feat: get pseudo-version from Go Proxy if no tagged version exists

pkg/versiongetter/go.go

@@ -22,11 +22,11 @@ func NewGoGetter(gc GoProxyClient) *GoGetter {
 }
 
 type GoProxyClient interface {
-	List(ctx context.Context, path string) ([]string, error)
+	List(ctx context.Context, logE *logrus.Entry, path string) ([]string, error)
 }
 
 func (g *GoGetter) Get(ctx context.Context, logE *logrus.Entry, pkg *registry.PackageInfo, _ []*Filter) (string, error) { //nolint:cyclop
-	versions, err := g.gc.List(ctx, pkg.GoVersionPath)
+	versions, err := g.gc.List(ctx, logE, pkg.GoVersionPath)
 	if err != nil {
 		return "", fmt.Errorf("list versions: %w", err)
 	}
@@ -57,7 +57,7 @@ func (g *GoGetter) Get(ctx context.Context, logE *logrus.Entry, pkg *registry.Pa
 }
 
 func (g *GoGetter) List(ctx context.Context, logE *logrus.Entry, pkg *registry.PackageInfo, _ []*Filter, _ int) ([]*fuzzyfinder.Item, error) {
-	vs, err := g.gc.List(ctx, pkg.GoVersionPath)
+	vs, err := g.gc.List(ctx, logE, pkg.GoVersionPath)
 	if err != nil {
 		return nil, fmt.Errorf("list versions: %w", err)
 	}

pkg/versiongetter/goproxy/client.go

@@ -2,12 +2,20 @@ package goproxy
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"io"
 	"net/http"
 	"strings"
+
+	"github.com/sirupsen/logrus"
+	"github.com/suzuki-shunsuke/logrus-error/logerr"
 )
 
+type InfoPayload struct {
+	Version string
+}
+
 type Client struct {
 	client *http.Client
 }
@@ -18,8 +26,41 @@ func New(client *http.Client) *Client {
 	}
 }
 
-func (c *Client) List(ctx context.Context, path string) ([]string, error) {
-	req, err := http.NewRequestWithContext(ctx, http.MethodGet, fmt.Sprintf("https://proxy.golang.org/%s/@v/list", path), nil)
+func (c *Client) List(ctx context.Context, logE *logrus.Entry, path string) ([]string, error) {
+	listEndpoint := fmt.Sprintf("https://proxy.golang.org/%s/@v/list", path)
+	b, err := c.doHTTPRequest(ctx, listEndpoint)
+	if err != nil {
+		return nil, fmt.Errorf("retrieve package versions: %w", logerr.WithFields(err, logrus.Fields{
+			"api_endpoint": listEndpoint,
+		}))
+	}
+	if s := strings.TrimSpace(string(b)); s != "" {
+		return strings.Split(s, "\n"), nil
+	}
+
+	// Find the latest version (including pseudo-versions) if $module/@v/list is empty
+	latestEndpoint := fmt.Sprintf("https://proxy.golang.org/%s/@latest", path)
+	fields := logrus.Fields{
+		"api_endpoint": latestEndpoint,
+	}
+	logE = logE.WithFields(fields)
+	b, err = c.doHTTPRequest(ctx, latestEndpoint)
+	if err != nil {
+		return nil, fmt.Errorf("retrieve the latest version: %w", logerr.WithFields(err, fields))
+	}
+	if len(b) == 0 {
+		logE.Debug("the response body from go proxy is empty")
+		return nil, nil
+	}
+	payload := &InfoPayload{}
+	if err := json.Unmarshal(b, &payload); err != nil {
+		return nil, fmt.Errorf("decode the response body as JSON: %w", logerr.WithFields(err, fields))
+	}
+	return []string{payload.Version}, nil
+}
+
+func (c *Client) doHTTPRequest(ctx context.Context, uri string) ([]byte, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, uri, nil)
 	if err != nil {
 		return nil, fmt.Errorf("create a http request: %w", err)
 	}
@@ -35,9 +76,5 @@ func (c *Client) List(ctx context.Context, path string) ([]string, error) {
 	if err != nil {
 		return nil, fmt.Errorf("read a response body: %w", err)
 	}
-	s := strings.TrimSpace(string(b))
-	if s == "" {
-		return nil, nil
-	}
-	return strings.Split(s, "\n"), nil
+	return b, nil
 }