Sid.Net

A tiny library for time-sortable, URL-safe string IDs.

The format of a SID is as follows:

[<prefix>]<timestamp><counter><randomChars>

Where

• prefix is an optional string supplied by the caller
• timestamp is a base62-encoded UNIX timestamp in which the SID was created
• counter is a simple incrementing counter that ensures sortability within the same millisecond
• randomChars is a string of 16 random base62 characters.

The timestamp is the number of milliseconds since the Unix epoch, encoded in such a way that SIDs will naturally sort into the order in which they were created. Remember that in .NET you must use StringComparer.Ordinal to sort SIDs correctly (by default strings are sorted using the current CultureInfo, which usually means a sort order that ignores case).

The entropy of a SID is at least that of a v7 GUID (which also includes a timestamp component), but a SID is more compact whilst remaining URL-safe.

Component	String length	Possible values	Entropy
Guid	36	2^122	122 bits
Guid v7	36	2^122	74 bits per ms
SID	22	2^137	84 bits per ms

Usage

Creating a new ID is as simple as calling Sid.Create().

using Sid.Net;
string s = Sid.Create(); // Uf2WHnIaa6R9Hiw3HABMMLH

Prefixed IDs are nice; you can also provide a prefix to the ID by calling Sid.Create("prefix.").

string s = Sid.Create("prefix"); // prefixUf2WICe9roQFNb8RRVe0Y1O

If desired, a generated SID can be parsed into a Sid struct instance if you'd like to deconstruct the SID into the inputs that were used to create it:

Sid parsed = Sid.Parse("AB.Uf2WHnIaa6R9Hiw3HABMMLH");
long timestamp = parsed.Timestamp; 
    // 1625097600000

char[] prefix = parsed.Prefix; 
    // ['A', 'B', '.']

char[] randomChars = parsed.RandomChars; 
    // ['a', 'a', '6', 'R', '9', 'H', 'i', 'w', '3', 'H', 'A','B', 'M', 'M', 'L', 'H']

You can also easily convert the timestamp to a DateTimeOffset:

DateTimeOffset dt = DateTimeOffset.FromUnixTimeMilliseconds(timestamp);
    // 2021-07-01T00:00:00.0000000+00:00

It's fast

Sid.NET is extremely fast, taking less than 300ns on a dev laptop to generate a new ID, even with a prefix. It also allocates no memory beside the returned string, making it appropriate for high-performance applications.

Method	Mean	Error	StdDev	Median	Ratio	RatioSD	Rank	Allocated	Alloc Ratio
Create	256.3 ns	6.22 ns	17.43 ns	251.0 ns	1.00	0.09	1	72 B	1.00
CreateWithPrefix	263.3 ns	6.99 ns	20.05 ns	257.4 ns	1.03	0.10	1	80 B	1.11

Caveats

Since it's possible for mulitple SIDs to be created in the same millisecond, a counter is included in the SID to ensure that each SID is unique. The counter is a base62-encoded number that is incremented (in a thread-safe way) each time a new SID is created in the same millisecond. The counter has two characters, allowing for 3844 SIDs to be created in the same millisecond whilst remaining sortable. Creating more SIDs per millisecond will work, but they will not order correctly as the counter will overflow.

Also, it may be stating the obvious, but ordering of SIDs requires that the datetime of the host machine(s) is configured correctly.