cmd/golangorg: fix CachedURL, update rebuild template

The "not modified" response code is 304, not 206. Oops.
Use named constants to avoid similar mistakes in the future.

Also update rebuild template to show more version information.

For golang/go#57120.
For golang/go#58884.

Change-Id: I2c3ddf25cede0b5a853fa971226463a997f168c7
Reviewed-on: https://go-review.googlesource.com/c/website/+/515455
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Run-TryBot: Russ Cox <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: rsc

_content/rebuild.html

@@ -55,8 +55,9 @@
 {{$Report := json gorebuild}}
 {{with $Report}}
 
-Using gorebuild from {{.Version}}<br><br>
-
+Gorebuild version {{.Version}}.<br>
+Built with Go version {{.GoVersion}}, {{.GOOS}}-{{.GOARCH}}.<br>
+<br>
 Rebuild started at {{(rfc3339 .Start).UTC.Format "2006-01-02 15:04:05"}} UTC.<br>
 Rebuild finished at {{(rfc3339 .End).UTC.Format "2006-01-02 15:04:05"}} UTC.<br>
 Elapsed time: {{((rfc3339 .End).Sub (rfc3339 .Start)).Round 1e9}}.

cmd/golangorg/server.go

@@ -855,13 +855,13 @@ func (c *CachedURL) Get() (data []byte, err error) {
 		return nil, fmt.Errorf("loading rebuild report JSON: %v", err)
 	}
 	defer resp.Body.Close()
-	if resp.StatusCode == 206 {
+	if resp.StatusCode == http.StatusNotModified {
 		// Unmodified.
 		log.Printf("checked %s - unmodified", c.url)
 		return c.data, c.err
 	}
 	log.Printf("reloading %s", c.url)
-	if resp.StatusCode != 200 {
+	if resp.StatusCode != http.StatusOK {
 		return nil, fmt.Errorf("loading rebuild report JSON: %v", resp.Status)
 	}
 	c.etag = resp.Header.Get("Etag")