How do I find all the constants in a package using go doc?

Question

I've wasted way too much time the past couple of days searching for constants like time.Second and http.StatusOK because they aren't mentioned in go doc time or go doc http respectively.

I specifically searched for a constant representing the duration 1 second by doing:

go doc time | grep Second

With no results, before reading through the entire doc page before concluding that the constant didn't exist. It was only after Googling around for about 15 minutes I happened to see time.Second mentioned somewhere, and when I looked it up directly (go doc time.Second) I found all the duration constants.

How are people supposed to find out about these constants when they're not even mentioned in the official documentation of the package? Am I missing something obvious?

Answer 1

Just run go doc with the flag -all to display the full documentation for a package including its constants:

Flags:
        -all
                Show all the documentation for the package.

Source: go help doc

You can then filter the output i.e. with sed to include only the constants.

Here are some constants from the http package:

$ go doc -all http | sed -n '/^const (/,/^)/p'
const (
        MethodGet     = "GET"
        MethodHead    = "HEAD"
        MethodPost    = "POST"
        MethodPut     = "PUT"
        MethodPatch   = "PATCH" // RFC 5789
        MethodDelete  = "DELETE"
        MethodConnect = "CONNECT"
        MethodOptions = "OPTIONS"
        MethodTrace   = "TRACE"
)
const (
        StatusContinue           = 100 // RFC 9110, 15.2.1
        StatusSwitchingProtocols = 101 // RFC 9110, 15.2.2
        StatusProcessing         = 102 // RFC 2518, 10.1
        StatusEarlyHints         = 103 // RFC 8297

        StatusOK                   = 200 // RFC 9110, 15.3.1
        StatusCreated              = 201 // RFC 9110, 15.3.2
        StatusAccepted             = 202 // RFC 9110, 15.3.3
...

The same for the time package:

$ go doc -all time | sed -n '/^const (/,/^)/p'
const (
        Layout      = "01/02 03:04:05PM '06 -0700" // The reference time, in numerical order.
        ANSIC       = "Mon Jan _2 15:04:05 2006"
        UnixDate    = "Mon Jan _2 15:04:05 MST 2006"
        RubyDate    = "Mon Jan 02 15:04:05 -0700 2006"
        RFC822      = "02 Jan 06 15:04 MST"
        RFC822Z     = "02 Jan 06 15:04 -0700" // RFC822 with numeric zone
        RFC850      = "Monday, 02-Jan-06 15:04:05 MST"
        RFC1123     = "Mon, 02 Jan 2006 15:04:05 MST"
        RFC1123Z    = "Mon, 02 Jan 2006 15:04:05 -0700" // RFC1123 with numeric zone
        RFC3339     = "2006-01-02T15:04:05Z07:00"
        RFC3339Nano = "2006-01-02T15:04:05.999999999Z07:00"
        Kitchen     = "3:04PM"
        // Handy time stamps.
        Stamp      = "Jan _2 15:04:05"
        StampMilli = "Jan _2 15:04:05.000"
        StampMicro = "Jan _2 15:04:05.000000"
        StampNano  = "Jan _2 15:04:05.000000000"
        DateTime   = "2006-01-02 15:04:05"
        DateOnly   = "2006-01-02"
        TimeOnly   = "15:04:05"
)
const (
        Nanosecond  Duration = 1
        Microsecond          = 1000 * Nanosecond
        Millisecond          = 1000 * Microsecond
        Second               = 1000 * Millisecond
        Minute               = 60 * Second
        Hour                 = 60 * Minute
)
const (
        January Month = 1 + iota
        February
        March
        April
        May
        June
        July
        August
        September
...

The online package documentation on https://pkg.go.dev/ includes "Constants" sections as well.

Answer 2

Sorry, took me some time to realize it. Actually, we're looking at a wrong command line tool. Use godoc time instead.

If you don't have it, you can install it as follows:

$ go get golang.org/x/tools/cmd/godoc
$ go build golang.org/x/tools/cmd/godoc

Then copy it to your path (or run from where it is).

Answer 3

Start with go doc time | grep 'const ':

$ go doc time | grep 'const '
const ANSIC = "Mon Jan _2 15:04:05 2006" ...
const Nanosecond Duration = 1 ...
    const January Month = 1 + iota ...
    const Sunday Weekday = iota ...
$

Then go doc time.Nanosecond:

$ go doc time.Nanosecond
const (
    Nanosecond  Duration = 1
    Microsecond          = 1000 * Nanosecond
    Millisecond          = 1000 * Microsecond
    Second               = 1000 * Millisecond
    Minute               = 60 * Second
    Hour                 = 60 * Minute
)
    Common durations. There is no definition for units of Day or larger to avoid
    confusion across daylight savings time zone transitions.

