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", "numbuilds", or "num_builds" http param from
+// the request, or returns "-1" implying no limit was specified.
+func GetLimit(r *http.Request) (int, error) {
+        sLimit := r.FormValue("limit")
+        if sLimit == "" {
+                sLimit = r.FormValue("numbuilds")
+                if sLimit == "" {
+                        sLimit = r.FormValue("num_builds")
+                        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
+}