initial commit

config.go

@@ -0,0 +1,84 @@
+// Package config defines utils to simplify configuration
+// management
+package conf
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+// LoadFile reads the file at path, parses its json content and fills the struct
+// with the content of the file.
+func LoadFile(path string, data interface{}) error {
+	return read(path, data)
+}
+
+// SaveFile writes the given data serialized in JSON in the given path
+func SaveFile(path string, data interface{}) error {
+	return write(path, data)
+}
+
+// LoadAndUpdateFile reads the config fileat path and
+// updates it, meaning that it adds new options, removes
+// old ones, and update it by calling the Update method of
+// data if it implements the interface Updater.
+//
+// If no file is found at path, it is created and
+// initialized with the default values.
+//
+// An error is returned only if the config file cannot be
+// written.
+func LoadAndUpdateFile(path string, data interface{}) error {
+	if _, err := os.Stat(path); !os.IsNotExist(err) {
+		err2 := read(path, data)
+		if err2 != nil {
+			return err2
+		}
+
+		if data, ok := data.(Updater); ok {
+			data.Update()
+		}
+	}
+
+	return write(path, data)
+}
+
+// Updater is the interface that can be implemented by
+// config structs. If it is implemented, Update() is
+// called by LoadAndUpdateFile(). It allows one to modify
+// the data and persist those changes, for example to
+// change default values
+type Updater interface {
+	Update()
+}
+
+func read(path string, data interface{}) error {
+	content, err := ioutil.ReadFile(filepath.Clean(path))
+	if err != nil {
+		return fmt.Errorf("cannot read config file: %w", err)
+	}
+
+	err = json.Unmarshal(content, &data)
+	if err != nil {
+		return fmt.Errorf("cannot parse config file: %w", err)
+	}
+
+	return nil
+}
+
+func write(path string, data interface{}) error {
+	content, err := json.MarshalIndent(data, "", "  ")
+	if err != nil {
+		return fmt.Errorf("cannot generate config content: %w", err)
+	}
+
+	err = ioutil.WriteFile(path, content, 0644)
+	if err != nil {
+		return fmt.Errorf("cannot write config file '%s': %w", path, err)
+	}
+
+	return nil
+}

config_test.go

@@ -0,0 +1,313 @@
+package conf
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+type testconf struct {
+	String    string
+	Int       int
+	Invariant string
+	inUpdate  func()
+}
+
+func (t testconf) Update() {
+	if t.inUpdate != nil {
+		t.inUpdate()
+	}
+}
+
+func TestLoadFile(t *testing.T) {
+	Convey("Given a config struct", t, func() {
+		c := testconf{
+			String:    "default string",
+			Int:       1,
+			Invariant: "should not change",
+		}
+
+		Convey("Given a valid config file", func() {
+			file := "test.conf"
+			content := []byte(`{"String": "config string", "Int": 42}`)
+			err := ioutil.WriteFile(file, content, 0o644)
+			So(err, ShouldBeNil)
+			defer func() { _ = os.Remove(file) }()
+
+			Convey("When the config file is loaded", func() {
+				err := LoadFile(file, &c)
+
+				Convey("Then there is no error", func() {
+					So(err, ShouldBeNil)
+				})
+
+				Convey("Then the struct fields are filled", func() {
+					So(c.String, ShouldEqual, "config string")
+					So(c.Int, ShouldEqual, 42)
+				})
+
+				Convey("Then the default values are kept", func() {
+					So(c.Invariant, ShouldEqual, "should not change")
+				})
+			})
+		})
+
+		Convey("Given an invalid config file", func() {
+			file := "test.conf"
+			content := []byte(`String: not json`)
