github.com/linapex/ethereum-dpos-chinese@v0.0.0-20190316121959-b78b3a4a1ece/p2p/discv5/udp_test.go (about)

     1  
     2  //<developer>
     3  //    <name>linapex 曹一峰</name>
     4  //    <email>linapex@163.com</email>
     5  //    <wx>superexc</wx>
     6  //    <qqgroup>128148617</qqgroup>
     7  //    <url>https://jsq.ink</url>
     8  //    <role>pku engineer</role>
     9  //    <date>2019-03-16 12:09:44</date>
    10  //</624342658021593088>
    11  
    12  
    13  package discv5
    14  
    15  import (
    16  	"encoding/hex"
    17  	"errors"
    18  	"io"
    19  	"net"
    20  	"reflect"
    21  	"sync"
    22  	"testing"
    23  
    24  	"github.com/davecgh/go-spew/spew"
    25  	"github.com/ethereum/go-ethereum/common"
    26  	"github.com/ethereum/go-ethereum/crypto"
    27  	"github.com/ethereum/go-ethereum/rlp"
    28  )
    29  
    30  func init() {
    31  	spew.Config.DisableMethods = true
    32  }
    33  
    34  //共享测试变量
    35  var (
    36  	testLocal = rpcEndpoint{IP: net.ParseIP("3.3.3.3").To4(), UDP: 5, TCP: 6}
    37  )
    38  
    39  //类型udptest struct_
    40  //t*测试.t
    41  //管道*柴油管道
    42  //表*表
    43  //UDP*UDP协议
    44  //发送了[]字节
    45  //本地密钥,远程密钥*ecdsa.privatekey
    46  //远程地址*net.udpaddr
    47  //}
    48  //
    49  //func newudptest(t*测试.t)*udptest
    50  //测试:=&udptest
    51  //T:
    52  //管道:newPipe(),
    53  //localkey:newkey(),
    54  //遥控键:newkey(),
    55  //远程地址:&net.udpaddr ip:net.ip 1、2、3、4,端口:30303,
    56  //}
    57  //test.table,test.udp,=newudp(test.localkey,test.pipe,nil,“”)
    58  //返回测试
    59  //}
    60  //
    61  ////处理一个数据包,就像它被发送到传输一样。
    62  //func(test*udptest)packetin(wanterror错误,ptype字节,数据包)错误
    63  //enc,err:=编码包(test.remotekey,ptype,data)
    64  //如果犯错!= nIL{
    65  //返回test.errorf(“数据包(%d)编码错误:%v”,ptype,err)
    66  //}
    67  //test.sent=附加(test.sent,enc)
    68  //如果err=test.udp.handlepacket(test.remoteaddr,enc);err!=万恐怖
    69  //返回test.errorf(“错误不匹配:得到%q,想要%q”,err,want error)
    70  //}
    71  //返回零
    72  //}
    73  //
    74  ////等待传输发送数据包。
    75  ////validate应具有func(*udptest,x)类型错误,其中x是数据包类型。
    76  //func(test*udptest)waitpacketout(validate interface)错误
    77  //dgram:=test.pipe.waitpacketout()。
    78  //P,uuuuerr:=解码包(dgram)
    79  //如果犯错!= nIL{
    80  //返回test.errorf(“发送数据包解码错误:%v”,err)
    81  //}
    82  //fn:=reflect.valueof(验证)
    83  //exptype:=fn.type().in(0)
    84  //如果反射。类型(P)!= ExpType {
    85  //return test.errorf(“发送的数据包类型不匹配,得到的数据包类型为%v,想要的数据包类型为%v”,reflect.typeof(p),exptype)
    86  //}
    87  //fn.调用([]reflect.value reflect.valueof(p))
    88  //返回零
    89  //}
    90  //
    91  //func(test*udptest)errorf(格式字符串,参数…接口)error
    92  //_u,file,line,ok:=runtime.caller(2)//errorf+waitpacketout
    93  //如果OK {
    94  //文件=filepath.base(文件)
    95  //}否则{
    96  //文件=???”
