Porter

A simple package for allocating free ports adapted from Consul's freeport.

Installation

Like most Go packages, installing Porter is easy. First go get the package.

go get github.com/walkergriggs/porter

Next, import Porter.

import "github.com/walkergriggs/porter"

Usage

config := porter.DefaultConfig()

p, err := porter.New(config)
if err != nil {
	panic(err)
}
defer p.Close()

ports := p.MustTake(5)

fmt.Println(ports)

// [10101 10102 10103 10104 10105]

Allocation

Porter takes three configuration variables: BlockSize, MaxBlocks, and LowerBound.

• BlockSize configures how many ports are alloted to a block.
• MaxBlocks configures how many blocks are considered.
• LowerBound configures the lowest allocatable port.

Starting from the lower bound, Porter checks the range of each block, picks one at random, and takes out a lock on the first port. From that block, Porter filters a list of all available ports, which can reserved with Take and MustTake.

LowerBound = 8000
BlockSize = 100
MaxBlocks = 3

+-----------+-----------+-----------+
| Port Blocks (3)                   |
+-----------+-----------+-----------+
| 8000-8099 | 8100-8199 | 8200-8299 |
+-----------+-----------+-----------+

Ephemeral Ports

Before picking a block and locking the first port, we first adjust the MaxBlocks based on the host's ephemeral port range.

If any block overlaps with ephemeral ports, we trim MaxBlocks so the allocated blocks end just before the ephemeral ports.

LowerBound = 32600
BlockSize = 100
MaxBlocks = 3

+-----------------+-------------+-------------+
| Port Blocks (1) | Free        | Ephemeral  |
+-----------------+-------------+-------------+
| 32600-32699     | 32700-32767 | 32768-60999 |
+-----------------+-------------+-------------+