xgo

README

xgo

Enable function Trap for go, and provide tools like Mock and Trace to help go developers write unit test and debug both easier and faster.

xgo works as a drop-in replacement for go run,go build, and go test.

It adds missing abilities to go program by cooperating with(or hacking) the go compiler.

Thses abilities include Mock, Trap and Trace.

See Usage and Documentation for more details.

Want to help contribute to xgo? Great! Check CONTRIBUTING for help.

Installation

# macOS and Linux
curl -fsSL https://github.com/xhd2015/xgo/raw/master/install.sh | bash

If you've already installed xgo, you can upgrade it with:

xgo upgrade

If you want to build from source, run with:

git clone https://github.com/xhd2015/xgo
cd xgo
go run ./script/build-release --local

Requirement

xgo requires at least go1.17 to compile.

There is no specific limitation on OS and Architecture.

All OS and Architectures are supported by xgo as long as they are supported by go.

Usage

The following code demonstrates how to setup mock on a given function:

• The function add(a,b) normally adds a and b up, resulting in a+b,
• However, after mock.AddFuncInterceptor, the logic is changed to a-b.

(check test/testdata/mock_res/main.go for more details.)

package main

import (
    "context"
    "fmt"

    "github.com/xhd2015/xgo/runtime/core"
    "github.com/xhd2015/xgo/runtime/mock"
)

func main() {
    before := add(5, 2)
    fmt.Printf("before mock: add(5,2)=%d\n", before)
    mock.AddFuncInterceptor(add, func(ctx context.Context, fn *core.FuncInfo, args core.Object, results core.Object) error {
        a := args.GetField("a").Value().(int)
        b := args.GetField("b").Value().(int)
        res := a - b
        results.GetFieldIndex(0).Set(res)
        return nil
    })
    after := add(5, 2)
    fmt.Printf("after mock: add(5,2)=%d\n", after)
}

func add(a int, b int) int {
    return a + b
}

Run with go:

go run ./
# output:
#  before mock: add(5,2)=7
#  after mock: add(5,2)=7

Run with xgo:

xgo run ./
# output:
#  before mock: add(5,2)=7
#  after mock: add(5,2)=3

For mocking method, check Mock for more details.

Trap

Trap allows developer to intercept function execution on the fly.

Trap is the core of xgo as it is the basis of other abilities like Mock and Trace.

The following example logs function execution trace by adding a Trap interceptor:

(check test/testdata/trap/trap.go for more details.)

package main

import (
    "context"
    "fmt"

    "github.com/xhd2015/xgo/runtime/core"
    "github.com/xhd2015/xgo/runtime/trap"
)

func init() {
    trap.AddInterceptor(&trap.Interceptor{
        Pre: func(ctx context.Context, f *core.FuncInfo, args core.Object, results core.Object) (interface{}, error) {
            trap.Skip()
            if f.Name == "A" {
                fmt.Printf("trap A\n")
                return nil, nil
            }
            if f.Name == "B" {
                fmt.Printf("abort B\n")
                return nil, trap.ErrAbort
            }
            return nil, nil
        },
    })
}

func main() {
    A()
    B()
}

func A() {
    fmt.Printf("A\n")
}

func B() {
    fmt.Printf("B\n")
}

Run with go:

go run ./
# output:
#   A
#   B

Run with xgo:

xgo run ./
# output:
#   trap A
#   A
#   abort B

AddInterceptor() add given interceptor to either global or local, depending on whether it is called from init or after init:

• Before init: effective globally for all goroutines,
• After init: effective only for current goroutine, and will be cleared after current goroutine exits.

When AddInterceptor() is called after init, it will return a dispose function to clear the interceptor earlier before current goroutine exits.

Example:

func main(){
    clear := trap.AddInterceptor(...)
    defer clear()
    ...
}

Mock

Mock simplifies the process of setting up Trap interceptors.

