latest.go

package main

import (
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"
	"time"
)

type PackageInfo struct {
	Version string    `json:"Version"`
	Time    time.Time `json:"Time"`
	Origin  struct {
		VCS  string `json:"VCS"`
		URL  string `json:"URL"`
		Ref  string `json:"Ref"`
		Hash string `json:"Hash"`
	} `json:"Origin"`
}

func GetLatestPackageVersion(name string) (*PackageInfo, error) {
	u, err := url.Parse(fmt.Sprintf("https://proxy.golang.org/%s/@latest", name))
	if err != nil {
		return nil, err
	}

	req, err := http.NewRequest(http.MethodGet, u.String(), nil)
	if err != nil {
		return nil, err
	}

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("bad status: %s", resp.Status)
	}

	var ret PackageInfo
	err = json.NewDecoder(resp.Body).Decode(&ret)
	if err != nil {
		return nil, err
	}
	return &ret, nil
}