Merge pull request #50 from ilyakaznacheev/required-fields

Required fields

README.md

@@ -141,7 +141,7 @@ Here remote host and port may change in a distributed system architecture. Field
 
 ### Description
 
-You can get descriptions of all environment variables to use them in help documentation.
+You can get descriptions of all environment variables to use them in the help documentation.
 
 ```go
 import github.com/ilyakaznacheev/cleanenv
@@ -169,10 +169,11 @@ Environment variables:
 
 ## Model Format
 
-Library uses tags to configure model of configuration structure. There are following tags:
+Library uses tags to configure the model of configuration structure. There are the following tags:
 
 - `env="<name>"` - environment variable name (e.g. `env="PORT"`);
 - `env-upd` - flag to mark a field as updatable. Run `UpdateEnv(&cfg)` to refresh updatable variables from environment;
+- `env-required` - flag to mark a field as required. If set will return an error during environment parsing when the flagged as required field is empty (default Go value). Tag `env-default` is ignored in this case;
 - `env-default="<value>"` - default value. If the field wasn't filled from the environment variable default value will be used instead;
 - `env-separator="<value>"` - custom list and map separator. If not set, the default separator `,` will be used;
 - `env-description="<value>"` - environment variable description;
@@ -249,7 +250,7 @@ There are several most popular config file formats supported:
 
 ## Integration
 
-Package can be used with many other solutions. To make it more useful, we made some helpers.
+The package can be used with many other solutions. To make it more useful, we made some helpers.
 
 ### Flag
 

cleanenv.go

@@ -38,6 +38,24 @@ const (
 	DefaultSeparator = ","
 )
 
+// Supported tags
+const (
+	// Name of the environment variable or a list of names
+	TagEnv = "env"
+	// Value parsing layout (for types like time.Time)
+	TagEnvLayout = "env-layout"
+	// Default value
+	TagEnvDefault = "env-default"
+	// Custom list and map separator
+	TagEnvSeparator = "env-separator"
+	// Environment variable description
+	TagEnvDescription = "env-description"
+	// Flag to mark a field as updatable
+	TagEnvUpd = "env-upd"
+	// Flag to mark a field as required
+	TagEnvRequired = "env-required"
+)
+
 // Setter is an interface for a custom value setter.
 //
 // To implement a custom value setter you need to add a SetValue function to your type that will receive a string raw value:
@@ -179,12 +197,14 @@ func parseENV(r io.Reader, _ interface{}) error {
 // structMeta is a structure metadata entity
 type structMeta struct {
 	envList     []string
+	fieldName   string
 	fieldValue  reflect.Value
 	defValue    *string
 	layout      *string
 	separator   string
 	description string
 	updatable   bool
+	required    bool
 }
 
 // isFieldValueZero determines if fieldValue empty or not
@@ -230,7 +250,7 @@ func readStructMetadata(cfgRoot interface{}) ([]structMeta, error) {
 					continue
 				}
 				// process time.Time
-				if l, ok := fType.Tag.Lookup("env-layout"); ok {
+				if l, ok := fType.Tag.Lookup(TagEnvLayout); ok {
 					layout = &l
 				}
 			}
@@ -240,32 +260,36 @@ func readStructMetadata(cfgRoot interface{}) ([]structMeta, error) {
 				continue
 			}
 
-			if def, ok := fType.Tag.Lookup("env-default"); ok {
+			if def, ok := fType.Tag.Lookup(TagEnvDefault); ok {
 				defValue = &def
 			}
 
-			if sep, ok := fType.Tag.Lookup("env-separator"); ok {
+			if sep, ok := fType.Tag.Lookup(TagEnvSeparator); ok {
 				separator = sep
 			} else {
 				separator = DefaultSeparator
 			}
 
-			_, upd := fType.Tag.Lookup("env-upd")
+			_, upd := fType.Tag.Lookup(TagEnvUpd)
+
+			_, required := fType.Tag.Lookup(TagEnvRequired)
 
 			envList := make([]string, 0)
 
-			if envs, ok := fType.Tag.Lookup("env"); ok && len(envs) != 0 {
+			if envs, ok := fType.Tag.Lookup(TagEnv); ok && len(envs) != 0 {
 				envList = strings.Split(envs, DefaultSeparator)
 			}
 
 			metas = append(metas, structMeta{
 				envList:     envList,
+				fieldName:   s.Type().Field(idx).Name,
 				fieldValue:  s.Field(idx),
 				defValue:    defValue,
 				layout:      layout,
 				separator:   separator,
-				description: fType.Tag.Get("env-description"),
+				description: fType.Tag.Get(TagEnvDescription),
 				updatable:   upd,
+				required:    required,
 			})
 		}
 
@@ -302,6 +326,12 @@ func readEnvVars(cfg interface{}, update bool) error {
 			}
 		}
 
+		if rawValue == nil && meta.required && meta.isFieldValueZero() {
+			err := fmt.Errorf("field %q is required but the value is not provided",
+				meta.fieldName)
+			return err
+		}
+
 		if rawValue == nil && meta.isFieldValueZero() {
 			rawValue = meta.defValue
 		}

cleanenv_test.go

@@ -72,6 +72,11 @@ func TestReadEnvVars(t *testing.T) {
 		Time7 map[string]time.Time `env:"TEST_TIME7" env-separator:"|"`
 	}
 
+	type Required struct {
+		NotRequired int `env:"NOT_REQUIRED"`
+		Required    int `env:"REQUIRED" env-required:"true"`
+	}
+
 	tests := []struct {
 		name    string
 		env     map[string]string
@@ -285,6 +290,13 @@ func TestReadEnvVars(t *testing.T) {
 			want:    ta,
 			wantErr: true,
 		},
+
+		{
+			name:    "required error",
+			cfg:     &Required{},
+			want:    &Required{},
+			wantErr: true,
+		},
 	}
 
 	for _, tt := range tests {