The deadline applies to all future and pending / I/O, not just the immediately following call to read or / Write. After a deadline has been exceeded, the connection / can be refreshed by setting a deadline in the future. An idle timeout can be implemented by repeatedly extending / the deadline after successful read or Write calls. a zero value for t means I/O operations will not time out. Time ) error / SetReadDeadline sets the deadline for future read calls / and any currently-blocked read call. a zero value for t means read will not time out.
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read can be made to time out and return an Error with Timeout true / after a fixed time limit; see setDeadline and SetReadDeadline. Read(b byte ) (n int, err error ) / Write writes data to the connection. Write can be made to time out and return an Error with Timeout true / after a fixed time limit; see setDeadline and SetWritedeadline. Write(b byte ) (n int, err error ) / Close closes the connection. Any blocked read or measles Write operations will be unblocked and return errors. Close error / LocalAddr returns the local network address. LocalAddr Addr / RemoteAddr returns the remote network address. RemoteAddr Addr / SetDeadline sets the read and write deadlines associated / with the connection. It is equivalent to calling both / SetReadDeadline essay and SetWritedeadline. A deadline is an absolute time after which I/O operations / fail with a timeout (see type Error) instead of / blocking.
The two methods Network and String conventionally return strings that can be passed as the arguments to dial, but the exact form and meaning of the strings is up to the implementation. Type Addr interface network string / name of the network (for example, "tcp "udp String string / string form of address (for example, 25 "2001:db8:1:80 type AddrError struct Err string Addr string func AddrError) Error func (e * AddrError ) Error string func AddrError) Temporary. On certain machines, for certain types of connections, this is optimized into an os-specific batch write operation (such slave as "writev. Type buffers byte func buffers) read func (v * Buffers ) read(p byte ) (n int, err error ) func buffers) Writeto func (v * Buffers ) WriteTo(w. Writer ) (n int64, err error ) Conn is a generic stream-oriented network connection. Multiple goroutines may invoke methods on a conn simultaneously. Type conn interface / read reads data from the connection.
That is, it looks up _me. To accommodate services publishing srv records under non-standard names, if both service and proto are empty strings, lookupsrv looks up name directly. Func lookupTXT(name string ) rehabilitation ( string, error ) lookuptxt returns the dns txt records for the given domain name. Func SplitHostPort(hostport string ) (host, port string, err error ) SplitHostPort splits a network address of the form "host:port "hostzone:port "host:port" or "hostzone:port" into host or hostzone and port. A literal ipv6 address in hostport must be enclosed in square brackets, as in 1:80 1lo0:80". See func dial for a description of the hostport parameter, and host and port results. Addr represents a network end point address.
Func lookupIP(host string ) ( ip, error ) lookupIP looks up host using the local resolver. It returns a slice of that host's ipv4 and ipv6 addresses. Func lookupMX(name string ) mx, error ) lookupMX returns the dns mx records for the given domain name sorted by preference. Func lookupNS(name string ) ns, error ) lookupNS returns the dns ns records for the given domain name. Func lookupPort(network, service string ) (port int, err error ) lookupPort looks up the port for the given network and service. Func lookupSRV(service, proto, name string ) (cname string, addrs * srv, err error ) lookupsrv tries to resolve an srv query of the given service, protocol, and domain name. The proto is "tcp" or "udp". The returned records are sorted by priority and randomized by weight within a priority. Lookupsrv constructs the dns name to look up following rfc 2782.
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Func joinHostPort(host, port string ) string joinHostPort combines host gates and port into a network address of the form "host:port". If host contains a colon, as found in literal ipv6 addresses, then joinHostPort returns "host:port". See func dial for a description of the host and port parameters. Func lookupAddr(addr string ) (names string, err error ) lookupAddr performs a reverse lookup for the given address, returning a list of names mapping to that address. When using the host C library resolver, at most one result will be returned. To bypass the host resolver, use a custom Resolver. Func lookupcname(host string ) (cname string, err error ) lookupcname returns the canonical name for the given host.
Callers that do not all care about the canonical name can call lookupHost or lookupIP directly; both take care of resolving the canonical name as part of the lookup. A canonical name is the final name after following zero or more cname records. Lookupcname does not return an error if host does not contain dns "cname" records, as long as host resolves to address records. Func lookupHost(host string ) (addrs string, err error ) lookupHost looks up the given host using the local resolver. It returns a slice of that host's addresses.
