Initial distributor implementation

appengine/cmd/dm/distributor/registry.go

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package distributor
+
+import (
+        "fmt"
+        "reflect"
+        "sync"
+
+        "github.com/golang/protobuf/proto"
+        "github.com/luci/gae/service/info"
+        protos "github.com/luci/luci-go/appengine/cmd/dm/distributor/protos"
+        "golang.org/x/net/context"
+)
+
+var registry = struct {
+        sync.RWMutex
+        data map[reflect.Type]Factory
+}{data: map[reflect.Type]Factory{}}
+
+// Register enrolls a new distributor type in the registry. Calling
+// this multiple times for the same proto Message will panic.
+func Register(p proto.Message, factory Factory) {
+        if factory == nil {
+                panic("factory is nil")
+        }
+        if p == nil {
+                panic("proto.Message is nil")
+        }
+
+        typ := reflect.TypeOf(p)
+
+        registry.Lock()
+        defer registry.Unlock()
+        if _, ok := registry.data[typ]; ok {
+                panic(fmt.Errorf("trying to register %q twice", typ))
+        }
+        registry.data[typ] = factory
+}
+
+// MakeDistributor builds a distributor instance that's configured with the
+// provided config.
+//
+// The configuration for this distributor are obtained from luci-config at the
+// time an Execution is started.
+func MakeDistributor(c context.Context, cfg *Config) (D, error) {
+        typ := reflect.TypeOf(cfg.ImplConfig)
+
+        registry.RLock()
+        fn, ok := registry.data[typ]
+        registry.RUnlock()
+
+        if !ok {
+                return nil, fmt.Errorf("unknown distributor type %T", cfg.ImplConfig)
+        }
+
+        return fn(c, cfg)
+}
+
+// LoadConfiguration loads the named distributor configurtaion from luci-config,
+// possibly using the in-memory or memcache version.
+func LoadConfiguration(c context.Context, cfgName string) (ret *Config, err error) {
+        cfgVersion := ""
+        fullDMConfig := proto.Message(nil)
+        // TODO(riannucci): get config and version from luci-config in a fast cached way.
+
+        configs := fullDMConfig.(*protos.Config)
+        cfg, ok := configs.DistributorConfigs[cfgName]
+        if !ok {
+                err = fmt.Errorf("unknown distributor configuration: %q", cfgName)
+                return
+        }
+        if alias := cfg.GetAlias(); alias != nil {
+                cfg, ok = configs.DistributorConfigs[alias.OtherConfig]
+                if !ok {
+                        err = fmt.Errorf("unknown distributor configuration: %q (via alias %q)", cfgName, alias.OtherConfig)
+                        return
+                }
+                if cfg.GetAlias() != nil {
+                        err = fmt.Errorf("too many levels of indirection for alias %q (points to alias %q)", cfgName, alias.OtherConfig)
+                        return
+                }
+        }
+
+        dt := cfg.GetDistributorType()
+        if dt == nil {
+                err = fmt.Errorf("blank or unrecognized distributor_type")
+                return
+        }
+        dVal := reflect.ValueOf(dt)
+
+        // All non-nil DistributorType's have a single field which is the actual oneof
+        // value.
+        implConfig := dVal.Field(0).Interface().(proto.Message)
+
+        baseURL := fmt.Sprintf("https://%s/", info.Get(c).DefaultVersionHostname())
+        ret = &Config{
+                baseURL,
+                baseURL + handlerPath(cfgName),
+                cfgName,
+                cfgVersion,
+                implConfig,
+        }
+        return
+}