    97  //线=1
    98  //}
    99  //错误:=fmt.errorf(格式,参数…)
   100  //fmt.printf(“\t%s:%d:%v\n”,文件,行,错误)
   101  //测试失败()
   102  //返回错误
   103  //}
   104  //
   105  //func testudp_packeterrors(t*testing.t)
   106  //测试:=newudptest(t)
   107  //推迟test.table.close()。
   108  //
   109  //test.packetin(errfired、pingpacket和ping从:testmemote到:testlocallowered,版本:version)
   110  //test.packetin(errUnsolicitedReply、pongPacket和pong replytok:[]byte,expiration:futureexp)
   111  //test.packetin(errunknownnode,findnodepacket,&findnode expiration:futureexp)
   112  //test.packetin(errUnsolicitedReply、neighborsPacket和neighbors expiration:futureexp)
   113  //}
   114  //
   115  //func testudp_findnode(t*testing.t)
   116  //测试:=newudptest(t)
   117  //推迟test.table.close()。
   118  //
   119  ////在表中放入几个节点。他们确切
   120  ////分配不太重要,尽管我们需要
   121  ////注意不要溢出任何桶。
   122  //targetHash:=crypto.keccak256hash(testTarget[:])
   123  //节点:=&nodesbyDistance目标:targetHash
   124  //对于i:=0;i<bucketsize;i++
   125  //nodes.push(nodeatDistance(test.table.self.sha,i+2),bucketsize)
   126  //}
   127  //test.table.stuff(nodes.entries)
   128  //
   129  ////确保与测试节点有连接,
   130  ////否则将不接受findnode。
   131  //test.table.db.updatenode(newnode(
   132  //pubkeyid(&test.remotekey.publickey),。
   133  //测试.remoteaddr.ip,
   134  //uint16(test.remoteaddr.port)
   135  //99,
   136  //)
   137  ////检查是否返回最近的邻居。
   138  //test.packetin(nil,findnodepacket,&findnode target:test target,expiration:futureexp)
   139  //应输入:=test.table.closest(targetHash,bucketsize)
   140  //
   141  //waitneighbors:=func(want[]*节点)
   142  //test.waitpacketout(func(p*邻居)
   143  //如果len(p.nodes)!= LEN(WAY){
   144  //t.errorf(“错误的结果数:得到%d,想要%d”,len(p.nodes),bucketsize)
   145  //}
   146  //对于i:=范围p.节点
   147  //如果p.nodes[i].id!=想要[ i]。ID {
   148  //t.errorf(“结果在%d不匹配:\n得到的:%v\n想要的:%v”,i,p.nodes[i],需要的是.entries[i])
   149  //}
   150  //}
   151  //})
   152  //}
   153  //waitneighbors(应为.entries[:maxneighbors])
   154  //waitneighbors(应为.entries[maxneighbors:)
   155  //}
   156  //
   157  //func testudp_findnodemultirreply(t*testing.t)
   158  //测试:=newudptest(t)
   159  //推迟test.table.close()。
   160  //
   161  ////将挂起的findnode请求排队
   162  //结果c,errc:=make(chan[]*节点),make(chan错误)
   163  //转到函数()
   164  //rid:=pubkeyid(&test.remotekey.publickey)
   165  //ns,err:=test.udp.findnode(rid,test.remoteaddr,测试目标)
   166  //如果犯错!=nil和len(ns)==0_
   167  //Err<Err
   168  //}否则{
   169  //结果<<NS
   170  //}
   171  //}()
   172  //
   173  ////等待发送findnode。
   174  ////发送后,传输正在等待答复
   175  //测试.waitpacketout(func(p*findnode)
   176  //如果P目标!=测试目标{
   177  //t.errorf(“错误目标:得到%v,想要%v”,p.target,testtarget)
   178  //}
   179  //})
   180  //
   181  ////以两个数据包的形式发送回复。
   182  //列表:=[]*节点
   183  //必须分析节点(“enode://ba8501c70bcc5c04d8607d3a0ed29aa6179c092cbdda10d5d2684fb33ed01bd94f588ca8f91ac48318087dcb02eaf36773a7a453f0eedd6742af668097b29c@10.0.1.16:30303”?discport=30304”),
   184  //mustParseNode(“enode://81fa361d25f157cd421c60dcc28d8dac5ef6a89476633339c5df30287474520caa09627da18543d9079b5b288698b542d56167aa5c09111e55acdbbdf2ef799@10.0.1.16:30303”),
   185  //must parsenode(“enode://9bffeffd833d53fac8e652415f4973be289e8ba5c6c4cbe70abf817ce8a64cee1b823b66a987f51aaa9fbad6a91b3e6bf0d5a5d1042de8e9ee057b217f8@10.0.1.36:30301?”CdPoT=17“”,
