Remove default values for file and vault

and add `must*` variants for them

Signed-off-by: Knut Ahlers <knut@ahlers.me>

README.md

@@ -16,8 +16,8 @@ Starting with `v1.0.0` Korvike is based on the [sprig functions collection](http
   $ echo "{{ .foo }}" | korvike -v foo=bar
   bar
   ```
-- `{{ file <file name> [default value] }}`  
-  Read a file and place it inside the template
+- `{{ file <file name> }}` / `{{ mustFile <file name> }}`  
+  Read a file and place it inside the template, `file` returns an empty string on error, `mustFile` an error
   ```console
   $ echo "Hello World" > hello
   $ echo '{{ file "hello" }}' | korvike
@@ -43,8 +43,8 @@ Starting with `v1.0.0` Korvike is based on the [sprig functions collection](http
   $ echo '{{ urlescape "Hellö Wörld@Golang" }}' | korvike 
   Hell%C3%B6+W%C3%B6rld%40Golang
   ```
-- `{{ vault <path> <key> [default value] }}`  
-  Read a key from Vault using `VAULT_ADDR` and `VAULT_TOKEN` environment variables (or `~/.vault-token` file) for authentication.
+- `{{ vault <path> <key> }}` / `{{ mustVault <path> <key> }}`  
+  Read a key from Vault using `VAULT_ADDR` and `VAULT_TOKEN` environment variables (or `~/.vault-token` file) for authentication. `vault` returns an empty string on error, `mustVault` an error
   ```console
   $ vault write secret/test foo=bar
   $ echo '{{ vault "secret/test" "foo" }}' | korvike

functions/func_file.go

@@ -1,21 +1,27 @@
 package functions
 
 import (
+	"fmt"
 	"os"
 )
 
 func init() {
-	registerFunction("file", func(name string, v ...string) string {
-		defaultValue := ""
-		if len(v) > 0 {
-			defaultValue = v[0]
+	registerFunction("file", func(name string) string {
+		fc, err := tplReadFile(name)
+		if err != nil {
+			return ""
 		}
-		if _, err := os.Stat(name); err == nil {
-			//#nosec:G304 // Intended to load custom file
-			if rawValue, err := os.ReadFile(name); err == nil {
-				return string(rawValue)
-			}
-		}
-		return defaultValue
+		return fc
 	})
+
+	registerFunction("mustFile", tplReadFile)
+}
+
+func tplReadFile(name string) (string, error) {
+	rawValue, err := os.ReadFile(name) //#nosec:G304 // Intended to load custom file
+	if err != nil {
+		return "", fmt.Errorf("reading file: %w", err)
+	}
+
+	return string(rawValue), nil
 }

functions/func_vault.go

@@ -10,38 +10,44 @@ import (
 )
 
 func init() {
-	registerFunction("vault", func(name string, v ...string) (interface{}, error) {
-		if name == "" {
-			return nil, fmt.Errorf("path is not set")
-		}
-		if len(v) < 1 {
-			return nil, fmt.Errorf("key is not set")
-		}
+	registerFunction("mustVault", tplVaultKeyFetch)
 
-		client, err := vaultClientFromEnvOrFile()
+	registerFunction("vault", func(name string, key string) string {
+		v, err := tplVaultKeyFetch(name, key)
 		if err != nil {
-			return nil, err
+			return ""
 		}
-
-		secret, err := client.Logical().Read(name)
-		if err != nil {
-			return nil, fmt.Errorf("reading secret: %s", err)
-		}
-
-		if secret != nil && secret.Data != nil {
-			if val, ok := secret.Data[v[0]]; ok {
-				return val, nil
-			}
-		}
-
-		if len(v) < 2 { //nolint:gomnd
-			return nil, fmt.Errorf("requested value %q in key %q was not found in Vault and no default was set", v[0], name)
-		}
-
-		return v[1], nil
+		return v
 	})
 }
 
+func tplVaultKeyFetch(name string, key string) (string, error) {
+	if name == "" {
+		return "", fmt.Errorf("path is not set")
+	}
+	if key == "" {
+		return "", fmt.Errorf("key is not set")
+	}
+
+	client, err := vaultClientFromEnvOrFile()
+	if err != nil {
+		return "", err
+	}
+
+	secret, err := client.Logical().Read(name)
+	if err != nil {
+		return "", fmt.Errorf("reading secret: %s", err)
+	}
+
+	if secret != nil && secret.Data != nil {
+		if val, ok := secret.Data[key].(string); ok {
+			return val, nil
+		}
+	}
+
+	return "", fmt.Errorf("requested value %q in key %q was not found in Vault and no default was set", key, name)
+}
+
 func vaultClientFromEnvOrFile() (*api.Client, error) {
 	client, err := api.NewClient(&api.Config{
 		Address: os.Getenv(api.EnvVaultAddress),