Download go modules before building (#20)

Fixes #14

internal/builder/main.go

@@ -21,6 +21,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"text/template"
+	"time"
 
 	"github.com/open-telemetry/opentelemetry-collector-builder/internal/scaffold"
 )
@@ -33,12 +34,17 @@ var (
 	ErrGoNotFound = errors.New("Go binary not found")
 )
 
-// GenerateAndCompile will generate the source files based on the given configuration and will compile it into a binary
+// GenerateAndCompile will generate the source files based on the given configuration, update go mod, and will compile into a binary
 func GenerateAndCompile(cfg Config) error {
 	if err := Generate(cfg); err != nil {
 		return err
 	}
 
+	// run go get to update go.mod and go.sum files
+	if err := GetModules(cfg); err != nil {
+		return err
+	}
+
 	return Compile(cfg)
 }
 
@@ -83,15 +89,10 @@ func Generate(cfg Config) error {
 
 // Compile generates a binary from the sources based on the configuration
 func Compile(cfg Config) error {
-	goBinary := cfg.Distribution.Go
 	// first, we test to check if we have Go at all
-	if _, err := exec.Command(goBinary, "env").CombinedOutput(); err != nil {
-		path, err := exec.LookPath("go")
-		if err != nil {
-			return ErrGoNotFound
-		}
-		goBinary = path
-		cfg.Logger.Info("Using go from PATH", "Go executable", path)
+	goBinary, err := getGoPath(cfg)
+	if err != nil {
+		return err
 	}
 
 	cfg.Logger.Info("Compiling")
@@ -105,6 +106,49 @@ func Compile(cfg Config) error {
 	return nil
 }
 
+// GetModules retrieves the go modules, updating go.mod and go.sum in the process
+func GetModules(cfg Config) error {
+	// first, we test to check if we have Go at all
+	goBinary, err := getGoPath(cfg)
+	if err != nil {
+		return err
+	}
+
+	cfg.Logger.Info("Getting go modules")
+	cmd := exec.Command(goBinary, "mod", "download")
+	cmd.Dir = cfg.Distribution.OutputPath
+
+	// basic retry if error from go mod command (in case of transient network error). This could be improved
+	// retry 3 times with 5 second spacing interval
+	retries := 3
+	failReason := "unknown"
+	for i := 1; i <= retries; i++ {
+		if out, err := cmd.CombinedOutput(); err != nil {
+			failReason = fmt.Sprintf("%s. Output: %q", err, out)
+			cfg.Logger.Info("Failed modules download", "retry", fmt.Sprintf("%d/%d", i, retries))
+			time.Sleep(5 * time.Second)
+			continue
+		}
+		return nil
+	}
+	return fmt.Errorf("failed to download go modules: %s", failReason)
+}
+
+// getGoPath checks if go is present and correct, and returns a useable go bin location
+func getGoPath(cfg Config) (string, error) {
+	goBinary := cfg.Distribution.Go
+	if _, err := exec.Command(goBinary, "env").CombinedOutput(); err != nil {
+		path, err := exec.LookPath("go")
+		if err != nil {
+			return "", ErrGoNotFound
+		}
+		goBinary = path
+		cfg.Logger.Info("Using go from PATH", "Go executable", path)
+	}
+
+	return goBinary, nil
+}
+
 func processAndWrite(cfg Config, tmpl string, outFile string, tmplParams interface{}) error {
 	t, err := template.New("template").Parse(tmpl)
 	if err != nil {