   186  //mustParseNode(“enode://1b5b4aa662d7cb44a7221bfba67302590b643028197a7d214790f3bac7aa4a32441be9e83c09cf1f6c69d007c634faae3dc1b221793e8446c0b3a09de65960@10.0.1.16:30303”),
   187  //}
   188  //rpclist:=make([]rpcnode,len(list))。
   189  //对于i:=范围列表
   190  //rpclist[i]=nodetorpc(列表[i])
   191  //}
   192  //test.packetin(nil,neighborspacket,&neighbors expiration:futureexp,nodes:rpclist[:2])
   193  //test.packetin(nil,neighborspacket,&neighbors expiration:futureexp,nodes:rpclist[2:])
   194  //
   195  ////检查发送的邻居是否都由findnode返回
   196  //选择{
   197  //案例结果:=<-结果C:
   198  //如果!反映.深度相等(结果,列表)
   199  //t.errorf(“邻居不匹配:\n获得:%v\n想要:%v”,结果,列表)
   200  //}
   201  //大小写错误:=<-errc:
   202  //t.errorf(“findnode错误:%v”,err)
   203  //case<-time.after(5*time.second):
   204  //t.error(“findnode在5秒内未返回”)
   205  //}
   206  //}
   207  //
   208  //func testudp_成功(t*testing.t)
   209  //测试:=newudptest(t)
   210  //添加:=make(chan*节点,1)
   211  //test.table.nodeadhook=func(n*node)added<-n
   212  //推迟test.table.close()。
   213  //
   214  ////远程端发送一个ping包来启动交换。
   215  //go test.packettin(nil,pingpacket,&ping从:testmremote,到:testloclaunted,版本:version,过期:futureexp)
   216  //
   217  ////ping被回复。
   218  //测试.waitpacketout(func(p*pong)
   219  //PingHash:=测试。已发送[0][:MacSize]
   220  //如果!bytes.equal(p.replytok,pinghash)
   221  //t.errorf(“got pong.replytok%x,want%x”,p.replytok,pinghash)
   222  //}
   223  //wantto:=rpcendpoint_
   224  ////镜像的udp地址是udp包发送器
   225  //ip:test.remoteaddr.ip,udp:uint16(test.remoteaddr.port),
   226  ////镜像TCP端口是来自ping包的端口
   227  //tcp:测试远程.tcp,
   228  //}
   229  //如果!反省。深相等(P.to,Wantto)
   230  //t.errorf(“pong.to%v,want%v”,p.to,want to)
   231  //}
   232  //})
   233  //
   234  ////远程未知,表返回ping。
   235  //test.waitpacketout(func(p*ping)错误
   236  //如果!反射.deepequal(p.from,test.udp.ourendpoint)
   237  //t.errorf(“从%v得到ping.from,想要%v”,p.from,test.udp.ourendpoint)
   238  //}
   239  //wantto:=rpcendpoint_
   240  ////镜像的UDP地址是UDP数据包发送器。
   241  //ip:test.remoteaddr.ip,udp:uint16(test.remoteaddr.port),
   242  //TCP:0,
   243  //}
   244  //如果!反省。深相等(P.to,Wantto)
   245  //t.errorf(“得到ping.to%v,想要%v”,p.to,want to)
   246  //}
   247  //返回零
   248  //})
   249  //测试.包装纸(无、包装纸和包装到期日:FutureExp)
   250  //
   251  ////在获取
   252  ///P/包。
   253  //选择{
   254  //案例n:=<-添加:
   255  //rid:=pubkeyid(&test.remotekey.publickey)
   256  //如果N.ID!= RID{
   257  //t.errorf(“节点的ID错误:得到了%v,想要%v”,n.id,rid)
   258  //}
   259  //如果!bytes.equal(n.ip,test.remoteaddr.ip)
   260  //t.errorf(“节点的IP错误:得到了%v,想要的是:%v”,n.ip,test.remoteaddr.ip)
   261  //}
   262  //如果int(N.UDP)!=test.remoteaddr.port_
   263  //t.errorf(“节点有错误的udp端口:已获取%v,需要:%v”,n.udp,test.remoteaddr.port)
   264  //}
   265  //如果N.TCP!=测试远程.tcp
   266  //t.errorf(“节点有错误的TCP端口:获取了%v,需要:%v”,n.tcp,testmremote.tcp)
   267  //}
   268  //case<-time.after(2*time.second):
   269  //t.errorf(“2秒内未添加节点”)
   270  //}
   271  //}
   272  
   273  var testPackets = []struct {
   274  	input      string
   275  	wantPacket interface{}
   276  }{
   277  	{
   278  		input: "71dbda3a79554728d4f94411e42ee1f8b0d561c10e1e5f5893367948c6a7d70bb87b235fa28a77070271b6c164a2dce8c7e13a5739b53b5e96f2e5acb0e458a02902f5965d55ecbeb2ebb6cabb8b2b232896a36b737666c55265ad0a68412f250001ea04cb847f000001820cfa8215a8d790000000000000000000000000000000018208ae820d058443b9a355",
