Fix long descriptions in audit statuses (#73)

The GitHub API limits status descriptions to 140 characters, but the
status we posted when detecting an overwrite could be longer than that,
depending on the formatted values. Update the audit code to log the full
message but post an abbreviated message that is under the character
limit.

server/handler/base.go

@@ -34,6 +34,8 @@ const (
 	DefaultPolicyPath         = ".policy.yml"
 	DefaultStatusCheckContext = "policy-bot"
 	DefaultAppName            = "policy-bot"
+
+	LogKeyGitHubSHA = "github_sha"
 )
 
 type Base struct {
@@ -114,7 +116,7 @@ func (b *Base) postGitHubRepoStatus(ctx context.Context, client *github.Client,
 func (b *Base) PreparePRContext(ctx context.Context, installationID int64, pr *github.PullRequest) (context.Context, zerolog.Logger) {
 	ctx, logger := githubapp.PreparePRContext(ctx, installationID, pr.GetBase().GetRepo(), pr.GetNumber())
 
-	logger = logger.With().Str("github_sha", pr.GetHead().GetSHA()).Logger()
+	logger = logger.With().Str(LogKeyGitHubSHA, pr.GetHead().GetSHA()).Logger()
 	ctx = logger.WithContext(ctx)
 
 	return ctx, logger

server/handler/status.go

@@ -61,24 +61,28 @@ func (h *Status) Handle(ctx context.Context, eventType, deliveryID string, paylo
 	commitSHA := event.GetCommit().GetSHA()
 
 	if sender.GetLogin() != h.PullOpts.AppName+"[bot]" {
-		auditMessage := fmt.Sprintf(
-			"Entity '%s' overwrote status check '%s' on ref=%s to status='%s' description='%s' targetURL='%s'",
-			sender.GetLogin(),
-			event.GetContext(),
-			commitSHA,
-			event.GetState(),
-			event.GetDescription(),
-			event.GetTargetURL(),
-		)
-		logger.Warn().Str(LogKeyAudit, eventType).Msg(auditMessage)
+		logger.Warn().
+			Str(LogKeyAudit, eventType).
+			Str(LogKeyGitHubSHA, commitSHA).
+			Msgf(
+				"Entity '%s' overwrote status check '%s' to state='%s' description='%s' targetURL='%s'",
+				sender.GetLogin(),
+				event.GetContext(),
+				event.GetState(),
+				event.GetDescription(),
+				event.GetTargetURL(),
+			)
+
+		// must be less than 140 characters to satisfy GitHub API
+		desc := fmt.Sprintf("'%s' overwrote status to '%s'", sender.GetLogin(), event.GetState())
 
 		// unlike in other code, use a single context here because we want to
 		// replace a forged context with a failure, not post a general status
 		// if multiple contexts are forged, we will handle multiple events
 		status := &github.RepoStatus{
 			Context:     event.Context,
 			State:       github.String("failure"),
-			Description: &auditMessage,
+			Description: &desc,
 		}
 
 		_, _, err := client.Repositories.CreateStatus(ctx, ownerName, repoName, commitSHA, status)