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lrpc/server/server.go

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/*
* lrpc allows for clients to call functions on a server remotely.
* Copyright (C) 2022 Arsen Musayelyan
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
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package server
import (
"errors"
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"io"
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"net"
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"net/http"
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"reflect"
"sync"
"go.arsenm.dev/lrpc/codec"
"go.arsenm.dev/lrpc/internal/reflectutil"
"go.arsenm.dev/lrpc/internal/types"
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"golang.org/x/net/websocket"
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)
// <= go1.17 compatibility
type any = interface{}
var (
ErrInvalidType = errors.New("type must be struct or pointer to struct")
ErrTooManyInputs = errors.New("method may not have more than two inputs")
ErrTooManyOutputs = errors.New("method may not have more than two return values")
ErrNoSuchReceiver = errors.New("no such receiver registered")
ErrNoSuchMethod = errors.New("no such method was found")
ErrInvalidSecondReturn = errors.New("second return value must be error")
ErrInvalidFirstInput = errors.New("first input must be *Context")
)
// Server is an lrpc server
type Server struct {
rcvrs map[string]reflect.Value
contextsMtx sync.Mutex
contexts map[string]*Context
}
// New creates and returns a new server
func New() *Server {
// Create new server
out := &Server{
rcvrs: map[string]reflect.Value{},
contexts: map[string]*Context{},
}
// Register lrpc functions
out.Register(lrpc{out})
return out
}
// Close closes the server
func (s *Server) Close() {
for _, ctx := range s.contexts {
ctx.Cancel()
}
}
// Register registers a value to be called by a client
func (s *Server) Register(v any) error {
// Get reflect values for v
val := reflect.ValueOf(v)
kind := val.Kind()
// create variable to store name of v
var name string
switch kind {
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case reflect.Ptr:
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// If v is a pointer, get the name of the underlying type
name = val.Elem().Type().Name()
case reflect.Struct:
// If v is a struct, get its name
name = val.Type().Name()
default:
// If v is not pointer or struct, return error
return ErrInvalidType
}
// Add v to receivers map
s.rcvrs[name] = val
return nil
}
// execute runs a method of a registered value
func (s *Server) execute(typ string, name string, arg any, c codec.Codec) (a any, ctx *Context, err error) {
// Try to get value from receivers map
val, ok := s.rcvrs[typ]
if !ok {
return nil, nil, ErrNoSuchReceiver
}
// Try to retrieve given method
mtd := val.MethodByName(name)
if !mtd.IsValid() {
return nil, nil, ErrNoSuchMethod
}
// Get method's type
mtdType := mtd.Type()
if mtdType.NumIn() > 2 {
return nil, nil, ErrTooManyInputs
} else if mtdType.NumIn() < 1 {
return nil, nil, ErrInvalidFirstInput
}
if mtdType.NumOut() > 2 {
return nil, nil, ErrTooManyOutputs
}
// Check to ensure first parameter is context
if mtdType.In(0) != reflect.TypeOf(&Context{}) {
return nil, nil, ErrInvalidFirstInput
}
//TODO: if arg not nil but fn has no arg, err
// IF argument is []any
anySlice, ok := arg.([]any)
if ok {
// Convert slice to the method's arg type and
// set arg to the newly-converted slice
arg = reflectutil.ConvertSlice(anySlice, mtdType.In(1))
}
// Get argument value
argVal := reflect.ValueOf(arg)
// If argument's type does not match method's argument type
if arg != nil && argVal.Type() != mtdType.In(1) {
val, err = reflectutil.Convert(argVal, mtdType.In(1))
if err != nil {
return nil, nil, err
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}
arg = val.Interface()
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}
// Create new context
ctx = &Context{
doneCh: make(chan struct{}, 1),
codec: c,
}
// Get reflect value of context
ctxVal := reflect.ValueOf(ctx)
switch mtdType.NumOut() {
case 0: // If method has no return values
if mtdType.NumIn() == 2 {
// Call method with arg, ignore returned value
mtd.Call([]reflect.Value{ctxVal, reflect.ValueOf(arg)})
} else {
// Call method without arg, ignore returned value
mtd.Call([]reflect.Value{ctxVal})
}
case 1: // If method has one return value
if mtdType.NumIn() == 2 {
// Call method with arg, get returned values
out := mtd.Call([]reflect.Value{ctxVal, reflect.ValueOf(arg)})
// If the first return value's type is error
if mtdType.Out(0).Name() == "error" {
// Get first return value as interface
out0 := out[0].Interface()
if out0 == nil {
a, err = nil, nil
} else {
a, err = nil, out0.(error)
}
} else {
a, err = out[0].Interface(), nil
}
} else {
