config: add SetDirectory (#250)

Signed-off-by: Andy Bursavich <abursavich@gmail.com>

config/config.go

@@ -16,6 +16,8 @@
 
 package config
 
+import "path/filepath"
+
 // Secret special type for storing secrets.
 type Secret string
 
@@ -32,3 +34,20 @@ func (s *Secret) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	type plain Secret
 	return unmarshal((*plain)(s))
 }
+
+// DirectorySetter is a config type that contains file paths that may
+// be relative to the file containing the config.
+type DirectorySetter interface {
+	// SetDirectory joins any relative file paths with dir.
+	// Any paths that are empty or absolute remain unchanged.
+	SetDirectory(dir string)
+}
+
+// JoinDir joins dir and path if path is relative.
+// If path is empty or absolute, it is returned unchanged.
+func JoinDir(dir, path string) string {
+	if path == "" || filepath.IsAbs(path) {
+		return path
+	}
+	return filepath.Join(dir, path)
+}

config/http_config.go

@@ -44,6 +44,14 @@ type BasicAuth struct {
 	PasswordFile string `yaml:"password_file,omitempty"`
 }
 
+// SetDirectory joins any relative file paths with dir.
+func (a *BasicAuth) SetDirectory(dir string) {
+	if a == nil {
+		return
+	}
+	a.PasswordFile = JoinDir(dir, a.PasswordFile)
+}
+
 // URL is a custom URL type that allows validation at configuration load time.
 type URL struct {
 	*url.URL
@@ -86,6 +94,16 @@ type HTTPClientConfig struct {
 	TLSConfig TLSConfig `yaml:"tls_config,omitempty"`
 }
 
+// SetDirectory joins any relative file paths with dir.
+func (c *HTTPClientConfig) SetDirectory(dir string) {
+	if c == nil {
+		return
+	}
+	c.TLSConfig.SetDirectory(dir)
+	c.BasicAuth.SetDirectory(dir)
+	c.BearerTokenFile = JoinDir(dir, c.BearerTokenFile)
+}
+
 // Validate validates the HTTPClientConfig to check only one of BearerToken,
 // BasicAuth and BearerTokenFile is configured.
 func (c *HTTPClientConfig) Validate() error {
@@ -352,6 +370,16 @@ type TLSConfig struct {
 	InsecureSkipVerify bool `yaml:"insecure_skip_verify"`
 }
 
+// SetDirectory joins any relative file paths with dir.
+func (c *TLSConfig) SetDirectory(dir string) {
+	if c == nil {
+		return
+	}
+	c.CAFile = JoinDir(dir, c.CAFile)
+	c.CertFile = JoinDir(dir, c.CertFile)
+	c.KeyFile = JoinDir(dir, c.KeyFile)
+}
+
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
 func (c *TLSConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	type plain TLSConfig