util: Add simple distro release version function

This helps us determine the latest version automatically as a user
convenience.

util/distro.go

@@ -0,0 +1,112 @@
+// Mgmt
+// Copyright (C) 2013-2024+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+package util
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"strconv"
+)
+
+const (
+	// FedoraReleasesEndpointJSON is the location of the fedora release data
+	// as specified in json format.
+	FedoraReleasesEndpointJSON = "https://fedoraproject.org/releases.json"
+)
+
+// FedoraRelease is a partial struct of the available data in the json releases
+// file found. This was determined by inspection.
+type FedoraRelease struct {
+	Version string `json:"version"`
+	Arch    string `json:"arch"`
+	Variant string `json:"variant"`
+}
+
+// LatestFedoraVersion returns the version number (as a string) of the latest
+// fedora release known. This looks at a well-known endpoint to get the value.
+// If you specify a non-empty arch, it will filter to that.
+func LatestFedoraVersion(ctx context.Context, arch string) (string, error) {
+	client := &http.Client{}
+
+	req, err := http.NewRequestWithContext(ctx, "GET", FedoraReleasesEndpointJSON, nil)
+	if err != nil {
+		return "", err
+	}
+
+	res, err := client.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer res.Body.Close()
+
+	// XXX: We should stream decode this instead.
+	b, err := io.ReadAll(res.Body)
+	if err != nil {
+		return "", err
+	}
+
+	var data []FedoraRelease
+	if err := json.Unmarshal(b, &data); err != nil {
+		return "", err
+	}
+
+	//fmt.Printf("len: %d\n", len(data))
+	m := 0
+	for _, r := range data {
+		version, err := strconv.Atoi(r.Version)
+		if err != nil {
+			return "", err
+		}
+		if arch != "" && arch != r.Arch { // skip others
+			continue
+		}
+
+		m = max(m, version)
+	}
+	if m == 0 {
+		if arch == "" {
+			return "", fmt.Errorf("no versions found")
+		}
+		return "", fmt.Errorf("no versions found with arch: %s", arch)
+	}
+	//fmt.Printf("max: %d\n", m)
+	return strconv.Itoa(m), nil
+}
+
+// TODO: remove this once golang 1.21 is out and it's a built-in.
+func max(x, y int) int {
+	if x > y {
+		return x
+	}
+	return y
+}