speculator: Tool to preview spec pull requests

Not the prettiest thing in the world, and horribly unperformant, but
useful :)

scripts/speculator/README

@@ -0,0 +1,4 @@
+speculator allows you to preview pull requests to the matrix.org specification.
+
+To run it, you must install the `go` tool, and run:
+ `go run main.go`

scripts/speculator/main.go

@@ -0,0 +1,220 @@
+// speculator allows you to preview pull requests to the matrix.org specification.
+// It serves two HTTP endpoints:
+//  - /spec/123 which renders the spec as html at pull request 123.
+//  - /diff/rst/123 which gives a diff of the spec's rst at pull request 123.
+// It is currently woefully inefficient, and there is a lot of low hanging fruit for improvement.
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"math/rand"
+	"net/http"
+	"os"
+	"os/exec"
+	"path"
+	"strconv"
+	"strings"
+	"syscall"
+)
+
+type PullRequest struct {
+	Base Commit
+	Head Commit
+	User User
+}
+
+type Commit struct {
+	SHA  string
+	Repo RequestRepo
+}
+
+type RequestRepo struct {
+	CloneURL string `json:"clone_url"`
+}
+
+type User struct {
+	Login string
+}
+
+var (
+	port           = flag.Int("port", 9000, "Port on which to listen for HTTP")
+	allowedMembers map[string]bool
+)
+
+func gitClone(url string) (string, error) {
+	dst := path.Join("/tmp/matrix-doc", strconv.FormatInt(rand.Int63(), 10))
+	cmd := exec.Command("git", "clone", url, dst)
+	err := cmd.Run()
+	if err != nil {
+		return "", fmt.Errorf("error cloning repo: %v", err)
+	}
+	return dst, nil
+}
+
+func gitCheckout(path, sha string) error {
+	cmd := exec.Command("git", "checkout", sha)
+	cmd.Dir = path
+	err := cmd.Run()
+	if err != nil {
+		return fmt.Errorf("error checking out repo: %v", err)
+	}
+	return nil
+}
+
+func lookupPullRequest(prNumber string) (PullRequest, error) {
+	resp, _ := http.Get("https://api.github.com/repos/matrix-org/matrix-doc/pulls/" + prNumber)
+	defer resp.Body.Close()
+	dec := json.NewDecoder(resp.Body)
+	var pr PullRequest
+	_ = dec.Decode(&pr)
+	return pr, nil
+}
+
+func generate(dir string) error {
+	cmd := exec.Command("python", "gendoc.py", "--nodelete")
+	cmd.Dir = path.Join(dir, "scripts")
+	var b bytes.Buffer
+	cmd.Stderr = &b
+	err := cmd.Run()
+	if err != nil {
+		return fmt.Errorf("error generating spec: %v\nOutput from gendoc:\n%v", err, b.String())
+	}
+	return nil
+}
+
+func writeError(w http.ResponseWriter, err error) {
+	w.WriteHeader(500)
+	io.WriteString(w, fmt.Sprintf("%v\n", err))
+}
+
+// generateAt generates spec from repo at sha.
+// Returns the path where the generation was done.
+func generateAt(repo, sha string) (dst string, err error) {
+	dst, err = gitClone(repo)
+	if err != nil {
+		return
+	}
+
+	if err = gitCheckout(dst, sha); err != nil {
+		return
+	}
+
+	err = generate(dst)
+	return
+}
+
+func serveSpec(w http.ResponseWriter, req *http.Request) {
+	parts := strings.Split(req.URL.Path, "/")
+	if len(parts) != 3 {
+		w.WriteHeader(400)
+		io.WriteString(w, fmt.Sprintf("Invalid path passed: %v expect /pull/123", req.URL.Path))
+		return
+	}
+
+	pr, err := lookupPullRequest(parts[2])
+	if err != nil {
+		writeError(w, err)
+		return
+	}
+
+	if !allowedMembers[pr.User.Login] {
+		w.WriteHeader(403)
+		io.WriteString(w, fmt.Sprintf("%q is not a trusted pull requester", pr.User.Login))
+		return
+	}
+
+	dst, err := generateAt(pr.Head.Repo.CloneURL, pr.Head.SHA)
+	defer os.RemoveAll(dst)
+	if err != nil {
+		writeError(w, err)
+		return
+	}
+
+	b, err := ioutil.ReadFile(path.Join(dst, "scripts/gen/specification.html"))
+	if err != nil {
+		writeError(w, fmt.Errorf("Error reading spec: %v", err))
+		return
+	}
+	w.Write(b)
+}
+
+func serveRstDiff(w http.ResponseWriter, req *http.Request) {
+	parts := strings.Split(req.URL.Path, "/")
+	if len(parts) != 4 {
+		w.WriteHeader(400)
+		io.WriteString(w, fmt.Sprintf("Invalid path passed: %v expect /diff/rst/123", req.URL.Path))
+		return
+	}
+
+	pr, err := lookupPullRequest(parts[3])
+	if err != nil {
+		writeError(w, err)
+		return
+	}
+
+	if !allowedMembers[pr.User.Login] {
+		w.WriteHeader(403)
+		io.WriteString(w, fmt.Sprintf("%q is not a trusted pull requester", pr.User.Login))
+		return
+	}
+
+	base, err := generateAt(pr.Base.Repo.CloneURL, pr.Base.SHA)
+	defer os.RemoveAll(base)
+	if err != nil {
+		writeError(w, err)
+		return
+	}
+
+	head, err := generateAt(pr.Head.Repo.CloneURL, pr.Head.SHA)
+	defer os.RemoveAll(head)
+	if err != nil {
+		writeError(w, err)
+		return
+	}
+
+	diffCmd := exec.Command("diff", path.Join(base, "scripts", "tmp", "full_spec.rst"), path.Join(head, "scripts", "tmp", "full_spec.rst"))
+	var diff bytes.Buffer
+	diffCmd.Stdout = &diff
+	if err := ignoreExitCodeOne(diffCmd.Run()); err != nil {
+		writeError(w, fmt.Errorf("error running diff: %v", err))
+		return
+	}
+	w.Write(diff.Bytes())
+}
+
+func ignoreExitCodeOne(err error) error {
+	if err == nil {
+		return err
+	}
+
+	if exiterr, ok := err.(*exec.ExitError); ok {
+		if status, ok := exiterr.Sys().(syscall.WaitStatus); ok {
+			if status.ExitStatus() == 1 {
+				return nil
+			}
+		}
+	}
+	return err
+}
+
+func main() {
+	flag.Parse()
+	// It would be great to read this from github, but there's no convenient way to do so.
+	// Most of these memberships are "private", so would require some kind of auth.
+	allowedMembers = map[string]bool{
+		"dbkr":          true,
+		"erikjohnston":  true,
+		"illicitonion":  true,
+		"Kegsay":        true,
+		"NegativeMjark": true,
+	}
+	http.HandleFunc("/spec/", serveSpec)
+	http.HandleFunc("/diff/rst/", serveRstDiff)
+	log.Fatal(http.ListenAndServe(fmt.Sprintf(":%d", *port), nil))
+}