Golang regular expression for parsing key value pair into a string map

I'm looking to parse the following string into a map[string]string using a regular expression:

time="2017-05-30T19:02:08-05:00" level=info msg="some log message" app=sample size=10

I'm trying to create a map that would have

m["time"] = "2017-05-30T19:02:08-05:00"
m["level"] = "info"

etc

I have tried using regex.FindAllStringIndex but can't quite come up with an appropriate regex? Is this the correct way to go?

This is not using regex but is just an example of how to achieve the same by using strings.FieldsFunc.

https://play.golang.org/p/rr6U8xTJZT

package main

import (
	"fmt"
	"strings"
	"unicode"
)

const foo = `time="2017-05-30T19:02:08-05:00" level=info msg="some log message" app=sample size=10`

func main() {
	lastQuote := rune(0)
	f := func(c rune) bool {
		switch {
		case c == lastQuote:
			lastQuote = rune(0)
			return false
		case lastQuote != rune(0):
			return false
		case unicode.In(c, unicode.Quotation_Mark):
			lastQuote = c
			return false
		default:
			return unicode.IsSpace(c)

		}
	}

	// splitting string by space but considering quoted section
	items := strings.FieldsFunc(foo, f)

	// create and fill the map
	m := make(map[string]string)
	for _, item := range items {
		x := strings.Split(item, "=")
		m[x[0]] = x[1]
	}

	// print the map
	for k, v := range m {
		fmt.Printf("%s: %s\n", k, v)
	}
}

Instead of writing regex of your own, you could simply use the github.com/kr/logfmt package.

> Package implements the decoding of logfmt key-value pairs.
>
> Example logfmt message:
>
> foo=bar a=14 baz="hello kitty" cool%story=bro f %^asdf
>
> Example result in JSON:
>
> {
> "foo": "bar",
> "a": 14,
> "baz": "hello kitty",
> "cool%story": "bro",
> "f": true,
> "%^asdf": true
> }

Use named capturing groups in your regular expression and the FindStringSubmatch and SubexpNames functions. E.g.:

s := `time="2017-05-30T19:02:08-05:00" level=info msg="some log message" app=sample size=10`
re := regexp.MustCompile(`time="(?P<time>.*?)"\slevel=(?P<level>.*?)\s`)
values := re.FindStringSubmatch(s)
keys := re.SubexpNames()

// create map
d := make(map[string]string)
for i := 1; i < len(keys); i++ {
	d[keys[i]] = values[i]
}
fmt.Println(d)
// OUTPUT: map[time:2017-05-30T19:02:08-05:00 level:info]

values is a list containing all submatches. The first submatch is the whole expression that matches the regexp, followed by a submatch for each capturing group.

You can wrap the code into a function if you need this more frequently (i.e. if you need something like pythons match.groupdict):

package main

import (
    "fmt"
	"regexp"
)

func groupmap(s string, r *regexp.Regexp) map[string]string {
    values := r.FindStringSubmatch(s)
    keys := r.SubexpNames()

	// create map
    d := make(map[string]string)
    for i := 1; i < len(keys); i++ {
    	d[keys[i]] = values[i]
    }

    return d
}

func main() {
    s := `time="2017-05-30T19:02:08-05:00" level=info msg="some log message" app=sample size=10`
    re := regexp.MustCompile(`time="(?P<time>.*?)"\slevel=(?P<level>.*?)\s`)

    fmt.Println(groupmap(s, re))
    // OUTPUT: map[time:2017-05-30T19:02:08-05:00 level:info]
}