    To count the number of units in a Duration, divide:

    second := time.Second
    fmt.Print(int64(second/time.Millisecond)) // prints 1000

    To convert an integer number of units to a Duration, multiply:

    seconds := 10
    fmt.Print(time.Duration(seconds)*time.Second) // prints 10s

$ 

---

Start with go doc http | grep 'const ':

$ go doc http | grep 'const '
const MethodGet = "GET" ...
const StatusContinue = 100 ...
const DefaultMaxHeaderBytes = 1 << 20
const DefaultMaxIdleConnsPerHost = 2
const TimeFormat = "Mon, 02 Jan 2006 15:04:05 GMT"
const TrailerPrefix = "Trailer:"
    const StateNew ConnState = iota ...
$

Then go doc http.StatusContinue:

$ go doc http.StatusContinue

package http // import "net/http"

const (
    StatusContinue           = 100 // RFC 7231, 6.2.1
    StatusSwitchingProtocols = 101 // RFC 7231, 6.2.2
    StatusProcessing         = 102 // RFC 2518, 10.1

    StatusOK                   = 200 // RFC 7231, 6.3.1
    StatusCreated              = 201 // RFC 7231, 6.3.2
    StatusAccepted             = 202 // RFC 7231, 6.3.3
    StatusNonAuthoritativeInfo = 203 // RFC 7231, 6.3.4
    StatusNoContent            = 204 // RFC 7231, 6.3.5
    StatusResetContent         = 205 // RFC 7231, 6.3.6
    StatusPartialContent       = 206 // RFC 7233, 4.1
    StatusMultiStatus          = 207 // RFC 4918, 11.1
    StatusAlreadyReported      = 208 // RFC 5842, 7.1
    StatusIMUsed               = 226 // RFC 3229, 10.4.1

    StatusMultipleChoices  = 300 // RFC 7231, 6.4.1
    StatusMovedPermanently = 301 // RFC 7231, 6.4.2
    StatusFound            = 302 // RFC 7231, 6.4.3
    StatusSeeOther         = 303 // RFC 7231, 6.4.4
    StatusNotModified      = 304 // RFC 7232, 4.1
    StatusUseProxy         = 305 // RFC 7231, 6.4.5

    StatusTemporaryRedirect = 307 // RFC 7231, 6.4.7
    StatusPermanentRedirect = 308 // RFC 7538, 3

    StatusBadRequest                   = 400 // RFC 7231, 6.5.1
    StatusUnauthorized                 = 401 // RFC 7235, 3.1
    StatusPaymentRequired              = 402 // RFC 7231, 6.5.2
    StatusForbidden                    = 403 // RFC 7231, 6.5.3
    StatusNotFound                     = 404 // RFC 7231, 6.5.4
    StatusMethodNotAllowed             = 405 // RFC 7231, 6.5.5
    StatusNotAcceptable                = 406 // RFC 7231, 6.5.6
    StatusProxyAuthRequired            = 407 // RFC 7235, 3.2
    StatusRequestTimeout               = 408 // RFC 7231, 6.5.7
    StatusConflict                     = 409 // RFC 7231, 6.5.8
    StatusGone                         = 410 // RFC 7231, 6.5.9
    StatusLengthRequired               = 411 // RFC 7231, 6.5.10
    StatusPreconditionFailed           = 412 // RFC 7232, 4.2
    StatusRequestEntityTooLarge        = 413 // RFC 7231, 6.5.11
    StatusRequestURITooLong            = 414 // RFC 7231, 6.5.12
    StatusUnsupportedMediaType         = 415 // RFC 7231, 6.5.13
    StatusRequestedRangeNotSatisfiable = 416 // RFC 7233, 4.4
    StatusExpectationFailed            = 417 // RFC 7231, 6.5.14
    StatusTeapot                       = 418 // RFC 7168, 2.3.3
    StatusMisdirectedRequest           = 421 // RFC 7540, 9.1.2
    StatusUnprocessableEntity          = 422 // RFC 4918, 11.2
    StatusLocked                       = 423 // RFC 4918, 11.3
    StatusFailedDependency             = 424 // RFC 4918, 11.4
    StatusUpgradeRequired              = 426 // RFC 7231, 6.5.15
    StatusPreconditionRequired         = 428 // RFC 6585, 3
    StatusTooManyRequests              = 429 // RFC 6585, 4
    StatusRequestHeaderFieldsTooLarge  = 431 // RFC 6585, 5
    StatusUnavailableForLegalReasons   = 451 // RFC 7725, 3

    StatusInternalServerError           = 500 // RFC 7231, 6.6.1
    StatusNotImplemented                = 501 // RFC 7231, 6.6.2
    StatusBadGateway                    = 502 // RFC 7231, 6.6.3
    StatusServiceUnavailable            = 503 // RFC 7231, 6.6.4
    StatusGatewayTimeout                = 504 // RFC 7231, 6.6.5
    StatusHTTPVersionNotSupported       = 505 // RFC 7231, 6.6.6
    StatusVariantAlsoNegotiates         = 506 // RFC 2295, 8.1
    StatusInsufficientStorage           = 507 // RFC 4918, 11.5
    StatusLoopDetected                  = 508 // RFC 5842, 7.2
    StatusNotExtended                   = 510 // RFC 2774, 7
    StatusNetworkAuthenticationRequired = 511 // RFC 6585, 6
)
    HTTP status codes as registered with IANA. See:
    https://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml
$