Milo: Add ?limit= support to builders

milo/appengine/settings/settings.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package settings
 
 import (
         "encoding/base64"
         "encoding/json"
         "fmt"
         "net/http"
+        "strconv"
 
         ds "github.com/luci/gae/service/datastore"
         "github.com/luci/luci-go/milo/api/resp"
         "github.com/luci/luci-go/milo/appengine/model"
+        "github.com/luci/luci-go/milo/common/miloerror"
         "github.com/luci/luci-go/server/auth"
         "github.com/luci/luci-go/server/auth/identity"
         "github.com/luci/luci-go/server/auth/xsrf"
         "github.com/luci/luci-go/server/router"
 
         "golang.org/x/net/context"
 )
 
 type updateReq struct {
         Theme string
@@ skipping 116 matching lines @@
 
         result := &resp.Settings{}
         result.ActionURL = r.URL.String()
         result.Theme = &resp.Choices{
                 Choices:  GetAllThemes(),
                 Selected: userSettings.Theme,
         }
 
         return result, nil
 }
+
+// GetLimit extracts the "limit" http param from the request, or returns "-1"
+// implying no limit was specified.
+func GetLimit(r *http.Request) (int, error) {

[nodir, 2016/10/28 07:17:54]

why this is in settings package? what does limit query string parameter have to
do with settings?

[hinoka, 2016/10/28 19:47:30]

Technically nothing, i'm using the settings package as sort of a "misc" or
"utils" package, since it has to be imported everywhere anyways.  I could split
it out, but I feel like theres too many top-level packages already, and that
would only complicate things.

[nodir, 2016/10/28 19:52:51]

Perhaps this needs some refactoring. Go does not encourage misc/utils packages.

[hinoka, 2016/10/28 19:53:42]

The alternative would be copypasta code...?

+        sLimit := r.FormValue("limit")

[nodir, 2016/10/28 07:17:54]

can you also fall back to "numBuilds"? this is what buildbucket builder view
uses because buildbot uses it

[hinoka, 2016/10/28 19:47:30]

Done.

+        if sLimit == "" {
+                return -1, nil
+        }
+        limit, err := strconv.Atoi(sLimit)
+        if err != nil {
+                return -1, &miloerror.Error{
+                        Message: fmt.Sprintf("limit parameter value %q is not a number: %s", sLimit, err),
+                        Code:    http.StatusBadRequest,
+                }
+        }
+        if limit < 0 {
+                return -1, &miloerror.Error{
+                        Message: fmt.Sprintf("limit parameter value %q is less than 0", sLimit),
+                        Code:    http.StatusBadRequest,
+                }
+        }
+        return limit, nil
+}