Listen for job finished events and fail fast on builds

main.go

package main

import (
	"bytes"
	"context"
	"encoding/base64"
	"encoding/json"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"strconv"

	"golang.org/x/oauth2"
)

// general config values - org pipeline and generated api token with full access
var (
	apiToken               = flag.String("token", "", "GRAPHQL API token")
	orgSlug                = flag.String("org", "", "Orginization slug")
	port                   = 4587
	defaultAnnotationStyle = "ERROR"
	graphAPI               = "https://graphql.buildkite.com/v1"
)

// Buildkite job (unused values omitted)
type job struct {
	ID              string  `json:"id"`
	State           string  `json:"state"`
	WebURL          string  `json:"web_url"`
	ExitStatus      int     `json:"exit_status"`
	SoftFailed      bool    `json:"soft_failed"`
	RetriedInNewJob *string `json:"retried_in_job_id"`
}

// Buildkite build (unused values omitted)
type build struct {
	ID     string `json:"id"`
	Number *int   `json:"number"`
	URL    string `json:"url"`
}

// Buildkite pipeline (unused values omitted)
type pipeline struct {
	Slug string `json:"slug"`
}

// Buildkite webhook event payload
type payload struct {
	Event    string   `json:"event"`
	Job      job      `json:"job"`
	Build    build    `json:"build"`
	Pipeline pipeline `json:"pipeline"`
}

// Buildkite GraphQL API requires a base64 encoded id in the fromat Build---UUID
func buildGQLID(uuid string) string {
	return base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("Build---%s", uuid)))
}

// Nothing fancy, lets just post using http client
func jsonPost(c *http.Client, jsonData *map[string]string) {
	jsonValue, _ := json.Marshal(jsonData)
	payload := bytes.NewBuffer(jsonValue)
	if _, err := c.Post(graphAPI, "application/json", payload); err != nil {
		log.Printf("%v", err)
	}
}

// cancel build grapthql query
func cancel(buildUUID string) *map[string]string {
	cancelTemplate := `mutation {
		buildCancel(input: {id: "%s"}) {
			build {
				canceledAt
		  	}
		}
	}`

	return &map[string]string{"query": fmt.Sprintf(cancelTemplate, buildGQLID(buildUUID))}
}

// annotate build grapthql query
func annotate(buildUUID string, body string, style string) *map[string]string {
	annotateTemplate := `mutation {
		buildAnnotate(input: {buildID: "%s", body: "%s", style: %s}) {
			annotation {
			uuid
			body { text }
			style
			context
			}
		}
	}`

	return &map[string]string{"query": fmt.Sprintf(annotateTemplate, buildGQLID(buildUUID), body, style)}
}

// handler with a http client - best effort fast failing
func handler(c *http.Client) func(w http.ResponseWriter, r *http.Request) {
	return func(w http.ResponseWriter, r *http.Request) {
		var p payload
		b, _ := ioutil.ReadAll(r.Body)
		json.Unmarshal(b, &p)

		// call the API and fail fast if the build is hard failing
		if (p.Job.State == "failed") && (p.Job.ExitStatus > 0) && (p.Job.SoftFailed == false) && (p.Job.RetriedInNewJob == nil) {
			log.Println("hardfailed job, attempting to cancel build")
			jsonPost(c, cancel(p.Build.ID))
			log.Printf("Build #%s canceled, %s", strconv.Itoa(*p.Build.Number), *&p.Build.URL)
			jsonPost(c, annotate(p.Build.ID, fmt.Sprintf("Canceled because of hard failure at %s", p.Job.WebURL), defaultAnnotationStyle))
		}

		w.WriteHeader(http.StatusNoContent)
	}
}

// small server to listen for webhooks
func main() {
	flag.Parse()
	src := oauth2.StaticTokenSource(&oauth2.Token{AccessToken: *apiToken})
	httpClient := oauth2.NewClient(context.Background(), src)

	webhookHandler := handler(httpClient)
	http.HandleFunc("/", webhookHandler)

	log.Printf("starting server, listening on port %v \n", port)
	http.ListenAndServe(fmt.Sprintf(":%v", port), nil)
}

Using the API, the build is cancelled when the job publishes a 'job.finished' event and has hard failed (no retries). The build is updated with an annotation to visually show the reason for cancellation and link to the failed job.

Link to Buildkite build demo video https://www.loom.com/share/e6624f8d6d534e1195d551dffbe64540

Webhook setup https://buildkite.com/organizations/your-org/services: