piston/api/main.go

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"os/exec"
	"regexp"
	"strings"
	"time"
)

type inbound struct {
	Language string   `json:"language"`
	Source   string   `json:"source"`
	Args     []string `json:"args"`
}

type problem struct {
	Code    string `json:"code"`
	Message string `json:"message"`
}

type outbound struct {
	Ran    bool   `json:"ran"`
	Output string `json:"output"`
}

type Language struct {
	Name    string `json:"name,omitempty"`
	Version string `json:"version,omitempty"`
}

type Languages struct {
	Languages []Language `json:"languages"`
}

var instance int
var versionRegex = regexp.MustCompile("([0-9]+\\.[0-9]+\\.[0-9]+)")

func main() {
	port := "2000"

	updateVersions()

	fmt.Println("starting api on port", port)
	http.HandleFunc("/execute", Execute)
	http.ListenAndServe(":"+port, nil)
}

func Execute(res http.ResponseWriter, req *http.Request) {
	res.Header().Set("Content-Type", "application/json")

	// get json
	inbound := inbound{}
	message := json.NewDecoder(req.Body)
	message.Decode(&inbound)

	whitelist := []string{
		"c",
		"cpp", "c++",
		"c#", "csharp", "cs",
		"go",
		"java",
		"nasm", "asm",
		"javascript", "js", "node",
		"typescript", "ts",
		"php",
		"python", "python2", "python3",
		"ruby",
		"swift",
		"rust",
		"bash",
	}

	// check if the supplied language is supported
	// now calls function and returns
	for _, lang := range whitelist {
		if lang == inbound.Language {
			launch(inbound, res)
			return
		}
	}

	// now only called when the language is not supported
	problem := problem{
		Code:    "unsupported_language",
		Message: inbound.Language + " is not supported by Piston",
	}

	pres, _ := json.Marshal(problem)

	res.Write(pres)
}

func launch(request inbound, res http.ResponseWriter) {
	stamp := time.Now().UnixNano()

	// write the code to temp dir
	srcfile := fmt.Sprintf("/tmp/%d.code", stamp)

	ioutil.WriteFile(srcfile, []byte(request.Source), 0644)

	// set up the arguments to send to the execute command
	var args []string

	args = append(args, request.Language)
	args = append(args, srcfile)

	args = append(args, strings.Join(request.Args, "\n"))

	// set up the execution
	cmd := exec.Command("../lxc/execute", args...)

	// capture out/err
	var stdout, stderr bytes.Buffer
	cmd.Stdout = &stdout
	cmd.Stderr = &stderr

	err := cmd.Run()

	// prepare response
	outbound := outbound{
		Ran:    err == nil,
		Output: strings.TrimSpace(stdout.String()),
	}

	response, _ := json.Marshal(outbound)

	res.Write(response)
}

func updateVersions() {
	f, err := os.Create("versions.json")
	if err != nil {
		log.Println(err)
		return
	}
	defer f.Close()
	langs, err := getVersions()
	if err != nil {
		log.Println(err)
		return
	}
	res, err := json.Marshal(langs)
	if err != nil {
		log.Println(err)
		return
	}
	f.Write(res)
}

// get all the language and their current version
func getVersions() ([]Language, error) {
	var languages []Language
	res, err := execVersionScript()
	if err != nil {
		return nil, err
	}
	languageInfo := strings.Split(res, "---")
	for _, v := range languageInfo {
		if len(v) < 2 {
			continue
		}
		name, version := getVersion(v)
		languages = append(languages, Language{
			Name:    name,
			Version: version,
		})
	}
	return languages, nil
}

// run the script that retrieves all the language versions
func execVersionScript() (string, error) {
	fmt.Println("running script")
	output := bytes.Buffer{}
	cmd := exec.Command("../lcx/versions")
	cmd.Stdout = &output
	err := cmd.Run()
	return strings.ToLower(output.String()), err
}

// return the language and its version
// most of the time it is easy to get the name and version
// but for some languages helper functions are used
func getVersion(s string) (string, string) {
	lines := strings.Split(s, "\n")
	return lines[1], versionRegex.FindString(lines[2])
}