From a2b6f5687652e93b0220bf68a76151d9d3a00792 Mon Sep 17 00:00:00 2001
From: Brian Picciano <mediocregopher@gmail.com>
Date: Sun, 11 Mar 2018 18:25:04 +0000
Subject: [PATCH] implement mcrypto.UUID

---
 mcrypto/mcrypto.go   |   4 ++
 mcrypto/uuid.go      | 103 +++++++++++++++++++++++++++++++++++++++++++
 mcrypto/uuid_test.go |  40 +++++++++++++++++
 3 files changed, 147 insertions(+)
 create mode 100644 mcrypto/mcrypto.go
 create mode 100644 mcrypto/uuid.go
 create mode 100644 mcrypto/uuid_test.go

diff --git a/mcrypto/mcrypto.go b/mcrypto/mcrypto.go
new file mode 100644
index 0000000..3e64660
--- /dev/null
+++ b/mcrypto/mcrypto.go
@@ -0,0 +1,4 @@
+// Package mcrypto contains general purpose functionality related to
+// cryptography, notably related to unique identifiers, signing/verifying data,
+// and encrypting/decrypting data
+package mcrypto
diff --git a/mcrypto/uuid.go b/mcrypto/uuid.go
new file mode 100644
index 0000000..58dd7a3
--- /dev/null
+++ b/mcrypto/uuid.go
@@ -0,0 +1,103 @@
+package mcrypto
+
+import (
+	"bytes"
+	"crypto/rand"
+	"encoding/binary"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/mediocregopher/mediocre-go-lib/mlog"
+)
+
+const (
+	uuidV0Prefix = "0u"
+	uuidV0Len    = 34 // prefix:2 + hexEncodedLen(time:8 + random:8)
+)
+
+// UUID is a universally unique identifier which embeds within it a timestamp.
+//
+// Only Unmarshal methods should be called on the zero UUID value.
+//
+// Comparing the equality of two UUID's should always be done using the Equal
+// method, or by comparing their string forms.
+//
+// The string form of UUIDs (returned by String or MarshalText) are
+// lexigraphically order-able by their embedded timestamp.
+type UUID struct {
+	// the UUID type is actually just an opaque wrapper. For the most part
+	// UUID's don't ever need the information in them (like their timestamp)
+	// unpacked, so it's more efficient to just keep the string and unpack
+	// on-the-fly
+	str string
+}
+
+// NewUUID populates and returns a new UUID instance which embeds the given time
+func NewUUID(t time.Time) UUID {
+	b := make([]byte, 16)
+	binary.BigEndian.PutUint64(b[:8], uint64(t.UnixNano()))
+	if _, err := rand.Read(b[8:]); err != nil {
+		panic(err)
+	}
+	return UUID{
+		str: uuidV0Prefix + hex.EncodeToString(b),
+	}
+}
+
+func (u UUID) String() string {
+	return u.str
+}
+
+// Equal returns whether or not the two UUID's are the same value
+func (u UUID) Equal(u2 UUID) bool {
+	return u.str == u2.str
+}
+
+// Time unpacks and returns the timestamp embedded in the UUID
+func (u UUID) Time() time.Time {
+	b, err := hex.DecodeString(u.str[2:])
+	if err != nil {
+		// once a UUID has been created it should always be valid
+		panic(fmt.Sprintf("malformed UUID: %q", u.str))
+	}
+	unixNano := int64(binary.BigEndian.Uint64(b[:8]))
+	return time.Unix(0, unixNano).Local()
+}
+
+// KV implements the method for the mlog.KVer interface
+func (u UUID) KV() mlog.KV {
+	return mlog.KV{"uuid": u.String()}
+}
+
+// MarshalText implements the method for the encoding.TextMarshaler interface
+func (u UUID) MarshalText() ([]byte, error) {
+	return []byte(u.String()), nil
+}
+
+// UnmarshalText implements the method for the encoding.TextUnmarshaler
+// interface
+func (u *UUID) UnmarshalText(b []byte) error {
+	if !bytes.HasPrefix(b, []byte(uuidV0Prefix)) || len(b) != uuidV0Len {
+		err := errors.New("malformed uuid string")
+		return mlog.ErrWithKV(err, mlog.KV{"uuidStr": string(b)})
+	}
+	u.str = string(b)
+	return nil
+}
+
+// MarshalJSON implements the method for the json.Marshaler interface
+func (u UUID) MarshalJSON() ([]byte, error) {
+	return json.Marshal(u.String())
+}
+
+// UnmarshalJSON implements the method for the json.Unmarshaler interface
+func (u *UUID) UnmarshalJSON(b []byte) error {
+	var s string
+	if err := json.Unmarshal(b, &s); err != nil {
+		return err
+	}
+	return u.UnmarshalText([]byte(s))
+}
diff --git a/mcrypto/uuid_test.go b/mcrypto/uuid_test.go
new file mode 100644
index 0000000..00a0bbb
--- /dev/null
+++ b/mcrypto/uuid_test.go
@@ -0,0 +1,40 @@
+package mcrypto
+
+import (
+	"strings"
+	. "testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestUUID(t *T) {
+	var prevT time.Time
+	var prev UUID
+	for i := 0; i < 10000; i++ {
+		thisT := time.Now().Round(0)        // strip monotonic clock
+		require.True(t, thisT.After(prevT)) // sanity check
+		this := NewUUID(thisT)
+
+		// basic
+		assert.True(t, strings.HasPrefix(this.String(), uuidV0Prefix))
+		assert.Len(t, this.String(), uuidV0Len)
+
+		// comparisons with prev
+		assert.False(t, prev.Equal(this))
+		assert.NotEqual(t, prev.String(), this.String())
+		assert.True(t, this.String() > prev.String())
+		prev = this
+
+		// check time unpacking
+		assert.Equal(t, thisT, this.Time())
+
+		// check marshal/unmarshal
+		thisStr, err := this.MarshalText()
+		require.NoError(t, err)
+		var this2 UUID
+		require.NoError(t, this2.UnmarshalText(thisStr))
+		assert.True(t, this.Equal(this2))
+	}
+}