gistfile1.go

package main

import (
    "fmt"
    "os"
    "io"
    "encoding/binary"
    "encoding/json"
    "compress/gzip"
)

type Device struct {
    Id uint `json:"id"`
    Device string `json:"device"`
    Ip string `json:"ip"`
    Meta string `json:"meta"`
    Port uint `json:"port"`
    Region uint `json:"region"`
    ReplicationIp string `json:"replication_ip"`
    ReplicationPort uint `json:"replication_port"`
    Weight float64 `json:"weight"`
    Zone uint `json:"zone"`
}

type Ring struct {
    Devs []Device `json:"devs"`
    ReplicaCount uint `json:"replica_count"`
    PartShift uint `json:"part_shift"`
    replica2part2dev_id [][]uint16
}

func (r Ring) GetPartitionNodes(partition uint) ([]Device) {
    var response []Device
    for i := uint(0); i < r.ReplicaCount ; i++ {
        response = append(response, r.Devs[r.replica2part2dev_id[i][partition]])
    }
    return response
}

func LoadRing(path string) (Ring) {
    fp, _ := os.Open(path)
    gz, _ := gzip.NewReader(fp)
    magic_buf := make([]byte, 4)
    io.ReadFull(gz, magic_buf)
    // TODO: assert magic_buf == "R1NG"
    var ring_version uint16
    binary.Read(gz, binary.BigEndian, &ring_version)
    // TODO: assert ring_version == 1
    var json_len uint32
    binary.Read(gz, binary.BigEndian, &json_len)
    json_buf := make([]byte, json_len)
    io.ReadFull(gz, json_buf)
    var ring Ring
    json.Unmarshal(json_buf, &ring)
    partition_count := 1 << (32 - ring.PartShift)
    for i := uint(0); i < ring.ReplicaCount; i++ {
        part2dev := make([]uint16, partition_count)
        binary.Read(gz, binary.LittleEndian, &part2dev)
        ring.replica2part2dev_id = append(ring.replica2part2dev_id, part2dev)
    }
    return ring
}

func main() {
    ring := LoadRing("/etc/swift/object.ring.gz")
    fmt.Println(ring.GetPartitionNodes(25))
}