Find new versions by parsing json

cmd/builder-bumper/main.go

@@ -16,6 +16,7 @@ package main
 
 import (
 	"bufio"
+	"encoding/json"
 	"flag"
 	"fmt"
 	"io"
@@ -46,6 +47,10 @@ type goVersion struct {
 	minor int
 }
 
+type VersionInfo struct {
+	Version string `json:"version"`
+}
+
 func newGoVersion(v string) *goVersion {
 	c := semver.Canonical("v" + v)
 	if c == "" {
@@ -101,6 +106,47 @@ func (g *goVersion) url() string {
 	return fmt.Sprintf("https://dl.google.com/go/go%s.linux-amd64.tar.gz", g.golangVersion())
 }
 
+func fetchJSON(url string) ([]byte, error) {
+	resp, err := http.Get(url)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("unexpected status code: %d", resp.StatusCode)
+	}
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	return body, nil
+}
+
+func availableVersions() []goVersion {
+
+	const url = "https://go.dev/dl/?mode=json"
+
+	jsonData, err := fetchJSON(url)
+	if err != nil {
+		fmt.Println("Error fetching JSON:", err)
+	}
+
+	var availableVersionsJSON []VersionInfo
+	var availableVersions []goVersion
+	if err := json.Unmarshal(jsonData, &availableVersionsJSON); err != nil {
+		fmt.Println("Error parsing JSON:", err)
+	}
+	for i := range availableVersionsJSON {
+		// remove "go" from a string like "go1.22.0"
+		newGoVersion := newGoVersion(strings.TrimLeft("go", availableVersionsJSON[i].Version))
+		availableVersions = append(availableVersions, *newGoVersion)
+	}
+	return availableVersions
+}
+
 // getSHA256 returns the SHA256 of the Go archive.
 func (g *goVersion) getSHA256() (string, error) {
 	resp, err := http.Get(g.url() + ".sha256")
@@ -116,40 +162,34 @@ func (g *goVersion) getSHA256() (string, error) {
 }
 
 // getLastMinorVersion returns the last minor version for a given Go version.
-func (g *goVersion) getLastMinorVersion() (*goVersion, error) {
+// if no new minor version available, it will return the given Go version back.
+func (g *goVersion) getLastMinorVersion(availableVersions []goVersion) *goVersion {
 	last := *g
-	for {
-		next := last
+	next := last
+	// let's check max 40 minor revisions for now before giving up
+	for next.minor < 40 {
 		next.minor++
-		resp, err := http.Head(next.url())
-		if err != nil {
-			return nil, err
-		}
-		defer resp.Body.Close()
-
-		if resp.StatusCode/100 != 2 {
-			return &last, nil
+		for _, availableVersion := range availableVersions {
+			if next == availableVersion {
+				return &next
+			}
 		}
-		last = next
 	}
+	return &last
 }
 
 // getNextMajor returns the next Go major version for a given Go version.
 // It returns nil if the current version is already the latest.
-func (g *goVersion) getNextMajor() *goVersion {
+func (g *goVersion) getNextMajor(availableVersions []goVersion) *goVersion {
 	version := newGoVersion(g.Major() + ".0")
 	version.major++
 
-	resp, err := http.Head(version.url())
-	if err != nil {
-		return nil
-	}
-	defer resp.Body.Close()
-	if resp.StatusCode/100 != 2 {
-		return nil
+	for _, availableVersion := range availableVersions {
+		if version.major == availableVersion.major {
+			return version
+		}
 	}
-
-	return version
+	return nil
 }
 
 // getExactVersionFromDir reads the current Go version from a directory.
@@ -301,10 +341,8 @@ func updateNextMinor(dir string) (*goVersion, error) {
 		return nil, fmt.Errorf("failed to detect current version of %s: %w", dir, err)
 	}
 
-	next, err := current.getLastMinorVersion()
-	if err != nil {
-		return nil, err
-	}
+	next := current.getLastMinorVersion(availableVersions())
+
 	if next.equal(current) {
 		log.Printf("no version change for Go %s", next.golangVersion())
 		return nil, nil
@@ -374,9 +412,12 @@ func run() error {
 		return fmt.Errorf("Expected 2 versions of Go but got %d\n", len(dirs))
 	}
 
+	// Get list of available versions
+	availableVersions := availableVersions()
+
 	// Check if a new major Go version exists.
 	nexts := make([]*goVersion, 0)
-	if next := newGoVersion(dirs[1] + ".0").getNextMajor(); next != nil {
+	if next := newGoVersion(dirs[1] + ".0").getNextMajor(availableVersions); next != nil {
 		log.Printf("found a new major version of Go: %s", next)
 		old, err := getExactVersionFromDir(dirs[0])
 		if err != nil {