config: add a Require message.

Also update explanation of the intended use-case for this package.

README.md

@@ -7,6 +7,9 @@ Note that for packaging purposes, the goutils-pkg repo should be used: it
 pins the library versions to working copies and vendors all depdencies. See
 https://github.com/kisom/goutils-pkg for more details.
 
+The goutils-pkg repo [1] has stable versions of the command line
+utilities here, along with a vendored snapshot of any dependencies.
+
 Contents:
 
     ahash/          Provides hashes from string algorithm specifiers.
@@ -62,3 +65,5 @@ Each program should have a small README in the directory with more
 information.
 
 All code here is licensed under the MIT license.
+
+[1] https://github.com/kisom/goutils-pkg/

cmd/parts/README

@@ -0,0 +1,9 @@
+parts: simple parts database for electronic components
+
+Usage:  parts [id] -- query the database for a part
+	parts [-c class] [id] [description] -- store a part in the database
+
+	Options:
+		-f path		Path to parts database (default is
+				/home/kyle/.parts.json).
+

cmd/parts/main.go

@@ -0,0 +1,142 @@
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+
+	"github.com/kisom/goutils/die"
+)
+
+const dbVersion = "1"
+
+var dbFile = filepath.Join(os.Getenv("HOME"), ".parts.json")
+var partsDB = &database{Version: dbVersion}
+
+type part struct {
+	Name        string `json:"name"`
+	Description string `json:"description"`
+	Class       string `json:"class,omitempty"`
+}
+
+func (p part) String() string {
+	return fmt.Sprintf("%s: %s", p.Name, p.Description)
+}
+
+type database struct {
+	Version    string          `json:"version"`
+	LastUpdate int64           `json:"json"`
+	Parts      map[string]part `json:"parts"`
+}
+
+func help(w io.Writer) {
+	fmt.Fprintf(w, `Usage:  parts [id] -- query the database for a part
+	parts [-c class] [id] [description] -- store a part in the database
+
+	Options:
+		-f path		Path to parts database (default is
+				%s).
+          
+`, dbFile)
+}
+
+func loadDatabase() {
+	data, err := ioutil.ReadFile(dbFile)
+	if err != nil && os.IsNotExist(err) {
+		partsDB = &database{
+			Version: dbVersion,
+			Parts:   map[string]part{},
+		}
+		return
+	}
+	die.If(err)
+
+	err = json.Unmarshal(data, partsDB)
+	die.If(err)
+}
+
+func findPart(partName string) {
+	partName = strings.ToLower(partName)
+	for name, part := range partsDB.Parts {
+		if strings.Contains(strings.ToLower(name), partName) {
+			fmt.Println(part.String())
+		}
+	}
+}
+
+func writeDB() {
+	data, err := json.Marshal(partsDB)
+	die.If(err)
+
+	err = ioutil.WriteFile(dbFile, data, 0644)
+	die.If(err)
+}
+
+func storePart(name, class, description string) {
+	p, exists := partsDB.Parts[name]
+	if exists {
+		fmt.Printf("warning: replacing part %s\n", name)
+		fmt.Printf("\t%s\n", p.String())
+	}
+
+	partsDB.Parts[name] = part{
+		Name:        name,
+		Class:       class,
+		Description: description,
+	}
+
+	writeDB()
+}
+
+func listParts() {
+	parts := make([]string, 0, len(partsDB.Parts))
+	for partName := range partsDB.Parts {
+		parts = append(parts, partName)
+	}
+
+	sort.Strings(parts)
+	for _, partName := range parts {
+		fmt.Println(partsDB.Parts[partName].String())
+	}
+}
+
+func main() {
+	var class string
+	var helpFlag bool
+
+	flag.StringVar(&class, "c", "", "device class")
+	flag.StringVar(&dbFile, "f", dbFile, "`path` to database")
+	flag.BoolVar(&helpFlag, "h", false, "Print a help message.")
+	flag.Parse()
+
+	if helpFlag {
+		help(os.Stdout)
+		return
+	}
+
+	loadDatabase()
+
+	switch flag.NArg() {
+	case 0:
+		help(os.Stdout)
+		return
+	case 1:
+		partName := flag.Arg(0)
+		if partName == "list" {
+			listParts()
+		} else {
+			findPart(flag.Arg(0))
+		}
+		return
+	default:
+		description := strings.Join(flag.Args()[1:], " ")
+		storePart(flag.Arg(0), class, description)
+		return
+	}
+}

