piston/api/main.go

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"net/http"
	"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"`
	Language string `json:"language"`
	Version  string `json:"version"`
	Output   string `json:"output"`
	Stdout   string `json:"stdout"`
	Stderr   string `json:"stderr"`
}

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

var instance int
var languages []Language

func main() {
	port := "2000"

	var err error
	languages, err = UpdateVersions()

	if err != nil {
		fmt.Println("could not get version info and therefore couldn't start")
		fmt.Println(err)
		return
	}

	fmt.Println("starting api on port", port)
	http.HandleFunc("/execute", Execute)
	http.HandleFunc("/versions", Versions)
	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{
		"awk",
		"bash",
		"brainfuck", "bf",
		"c",
		"cpp", "c++",
		"csharp", "cs", "c#",
		"deno", "denojs", "denots",
		"elixir", "exs",
		"emacs", "elisp", "el",
		"go",
		"haskell", "hs",
		"java",
		"jelly",
		"julia", "jl",
		"kotlin",
		"lua",
		"nasm", "asm",
		"nasm64", "asm64",
		"node", "javascript", "js",
		"perl", "pl",
		"php",
		"python2",
		"python3", "python",
		"paradoc",
		"ruby",
		"rust",
		"swift",
		"typescript", "ts",
	}

	// 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.WriteHeader(http.StatusBadRequest)
	res.Write(pres)
}

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

	data, _ := json.Marshal(languages)

	res.Write(data)
}

type StdWriter struct {
	combined *string
	separate *string
}

func (writer *StdWriter) Write(data []byte) (int, error) {
	*writer.combined += string(data)
	*writer.separate += string(data)

	return len(data), nil
}

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
	cmd := exec.Command("../lxc/execute", request.Language, srcfile, strings.Join(request.Args, "\n"))

	// capture out/err
	var stdout, stderr, combined string

	cmd.Stdout = &StdWriter{
		combined: &combined,
		separate: &stdout,
	}

	cmd.Stderr = &StdWriter{
		combined: &combined,
		separate: &stderr,
	}

	stdout = strings.TrimSpace(stdout)
	stderr = strings.TrimSpace(stderr)
	combined = strings.TrimSpace(combined)

	if len(stdout) > 65536 {
		stdout = stdout[:65536]
	}

	if len(stderr) > 65536 {
		stderr = stdout[:65536]
	}

	if len(combined) > 65536 {
		combined = combined[:65536]
	}

	err := cmd.Run()

	// get the executing version of the language
	execlang := request.Language

	switch execlang {
	case "bf":
		execlang = "brainfuck"
	case "c++":
		execlang = "cpp"
	case "cs", "c#":
		execlang = "csharp"
	case "denojs", "denots":
		execlang = "deno"
	case "el", "elisp":
		execlang = "emacs"
	case "exs":
		execlang = "elixir"
	case "hs":
		execlang = "haskell"
	case "asm":
		execlang = "nasm"
	case "asm64":
		execlang = "nasm64"
	case "js", "javascript":
		execlang = "node"
	case "jl":
		execlang = "julia"
	case "python":
		execlang = "python3"
	case "ts":
		execlang = "typescript"
	}

	// prepare response
	outbound := Outbound{
		Ran:      err == nil,
		Language: request.Language,
		Version:  "",
		Output:   combined,
		Stdout:   stdout,
		Stderr:   stderr,
	}

	// retrieve the language version
	for _, lang := range languages {
		if lang.Name == execlang {
			outbound.Version = lang.Version
			break
		}
	}

	response, _ := json.Marshal(outbound)

	res.Write(response)
}

func UpdateVersions() ([]Language, error) {
	langs, err := GetVersions()

	if err != nil {
		return nil, err
	}

	return langs, nil
}

// get all the language and their current version
func GetVersions() ([]Language, error) {
	var languages []Language

	res, err := ExecVersionScript()

	if err != nil {
		return nil, err
	}

	info := strings.Split(res, "---")

	for _, v := range info {
		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) {
	cmd := exec.Command("../lxc/versions")

	var stdout bytes.Buffer
	cmd.Stdout = &stdout
	cmd.Stderr = &stdout

	err := cmd.Run()

	return strings.ToLower(stdout.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")

	if lines[1] == "java" {
		return "java", regexp.MustCompile("([0-9]+)").FindString(lines[2])
	}

	if lines[1] == "emacs" {
		return "emacs", regexp.MustCompile("([0-9]+\\.[0-9]+)").FindString(lines[2])
	}

	return lines[1], regexp.MustCompile("([0-9]+\\.[0-9]+\\.[0-9]+)").FindString(s)
}