Add PullRequestResource functionality for updating labels and comments.

Missing from this change:
* Statuses, since this might involve more discussion on the set of statuses
  that we want to support.
* Updating from changes to the raw payloads. Unclear how we want to
  handle these at the moment. Punting on this for now.

First step for supporting #778.

Co-authored-by: Dan Lorenc <[email protected]>
Co-authored-by: Billy Lynch <[email protected]>

cmd/pullrequest-init/README.md

@@ -0,0 +1,64 @@
+# pullrequest-init
+
+pullrequest-init fetches pull request data from the given URL and places it in
+the provided path.
+
+This binary outputs a generic pull request object into `pr.json`, as well as
+provider specific payloads.
+
+Currently supported providers:
+
+*   GitHub
+
+## Generic pull request payload
+
+The payload generated by default aims to abstract the base features of any pull
+request provider. Since there is no one true spec for pull requests, not every
+feature may be available. The payload is output to `$PATH/pr.json` and looks
+like:
+
+```json
+{
+    "Type": "github",
+    "ID": 188184279,
+    "Head": {
+        "Repo": "https://github.com/wlynch/test.git",
+        "Branch": "dev",
+        "SHA": "9bcde245572c74329827acdcab88792ebb84d578"
+    },
+    "Base": {
+        "Repo": "https://github.com/wlynch/test.git",
+        "Branch": "master",
+        "SHA": "1e80c83ed01e187669b836096335d1c8a2c57182"
+    },
+    "Comments": [
+        {
+            "Text": "test comment",
+            "Author": "wlynch",
+            "ID": 494418247,
+            "Raw": "/tmp/prtest/github/comments/494418247.json"
+        }
+    ],
+    "Labels": [
+        {
+            "Text": "my-label"
+        }
+    ],
+    "Raw": "/tmp/prtest/github/pr.json"
+}
+```
+
+## GitHub
+
+GitHub pull requests will output these additional files:
+
+*   `$PATH/github/pr.json`: The raw GitHub payload as specified by
+    https://developer.github.com/v3/pulls/#get-a-single-pull-request
+*   `$PATH/github/comments/#.json`: Comments associated to the PR as specified
+    by https://developer.github.com/v3/issues/comments/#get-a-single-comment
+
+For now, these files are *read-only*.
+
+The binary will look for GitHub credentials in the `${GITHUBTOKEN}` environment
+variable. This should generally be specified as a secret with the field name
+`githubToken` in the `PullRequestResource` definition.

