hashstructure

README

hashstructure

a go library for creating a unique hash value for arbitrary values

This can be used to key values in a hash (for use in a map, set, etc.) that are complex. The most common use case is comparing two values without sending data across the network, caching values locally (de-dup), etc.

Features

• Hash any arbitrary Go value, including complex types.

• Tag a struct field to ignore it and not affect the hash value.

• Tag a slice type struct field to treat it as a set where ordering doesn't affect the hash code but the field itself is still taken into account to create the hash value.

• Optionally, specify a custom hash function to optimize for speed, collision avoidance for your data set, etc.

• Optionally, hash the output of .String() on structs that implement fmt.Stringer, allowing effective hashing of time.Time

• Optionally, override the hashing process with a hash field or by implementing hashstructure.Hashable.

Installation

go get -u github.com/gofunky/hashstructure

Example

package hashstructure

import (
	"fmt"
)

func ExampleHash() {
	type ComplexStruct struct {
		Name     string
		Age      uint
		Metadata map[string]interface{}
	}

	v := ComplexStruct{
		Name: "gofunky",
		Age:  64,
		Metadata: map[string]interface{}{
			"car":      true,
			"location": "California",
			"siblings": []string{"Bob", "John"},
		},
	}

	hash, err := Hash(v, nil)
	if err != nil {
		panic(err)
	}

	fmt.Printf("%d", hash)
	// Output:
	// 12836943650294093551
}

Documentation

Index

• func Hash(v interface{}, opts *HashOptions) (uint64, error)
• type ErrNotStringer
  • func (ens *ErrNotStringer) Error() string
• type HashOptions
• type Hashable
• type Includable
• type IncludableMap

Examples

• Hash

Functions

func Hash

func Hash(v interface{}, opts *HashOptions) (uint64, error)

Hash returns the hash value of an arbitrary value.

If opts is nil, then default options will be used. See HashOptions for the default values. The same *HashOptions value cannot be used concurrently. None of the values within a *HashOptions struct are safe to read/write while hashing is being done.

Notes on the value:

• Unexported fields on structs are ignored and do not affect the hash value.

• Adding an exported field to a struct with the zero value will change the hash value.

• Adding an unexported `hash` field or a `Hash()` function will override the hash generation.

For structs, the hashing can be controlled using tags. For example:

struct {
    Name string
    UUID string `hash:"ignore"`
}

The available tag values are:

• "ignore" or "-" - The field will be ignored and not affect the hash code.

• "set" - The field will be treated as a set, where ordering doesn't affect the hash code. This only works for slices.

• "string" - The field will be hashed as a string, only works when the field implements fmt.Stringer

Example

type ComplexStruct struct {
	Name     string
	Age      uint
	Metadata map[string]interface{}
}

v := ComplexStruct{
	Name: "gofunky",
	Age:  64,
	Metadata: map[string]interface{}{
		"car":      true,
		"location": "California",
		"siblings": []string{"Bob", "John"},
	},
}

hash, err := Hash(v, nil)
if err != nil {
	panic(err)
}

fmt.Printf("%d", hash)

Output:

12836943650294093551

Types

type ErrNotStringer

type ErrNotStringer struct {
	Field string
}

ErrNotStringer is returned when there's an error with hash:"string"

func (*ErrNotStringer) Error

func (ens *ErrNotStringer) Error() string

Error implements error for ErrNotStringer

type HashOptions

type HashOptions struct {
	// Hasher is the hash function to use. If this isn't set, it will
	// default to FNV.
	Hasher hash.Hash64

	// TagName is the struct tag to look at when hashing the structure.
	// By default this is "hash".
	TagName string

	// ZeroNil is flag determining if nil pointer should be treated equal
	// to a zero value of pointed type. By default this is false.
	ZeroNil bool
}

HashOptions are options that are available for hashing.

type Hashable

type Hashable interface {
	Hash() uint64
}

Hashable is an interface that can optionally be implemented by a struct to override the hash generation.

type Includable

type Includable interface {
	HashInclude(field string, v interface{}) (bool, error)
}

Includable is an interface that can optionally be implemented by a struct. It will be called for each field in the struct to check whether it should be included in the hash.

type IncludableMap

type IncludableMap interface {
	HashIncludeMap(field string, k, v interface{}) (bool, error)
}

IncludableMap is an interface that can optionally be implemented by a struct. It will be called when a map-type field is found to ask the struct if the map item should be included in the hash.