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/*
*
* Copyright 2020 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
// Package resolver provides internal resolver-related functionality.
package resolver
import (
"context"
"sync"
"google.golang.org/grpc/internal/serviceconfig"
"google.golang.org/grpc/metadata"
"google.golang.org/grpc/resolver"
)
// ConfigSelector controls what configuration to use for every RPC.
type ConfigSelector interface {
// Selects the configuration for the RPC, or terminates it using the error.
// This error will be converted by the gRPC library to a status error with
// code UNKNOWN if it is not returned as a status error.
SelectConfig(RPCInfo) (*RPCConfig, error)
}
// RPCInfo contains RPC information needed by a ConfigSelector.
type RPCInfo struct {
// Context is the user's context for the RPC and contains headers and
// application timeout. It is passed for interception purposes and for
// efficiency reasons. SelectConfig should not be blocking.
Context context.Context
Method string // i.e. "/Service/Method"
}
// RPCConfig describes the configuration to use for each RPC.
type RPCConfig struct {
// The context to use for the remainder of the RPC; can pass info to LB
// policy or affect timeout or metadata.
Context context.Context
MethodConfig serviceconfig.MethodConfig // configuration to use for this RPC
OnCommitted func() // Called when the RPC has been committed (retries no longer possible)
Interceptor ClientInterceptor
}
// ClientStream is the same as grpc.ClientStream, but defined here for circular
// dependency reasons.
type ClientStream interface {
// Header returns the header metadata received from the server if there
// is any. It blocks if the metadata is not ready to read.
Header() (metadata.MD, error)
// Trailer returns the trailer metadata from the server, if there is any.
// It must only be called after stream.CloseAndRecv has returned, or
// stream.Recv has returned a non-nil error (including io.EOF).
Trailer() metadata.MD
// CloseSend closes the send direction of the stream. It closes the stream
// when non-nil error is met. It is also not safe to call CloseSend
// concurrently with SendMsg.
CloseSend() error
// Context returns the context for this stream.
//
// It should not be called until after Header or RecvMsg has returned. Once
// called, subsequent client-side retries are disabled.
Context() context.Context
// SendMsg is generally called by generated code. On error, SendMsg aborts
// the stream. If the error was generated by the client, the status is
// returned directly; otherwise, io.EOF is returned and the status of
// the stream may be discovered using RecvMsg.
//
// SendMsg blocks until:
// - There is sufficient flow control to schedule m with the transport, or
// - The stream is done, or
// - The stream breaks.
//
// SendMsg does not wait until the message is received by the server. An
// untimely stream closure may result in lost messages. To ensure delivery,
// users should ensure the RPC completed successfully using RecvMsg.
//
// It is safe to have a goroutine calling SendMsg and another goroutine
// calling RecvMsg on the same stream at the same time, but it is not safe
// to call SendMsg on the same stream in different goroutines. It is also
// not safe to call CloseSend concurrently with SendMsg.
SendMsg(m interface{}) error
// RecvMsg blocks until it receives a message into m or the stream is
// done. It returns io.EOF when the stream completes successfully. On
// any other error, the stream is aborted and the error contains the RPC
// status.
//
// It is safe to have a goroutine calling SendMsg and another goroutine
// calling RecvMsg on the same stream at the same time, but it is not
// safe to call RecvMsg on the same stream in different goroutines.
RecvMsg(m interface{}) error
}
// ClientInterceptor is an interceptor for gRPC client streams.
type ClientInterceptor interface {
// NewStream produces a ClientStream for an RPC which may optionally use
// the provided function to produce a stream for delegation. Note:
// RPCInfo.Context should not be used (will be nil).
//
// done is invoked when the RPC is finished using its connection, or could
// not be assigned a connection. RPC operations may still occur on
// ClientStream after done is called, since the interceptor is invoked by
// application-layer operations. done must never be nil when called.
NewStream(ctx context.Context, ri RPCInfo, done func(), newStream func(ctx context.Context, done func()) (ClientStream, error)) (ClientStream, error)
}
// ServerInterceptor is an interceptor for incoming RPC's on gRPC server side.
type ServerInterceptor interface {
// AllowRPC checks if an incoming RPC is allowed to proceed based on
// information about connection RPC was received on, and HTTP Headers. This
// information will be piped into context.
AllowRPC(ctx context.Context) error // TODO: Make this a real interceptor for filters such as rate limiting.
}
type csKeyType string
const csKey = csKeyType("grpc.internal.resolver.configSelector")
// SetConfigSelector sets the config selector in state and returns the new
// state.
func SetConfigSelector(state resolver.State, cs ConfigSelector) resolver.State {
state.Attributes = state.Attributes.WithValue(csKey, cs)
return state
}
// GetConfigSelector retrieves the config selector from state, if present, and
// returns it or nil if absent.
func GetConfigSelector(state resolver.State) ConfigSelector {
cs, _ := state.Attributes.Value(csKey).(ConfigSelector)
return cs
}
// SafeConfigSelector allows for safe switching of ConfigSelector
// implementations such that previous values are guaranteed to not be in use
// when UpdateConfigSelector returns.
type SafeConfigSelector struct {
mu sync.RWMutex
cs ConfigSelector
}
// UpdateConfigSelector swaps to the provided ConfigSelector and blocks until
// all uses of the previous ConfigSelector have completed.
func (scs *SafeConfigSelector) UpdateConfigSelector(cs ConfigSelector) {
scs.mu.Lock()
defer scs.mu.Unlock()
scs.cs = cs
}
// SelectConfig defers to the current ConfigSelector in scs.
func (scs *SafeConfigSelector) SelectConfig(r RPCInfo) (*RPCConfig, error) {
scs.mu.RLock()
defer scs.mu.RUnlock()
return scs.cs.SelectConfig(r)
}
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