Provide a stateless blubberoid microservice

The `blubber` command already gets everything it needs from explicit
inputs, which makes it an easy candidate for running as a simple
microservice. This patch provides exactly that in the form of
`blubberoid`, an HTTP server that processes Blubber configuration.

To start the daemon:

    make && blubberoid

To use it:

    curl -i -X POST --data-binary @blubber.example.yaml http://:8748/[variant]

Change-Id: Ieea73048d092b974da424ba40ddc90eaf693af0b

2 files changed, 203 insertions, 0 deletions

diff --git a/cmd/blubber/main.go b/cmd/blubber/main.go
new file mode 100644
index 0000000..53009ea
--- /dev/null
+++ b/cmd/blubber/main.go
@@ -0,0 +1,84 @@
+// Package main provides the command line interface.
+//
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+
+	"github.com/pborman/getopt/v2"
+
+	"gerrit.wikimedia.org/r/blubber/config"
+	"gerrit.wikimedia.org/r/blubber/docker"
+	"gerrit.wikimedia.org/r/blubber/meta"
+)
+
+const parameters = "config.yaml variant"
+
+var (
+	showHelp    *bool   = getopt.BoolLong("help", 'h', "show help/usage")
+	showVersion *bool   = getopt.BoolLong("version", 'v', "show version information")
+	policyURI   *string = getopt.StringLong("policy", 'p', "", "policy file URI", "uri")
+)
+
+func main() {
+	getopt.SetParameters(parameters)
+	getopt.Parse()
+
+	if *showHelp {
+		getopt.Usage()
+		os.Exit(1)
+	}
+
+	if *showVersion {
+		fmt.Println(meta.FullVersion())
+		os.Exit(0)
+	}
+
+	args := getopt.Args()
+
+	if len(args) < 2 {
+		getopt.Usage()
+		os.Exit(1)
+	}
+
+	cfgPath, variant := args[0], args[1]
+
+	cfg, err := config.ReadConfigFile(cfgPath)
+
+	if err != nil {
+		if config.IsValidationError(err) {
+			log.Printf("%s is invalid:\n%v", cfgPath, config.HumanizeValidationError(err))
+			os.Exit(4)
+		} else {
+			log.Printf("Error reading %s: %v\n", cfgPath, err)
+			os.Exit(2)
+		}
+	}
+
+	if *policyURI != "" {
+		policy, err := config.ReadPolicyFromURI(*policyURI)
+
+		if err != nil {
+			log.Printf("Error loading policy from %s: %v\n", *policyURI, err)
+			os.Exit(5)
+		}
+
+		err = policy.Validate(*cfg)
+
+		if err != nil {
+			log.Printf("Configuration fails policy check against:\npolicy: %s\nviolation: %v\n", *policyURI, err)
+			os.Exit(6)
+		}
+	}
+
+	dockerFile, err := docker.Compile(cfg, variant)
+
+	if err != nil {
+		log.Printf("Error compiling config: %v\n", err)
+		os.Exit(3)
+	}
+
+	dockerFile.WriteTo(os.Stdout)
+}
diff --git a/cmd/blubberoid/main.go b/cmd/blubberoid/main.go
new file mode 100644
index 0000000..b15f603
--- /dev/null
+++ b/cmd/blubberoid/main.go
@@ -0,0 +1,119 @@
+// Package main provides the blubberoid server.
+//
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"path"
+
+	"github.com/pborman/getopt/v2"
+
+	"gerrit.wikimedia.org/r/blubber/config"
+	"gerrit.wikimedia.org/r/blubber/docker"
+)
+
+var (
+	showHelp  *bool   = getopt.BoolLong("help", 'h', "show help/usage")
+	address   *string = getopt.StringLong("address", 'a', ":8748", "socket address/port to listen on (default ':8748')", "address:port")
+	endpoint  *string = getopt.StringLong("endpoint", 'e', "/", "server endpoint (default '/')", "path")
+	policyURI *string = getopt.StringLong("policy", 'p', "", "policy file URI", "uri")
+	policy    *config.Policy
+)
+
+func main() {
+	getopt.Parse()
+
+	if *showHelp {
+		getopt.Usage()
+		os.Exit(1)
+	}
+
+	if *policyURI != "" {
+		var err error
+
+		policy, err = config.ReadPolicyFromURI(*policyURI)
+
+		if err != nil {
+			log.Fatalf("Error loading policy from %s: %v\n", *policyURI, err)
+		}
+	}
+
+	// Ensure endpoint is always an absolute path starting and ending with "/"
+	*endpoint = path.Clean("/" + *endpoint)
+
+	if *endpoint != "/" {
+		*endpoint += "/"
+	}
+
+	log.Printf("listening on %s for requests to %s[variant]\n", *address, *endpoint)
+
+	http.HandleFunc(*endpoint, blubberoid)
+	log.Fatal(http.ListenAndServe(*address, nil))
+}
+
+func blubberoid(res http.ResponseWriter, req *http.Request) {
+	if len(req.URL.Path) <= len(*endpoint) {
+		res.WriteHeader(http.StatusNotFound)
+		res.Write(responseBody("request a variant at %s[variant]", *endpoint))
+		return
+	}
+
+	variant := req.URL.Path[len(*endpoint):]
+	body, err := ioutil.ReadAll(req.Body)
+
+	if err != nil {
+		res.WriteHeader(http.StatusInternalServerError)
+		log.Printf("failed to read request body: %s\n", err)
+		return
+	}
+
+	cfg, err := config.ReadConfig(body)
+
+	if err != nil {
+		if config.IsValidationError(err) {
+			res.WriteHeader(http.StatusUnprocessableEntity)
+			res.Write(responseBody(config.HumanizeValidationError(err)))
+			return
+		}
+
+		res.WriteHeader(http.StatusBadRequest)
+		res.Write(responseBody(
+			"Failed to read config YAML from request body. "+
+				"Was it formatted correctly and encoded as binary data?\nerror: %s",
+			err.Error(),
+		))
+		return
+	}
+
+	if policy != nil {
+		err = policy.Validate(*cfg)
+
+		if err != nil {
+			res.WriteHeader(http.StatusUnprocessableEntity)
+			res.Write(responseBody(
+				"Configuration fails policy check against:\npolicy: %s\nviolation: %v",
+				*policyURI, err,
+			))
+			return
+		}
+	}
+
+	dockerFile, err := docker.Compile(cfg, variant)
+
+	if err != nil {
+		res.WriteHeader(http.StatusNotFound)
+		res.Write(responseBody(err.Error()))
+		return
+	}
+
+	res.Header().Set("Content-Type", "text/plain")
+	res.Write(dockerFile.Bytes())
+}
+
+func responseBody(msg string, a ...interface{}) []byte {
+	return []byte(fmt.Sprintf(msg+"\n", a...))
+}