Fail immediately when commands missing

2 files changed, 34 insertions, 0 deletions

diff --git a/internal/exec.go b/internal/exec.go
new file mode 100644
index 0000000..6ed3e5c
--- /dev/null
+++ b/internal/exec.go
@@ -0,0 +1,21 @@
+package internal
+
+import (
+	"fmt"
+	"os/exec"
+)
+
+type CommandNotFound string
+
+func (e CommandNotFound) Error() string {
+	return fmt.Sprintf("command '%s' is missing and must be present for operation", string(e))
+}
+
+func RequireCommand(cmd string) error {
+	_, err := exec.LookPath(cmd)
+	if err != nil {
+		return CommandNotFound(cmd)
+	}
+
+	return nil
+}
diff --git a/internal/service/service.go b/internal/service/service.go
index 38cabf8..9fbacfb 100644
--- a/internal/service/service.go
+++ b/internal/service/service.go
@@ -10,9 +10,16 @@ import (
 	"sync"
 	"time"
 
+	"git.server.ky/slackcoder/mirror/internal"
 	"git.server.ky/slackcoder/mirror/internal/github"
 )
 
+// These commands are required by the service to operate.
+var requiredCommands = []string{
+	"git",
+	"rsync",
+}
+
 type Service struct {
 	cfg *Config
 
@@ -26,6 +33,12 @@ type Service struct {
 func NewService(cfg *Config) (*Service, error) {
 	cfg.Apply(DefaultConfig)
 
+	for _, cmd := range requiredCommands {
+		if err := internal.RequireCommand(cmd); err != nil {
+			return nil, err
+		}
+	}
+
 	srv := &Service{
 		cfg:     cfg,
 		mirrors: nil,