func BenchmarkUnmarshalIntoTypedValue(b *testing.B) {
var msg testMessage
for i := 0; i < b.N; i++ {
json.Unmarshal([]byte(testPayload), &msg)
}
}