Parsing Date in Go

I am writing a service in Go that takes a timetstamp passed in as a HTTP request parameter and parses it.

A sample call is GET /values?from=2015-02-11T15:01:00+00:00

An example of he value that is being passed into the function is 2015-02-11T15:01:00+00:00.

I am trying to parse it thus:

dateTime := request.URL.Query.Get("from")
layout := "2006-01-02T15:04:05Z07:00"
formattedTime, _ := time.Parse(layout, dateTime)

(I am using Go's layout numbers to to do this - more information here: https://golang.org/pkg/time/#pkg-constants)

However, the output from this is 0001-01-01 00:00:00 +0000 UTC.

I should also point out that when I do a fmt.Println(dateTime), I get 2015-02-11T15:01:00 00:00 (not 2015-02-11T15:01:00+00:00 as I might expect).

Also, when I hardcode a datetime into the function and parse it using time.Parse(layout, dateTime), it is parsed successfully and gives the output 2015-02-11 15:01:00 +000 GMT.

Does anyone know what might be happening here?

Thanks,

Sean

You should check returned errors. time.Parse() returns an error:

formattedTime, err := time.Parse(layout, dateTime)
if err != nil {
    fmt.Println(err)
}

Your error will lie in the '+' character in the URL query. The URL query uses URL encoding where the + sign is special: it is used to encode the space character. So when you do this:

dateTime := request.URL.Query.Get("from")

Your dateTime will contain the decoded value where + will be replaced by a space. Check it like:

fmt.Printf("%q\n", dateTime)

Output:

"2015-02-11T15:01:00 00:00"

And of course this is not a valid format for the layout you specified, which will give you the following error:

> parsing time "2015-02-11T15:01:00 00:00" as "2006-01-02T15:04:05Z07:00": cannot parse "" as "Z07:00"

You have to use %2B in the URL query which is the code for the + sign, and you also have to include the Z char which you used in your layout:

GET /values?from=2015-02-11T15:01:00Z%2B00:00

And also note that the layout has to contain the -07:00 reference time zone and not 07:00:

layout := "2006-01-02T15:04:05Z-07:00"

Then the output (formattedTime):

2015-02-11 15:01:00 +0000 UTC

Try it on the Go Playground:

If you must use + in the query...

If you must use the + query (as you claim in the comment), then working with the unescaped value would be tricky, as if time zone in query is +, it is replaced with space, but if the time zone is -, it is not!

One way is to work with the Raw query and not the decoded one. This is available in URL.RawQuery.

Here's a solution which assumes there is only 1 request parameter: "from=". It fails if there are other, please take that into account:

param := "from="
layout := "2006-01-02T15:04:05-07:00"
length := len(param) + len(layout)

if s := request.URL.RawQuery; len(s) < length || !strings.HasPrefix(s, param) {
     // unexpected query
}
dateTime := request.URL.RawQuery[len(param):length]
formattedTime, err := time.Parse(layout, dateTime)
if err != nil {
    // handle error
}

You need to use a minus before the time zone offset, so the layout should be: "2006-01-02T15:04:05-07:00"

https://golang.org/pkg/time/#pkg-constants:

Numeric time zone offsets format as follows:

-0700  ±hhmm
-07:00 ±hh:mm
-07    ±hh

example: http://play.golang.org/p/ZG979Meuxz

When you print it out, it uses the default format, not the one you used to parse it, because it calls the String method: https://golang.org/pkg/time/#Time.String

To format it using a custom format, use Format: https://golang.org/pkg/time/#Time.Format