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 tektoncd#778.

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

cmd/pullrequest-init/README.md

@@ -0,0 +1,58 @@
+# 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

cmd/pullrequest-init/fake_github.go

@@ -0,0 +1,171 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strconv"
+
+	"github.com/google/go-github/github"
+	"github.com/gorilla/mux"
+)
+
+// 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
+	comments map[key][]*github.IssueComment
+}
+
+// NewFakeGitHub returns a new FakeGitHub.
+func NewFakeGitHub() *FakeGitHub {
+	s := &FakeGitHub{
+		Router:   mux.NewRouter(),
+		pr:       make(map[key]*github.PullRequest),
+		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/{number}/labels", s.updateLabels).Methods(http.MethodPut)
+
+	return s
+}
+
+// AddPullRequest adds the given pull request to the fake GitHub server.
+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
+}
+
+// AddComment adds a comment to the fake GitHub server.
+func (g *FakeGitHub) AddComment(owner string, repo string, pr int64, comment *github.IssueComment) {
+	key := key{
+		owner: owner,
+		repo:  repo,
+		id:    pr,
+	}
+	c := g.comments[key]
+	if c == nil {
+		c = []*github.IssueComment{comment}
+	} else {
+		c = append(c, comment)
+	}
+	g.comments[key] = c
+}
+
+func (g *FakeGitHub) getPullRequest(w http.ResponseWriter, r *http.Request) {
+	id, err := strconv.ParseInt(mux.Vars(r)["number"], 10, 64)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+	key := key{
+		owner: mux.Vars(r)["owner"],
+		repo:  mux.Vars(r)["repo"],
+		id:    id,
+	}
+
+	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) {
+	id, err := strconv.ParseInt(mux.Vars(r)["number"], 10, 64)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+	key := key{
+		owner: mux.Vars(r)["owner"],
+		repo:  mux.Vars(r)["repo"],
+		id:    id,
+	}
+	comments, ok := g.comments[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) {
+	id, err := strconv.ParseInt(mux.Vars(r)["number"], 10, 64)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+	key := key{
+		owner: mux.Vars(r)["owner"],
+		repo:  mux.Vars(r)["repo"],
+		id:    id,
+	}
+
+	c := new(github.IssueComment)
+	if err := json.NewDecoder(r.Body).Decode(c); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	comments, ok := g.comments[key]
+	if !ok {
+		comments = []*github.IssueComment{}
+	}
+	c.ID = github.Int64(int64(len(comments) + 1))
+	g.comments[key] = append(comments, c)
+
+	w.WriteHeader(http.StatusOK)
+}
+
+func (g *FakeGitHub) updateLabels(w http.ResponseWriter, r *http.Request) {
+	id, err := strconv.ParseInt(mux.Vars(r)["number"], 10, 64)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+	key := key{
+		owner: mux.Vars(r)["owner"],
+		repo:  mux.Vars(r)["repo"],
+		id:    id,
+	}
+	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)
+}