build: move version-info into checksum file (#28324)

* build: upgrade to golang 1.21.2

* build: verify checksums via tool

* deps: upgrade go to 1.21.3

* build: move more build metadata into checksum file

* build: move gobootsrc to checksums

internal/build/gotool.go

@@ -84,7 +84,11 @@ func (g *GoToolchain) goTool(command string, args ...string) *exec.Cmd {
 
 // DownloadGo downloads the Go binary distribution and unpacks it into a temporary
 // directory. It returns the GOROOT of the unpacked toolchain.
-func DownloadGo(csdb *ChecksumDB, version string) string {
+func DownloadGo(csdb *ChecksumDB) string {
+	version, err := Version(csdb, "golang")
+	if err != nil {
+		log.Fatal(err)
+	}
 	// Shortcut: if the Go version that runs this script matches the
 	// requested version exactly, there is no need to download anything.
 	activeGo := strings.TrimPrefix(runtime.Version(), "go")
@@ -126,3 +130,52 @@ func DownloadGo(csdb *ChecksumDB, version string) string {
 	}
 	return goroot
 }
+
+// Version returns the versions defined in the checksumdb.
+func Version(csdb *ChecksumDB, version string) (string, error) {
+	for _, l := range csdb.allChecksums {
+		if !strings.HasPrefix(l, "# version:") {
+			continue
+		}
+		v := strings.Split(l, ":")[1]
+		parts := strings.Split(v, " ")
+		if len(parts) != 2 {
+			log.Print("Erroneous version-string", "v", l)
+			continue
+		}
+		if parts[0] == version {
+			log.Printf("Found version %q", parts[1])
+			return parts[1], nil
+		}
+	}
+	return "", fmt.Errorf("no version found for '%v'", version)
+}
+
+// DownloadAndVerifyChecksums downloads all files and checks that they match
+// the checksum given in checksums.txt.
+// This task can be used to sanity-check new checksums.
+func DownloadAndVerifyChecksums(csdb *ChecksumDB) {
+	var (
+		base   = ""
+		ucache = os.TempDir()
+	)
+	for _, l := range csdb.allChecksums {
+		if strings.HasPrefix(l, "# https://") {
+			base = l[2:]
+			continue
+		}
+		if strings.HasPrefix(l, "#") {
+			continue
+		}
+		hashFile := strings.Split(l, "  ")
+		if len(hashFile) != 2 {
+			continue
+		}
+		file := hashFile[1]
+		url := base + file
+		dst := filepath.Join(ucache, file)
+		if err := csdb.DownloadFile(url, dst); err != nil {
+			log.Print(err)
+		}
+	}
+}