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Implement HostProvider and connection options
- Added variadic options to zk.Connect - Initial implementation of HostProvider, and DNSHostProvider, the default HostProvider.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,87 @@ | ||
| package zk | ||
|
|
||
| import ( | ||
| "fmt" | ||
| "net" | ||
| "sync" | ||
| ) | ||
|
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||
| // DNSHostProvider is the default HostProvider. It currently matches | ||
| // the Java StaticHostProvider, resolving hosts from DNS once during | ||
| // the call to Init. It could be easily extended to re-query DNS | ||
| // periodically or if there is trouble connecting. | ||
| type DNSHostProvider struct { | ||
| mu sync.Mutex // Protects everything, so we can add asynchronous updates later. | ||
| servers []string | ||
| curr int | ||
| last int | ||
| lookupHost func(string) ([]string, error) // Override of net.LookupHost, for testing. | ||
| } | ||
|
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| // Init is called first, with the servers specified in the connection | ||
| // string. It uses DNS to look up addresses for each server, then | ||
| // shuffles them all together. | ||
| func (hp *DNSHostProvider) Init(servers []string) error { | ||
| hp.mu.Lock() | ||
| defer hp.mu.Unlock() | ||
|
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| lookupHost := hp.lookupHost | ||
| if lookupHost == nil { | ||
| lookupHost = net.LookupHost | ||
| } | ||
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| found := []string{} | ||
| for _, server := range servers { | ||
| host, port, err := net.SplitHostPort(server) | ||
| if err != nil { | ||
| return err | ||
| } | ||
| addrs, err := lookupHost(host) | ||
| if err != nil { | ||
| return err | ||
| } | ||
| for _, addr := range addrs { | ||
| found = append(found, net.JoinHostPort(addr, port)) | ||
| } | ||
| } | ||
|
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||
| if len(found) == 0 { | ||
| return fmt.Errorf("No hosts found for addresses %q", servers) | ||
| } | ||
|
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| // Randomize the order of the servers to avoid creating hotspots | ||
| stringShuffle(found) | ||
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| hp.servers = found | ||
| hp.curr = -1 | ||
| hp.last = -1 | ||
|
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| return nil | ||
| } | ||
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| func (hp *DNSHostProvider) Len() int { | ||
| hp.mu.Lock() | ||
| defer hp.mu.Unlock() | ||
| return len(hp.servers) | ||
| } | ||
|
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| // Next returns the next server to connect to. retryStart will be true | ||
| // if we've looped through all known servers without Connected() being | ||
| // called. | ||
| func (hp *DNSHostProvider) Next() (server string, retryStart bool) { | ||
| hp.mu.Lock() | ||
| defer hp.mu.Unlock() | ||
| hp.curr = (hp.curr + 1) % len(hp.servers) | ||
| retryStart = hp.curr == hp.last | ||
| if hp.last == -1 { | ||
| hp.last = 0 | ||
| } | ||
| return hp.servers[hp.curr], retryStart | ||
| } | ||
|
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| // Notify the HostProvider of a successful connection. | ||
| func (hp *DNSHostProvider) Connected() { | ||
| hp.mu.Lock() | ||
| defer hp.mu.Unlock() | ||
| hp.last = hp.curr | ||
| } |
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