cmd/pullrequest-init/fake_github.go

@@ -0,0 +1,232 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strconv"
+	"strings"
+
+	"github.com/google/go-github/github"
+	"github.com/gorilla/mux"
+)
+
+const (
+	// ErrorKeyword is a magic const used to denote PRs/Comments that should
+	// return errors to the client to simulate issues communicating with GitHub.
+	ErrorKeyword = "~~ERROR~~"
+)
+
+// key defines keys for associating data to PRs/issues in the fake server.
+type key struct {
+	owner string
+	repo  string
+	id    int64
+}
+
+// FakeGitHub is a fake GitHub server for use in tests.
+type FakeGitHub struct {
+	*mux.Router
+
+	pr map[key]*github.PullRequest
+	// GitHub references comments in 2 ways:
+	// 1) List by issue (PR) ID.
+	// 2) Get by comment ID.
+	// We need to store references to both to emulate the API properly.
+	prComments map[key][]*github.IssueComment
+	comments   map[key]*github.IssueComment
+}
+
+// NewFakeGitHub returns a new FakeGitHub.
+func NewFakeGitHub() *FakeGitHub {
+	s := &FakeGitHub{
+		Router:     mux.NewRouter(),
+		pr:         make(map[key]*github.PullRequest),
+		prComments: make(map[key][]*github.IssueComment),
+		comments:   make(map[key]*github.IssueComment),
+	}
+	s.HandleFunc("/repos/{owner}/{repo}/pulls/{number}", s.getPullRequest).Methods(http.MethodGet)
+	s.HandleFunc("/repos/{owner}/{repo}/issues/{number}/comments", s.getComments).Methods(http.MethodGet)
+	s.HandleFunc("/repos/{owner}/{repo}/issues/{number}/comments", s.createComment).Methods(http.MethodPost)
+	s.HandleFunc("/repos/{owner}/{repo}/issues/comments/{number}", s.updateComment).Methods(http.MethodPatch)
+	s.HandleFunc("/repos/{owner}/{repo}/issues/comments/{number}", s.deleteComment).Methods(http.MethodDelete)
+	s.HandleFunc("/repos/{owner}/{repo}/issues/{number}/labels", s.updateLabels).Methods(http.MethodPut)
+
+	return s
+}
+
+func prKey(r *http.Request) (key, error) {
+	pr, err := strconv.ParseInt(mux.Vars(r)["number"], 10, 64)
+	if err != nil {
+		return key{}, err
+	}
+	return key{
+		owner: mux.Vars(r)["owner"],
+		repo:  mux.Vars(r)["repo"],
+		id:    pr,
+	}, nil
+}
+
+// AddPullRequest adds the given pull request to the fake GitHub server.
+// This is done as a convenience over implementing PullReqests.Create in the
+// GitHub server since that method takes in a different type (NewPullRequest).
+func (g *FakeGitHub) AddPullRequest(pr *github.PullRequest) {
+	key := key{
+		owner: pr.GetBase().GetUser().GetLogin(),
+		repo:  pr.GetBase().GetRepo().GetName(),
+		id:    pr.GetID(),
+	}
+	g.pr[key] = pr
+}
+
+func (g *FakeGitHub) getPullRequest(w http.ResponseWriter, r *http.Request) {
+	key, err := prKey(r)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	pr, ok := g.pr[key]
+	if !ok {
+		http.Error(w, fmt.Sprintf("%v not found", key), http.StatusNotFound)
+		return
+	}
+
+	if err := json.NewEncoder(w).Encode(pr); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+}
+
+func (g *FakeGitHub) getComments(w http.ResponseWriter, r *http.Request) {
+	key, err := prKey(r)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+	}
+
+	comments, ok := g.prComments[key]
+	if !ok {
+		comments = []*github.IssueComment{}
+	}
+	if err := json.NewEncoder(w).Encode(comments); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+}
+
+func (g *FakeGitHub) createComment(w http.ResponseWriter, r *http.Request) {
+	prKey, err := prKey(r)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+	c := new(github.IssueComment)
+	if err := json.NewDecoder(r.Body).Decode(c); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	if strings.Contains(c.GetBody(), ErrorKeyword) {
+		http.Error(w, "intentional error", http.StatusInternalServerError)
+		return
+	}
+
+	c.ID = github.Int64(int64(len(g.comments) + 1))
+
+	if _, ok := g.prComments[prKey]; !ok {
+		g.prComments[prKey] = []*github.IssueComment{}
+	}
+	g.prComments[prKey] = append(g.prComments[prKey], c)
+
+	commentKey := key{
+		owner: prKey.owner,
+		repo:  prKey.repo,
+		id:    c.GetID(),
+	}
+	g.comments[commentKey] = c
+
+	if err := json.NewEncoder(w).Encode(c); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+}
+
+func (g *FakeGitHub) updateComment(w http.ResponseWriter, r *http.Request) {
+	key, err := prKey(r)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+	update := new(github.IssueComment)
+	if err := json.NewDecoder(r.Body).Decode(update); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	if strings.Contains(update.GetBody(), ErrorKeyword) {
+		http.Error(w, "intentional error", http.StatusInternalServerError)
+		return
+	}
+
+	existing, ok := g.comments[key]
+	if !ok {
+		http.Error(w, fmt.Sprintf("comment %+v not found", key), http.StatusNotFound)
+		return
+	}
+
+	*existing = *update
+	w.WriteHeader(http.StatusOK)
+}
+
+func (g *FakeGitHub) deleteComment(w http.ResponseWriter, r *http.Request) {
+	key, err := prKey(r)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	if _, ok := g.comments[key]; !ok {
+		http.Error(w, fmt.Sprintf("comment %+v not found", key), http.StatusNotFound)
+		return
+	}
+
+	// Remove comment from PR storage. Not particularly efficient, but we don't
+	// generally expect this to be used for large number of comments in unit
+	// tests.
+	for k := range g.prComments {
+		for i, c := range g.prComments[k] {
+			if c.GetID() == key.id {
+				g.prComments[k] = append(g.prComments[k][:i], g.prComments[k][i+1:]...)
+				break
+			}
+		}
+	}
+	delete(g.comments, key)
+
+	w.WriteHeader(http.StatusOK)
+}
+
+func (g *FakeGitHub) updateLabels(w http.ResponseWriter, r *http.Request) {
+	key, err := prKey(r)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+	}
+
+	pr, ok := g.pr[key]
+	if !ok {
+		http.Error(w, "pull request not found", http.StatusNotFound)
+		return
+	}
+
+	payload := []string{}
+	if err := json.NewDecoder(r.Body).Decode(&payload); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	pr.Labels = make([]*github.Label, 0, len(payload))
+	for _, l := range payload {
+		pr.Labels = append(pr.Labels, &github.Label{
+			Name: github.String(l),
+		})
+	}
+
+	w.WriteHeader(http.StatusOK)
+}