rtu_linux_modules/vendor/github.com/beevik/ntp/README.md

ntp

The ntp package is an implementation of a Simple NTP (SNTP) client based on RFC 5905. It allows you to connect to a remote NTP server and request information about the current time.

Querying the current time

If all you care about is the current time according to a remote NTP server, simply use the Time function:

time, err := ntp.Time("0.beevik-ntp.pool.ntp.org")

Querying time synchronization data

To obtain the current time as well as some additional synchronization data, use the Query function:

response, err := ntp.Query("0.beevik-ntp.pool.ntp.org")
time := time.Now().Add(response.ClockOffset)

The Response structure returned by Query includes the following information:

• ClockOffset: The estimated offset of the local system clock relative to the server's clock. For a more accurate time reading, you may add this offset to any subsequent system clock reading.
• Time: The time the server transmitted its response, according to its own clock.
• RTT: An estimate of the round-trip-time delay between the client and the server.
• Precision: The precision of the server's clock reading.
• Stratum: The server's stratum, which indicates the number of hops from the server to the reference clock. A stratum 1 server is directly attached to the reference clock. If the stratum is zero, the server has responded with the "kiss of death" and you should examine the KissCode.
• ReferenceID: A unique identifier for the consulted reference clock.
• ReferenceTime: The time at which the server last updated its local clock setting.
• RootDelay: The server's aggregate round-trip-time delay to the stratum 1 server.
• RootDispersion: The server's estimated maximum measurement error relative to the reference clock.
• RootDistance: An estimate of the root synchronization distance between the client and the stratum 1 server.
• Leap: The leap second indicator, indicating whether a second should be added to or removed from the current month's last minute.
• MinError: A lower bound on the clock error between the client and the server.
• KissCode: A 4-character string describing the reason for a "kiss of death" response (stratum=0).
• Poll: The maximum polling interval between successive messages to the server.

The Response structure's Validate function performs additional sanity checks to determine whether the response is suitable for time synchronization purposes.

err := response.Validate()
if err == nil {
    // response data is suitable for synchronization purposes
}

If you wish to customize the behavior of the NTP query, use the QueryWithOptions function:

options := ntp.QueryOptions{ Timeout: 30*time.Second, TTL: 5 }
response, err := ntp.QueryWithOptions("0.beevik-ntp.pool.ntp.org", options)
time := time.Now().Add(response.ClockOffset)

Configurable QueryOptions include:

• Timeout: How long to wait before giving up on a response from the NTP server.
• Version: Which version of the NTP protocol to use (2, 3 or 4).
• TTL: The maximum number of IP hops before the request packet is discarded.
• LocalAddress: The local IP address to use when sending the query. Useful when the host has multiple network interfaces.
• Auth: The symmetric authentication key and algorithm used by the server to authenticate the query. The same information is used by the client to authenticate the server's response.
• Extensions: Extensions may be added to modify NTP queries before they are transmitted and to process NTP responses after they arrive.
• GetSystemTime: A custom function to obtain the current system time, used to override the default time.Now function.
• Dialer: A custom network connection "dialer" function used to override the default UDP dialer function.

Using the NTP pool

The NTP pool is a shared resource provided by the NTP Pool Project and used by people and services all over the world. To prevent it from becoming overloaded, please avoid querying the standard pool.ntp.org zone names in your applications. Instead, consider requesting your own vendor zone or joining the pool.

Network Time Security (NTS)

Network Time Security (NTS) is a recent enhancement of NTP, designed to add better authentication and message integrity to the protocol. It is defined by RFC 8915. If you wish to use NTS, see the nts package. (The nts package is implemented as an extension to this package.)