Retry get pull request calls to github

These calls have been 404'ing lately, likely due to eventual consistency
issues on GitHub's side where they send the PR created webhook but it's
not yet available on their API.

To work around this, we will retry up to 3 times with a 1s delay.

server/events/vcs/github_client.go

@@ -17,6 +17,7 @@ import (
 	"context"
 	"fmt"
 	"strings"
+	"time"
 
 	"github.com/runatlantis/atlantis/server/events/models"
 	"github.com/runatlantis/atlantis/server/events/vcs/common"
@@ -273,7 +274,25 @@ func (g *GithubClient) PullIsMergeable(repo models.Repo, pull models.PullRequest
 
 // GetPullRequest returns the pull request.
 func (g *GithubClient) GetPullRequest(repo models.Repo, num int) (*github.PullRequest, error) {
-	pull, _, err := g.client.PullRequests.Get(g.ctx, repo.Owner, repo.Name, num)
+	var err error
+	var pull *github.PullRequest
+
+	// GitHub has started to return 404's here (#1019) even after they send the webhook.
+	// They've got some eventual consistency issues going on so we're just going
+	// to retry up to 3 times with a 1s sleep.
+	numRetries := 3
+	retryDelay := 1 * time.Second
+	for i := 0; i < numRetries; i++ {
+		pull, _, err = g.client.PullRequests.Get(g.ctx, repo.Owner, repo.Name, num)
+		if err == nil {
+			return pull, nil
+		}
+		ghErr, ok := err.(*github.ErrorResponse)
+		if !ok || ghErr.Response.StatusCode != 404 {
+			return pull, err
+		}
+		time.Sleep(retryDelay)
+	}
 	return pull, err
 }
 

server/events/vcs/github_client_test.go

@@ -852,3 +852,48 @@ func TestGithubClient_SplitComments(t *testing.T) {
 	Assert(t, strings.Contains(firstSplit, models.PlanCommand.String()), fmt.Sprintf("comment should contain the command name but was %q", firstSplit))
 	Assert(t, strings.Contains(secondSplit, "continued from previous comment"), fmt.Sprintf("comment should contain no reference to the command name but was %q", secondSplit))
 }
+
+// Test that we retry the get pull request call if it 404s.
+func TestGithubClient_Retry404(t *testing.T) {
+	var numCalls = 0
+
+	testServer := httptest.NewTLSServer(
+		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+
+			switch r.Method + " " + r.RequestURI {
+			case "GET /api/v3/repos/runatlantis/atlantis/pulls/1":
+				defer r.Body.Close() // nolint: errcheck
+				numCalls++
+				if numCalls < 3 {
+					w.WriteHeader(404)
+				} else {
+					w.WriteHeader(200)
+				}
+				return
+			default:
+				t.Errorf("got unexpected request at %q", r.RequestURI)
+				http.Error(w, "not found", http.StatusNotFound)
+				return
+			}
+		}))
+
+	testServerURL, err := url.Parse(testServer.URL)
+	Ok(t, err)
+	client, err := vcs.NewGithubClient(testServerURL.Host, &vcs.GithubUserCredentials{"user", "pass"}, nil)
+	Ok(t, err)
+	defer disableSSLVerification()()
+	repo := models.Repo{
+		FullName:          "runatlantis/atlantis",
+		Owner:             "runatlantis",
+		Name:              "atlantis",
+		CloneURL:          "",
+		SanitizedCloneURL: "",
+		VCSHost: models.VCSHost{
+			Type:     models.Github,
+			Hostname: "github.com",
+		},
+	}
+	_, err = client.GetPullRequest(repo, 1)
+	Ok(t, err)
+	Equals(t, 3, numCalls)
+}