Fetch config from env (#76)

Allows the cli to fetch configuration credentials from environment variables. Config credentials can now be specified directly in `ARDUINO_CLOUD_CLIENT` and `ARDUINO_CLOUD_SECRET` environment variables.

The config is now searched in this way:
- if credentials are found on environment variables, return them
- otherwise look for them in config files
- if not found anywhere return an error

Author: Paolo Calao

README.md

@@ -53,6 +53,8 @@ Configuration file is supported in two different format: json and yaml. Use the
 
 `$ arduino-cloud-cli config init --config-format json`
 
+It is also possible to specify credentials directly in `ARDUINO_CLOUD_CLIENT` and `ARDUINO_CLOUD_SECRET` environment variables. Credentials specified in environment variables have higher priority than the ones specified in config files.
+
 ## Device provisioning
 
 When provisioning a device, you can optionally specify the port to which the device is connected to and its fqbn. If they are not given, then the first device found will be provisioned.

cli/config/init.go

@@ -34,11 +34,6 @@ import (
 	"github.com/spf13/viper"
 )
 
-const (
-	clientIDLen     = 32
-	clientSecretLen = 64
-)
-
 var initFlags struct {
 	destDir   string
 	overwrite bool
@@ -122,7 +117,7 @@ func paramsPrompt() (id, key string, err error) {
 	prompt := promptui.Prompt{
 		Label: "Please enter the Client ID",
 		Validate: func(s string) error {
-			if len(s) != clientIDLen {
+			if len(s) != config.ClientIDLen {
 				return errors.New("client-id not valid")
 			}
 			return nil
@@ -137,7 +132,7 @@ func paramsPrompt() (id, key string, err error) {
 		Mask:  '*',
 		Label: "Please enter the Client Secret",
 		Validate: func(s string) error {
-			if len(s) != clientSecretLen {
+			if len(s) != config.ClientSecretLen {
 				return errors.New("client secret not valid")
 			}
 			return nil

internal/config/config.go

@@ -25,60 +25,182 @@ import (
 	"github.com/spf13/viper"
 )
 
+const (
+	// ClientIDLen specifies the length of Arduino IoT Cloud client ids.
+	ClientIDLen = 32
+	// ClientSecretLen specifies the length of Arduino IoT Cloud client secrets.
+	ClientSecretLen = 64
+
+	// EnvPrefix is the prefix environment variables should have to be
+	// fetched as config parameters during the config retrieval.
+	EnvPrefix = "ARDUINO_CLOUD"
+)
+
 // Config contains all the configuration parameters
 // known by arduino-cloud-cli.
 type Config struct {
 	Client string `map-structure:"client"` // Client ID of the user
 	Secret string `map-structure:"secret"` // Secret ID of the user, unique for each Client ID
 }
 
-// Retrieve returns the actual parameters contained in the
-// configuration file, if any. Returns error if no config file is found.
+// Validate the config.
+// If config is not valid, it returns an error explaining the reason.
+func (c *Config) Validate() error {
+	if len(c.Client) != ClientIDLen {
+		return fmt.Errorf(
+			"client id not valid, expected len %d but got %d",
+			ClientIDLen,
+			len(c.Client),
+		)
+	}
+	if len(c.Secret) != ClientSecretLen {
+		return fmt.Errorf(
+			"client secret not valid, expected len %d but got %d",
+			ClientSecretLen,
+			len(c.Secret),
+		)
+	}
+	return nil
+}
+
+// IsEmpty checks if config has no params set.
+func (c *Config) IsEmpty() bool {
+	return len(c.Client) == 0 && len(c.Secret) == 0
+}
+
+// Retrieve looks for configuration parameters in
+// environment variables or in configuration file.
+// Returns error if no config is found.
 func Retrieve() (*Config, error) {
+	// Config extracted from environment has highest priority
+	c, err := fromEnv()
+	if err != nil {
+		return nil, fmt.Errorf("reading config from environment variables: %w", err)
+	}
+	// Return the config only if it has been found
+	if c != nil {
+		return c, nil
+	}
+
+	c, err = fromFile()
+	if err != nil {
+		return nil, fmt.Errorf("reading config from file: %w", err)
+	}
+	if c != nil {
+		return c, nil
+	}
+
+	return nil, fmt.Errorf(
+		"config has not been found neither in environment variables " +
+			"nor in the current directory, its parents or in arduino15",
+	)
+}
+
+// fromFile looks for a configuration file.
+// If a config file is not found, it returns a nil config without raising errors.
+// If invalid config file is found, it returns an error.
+func fromFile() (*Config, error) {
+	// Looks for a configuration file
 	configDir, err := searchConfigDir()
 	if err != nil {
 		return nil, fmt.Errorf("can't get config directory: %w", err)
 	}
+	// Return nil config if no config file is found
+	if configDir == nil {
+		return nil, nil
+	}
 
