cmd/go/internal/modfetch: cache latest revinfo in Versions func

The responses have been cached by the web2 package before removed
it in CL 170879. This change add latest revinfo cache in Versions
func.

Fixes #51391

Change-Id: I73597e0a6b4938238e69d85e1cbbaa9007776db3
Reviewed-on: https://go-review.googlesource.com/c/go/+/403335
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Lee Baokun <bk@golangcn.org>
Reviewed-by: David Chase <drchase@google.com>

diff --git a/src/cmd/go/internal/modfetch/proxy.go b/src/cmd/go/internal/modfetch/proxy.go
index 4d63dd56487d068e298c82a92a10f568fb4a84da..2491b7d1852b7b7bb556ae31e659cce9c4ac8519 100644 (file)
--- a/src/cmd/go/internal/modfetch/proxy.go
+++ b/src/cmd/go/internal/modfetch/proxy.go
@@ -187,6 +187,10 @@ type proxyRepo struct {
        url         *url.URL
        path        string
        redactedURL string
+
+       listLatestOnce sync.Once
+       listLatest     *RevInfo
+       listLatestErr  error
 }
 
 func newProxyRepo(baseURL, path string) (Repo, error) {
@@ -214,7 +218,7 @@ func newProxyRepo(baseURL, path string) (Repo, error) {
        redactedURL := base.Redacted()
        base.Path = strings.TrimSuffix(base.Path, "/") + "/" + enc
        base.RawPath = strings.TrimSuffix(base.RawPath, "/") + "/" + pathEscape(enc)
-       return &proxyRepo{base, path, redactedURL}, nil
+       return &proxyRepo{base, path, redactedURL, sync.Once{}, nil, nil}, nil
 }
 
 func (p *proxyRepo) ModulePath() string {
@@ -278,32 +282,46 @@ func (p *proxyRepo) getBody(path string) (r io.ReadCloser, err error) {
 func (p *proxyRepo) Versions(prefix string) ([]string, error) {
        data, err := p.getBytes("@v/list")
        if err != nil {
+               p.listLatestOnce.Do(func() {
+                       p.listLatest, p.listLatestErr = nil, p.versionError("", err)
+               })
                return nil, p.versionError("", err)
        }
        var list []string
-       for _, line := range strings.Split(string(data), "\n") {
+       allLine := strings.Split(string(data), "\n")
+       for _, line := range allLine {
                f := strings.Fields(line)
                if len(f) >= 1 && semver.IsValid(f[0]) && strings.HasPrefix(f[0], prefix) && !module.IsPseudoVersion(f[0]) {
                        list = append(list, f[0])
                }
        }
+       p.listLatestOnce.Do(func() {
+               p.listLatest, p.listLatestErr = p.latestFromList(allLine)
+       })
        semver.Sort(list)
        return list, nil
 }
 
 func (p *proxyRepo) latest() (*RevInfo, error) {
-       data, err := p.getBytes("@v/list")
-       if err != nil {
-               return nil, p.versionError("", err)
-       }
+       p.listLatestOnce.Do(func() {
+               data, err := p.getBytes("@v/list")
+               if err != nil {
+                       p.listLatestErr = p.versionError("", err)
+                       return
+               }
+               list := strings.Split(string(data), "\n")
+               p.listLatest, p.listLatestErr = p.latestFromList(list)
+       })
+       return p.listLatest, p.listLatestErr
+}
 
+func (p *proxyRepo) latestFromList(allLine []string) (*RevInfo, error) {
        var (
                bestTime             time.Time
                bestTimeIsFromPseudo bool
                bestVersion          string
        )
-
-       for _, line := range strings.Split(string(data), "\n") {
+       for _, line := range allLine {
                f := strings.Fields(line)
                if len(f) >= 1 && semver.IsValid(f[0]) {
                        // If the proxy includes timestamps, prefer the timestamp it reports.