create version.go file

A file dedicated to handling+dispatching version information concerning
lnd. We’ll be using the semantic versioning standard.

I guess lnd is officially at 0.1.0-alpha now?

version.go

@@ -0,0 +1,70 @@
+package main
+
+// Heavily inspired by https://github.com/btcsuite/btcd/blob/master/version.go
+
+import (
+	"bytes"
+	"fmt"
+	"strings"
+)
+
+// semanticAlphabet
+const semanticAlphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-"
+
+// These constants define the application version and follow the semantic
+// versioning 2.0.0 spec (http://semver.org/).
+const (
+	appMajor uint = 0
+	appMinor uint = 1
+	appPatch uint = 0
+
+	// appPreRelease MUST only contain characters from semanticAlphabet
+	// per the semantic versioning spec.
+	appPreRelease = "alpha"
+)
+
+// appBuild is defined as a variable so it can be overridden during the build
+// process with '-ldflags "-X main.appBuild foo' if needed.  It MUST only
+// contain characters from semanticAlphabet per the semantic versioning spec.
+var appBuild string
+
+// version returns the application version as a properly formed string per the
+// semantic versioning 2.0.0 spec (http://semver.org/).
+func version() string {
+	// Start with the major, minor, and patch versions.
+	version := fmt.Sprintf("%d.%d.%d", appMajor, appMinor, appPatch)
+
+	// Append pre-release version if there is one.  The hyphen called for
+	// by the semantic versioning spec is automatically appended and should
+	// not be contained in the pre-release string.  The pre-release version
+	// is not appended if it contains invalid characters.
+	preRelease := normalizeVerString(appPreRelease)
+	if preRelease != "" {
+		version = fmt.Sprintf("%s-%s", version, preRelease)
+	}
+
+	// Append build metadata if there is any.  The plus called for
+	// by the semantic versioning spec is automatically appended and should
+	// not be contained in the build metadata string.  The build metadata
+	// string is not appended if it contains invalid characters.
+	build := normalizeVerString(appBuild)
+	if build != "" {
+		version = fmt.Sprintf("%s+%s", version, build)
+	}
+
+	return version
+}
+
+// normalizeVerString returns the passed string stripped of all characters which
+// are not valid according to the semantic versioning guidelines for pre-release
+// version and build metadata strings.  In particular they MUST only contain
+// characters in semanticAlphabet.
+func normalizeVerString(str string) string {
+	var result bytes.Buffer
+	for _, r := range str {
+		if strings.ContainsRune(semanticAlphabet, r) {
+			result.WriteRune(r)
+		}
+	}
+	return result.String()
+}