95 lines
2.5 KiB
Markdown
95 lines
2.5 KiB
Markdown
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# structhash [](https://godoc.org/github.com/cnf/structhash) [](https://travis-ci.org/cnf/structhash)
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structhash is a Go library for generating hash strings of arbitrary data structures.
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## Features
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* fields may be ignored or renamed (like in `json.Marshal`, but using different struct tag)
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* fields may be versioned
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* fields order in struct doesn't matter (unlike `json.Marshal`)
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* nil values are treated equally to zero values
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## Installation
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Standard `go get`:
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```
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$ go get github.com/cnf/structhash
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```
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## Documentation
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For usage and examples see the [Godoc](http://godoc.org/github.com/cnf/structhash).
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## Quick start
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```go
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package main
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import (
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"fmt"
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"crypto/md5"
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"crypto/sha1"
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"github.com/cnf/structhash"
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)
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type S struct {
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Str string
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Num int
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}
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func main() {
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s := S{"hello", 123}
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hash, err := structhash.Hash(s, 1)
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if err != nil {
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panic(err)
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}
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fmt.Println(hash)
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// Prints: v1_41011bfa1a996db6d0b1075981f5aa8f
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fmt.Println(structhash.Version(hash))
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// Prints: 1
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fmt.Printf("%x\n", structhash.Md5(s, 1))
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// Prints: 41011bfa1a996db6d0b1075981f5aa8f
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fmt.Printf("%x\n", structhash.Sha1(s, 1))
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// Prints: 5ff72df7212ce8c55838fb3ec6ad0c019881a772
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fmt.Printf("%x\n", md5.Sum(structhash.Dump(s, 1)))
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// Prints: 41011bfa1a996db6d0b1075981f5aa8f
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fmt.Printf("%x\n", sha1.Sum(structhash.Dump(s, 1)))
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// Prints: 5ff72df7212ce8c55838fb3ec6ad0c019881a772
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}
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```
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## Struct tags
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structhash supports struct tags in the following forms:
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* `hash:"-"`, or
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* `hash:"name:{string} version:{number} lastversion:{number}"`
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All fields are optional and may be ommitted. Their semantics is:
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* `-` - ignore field
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* `name:{string}` - rename field (may be useful when you want to rename field but keep hashes unchanged for backward compatibility)
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* `version:{number}` - ignore field if version passed to structhash is smaller than given number
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* `lastversion:{number}` - ignore field if version passed to structhash is greater than given number
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Example:
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```go
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type MyStruct struct {
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Ignored string `hash:"-"`
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Renamed string `hash:"name:OldName version:1"`
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Legacy string `hash:"version:1 lastversion:2"`
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}
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```
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## Nil values
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When hash is calculated, nil pointers, nil slices, and nil maps are treated equally to zero values of corresponding type. E.g., nil pointer to string is equivalent to empty string, and nil slice is equivalent to empty slice.
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