config/config.go

@@ -0,0 +1,110 @@
+// Package config implements a simple global configuration system that
+// supports a file with key=value pairs and environment variables. Note
+// that the config system is global.
+//
+// This package is intended to be used for small daemons: some configuration
+// file is optionally populated at program start, then this is used to
+// transparently look up configuration values from either that file or the
+// environment.
+package config
+
+import (
+	"bufio"
+	"log"
+	"os"
+	"strings"
+)
+
+// NB: Rather than define a singleton type, everything is defined at
+// the top-level
+
+var (
+	vars   = map[string]string{}
+	prefix = ""
+)
+
+// SetEnvPrefix sets the prefix for all environment variables; it's
+// assumed to not be needed for files.
+func SetEnvPrefix(pfx string) {
+	prefix = pfx
+}
+
+func addLine(line string) {
+	if strings.HasPrefix(line, "#") || line == "" {
+		return
+	}
+
+	lineParts := strings.SplitN(line, "=", 2)
+	if len(lineParts) != 2 {
+		log.Print("skipping line: ", line)
+		return // silently ignore empty keys
+	}
+
+	lineParts[0] = strings.TrimSpace(lineParts[0])
+	lineParts[1] = strings.TrimSpace(lineParts[1])
+	vars[lineParts[0]] = lineParts[1]
+}
+
+// LoadFile scans the file at path for key=value pairs and adds them
+// to the configuration.
+func LoadFile(path string) error {
+	file, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		addLine(line)
+	}
+
+	if err = scanner.Err(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Get retrieves a value from either a configuration file or the
+// environment. Note that values from a file will override environment
+// variables.
+func Get(key string) string {
+	if v, ok := vars[key]; ok {
+		return v
+	}
+	return os.Getenv(prefix + key)
+}
+
+// GetDefault retrieves a value from either a configuration file or
+// the environment. Note that value from a file will override
+// environment variables. If a value isn't found (e.g. Get returns an
+// empty string), the default value will be used.
+func GetDefault(key, def string) string {
+	if v := Get(key); v != "" {
+		return v
+	}
+	return def
+}
+
+// Require retrieves a value from either a configuration file or the
+// environment. If the key isn't present, it will call log.Fatal, printing
+// the missing key.
+func Require(key string) string {
+	if v, ok := vars[key]; ok {
+		return v
+	}
+
+	v, ok := os.LookupEnv(prefix + key)
+	if !ok {
+		var envMessage string
+		if prefix != "" {
+			envMessage = " (note: looked for the key " + prefix + key
+			envMessage += " in the local env)"
+		}
+		log.Fatalf("missing required configuration value %s%s", key, envMessage)
+	}
+
+	return v
+}

config/config_test.go

@@ -0,0 +1,66 @@
+package config
+
+import (
+	"os"
+	"testing"
+)
+
+const (
+	testFilePath = "testdata/test.env"
+
+	// Keys
+	kOrder   = "ORDER"
+	kSpecies = "SPECIES"
+	kName    = "COMMON_NAME"
+
+	// Env
+	eOrder   = "corvus"
+	eSpecies = "corvus corax"
+	eName    = "northern raven"
+
+	// File
+	fOrder   = "stringiformes"
+	fSpecies = "strix aluco"
+	// Name isn't set in the file to test fall through.
+)
+
+func init() {
+	os.Setenv(kOrder, eOrder)
+	os.Setenv(kSpecies, eSpecies)
+	os.Setenv(kName, eName)
+}
+
+func TestLoadEnvOnly(t *testing.T) {
+	order := Get(kOrder)
+	species := Get(kSpecies)
+	if order != eOrder {
+		t.Errorf("want %s, have %s", eOrder, order)
+	}
+
+	if species != eSpecies {
+		t.Errorf("want %s, have %s", eSpecies, species)
+	}
+}
+
+func TestLoadFile(t *testing.T) {
+	err := LoadFile(testFilePath)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	order := Get(kOrder)
+	species := Get(kSpecies)
+	name := Get(kName)
+
+	if order != fOrder {
+		t.Errorf("want %s, have %s", fOrder, order)
+	}
+
+	if species != fSpecies {
+		t.Errorf("want %s, have %s", fSpecies, species)
+	}
+
+	if name != eName {
+		t.Errorf("want %s, have %s", eName, name)
+	}
+}

config/testdata/test.env

@@ -0,0 +1,2 @@
+ORDER=stringiformes
+SPECIES=strix aluco

go.mod

@@ -0,0 +1,3 @@
+module github.com/kisom/goutils
+
+go 1.13

lib/ftime_bsd.go

@@ -1,4 +1,4 @@
-// +build freebsd darwin netbsd
+// +build freebsd darwin,386 netbsd
 
 package lib
 

lib/ftime_unix.go

@@ -1,4 +1,4 @@
-// +build unix linux openbsd
+// +build unix linux openbsd darwin,amd64
 
 package lib