https://github.com/alecthomas/replaylog

A type safe implementation of an op replay log
https://github.com/alecthomas/replaylog

Last synced: over 1 year ago
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A type safe implementation of an op replay log

• Host: GitHub
• URL: https://github.com/alecthomas/replaylog
• Owner: alecthomas
• License: apache-2.0
• Created: 2022-04-08T11:13:17.000Z (over 4 years ago)
• Default Branch: master
• Last Pushed: 2024-01-01T08:41:44.000Z (over 2 years ago)
• Last Synced: 2025-03-26T01:36:21.897Z (over 1 year ago)
• Language: Go
• Size: 11.7 KB
• Stars: 3
• Watchers: 2
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Funding: .github/FUNDING.yml
  • License: COPYING

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README

          
# A type safe implementation of a replay log for Go

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A [replay log](https://ahmet.im/blog/the-replay-pattern/)

([related](https://engineering.linkedin.com/distributed-systems/log-what-every-software-engineer-should-know-about-real-time-datas-unifying))

records the sequence of operations for mutating an empty

state to its final state. The previous final state can then be reconstructed

from the log by starting with an empty state, reading each operation

from the log, and applying it to the state until the final state is reached.

The Log is not safe for concurrent use across processes.

## Example

A simple key-value store:

```go

type KV map[string]string

type Set struct {

    Key   string `json:"k"`

    Value string `json:"v"`

}

func (s *Set) Apply(kv KV) error {

    kv[s.Key] = s.Value

    return nil

}

type Delete struct {

    Key string `json:"k"`

}

func (d *Delete) Apply(state KV) error {

    delete(state, d.Key)

    return nil

}

func main() {

    ops := []Op[KV]{&Set{}, &Delete{}}

    w, err := ioutil.TempFile("", "")

    log, err := New[KV](w, ops...)

    err = log.Append(&Set{Key: "foo", Value: "bar"})

    err = log.Append(&Set{Key: "bar", Value: "waz"})

    err = log.Append(&Delete{Key: "foo"})

    state := KV{}

	

    err = log.Rewind()

    err = log.Replay(state)

    fmt.Printf("%#v\n", state)

}

```