 	v := viper.New()
 	v.SetConfigName(Filename)
-	v.AddConfigPath(configDir)
+	v.AddConfigPath(*configDir)
 	err = v.ReadInConfig()
 	if err != nil {
-		err = fmt.Errorf("%s: %w", "retrieving config file", err)
+		err = fmt.Errorf(
+			"config file found at %s but cannot read its content: %w",
+			*configDir,
+			err,
+		)
 		return nil, err
 	}
 
 	conf := &Config{}
-	v.Unmarshal(conf)
+	err = v.Unmarshal(conf)
+	if err != nil {
+		return nil, fmt.Errorf(
+			"config file found at %s but cannot unmarshal it: %w",
+			*configDir,
+			err,
+		)
+	}
+	if err = conf.Validate(); err != nil {
+		return nil, fmt.Errorf(
+			"config file found at %s but is not valid: %w",
+			*configDir,
+			err,
+		)
+	}
 	return conf, nil
 }
 
-func searchConfigDir() (string, error) {
+// fromEnv looks for configuration credentials in environment variables.
+// If credentials are not found, it returns a nil config without raising errors.
+// If invalid credentials are found, it returns an error.
+func fromEnv() (*Config, error) {
+	v := viper.New()
+	SetDefaults(v)
+	v.SetEnvPrefix(EnvPrefix)
+	v.AutomaticEnv()
+
+	conf := &Config{}
+	err := v.Unmarshal(conf)
+	if err != nil {
+		return nil, fmt.Errorf("cannot unmarshal config from environment variables: %w", err)
+	}
+
+	if conf.IsEmpty() {
+		return nil, nil
+	}
+
+	if err = conf.Validate(); err != nil {
+		return nil, fmt.Errorf(
+			"config retrieved from environment variables with prefix '%s' are not valid: %w",
+			EnvPrefix,
+			err,
+		)
+	}
+	return conf, nil
+}
+
+// searchConfigDir configuration file in different directories in the following order:
+// current working directory, parents of the current working directory, arduino15 default directory.
+// Returns a nil string if no config file has been found, without raising errors.
+// Returns an error if any problem is encountered during the file research which prevents
+// to understand whether a config file exists or not.
+func searchConfigDir() (*string, error) {
 	// Search in current directory and its parents.
 	cwd, err := paths.Getwd()
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 	// Don't let bad naming mislead you, cwd.Parents()[0] is cwd itself so
 	// we look in the current directory first and then on its parents.
 	for _, path := range cwd.Parents() {
 		if path.Join(Filename+".yaml").Exist() || path.Join(Filename+".json").Exist() {
-			return path.String(), nil
+			p := path.String()
+			return &p, nil
 		}
 	}
 
 	// Search in arduino's default data directory.
 	arduino15, err := arduino.DataDir()
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 	if arduino15.Join(Filename+".yaml").Exist() || arduino15.Join(Filename+".json").Exist() {
-		return arduino15.String(), nil
+		p := arduino15.String()
+		return &p, nil
 	}
 
-	return "", fmt.Errorf(
-		"didn't find config file in the current directory, its parents or in %s",
-		arduino15.String(),
-	)
+	// Didn't find config file in the current directory, its parents or in arduino15"
+	return nil, nil
 }