simple check option

Dockerfile

@@ -4,7 +4,8 @@ WORKDIR /tmp/nomad-resource
 COPY . .
 
 RUN go build -o dist/out out/main.go && \
-    go build -o dist/in in/main.go
+    go build -o dist/in in/main.go   && \
+    go build -o dist/check check/main.go
 
 FROM alpine:edge
 

check/main.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"encoding/json"
+	"os"
+
+	resource "github.com/cioplenu/concourse-nomad-resource"
+	"github.com/cioplenu/concourse-nomad-resource/common"
+)
+
+type Request struct {
+	Source  resource.Source  `json:"source"`
+	Version resource.Version `json:"version,omitempty"`
+}
+
+func main() {
+	var request Request
+	err := json.NewDecoder(os.Stdin).Decode(&request)
+	common.Check(err, "Error parsing request")
+
+	lastVersion := request.Version.Version
+
+	history := common.GetHistory(request.Source)
+	versions := make([]resource.Version, 0)
+
+	for _, jobVersion := range history {
+		if lastVersion != 0 && lastVersion > jobVersion.Version {
+			continue
+		}
+		versions = append(versions, resource.Version{jobVersion.Version})
+		if lastVersion == 0 {
+			break
+		}
+	}
+
+	json.NewEncoder(os.Stdout).Encode(versions)
+
+}

common/common.go

@@ -1,8 +1,13 @@
 package common
 
 import (
+	"bytes"
+	"encoding/json"
 	"fmt"
 	"os"
+	"os/exec"
+
+	resource "github.com/cioplenu/concourse-nomad-resource"
 )
 
 func Check(err error, msg string) {
@@ -11,3 +16,24 @@ func Check(err error, msg string) {
 		os.Exit(1)
 	}
 }
+
+func GetHistory(source resource.Source) []resource.JobVersion {
+	cmd := exec.Command(
+		"nomad",
+		"job",
+		"history",
+		"-json",
+		"-address="+source.URL,
+		"-token="+source.Token,
+		source.Name,
+	)
+	var histResp bytes.Buffer
+	cmd.Stdout = &histResp
+	err := cmd.Run()
+	Check(err, "Error checking versions")
+
+	var history []resource.JobVersion
+	json.Unmarshal(histResp.Bytes(), &history)
+
+	return history
+}

out/main.go

@@ -86,22 +86,7 @@ func main() {
 
 	fmt.Fprint(os.Stderr, out.String())
 
-	cmd = exec.Command(
-		"nomad",
-		"job",
-		"history",
-		"-json",
-		"-address="+config.Source.URL,
-		"-token="+config.Source.Token,
-		config.Source.Name,
-	)
-	var histResp bytes.Buffer
-	cmd.Stdout = &histResp
-	err = cmd.Run()
-	common.Check(err, "Error checking versions")
-
-	var history []resource.JobVersion
-	json.Unmarshal(histResp.Bytes(), &history)
+	history := common.GetHistory(config.Source)
 
 	response := Response{
 		Version: resource.Version{