+			err := ioutil.WriteFile(file, content, 0o644)
+			So(err, ShouldBeNil)
+			defer func() { _ = os.Remove(file) }()
+
+			Convey("When the config file is loaded", func() {
+				err := LoadFile(file, &c)
+
+				Convey("Then an error is returned", func() {
+					So(err, ShouldBeError)
+				})
+
+				Convey("Then the struct fields are not filled", func() {
+					So(c.String, ShouldEqual, "default string")
+					So(c.Int, ShouldEqual, 1)
+				})
+			})
+		})
+
+		Convey("Given a non existent config file", func() {
+			file := "does-not-exist.conf.conf"
+
+			Convey("When the config file is loaded", func() {
+				err := LoadFile(file, &c)
+
+				Convey("Then an error is returned", func() {
+					So(err, ShouldBeError)
+				})
+
+				Convey("Then the struct fields are not filled", func() {
+					So(c.String, ShouldEqual, "default string")
+					So(c.Int, ShouldEqual, 1)
+				})
+			})
+		})
+	})
+}
+
+func TestSaveFile(t *testing.T) {
+	Convey("Given a config struct", t, func() {
+		c := testconf{
+			String:    "default string",
+			Int:       1,
+			Invariant: "should not change",
+		}
+
+		Convey("Given a valid path", func() {
+			file := "test.conf"
+
+			Convey("When the config file is saved", func() {
+				err := SaveFile(file, &c)
+				defer func() { _ = os.Remove(file) }()
+
+				Convey("Then there is no error", func() {
+					So(err, ShouldBeNil)
+				})
+
+				Convey("Then the file exists", func() {
+					_, err := os.Stat(file)
+					So(err, ShouldBeNil)
+
+					Convey("Then the content is correct", func() {
+						expected := "{\n  \"String\": \"default string\",\n  \"Int\": 1,\n  \"Invariant\": \"should not change\"\n}"
+						got, err := ioutil.ReadFile(file)
+						So(err, ShouldBeNil)
+						So(string(got), ShouldEqual, expected)
+					})
+				})
+			})
+
+			Convey("When the config file is saved with invalid data", func() {
+				err := SaveFile(file, func() error { return nil })
+				defer func() { _ = os.Remove(file) }()
+
+				Convey("Then an error is returned", func() {
+					So(err, ShouldBeError)
+				})
+
+				Convey("Then the file does not exist", func() {
+					_, err := os.Stat(file)
+					So(os.IsNotExist(err), ShouldBeTrue)
+				})
+			})
+		})
+
+		Convey("Given an invalid path", func() {
+			file := "cannot/write/here.conf"
+
+			Convey("When the config file is loaded", func() {
+				err := SaveFile(file, &c)
+
+				Convey("Then an error is returned", func() {
+					So(err, ShouldBeError)
+				})
+
+				Convey("Then the file does not exist", func() {
+					_, err := os.Stat(file)
+					So(os.IsNotExist(err), ShouldBeTrue)
+				})
+			})
+		})
+	})
+}
+
+func TestLoadAndUpdateFile(t *testing.T) {
+	Convey("Given a config struct and a path", t, func() {
+		updated := false
+
+		c := testconf{
+			String:    "default string",
+			Int:       1,
+			Invariant: "should not change",
+		}
+		c.inUpdate = func() { updated = true }
+		file := "test.conf"
+
+		Convey("Given no file exists at this path", func() {
+			_, err := os.Stat(file)
+			So(err, ShouldBeError)
+			So(os.IsNotExist(err), ShouldBeTrue)
+
+			Convey("When LoadAndUpdateFile is called", func() {
+				err := LoadAndUpdateFile(file, &c)
+				So(err, ShouldBeNil)
+				defer func() { _ = os.Remove(file) }()
+
+				Convey("Then the config file has been created", func() {
+					_, err := os.Stat(file)
+					So(err, ShouldBeNil)
+
+					Convey("and it has the default configuration", func() {
+						var c2 testconf