// Call method without arg, get returned values
out := mtd.Call([]reflect.Value{ctxVal})
// If the first return value's type is error
if mtdType.Out(0).Name() == "error" {
// Get first return value as interface
out0 := out[0].Interface()
if out0 == nil {
a, err = nil, nil
} else {
a, err = nil, out0.(error)
}
} else {
a, err = out[0].Interface(), nil
}
}
case 2: // If method has two return values
if mtdType.NumIn() == 2 {
// Call method with arg and get returned values
out := mtd.Call([]reflect.Value{ctxVal, reflect.ValueOf(arg)})
// Get second return value as interface
out1 := out[1].Interface()
if out1 != nil {
err, ok = out1.(error)
// If second return value is not an error, the function is invalid
if !ok {
a, err = nil, ErrInvalidSecondReturn
}
}
a = out[0].Interface()
} else {
// Call method without arg and get returned values
out := mtd.Call([]reflect.Value{ctxVal})
// Get second return value as interface
out1 := out[1].Interface()
if out1 != nil {
// If second return value is not an error, the function is invalid
err, ok = out1.(error)
if !ok {
a, err = nil, ErrInvalidSecondReturn
}
}
a = out[0].Interface()
}
}
return a, ctx, err
}
// Serve starts the server using the provided listener
// and codec function
func (s *Server) Serve(ln net.Listener, cf codec.CodecFunc) {
for {
conn, err := ln.Accept()
if err != nil {
continue
}
// Create new instance of codec bound to conn
c := cf(conn)
// Handle connection
go s.handleConn(c)
}
}
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// ServeWS starts a server using WebSocket. This may be useful for
// clients written in other languages, such as JS for a browser.
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func (s *Server) ServeWS(addr string, cf codec.CodecFunc) (err error) {
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// Create new WebSocket server
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ws := websocket.Server{}
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// Create new WebSocket config
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ws.Config = websocket.Config{
Version: websocket.ProtocolVersionHybi13,
}
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// Set server handler
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ws.Handler = func(c *websocket.Conn) {
s.handleConn(cf(c))
}
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// Listen and serve on given address
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return http.ListenAndServe(addr, http.HandlerFunc(ws.ServeHTTP))
}
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// handleConn handles a listener connection
func (s *Server) handleConn(c codec.Codec) {
for {
var call types.Request
// Read request using codec
err := c.Decode(&call)
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if err == io.EOF {
break
} else if err != nil {
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s.sendErr(c, call, nil, err)
continue
}
// Execute decoded call
val, ctx, err := s.execute(
call.Receiver,
call.Method,
call.Arg,
c,
)
if err != nil {
s.sendErr(c, call, val, err)
} else {
// Create response
res := types.Response{
ID: call.ID,
Return: val,
}
// If function has created a channel
if ctx.isChannel {
// Set IsChannel to true
res.IsChannel = true
// Overwrite return value with channel ID
res.Return = ctx.channelID
// Store context in map for future use
s.contextsMtx.Lock()
s.contexts[ctx.channelID] = ctx
s.contextsMtx.Unlock()
go func() {
// For every value received from channel
for val := range ctx.channel {
// Encode response using codec
c.Encode(types.Response{
ID: ctx.channelID,
Return: val,
})
}
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// Cancel context
ctx.Cancel()
// Delete context from map
s.contextsMtx.Lock()
delete(s.contexts, ctx.channelID)
s.contextsMtx.Unlock()
c.Encode(types.Response{
ID: ctx.channelID,
ChannelDone: true,
})
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}()
}
// Encode response using codec
c.Encode(res)
}
}
}
// sendErr sends an error response
func (s *Server) sendErr(c codec.Codec, req types.Request, val any, err error) {
// Encode error response using codec
c.Encode(types.Response{
ID: req.ID,
IsError: true,
Error: err.Error(),
Return: val,
})
}
// lrpc contains functions registered on every server
type lrpc struct {
srv *Server
}
// ChannelDone cancels a context and closes the associated channel
func (l lrpc) ChannelDone(_ *Context, id string) {
// Try to get context
ctx, ok := l.srv.contexts[id]
if !ok {
return
}
// Cancel context
ctx.Cancel()
// Delete context from map
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l.srv.contextsMtx.Lock()
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delete(l.srv.contexts, id)
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l.srv.contextsMtx.Unlock()
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}