Add new AppDataDir function.

This commit adds a new AppDataDir function that can be used to get an
operating system and application specific directory to be used for storing
application data.

For example:

dir := AppDataDir("myapp", false)

Would result in:

POSIX (Linux/BSD): ~/.myapp
Mac OS: $HOME/Library/Application Support/Myapp
Windows: %LOCALAPPDATA%\Myapp
Plan 9: $home/myapp

This is work toward conformal/btcd#30.

appdata.go

@@ -0,0 +1,107 @@
+// Copyright (c) 2013 Conformal Systems LLC.
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package btcutil
+
+import (
+	"os"
+	"os/user"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"unicode"
+)
+
+// appDataDir returns an operating system specific directory to be used for
+// storing application data for an application.  See AppDataDir for more
+// details.  This unexported version takes an operating system argument
+// primarily to enable the testing package to properly test the function by
+// forcing an operating system that is not the currently one.
+func appDataDir(goos, appName string, roaming bool) string {
+	if appName == "" || appName == "." {
+		return "."
+	}
+
+	// The caller really shouldn't prepend the appName with a period, but
+	// if they do, handle it gracefully by stripping it.
+	if strings.HasPrefix(appName, ".") {
+		appName = appName[1:]
+	}
+	appNameUpper := string(unicode.ToUpper(rune(appName[0]))) + appName[1:]
+	appNameLower := string(unicode.ToLower(rune(appName[0]))) + appName[1:]
+
+	// Get the OS specific home directory via the Go standard lib.
+	var homeDir string
+	usr, err := user.Current()
+	if err == nil {
+		homeDir = usr.HomeDir
+	}
+
+	// Fall back to standard HOME environment variable that works
+	// for most POSIX OSes if the directory from the Go standard
+	// lib failed.
+	if err != nil || homeDir == "" {
+		homeDir = os.Getenv("HOME")
+	}
+
+	switch goos {
+	// Attempt to use the LOCALAPPDATA or APPDATA environment variable on
+	// Windows.
+	case "windows":
+		// Windows XP and before didn't have a LOCALAPPDATA, so fallback
+		// to regular APPDATA when LOCALAPPDATA is not set.
+		appData := os.Getenv("LOCALAPPDATA")
+		if roaming || appData == "" {
+			appData = os.Getenv("APPDATA")
+		}
+
+		if appData != "" {
+			return filepath.Join(appData, appNameUpper)
+		}
+
+	case "darwin":
+		if homeDir != "" {
+			return filepath.Join(homeDir, "Library",
+				"Application Support", appNameUpper)
+		}
+
+	case "plan9":
+		if homeDir != "" {
+			return filepath.Join(homeDir, appNameLower)
+		}
+
+	default:
+		if homeDir != "" {
+			return filepath.Join(homeDir, "."+appNameLower)
+		}
+	}
+
+	// Fall back to the current directory if all else fails.
+	return "."
+}
+
+// AppDataDir returns an operating system specific directory to be used for
+// storing application data for an application.
+//
+// The appName parameter is the name of the application the data directory is
+// being requested for.  This function will prepend a period to the appName for
+// POSIX style operating systems since that is standard practice.  An empty
+// appName or one with a single dot is treated as requesting the current
+// directory so only "." will be returned.  Further, the first character
+// of appName will be made lowercase for POSIX style operating systems and
+// uppercase for Mac and Windows since that is standard practice.
+//
+// The roaming parameter only applies to Windows where it specifies the roaming
+// application data profile (%APPDATA%) should be used instead of the local one
+// (%LOCALAPPDATA%) that is used by default.
+//
+// Example results:
+//  dir := AppDataDir("myapp", false)
+//   POSIX (Linux/BSD): ~/.myapp
+//   Mac OS: $HOME/Library/Application Support/Myapp
+//   Windows: %LOCALAPPDATA%\Myapp
+//   Plan 9: $home/myapp
+func AppDataDir(appName string, roaming bool) string {
+	return appDataDir(runtime.GOOS, appName, roaming)
+}

