label matchers in labels API actually not work

[cssivision]

I am using thanos 0.22.0 in work, using the prometheus api /api/v1/label/<label_name>/values query label values, but thanos query always return all label values no matter what i set the match[] field, source code below.

package main

import (
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"time"
)

func main() {
	q := url.Values{
		"match[]": []string{`kube_node_labels{cluster="cluster1"}`},
		"start":   []string{fmt.Sprintf("%d", time.Now().Add(time.Hour*-1).Unix())},
		"end":     []string{fmt.Sprintf("%d", time.Now().Unix())},
	}
	fmt.Println(`http://127.0.0.1:8080/api/v1/label/node/values` + "?" + q.Encode())
	req, err := http.NewRequest(http.MethodPost, `http://127.0.0.1:8080/api/v1/label/node/values`+"?"+q.Encode(), nil)
	if err != nil {
		panic(err)
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer resp.Body.Close()
	io.Copy(os.Stdout, resp.Body)
}

after spending sometime digging into the source code.

according to this PR，we can use matcher to select the label values. the implementation use http.Request.From to get field match[] without calling ParseForm. http.Request.From only available after ParseForm is called. which meaning the r.Form always be empty map.

type Request struct {
        // Form contains the parsed form data, including both the URL
	// field's query parameters and the PATCH, POST, or PUT form data.
	// This field is `only available after ParseForm is called`.
	// The HTTP client ignores Form and uses Body instead.
	Form url.Values
}

maybe we can just call ParseFrom before get match[] to fix it.

[yeya24]

Umm, I just tested this and it is working well in my environment.

For the code you mentioned, during https://github.com/thanos-io/thanos/blob/main/pkg/api/query/v1.go#L516, when we parse time params https://github.com/thanos-io/thanos/blob/main/pkg/api/query/v1.go#L938, we will call r.FormValue so the form should be parsed anyway.

I will close this issue as this is not a bug. Please check out your code and environment.