The Mock API:

• Mock(fn, interceptor)

Arguments:

• If fn is a simple function(i.e. not a method of a struct or interface),then all call to that function will be intercepted,
• If fn is a method(i.e. file.Read),then only call to the instance will be intercepted, other instances will not be affected

Scope:

• If Mock is called from init, then all goroutines will be mocked.
• Otherwise, if Mock is called after init, the mock interceptor will only be effective for current gorotuine, other goroutines are not affected.

Interceptor Signature: func(ctx context.Context, fn *core.FuncInfo, args core.Object, results core.Object) error

• If the interceptor returns nil, then the target function is mocked,
• If the interceptor returns mock.ErrCallOld, then the target function is called again,
• Otherwise, the interceptor returns a non-nil error, that will be set to the function's return error.

Function mock example:

func MyFunc() string {
    return "my func"
}
func TestFuncMock(t *testing.T){
    mock.Mock(MyFunc, func(ctx context.Context, fn *core.FuncInfo, args core.Object, results core.Object) error {
        results.GetFieldIndex(0).Set("mock func")
        return nil
    })
    text := MyFunc()
    if text!="mock func"{
        t.Fatalf("expect MyFunc() to be 'mock func', actual: %s", text)
    }
}

Method mock example:

type MyStruct struct {
    name string
}
func (c *MyStruct) Name() string {
    return c.name
}

func TestMethodMock(t *testing.T){
    myStruct := &MyStruct{
        name: "my struct",
    }
    otherStruct := &MyStruct{
        name: "other struct",
    }
    mock.Mock(myStruct.Name, func(ctx context.Context, fn *core.FuncInfo, args core.Object, results core.Object) error {
        results.GetFieldIndex(0).Set("mock struct")
        return nil
    })

    // myStruct is affected
    name := myStruct.Name()
    if name!="mock struct"{
        t.Fatalf("expect myStruct.Name() to be 'mock struct', actual: %s", name)
    }

    // otherStruct is not affected
    otherName := otherStruct.Name()
    if otherName!="other struct"{
        t.Fatalf("expect otherStruct.Name() to be 'other struct', actual: %s", otherName)
    }
}

Trace

It is painful when debugging with a deep call stack.

Trace addresses this issue by collecting the hiearchical stack trace and stores it into file for later use.

Needless to say, with Trace, debug becomes less usual:

(check test/testdata/trace/trace.go for more details.)

package main

import (
    "fmt"

    "github.com/xhd2015/xgo/runtime/trace"
)

func init() {
    trace.Enable()
}

func main() {
    A()
    B()
    C()
}
func A() { fmt.Printf("A\n") }
func B() { fmt.Printf("B\n");C(); }
func C() { fmt.Printf("C\n") }

Run with go:

go run ./
# output:
#   A
#   B
#   C
#   C

Run with xgo:

XGO_TRACE_OUTPUT=stdout xgo run ./
# output a JSON representing the call stacktrace like:
#        {
#            "Name": "main",
#            "Children": [{
#                 "Name": "A"
#                },{
#                  "Name": "B",
#                  "Children": [{
#                       "Name": "C"
#                   }]
#                },{
#                   "Name": "C"
#                }
#            ]
#        }
#
# NOTE: other fields are ommited for displaying key information.

You can view the trace with:xgo tool trace TestExample.json

Output:

By default, Trace will write traces to a temp directory under current working directory. This behavior can be overridden by setting XGO_TRACE_OUTPUT to different values:

• XGO_TRACE_OUTPUT=stdout: traces will be written to stdout, for debugging purepose,
• XGO_TRACE_OUTPUT=<dir>: traces will be written to <dir>,
• XGO_TRACE_OUTPUT=off: turn off trace.

Evolution of xgo

xgo is the successor of the original go-mock, which works by rewriting go code before compile.

The strategy employed by go-mock works well but causes much longer build time for larger projects due to source code explosion.

However, go-mock is remarkable for it's discovery of Trap, Trace besides Mock, and additional abilities like trapping variable and disabling map randomness.

It is the shoulder which xgo stands on.