grpcfd

README

grpcfd is a simple set of tools to allow sending unix file descriptors over grpc when the grpc connection utilizes unix file sockets.

Introduction

On a POSIX system (ie Linux), whenever a process opens a file, it had an integer 'file descriptor' (usually abbreviated fd) that acts as a handle for that open file.

On a POSIX system, an open fd can be sent over an open socket connection to another process if and only if that socket connection is over a unix file socket. This allows the other process to access that open file itself, even if it normally couldn't open it because the file was in a different mount namespace.

Since in POSIX almost everything is a file, this means shared memory, normal files, even sockets themselves can be passed along with a GRPC RPC call.

GRPC is a popular high-performance, open source universal RPC framework with excellent Go support

When using the GRPC Go implementation, you do not normally have access to the net.Conn, and thus would not be able to send file descriptors over a connection in use for GRPC.

Client Setup

Simply wrap whatever normal transport credentials you use (nil is an acceptable value) using go grpcfd.TransportCredentials as a go grpc.WithTransportCredentials go grpc.DialOption when dialing:

var creds credentials.TransportCredentials
cc, err := grpc.DialContext(ctx ,grpc.WithTransportCredentials(grpcfd.TransportCredentials(creds)))

Note: If your client already using PerRPCCredentials by default consider to use:

var creds credentials.TransportCredentials
cc, err := grpc.DialContext(ctx, grpc.WithTransportCredentials(grpcfd.TransportCredentials(creds)), grpcfd.WithChainStreamInterceptor(), grpcfd.WithChainUnaryInterceptor())

This allows to grpcfd do not overwrite your grpc.PerRPCCredentials.

Server Setup

Simply wrap whatever normal credentials you use (nil is an acceptable value) using go grpcfd.TransportCredentials as a go grpc.Creds go grpc.ServerOption when creating a go *grpc.Server

var creds credentials.TransportCredentials
server := grpc.NewServer(grpc.Creds(grpcfd.TransportCredentials(creds))

Client To Server Example

Client sending a file descriptor (fd) to Server

// Wrap existing grpc.PerRPCCredentials using grpcfd.PerRPCredentials(...)
perRPCCredentials := grpcfd.PerRPCCredentials(perRPCCredentialsCanBeNilHere)
// Extract a grpcfd.FDSender from the rpcCredentials
sender, _ := grpcfd.FromPerRPCCredentials(perRPCCredentials)
// Send a file
errCh := sender.SendFilename(filename)
select {
case err := <-errCh:
    // If and error is immediately return... the file probably doesn't exist, handle that immediately
default:
    // Don't wait for any subsequent errors... they won't arrive till after we've sent the GRPC message
    // errCh will be closed after File is sent
}
client.MyRPC(ctx,arg,grpc.PerRPCCredentials(perRPCCredentials))

Server receiving a file descriptor (fd) from a Client

func (*myRPCImpl) MyRPC(ctx,arg) {
    // Extract a grpcfd.FDRecver from the ctx.  ok == false if one is not available
    recv, ok := grpcfd.FromContext(ctx)
    // Attempt to receive a filed by using a URL of the form inode://{{dev}}/{{ino}} where dev and ino are the values
    // from 
    fileCh, err := recv.RecvFileByURL(inodeURLStr)
}

Server To Client Example

Server sending a file descriptor (fd) to Client

func (*myRPCImpl) MyRPC(ctx,arg) {
    // Extract a grpcfd.FDRecver from the ctx.  ok == false if one is not available
    sender, ok := grpcfd.FromContext(ctx)
    // Send a file 
    errCh := sender.SendFilename(filename)
    select {
    case err := <-errCh:
        // If and error is immediately return... the file probably doesn't exist, handle that immediately
    default:
        // Don't wait for any subsequent errors... they won't arrive till after we've sent the GRPC message
        // errCh will be closed after File is sent
    }
    ...
    return
}

Client receiving file descriptor (fd) from Server

// Wrap existing grpc.PerRPCCredentials using grpcfd.PerRPCredentials(...)
perRPCCredentials := grpcfd.PerRPCCredentials(perRPCCredentialsCanBeNilHere)
// Extract a grpcfd.FDRecver from the ctx.  ok == false if one is not available
recv, ok := grpcfd.FromContext(ctx)
client.MyRPC(ctx,arg,grpc.PerRPCCredentials(perRPCCredentials))
// Attempt to receive a filed by using a URL of the form inode://{{dev}}/{{ino}} where dev and ino are the values
// from 
fileCh, err := recv.RecvFileByURL(inodeURLStr)

Documentation

Overview

Package grpcfd provides a TransportCredential that can wrap other TransportCredentials and cause the peer.Addr to be a FDSender or FDRecver such that it can send or receive files over unix file sockets (if available).

