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vendor/github.com/rs/xid/README.md

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+# Globally Unique ID Generator
+
+[![godoc](http://img.shields.io/badge/godoc-reference-blue.svg?style=flat)](https://godoc.org/github.com/rs/xid) [![license](http://img.shields.io/badge/license-MIT-red.svg?style=flat)](https://raw.githubusercontent.com/rs/xid/master/LICENSE) [![Build Status](https://travis-ci.org/rs/xid.svg?branch=master)](https://travis-ci.org/rs/xid) [![Coverage](http://gocover.io/_badge/github.com/rs/xid)](http://gocover.io/github.com/rs/xid)
+
+Package xid is a globally unique id generator suited for web scale
+
+Xid is using Mongo Object ID algorithm to generate globally unique ids:
+https://docs.mongodb.org/manual/reference/object-id/
+
+- 4-byte value representing the seconds since the Unix epoch,
+- 3-byte machine identifier,
+- 2-byte process id, and
+- 3-byte counter, starting with a random value.
+
+The binary representation of the id is compatible with Mongo 12 bytes Object IDs.
+The string representation is using URL safe base64 for better space efficiency when
+stored in that form (16 bytes).
+
+UUID is 16 bytes (128 bits), snowflake is 8 bytes (64 bits), xid stands in between
+with 12 bytes with a more compact string representation ready for the web and no
+required configuration or central generation server.
+
+Features:
+
+- Size: 12 bytes (96 bits), smaller than UUID, larger than snowflake
+- Base64 URL safe encoded by default (16 bytes storage when transported as printable string)
+- Non configured, you don't need set a unique machine and/or data center id
+- K-ordered
+- Embedded time with 1 second precision
+- Unicity guaranted for 16,777,216 (24 bits) unique ids per second and per host/process
+
+Best used with [xlog](https://github.com/rs/xlog)'s
+[RequestIDHandler](https://godoc.org/github.com/rs/xlog#RequestIDHandler).
+
+References:
+
+- http://www.slideshare.net/davegardnerisme/unique-id-generation-in-distributed-systems
+- https://en.wikipedia.org/wiki/Universally_unique_identifier
+- https://blog.twitter.com/2010/announcing-snowflake
+
+## Install
+
+    go get github.com/rs/xid
+
+## Usage
+
+```go
+guid := xid.New()
+
+println(guid.String())
+// Output: TYjhW2D0huQoQS3J
+```
+
+Get `xid` embedded info:
+
+```go
+guid.Machine()
+guid.Pid()
+guid.Time()
+guid.Counter()
+```
+
+## Licenses
+
+All source code is licensed under the [MIT License](https://raw.github.com/rs/xid/master/LICENSE).