Godebug environment variable (see package runtime) to go or cgo, as in: export godebugnetdnsgo # force pure go resolver export godebugnetdnscgo # force cgo resolver. The decision can also be forced while building the go source tree by setting the netgo or netcgo build tag. A numeric netdns setting, as in godebugnetdns1, causes the resolver to print debugging information about its decisions. To force a particular resolver while also printing debugging information, join the two settings by a plus sign, as in godebugnetdnsgo1. On Plan 9, the resolver always accesses /net/cs and /net/dns. On Windows, the resolver always uses C library functions, such as GetAddrInfo and DnsQuery.
Index constants ip address lengths (bytes). Const ( ipv4len 4 ipv6len 16 ) Variables Well-known ipv4 addresses var ( ipv4bcast ipv4 (255, 255, 255, 255) / limited broadcast ipv4allsys ipv4 (224, 0, 0, 1) / all systems ipv4allrouter ipv4 (224, 0, 0, 2) / all routers ipv4zero ipv4 (0, 0,. Var DefaultResolver resolver various errors contained in OpError. Var ( ErrWritetoconnected errors. New use of Writeto with pre-connected connection ) func InterfaceAddrs ( Addr, error ) InterfaceAddrs returns a list of the system's unicast interface addresses. The returned list does not identify the associated interface; use Interfaces and drs for more detail. Func Interfaces ( Interface, error ) Interfaces returns a list of the system's network interfaces.
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Name resolution, the method for resolving domain names, whether indirectly with functions like dial or directly with functions like lookupHost and lookupAddr, varies by operating system. On Unix systems, the resolver has essay two options for resolving names. It can use a listing pure go resolver that sends dns requests directly to the servers listed in /etc/nf, or it can use a cgo-based resolver that calls C library routines such as getaddrinfo and getnameinfo. By default the pure go resolver is used, because a blocked dns request consumes only a goroutine, while a blocked C call consumes an operating system thread. When cgo is available, the cgo-based resolver is used instead under a variety of conditions: on systems that do not let programs make direct dns requests (os x when the localdomain environment variable is present (even if empty when the res_options or hostaliases environment variable. Go resolver does not implement, and when the name being looked up ends. Local or is an mdns name. The resolver decision can be overridden by setting the netdns value of the.
The crypto/tls package uses the same interfaces and similar dial and Listen functions. The dial function connects to a server: conn, err : net. Nil / handle error fmt. Fprintf(conn, "get / http/1.0rnrn status, err : adString n /. The listen function creates servers: assignment ln, err : sten tcp 8080 if err! Nil / handle error for conn, err : cept if err! Nil / handle error go handleConnection(conn).
information it wants about the error. Two common error handlers are bug, which gives you a lua prompt so that you can inspect by yourself what was going on when the error happened (later we will see more about that, when we discuss the debug library and aceback, which builds. The latter is the function that the stand-alone interpreter uses to build its error messages. You also can call aceback at any moment to get a traceback of the current execution: print(aceback). Overview, overview, package net provides a portable interface for network I/o, including. Tcp/ip, udp, domain name resolution, and Unix domain sockets. Although the package provides access to low-level networking primitives, most clients will need only the basic interface provided by the dial, listen, and Accept functions and the associated. Conn and Listener interfaces.
The error aide function has an additional second parameter, which gives the level where it should report the error; with it, you can blame someone else for the error. For instance, suppose you write a function and its first task is to check whether it was called correctly: function foo (str) if type(str) "string" then error string expected end. End Then, someone calls your function with a wrong argument: foo(x1) lua points its finger to your function-after all, it was foo that called error-and not to the real culprit, the caller. To correct that, you inform error that the error you are reporting occurred on level 2 in the calling hierarchy (level 1 is your own function function foo (str) if type(str) "string" then error string expected 2) end. Frequently, when an error happens, we want more debug information than only the location where the error occurred. At least, we want a traceback, showing the complete stack of calls leading to the error. When pcall returns its error message, it destroys part of the stack (the part that went from it to the error point). Consequently, if we want a traceback, we must build it before pcall returns. To do that, lua provides the xpcall function.
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Programming in lua :.5, this first edition was written for lua.0. While still largely relevant for later versions, there are some differences. The fourth edition targets lua.3 and is available. Amazon and other bookstores. By buying the book, you also help to support the lua project. Although you can use a value of any type as an error message, usually error messages are strings describing what went wrong. When resume there is an internal error (such as an attempt to index a non-table value lua generates the error message; otherwise, the error message is the value passed to the error function. In any case, lua tries to add some information about the location where the error happened: local status, err pcall(function a 'a'1 end) print(err) - stdin:1: attempt to perform arithmetic on a string value local status, err pcall(function error my error end) print(err) - stdin:1.