Index

• func CaptureSender(capturer func(FDSender), dialopts ...grpc.DialOption) (opts []grpc.DialOption, ok bool)
• func FDToURL(fd uintptr) (*url.URL, error)
• func FileToURL(file SyscallConn) (u *url.URL, err error)
• func FilenameToURL(filename string) (u *url.URL, err error)
• func PerRPCCredentials(cred credentials.PerRPCCredentials) credentials.PerRPCCredentials
• func PerRPCCredentialsFromCallOptions(opts ...grpc.CallOption) credentials.PerRPCCredentials
• func TransportCredentials(cred credentials.TransportCredentials, capturers ...func(FDSender)) credentials.TransportCredentials
• func URLStringToDevIno(urlstr string) (dev, ino uint64, err error)
• func URLToDevIno(u *url.URL) (dev, ino uint64, err error)
• func WithChainStreamInterceptor() grpc.DialOption
• func WithChainUnaryInterceptor() grpc.DialOption
• func WithTransportCredentials(creds credentials.TransportCredentials, capturers ...func(FDSender)) grpc.DialOption
• type FDRecver
• type FDSender
• type FDTransceiver
  • func FromContext(ctx context.Context) (transceiver FDTransceiver, ok bool)
  • func FromPeer(p *peer.Peer) (transceiver FDTransceiver, ok bool)
  • func FromPerRPCCredentials(rpcCredentials credentials.PerRPCCredentials) (transceiver FDTransceiver, ok bool)
• type SyscallConn

Functions

func CaptureSender

func CaptureSender(capturer func(FDSender), dialopts ...grpc.DialOption) (opts []grpc.DialOption, ok bool)

CaptureSender - given a list of dialopts ... if one of them is a grpcfd.TransportCredentials option... add another capturer to capture FDSenders on dial

func FDToURL

func FDToURL(fd uintptr) (*url.URL, error)

FDToURL converts fd to URL of inode://${dev}/${ino}

func FileToURL

func FileToURL(file SyscallConn) (u *url.URL, err error)

FileToURL converts file to URL of inode://${dev}/${ino}

func FilenameToURL

func FilenameToURL(filename string) (u *url.URL, err error)

FilenameToURL converts filename to URL of inode://${dev}/${ino}

func PerRPCCredentials

func PerRPCCredentials(cred credentials.PerRPCCredentials) credentials.PerRPCCredentials

PerRPCCredentials - per rpc credentials that will, in addition to applying cred, invoke sendFunc Note: Must be used in concert with grpcfd.TransportCredentials

func PerRPCCredentialsFromCallOptions

func PerRPCCredentialsFromCallOptions(opts ...grpc.CallOption) credentials.PerRPCCredentials

PerRPCCredentialsFromCallOptions - extract credentials.PerRPCCredentials from a list of grpc.CallOptions

func TransportCredentials

func TransportCredentials(cred credentials.TransportCredentials, capturers ...func(FDSender)) credentials.TransportCredentials

TransportCredentials - transport credentials that will, in addition to applying cred, cause peer.Addr to supply the FDSender and FDRecver interfaces

func URLStringToDevIno

func URLStringToDevIno(urlstr string) (dev, ino uint64, err error)

URLStringToDevIno converts url of form inode://${dev}/${ino} to dev,ino

func URLToDevIno

func URLToDevIno(u *url.URL) (dev, ino uint64, err error)

URLToDevIno - converts url of form inode://${dev}/${ino} url to dev,ino

func WithChainStreamInterceptor

func WithChainStreamInterceptor() grpc.DialOption

WithChainStreamInterceptor returns a DialOption that specifies the chained interceptor for streaming RPCs.This interceptor combines all grpc.PerRPCCredsCallOption options into one. That allows using a few credentials.PerRPCCredentials passed from default call options and from the client call.

func WithChainUnaryInterceptor

func WithChainUnaryInterceptor() grpc.DialOption

WithChainUnaryInterceptor returns a DialOption that specifies the chained interceptor for unary RPCs. This interceptor combines all grpc.PerRPCCredsCallOption options into one. That allows using a few credentials.PerRPCCredentials passed from default call options and from the client call.

func WithTransportCredentials

func WithTransportCredentials(creds credentials.TransportCredentials, capturers ...func(FDSender)) grpc.DialOption

WithTransportCredentials - drop in replacement for grpc.WithTransportCredentials, that will, in addition to applying cred, cause peer.Addr to supply the FDSender and FDRecver interfaces.

Types

type FDRecver

type FDRecver interface {
	RecvFD(dev, inode uint64) <-chan uintptr
	RecvFile(dev, ino uint64) <-chan *os.File
	RecvFileByURL(urlStr string) (<-chan *os.File, error)
	RecvFDByURL(urlStr string) (<-chan uintptr, error)
}

FDRecver - capable of Recving an fd by (dev,ino)

type FDSender

type FDSender interface {
	SendFD(fd uintptr) <-chan error
	SendFile(file SyscallConn) <-chan error
	SendFilename(filename string) <-chan error
}

FDSender - capable of Sending a file

type FDTransceiver

type FDTransceiver interface {
	FDSender
	FDRecver
}

FDTransceiver - combination of FDSender and FDRecver

func FromContext

func FromContext(ctx context.Context) (transceiver FDTransceiver, ok bool)

FromContext - return grpcfd.FDTransceiver from context.Context

ok is true of successful, false otherwise

func FromPeer

func FromPeer(p *peer.Peer) (transceiver FDTransceiver, ok bool)

FromPeer - return grpcfd.FDTransceiver from peer.Peer

ok is true of successful, false otherwise

func FromPerRPCCredentials

func FromPerRPCCredentials(rpcCredentials credentials.PerRPCCredentials) (transceiver FDTransceiver, ok bool)

FromPerRPCCredentials - return grpcfd.FDTransceiver from credentials.PerRPCCredentials

ok is true of successful, false otherwise

type SyscallConn

type SyscallConn interface {
	SyscallConn() (syscall.RawConn, error)
}

SyscallConn - having the SyscallConn method to access syscall.RawConn