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Add caller package

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Gregory Eremin 2015-10-14 00:08:45 +03:00
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LICENCE Normal file
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Copyright (c) 2015 Gregory Eremin
MIT License
Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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# Caller
Package caller is used to dynamicly call functions with data unmarshalled
into the functions' first argument. It's main purpose is to hide common
unmarshalling code from each function's implementation thus reducing
boilerplate and making the code sexier.
[Documentation](https://godoc.org/github.com/localhots/uberdaemon/caller)
```go
package main
import (
"github.com/localhots/uberdaemon/caller"
)
type message struct {
Title string `json:"title"`
Body string `json:"body"`
}
func processMessage(m message) {
fmt.Printf("Title: %s\nBody: %s\n", m.Title, m.Body)
}
func main() {
c, _ := caller.New(processMessage)
c.Call(`{"title": "Hello", "body": "World"}`)
}
```

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// Package caller is used to dynamicly call functions with data unmarshalled
// into the functions' first argument. It's main purpose is to hide common
// unmarshalling code from each function's implementation thus reducing
// boilerplate and making the code sexier.
package caller
import (
"encoding/json"
"errors"
"reflect"
)
// Caller wraps a function and makes it ready to be dynamically called.
type Caller struct {
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{
fun: fval,
argtyp: ftyp.In(0),
}
return c, nil
}
// Call creates an instance of the Caller function's argument type, unmarshalls
// the JSON 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 = json.Unmarshal(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)
}

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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, _ := ioutil.ReadAll(r)
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)
}
}