+						err := read(file, &c2)
+						So(err, ShouldBeNil)
+						c.inUpdate = nil
+						So(c2, ShouldResemble, c)
+					})
+				})
+			})
+		})
+
+		Convey("Given the path cannot be written", func() {
+			file = "does-not-exist/test.conf"
+			_, err := os.Stat(file)
+			So(err, ShouldBeError)
+			So(os.IsNotExist(err), ShouldBeTrue)
+
+			Convey("When LoadAndUpdateFile is called", func() {
+				err := LoadAndUpdateFile(file, &c)
+				defer func() { _ = os.Remove(file) }()
+
+				Convey("Then an error is returned", func() {
+					So(err, ShouldBeError)
+				})
+			})
+		})
+
+		Convey("Given a config file with custom values", func() {
+			content := []byte(`{"String": "config string", "Int": 42}`)
+			err := ioutil.WriteFile(file, content, 0o644)
+			So(err, ShouldBeNil)
+			defer func() { _ = os.Remove(file) }()
+
+			Convey("When LoadAndUpdateFile is called", func() {
+				err := LoadAndUpdateFile(file, &c)
+
+				Convey("Then there is no error", func() {
+					So(err, ShouldBeNil)
+				})
+
+				Convey("Then the struct fields are filled", func() {
+					So(c.String, ShouldEqual, "config string")
+					So(c.Int, ShouldEqual, 42)
+				})
+			})
+		})
+
+		Convey("Given an invalid configuration file", func() {
+			content := []byte(`String: not json`)
+			err := ioutil.WriteFile(file, content, 0o644)
+			So(err, ShouldBeNil)
+			defer func() { _ = os.Remove(file) }()
+
+			Convey("When LoadAndUpdateFile is called", func() {
+				err := LoadAndUpdateFile(file, &c)
+				defer func() { _ = os.Remove(file) }()
+
+				Convey("Then an error is returned", func() {
+					So(err, ShouldBeError)
+				})
+			})
+		})
+
+		Convey("Given a config file with missing options", func() {
+			content := []byte(`{"String": "config string"}`)
+			err := ioutil.WriteFile(file, content, 0o644)
+			So(err, ShouldBeNil)
+			defer func() { _ = os.Remove(file) }()
+
+			Convey("When LoadAndUpdateFile is called", func() {
+				err := LoadAndUpdateFile(file, &c)
+
+				Convey("Then there is no error", func() {
+					So(err, ShouldBeNil)
+				})
+
+				Convey("Then the config file has been updated with new options", func() {
+					content, err := ioutil.ReadFile(file)
+					So(err, ShouldBeNil)
+					So(string(content), ShouldContainSubstring, `"Int"`)
+				})
+			})
+		})
+
+		Convey("Given a config file with old options", func() {
+			content := []byte(`{"String": "config string", "Foo": "blah"}`)
+			err := ioutil.WriteFile(file, content, 0o644)
+			So(err, ShouldBeNil)
+			defer func() { _ = os.Remove(file) }()
+
+			Convey("When LoadAndUpdateFile is called", func() {
+				err := LoadAndUpdateFile(file, &c)
+
+				Convey("Then there is no error", func() {
+					So(err, ShouldBeNil)
+				})
+
+				Convey("Then the config file has been updated with new options", func() {
+					content, err := ioutil.ReadFile(file)
+					So(err, ShouldBeNil)
+					So(string(content), ShouldNotContainSubstring, `"Foo"`)
+				})
+			})
+		})
+
+		Convey("Given a valid config file", func() {
+			content := []byte(`{"String": "config string"}`)
+			err := ioutil.WriteFile(file, content, 0o644)
+			So(err, ShouldBeNil)
+			defer func() { _ = os.Remove(file) }()
+
+			Convey("When LoadAndUpdateFile is called", func() {
+				err := LoadAndUpdateFile(file, &c)
+
+				Convey("Then there is no error", func() {
+					So(err, ShouldBeNil)
+				})
+
+				Convey("Then the update method of the struct has been called", func() {
+					So(updated, ShouldBeTrue)
+				})
+			})
+		})
+	})
+}