appdata_test.go

@@ -0,0 +1,132 @@
+// Copyright (c) 2013 Conformal Systems LLC.
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package btcutil_test
+
+import (
+	"github.com/conformal/btcutil"
+	"os"
+	"os/user"
+	"path/filepath"
+	"runtime"
+	"testing"
+	"unicode"
+)
+
+// TestAppDataDir tests the API for AppDataDir to ensure it gives expected
+// results for various operating systems.
+func TestAppDataDir(t *testing.T) {
+	// App name plus upper and lowercase variants.
+	appName := "myapp"
+	appNameUpper := string(unicode.ToUpper(rune(appName[0]))) + appName[1:]
+	appNameLower := string(unicode.ToLower(rune(appName[0]))) + appName[1:]
+
+	// When we're on Windows, set the expected local and roaming directories
+	// per the environment vars.  When we aren't on Windows, the function
+	// should return the current directory when forced to provide the
+	// Windows path since the environment variables won't exist.
+	winLocal := "."
+	winRoaming := "."
+	if runtime.GOOS == "windows" {
+		localAppData := os.Getenv("LOCALAPPDATA")
+		roamingAppData := os.Getenv("APPDATA")
+		if localAppData == "" {
+			localAppData = roamingAppData
+		}
+		winLocal = filepath.Join(localAppData, appNameUpper)
+		winRoaming = filepath.Join(roamingAppData, appNameUpper)
+	}
+
+	// Get the home directory to use for testing expected results.
+	var homeDir string
+	usr, err := user.Current()
+	if err != nil {
+		t.Errorf("user.Current: %v", err)
+		return
+	}
+	homeDir = usr.HomeDir
+
+	// Mac app data directory.
+	macAppData := filepath.Join(homeDir, "Library", "Application Support")
+
+	tests := []struct {
+		goos    string
+		appName string
+		roaming bool
+		want    string
+	}{
+		// Various combinations of application name casing, leading
+		// period, operating system, and roaming flags.
+		{"windows", appNameLower, false, winLocal},
+		{"windows", appNameUpper, false, winLocal},
+		{"windows", "." + appNameLower, false, winLocal},
+		{"windows", "." + appNameUpper, false, winLocal},
+		{"windows", appNameLower, true, winRoaming},
+		{"windows", appNameUpper, true, winRoaming},
+		{"windows", "." + appNameLower, true, winRoaming},
+		{"windows", "." + appNameUpper, true, winRoaming},
+		{"linux", appNameLower, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"linux", appNameUpper, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"linux", "." + appNameLower, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"linux", "." + appNameUpper, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"darwin", appNameLower, false, filepath.Join(macAppData, appNameUpper)},
+		{"darwin", appNameUpper, false, filepath.Join(macAppData, appNameUpper)},
+		{"darwin", "." + appNameLower, false, filepath.Join(macAppData, appNameUpper)},
+		{"darwin", "." + appNameUpper, false, filepath.Join(macAppData, appNameUpper)},
+		{"openbsd", appNameLower, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"openbsd", appNameUpper, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"openbsd", "." + appNameLower, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"openbsd", "." + appNameUpper, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"freebsd", appNameLower, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"freebsd", appNameUpper, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"freebsd", "." + appNameLower, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"freebsd", "." + appNameUpper, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"netbsd", appNameLower, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"netbsd", appNameUpper, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"netbsd", "." + appNameLower, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"netbsd", "." + appNameUpper, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"plan9", appNameLower, false, filepath.Join(homeDir, appNameLower)},
+		{"plan9", appNameUpper, false, filepath.Join(homeDir, appNameLower)},
+		{"plan9", "." + appNameLower, false, filepath.Join(homeDir, appNameLower)},
+		{"plan9", "." + appNameUpper, false, filepath.Join(homeDir, appNameLower)},
+		{"unrecognized", appNameLower, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"unrecognized", appNameUpper, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"unrecognized", "." + appNameLower, false, filepath.Join(homeDir, "."+appNameLower)},
+		{"unrecognized", "." + appNameUpper, false, filepath.Join(homeDir, "."+appNameLower)},
+
+		// No application name provided, so expect current directory.
+		{"windows", "", false, "."},
+		{"windows", "", true, "."},
+		{"linux", "", false, "."},
+		{"darwin", "", false, "."},
+		{"openbsd", "", false, "."},
+		{"freebsd", "", false, "."},
+		{"netbsd", "", false, "."},
+		{"plan9", "", false, "."},
+		{"unrecognized", "", false, "."},
+
+		// Single dot provided for application name, so expect current
+		// directory.
+		{"windows", ".", false, "."},
+		{"windows", ".", true, "."},
+		{"linux", ".", false, "."},
+		{"darwin", ".", false, "."},
+		{"openbsd", ".", false, "."},
+		{"freebsd", ".", false, "."},
+		{"netbsd", ".", false, "."},
+		{"plan9", ".", false, "."},
+		{"unrecognized", ".", false, "."},
+	}
+
+	t.Logf("Running %d tests", len(tests))
+	for i, test := range tests {
+		ret := btcutil.TstAppDataDir(test.goos, test.appName, test.roaming)
+		if ret != test.want {
+			t.Errorf("appDataDir #%d (%s) does not match - "+
+				"expected got %s, want %s", i, test.goos, ret,
+				test.want)
+			continue
+		}
+	}
+}

internal_test.go

@@ -17,3 +17,9 @@ package btcutil
 func (b *Block) SetBlockBytes(buf []byte) {
 	b.serializedBlock = buf
 }
+
+// TstAppDataDir makes the internal appDataDir function available to the test
+// package.
+func TstAppDataDir(goos, appName string, roaming bool) string {
+	return appDataDir(goos, appName, roaming)
+}