sumdb/internal/sumweb: simplify code, clarify comments

Followup work from CL 172964 review comments.
(That CL was in a different directory and is too hard to get back to.)

- Simplify to one cache for Conn.ReadTile.
- Replace Client.GetURL with Client.ReadRemote,
  which takes only a path, not a full URL.
  It works better for the client to take care of URL mapping.
- Rename FindKey to Lookup throughout (matches URL).
- Apply !-decoding in Handler.

Change-Id: Ib004ebb1b608d9ee2f8bdf768628acdd5b985158
Reviewed-on: https://go-review.googlesource.com/c/exp/+/173945
Run-TryBot: Russ Cox <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Filippo Valsorda <[email protected]>

Author: rsc

sumdb/gosumcheck/main.go

@@ -54,7 +54,7 @@ func usage() {
 
 var (
 	height = flag.Int("h", 8, "tile height")
-	vkey   = flag.String("k", "rsc-goog.appspot.com+eecb1dec+AbTy1QXWdqYd1TTpuaUqsk6u7p+n4AqLiLB8SBwoB831", "key") // TODO: Replace with real key.
+	vkey   = flag.String("k", "sum.golang.org+033de0ae+Ac4zctda0e5eza+HJyk9SxEdh+s3Ux18htTTAD8OuAn8", "key")
 	url    = flag.String("u", "", "url to server (overriding name)")
 	vflag  = flag.Bool("v", false, "enable verbose output")
 )
@@ -149,7 +149,7 @@ type client struct{}
 
 func (*client) ReadConfig(file string) ([]byte, error) {
 	if file == "key" {
-		return []byte(*vkey + "\n" + *url), nil
+		return []byte(*vkey), nil
 	}
 	if strings.HasSuffix(file, "/latest") {
 		// Looking for cached latest tree head.
@@ -184,22 +184,30 @@ func init() {
 	http.DefaultClient.Timeout = 1 * time.Minute
 }
 
-func (*client) GetURL(url string) ([]byte, error) {
+func (*client) ReadRemote(path string) ([]byte, error) {
+	name := *vkey
+	if i := strings.Index(name, "+"); i >= 0 {
+		name = name[:i]
+	}
 	start := time.Now()
-	resp, err := http.Get(url)
+	target := "https://" + name + path
+	if *url != "" {
+		target = *url + path
+	}
+	resp, err := http.Get(target)
 	if err != nil {
 		return nil, err
 	}
 	defer resp.Body.Close()
 	if resp.StatusCode != 200 {
-		return nil, fmt.Errorf("GET %v: %v", url, resp.Status)
+		return nil, fmt.Errorf("GET %v: %v", target, resp.Status)
 	}
 	data, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1<<20))
 	if err != nil {
 		return nil, err
 	}
 	if *vflag {
-		fmt.Fprintf(os.Stderr, "%.3fs %s\n", time.Since(start).Seconds(), url)
+		fmt.Fprintf(os.Stderr, "%.3fs %s\n", time.Since(start).Seconds(), target)
 	}
 	return data, nil
 }