   279  		wantPacket: &ping{
   280  			Version:    4,
   281  			From:       rpcEndpoint{net.ParseIP("127.0.0.1").To4(), 3322, 5544},
   282  			To:         rpcEndpoint{net.ParseIP("::1"), 2222, 3333},
   283  			Expiration: 1136239445,
   284  			Rest:       []rlp.RawValue{},
   285  		},
   286  	},
   287  	{
   288  		input: "e9614ccfd9fc3e74360018522d30e1419a143407ffcce748de3e22116b7e8dc92ff74788c0b6663aaa3d67d641936511c8f8d6ad8698b820a7cf9e1be7155e9a241f556658c55428ec0563514365799a4be2be5a685a80971ddcfa80cb422cdd0101ec04cb847f000001820cfa8215a8d790000000000000000000000000000000018208ae820d058443b9a3550102",
   289  		wantPacket: &ping{
   290  			Version:    4,
   291  			From:       rpcEndpoint{net.ParseIP("127.0.0.1").To4(), 3322, 5544},
   292  			To:         rpcEndpoint{net.ParseIP("::1"), 2222, 3333},
   293  			Expiration: 1136239445,
   294  			Rest:       []rlp.RawValue{{0x01}, {0x02}},
   295  		},
   296  	},
   297  	{
   298  		input: "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",
   299  		wantPacket: &ping{
   300  			Version:    555,
   301  			From:       rpcEndpoint{net.ParseIP("2001:db8:3c4d:15::abcd:ef12"), 3322, 5544},
   302  			To:         rpcEndpoint{net.ParseIP("2001:db8:85a3:8d3:1319:8a2e:370:7348"), 2222, 33338},
   303  			Expiration: 1136239445,
   304  			Rest:       []rlp.RawValue{{0xC5, 0x01, 0x02, 0x03, 0x04, 0x05}},
   305  		},
   306  	},
   307  	{
   308  		input: "09b2428d83348d27cdf7064ad9024f526cebc19e4958f0fdad87c15eb598dd61d08423e0bf66b2069869e1724125f820d851c136684082774f870e614d95a2855d000f05d1648b2d5945470bc187c2d2216fbe870f43ed0909009882e176a46b0102f846d79020010db885a308d313198a2e037073488208ae82823aa0fbc914b16819237dcd8801d7e53f69e9719adecb3cc0e790c57e91ca4461c9548443b9a355c6010203c2040506a0c969a58f6f9095004c0177a6b47f451530cab38966a25cca5cb58f055542124e",
   309  		wantPacket: &pong{
   310  			To:         rpcEndpoint{net.ParseIP("2001:db8:85a3:8d3:1319:8a2e:370:7348"), 2222, 33338},
   311  			ReplyTok:   common.Hex2Bytes("fbc914b16819237dcd8801d7e53f69e9719adecb3cc0e790c57e91ca4461c954"),
   312  			Expiration: 1136239445,
   313  			Rest:       []rlp.RawValue{{0xC6, 0x01, 0x02, 0x03, 0xC2, 0x04, 0x05}, {0x06}},
   314  		},
   315  	},
   316  	{
   317  		input: "c7c44041b9f7c7e41934417ebac9a8e1a4c6298f74553f2fcfdcae6ed6fe53163eb3d2b52e39fe91831b8a927bf4fc222c3902202027e5e9eb812195f95d20061ef5cd31d502e47ecb61183f74a504fe04c51e73df81f25c4d506b26db4517490103f84eb840ca634cae0d49acb401d8a4c6b6fe8c55b70d115bf400769cc1400f3258cd31387574077f301b421bc84df7266c44e9e6d569fc56be00812904767bf5ccd1fc7f8443b9a35582999983999999280dc62cc8255c73471e0a61da0c89acdc0e035e260add7fc0c04ad9ebf3919644c91cb247affc82b69bd2ca235c71eab8e49737c937a2c396",
   318  		wantPacket: &findnode{
   319  			Target:     MustHexID("ca634cae0d49acb401d8a4c6b6fe8c55b70d115bf400769cc1400f3258cd31387574077f301b421bc84df7266c44e9e6d569fc56be00812904767bf5ccd1fc7f"),
   320  			Expiration: 1136239445,
   321  			Rest:       []rlp.RawValue{{0x82, 0x99, 0x99}, {0x83, 0x99, 0x99, 0x99}},
   322  		},
   323  	},
   324  	{
   325  		input: "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",
   326  		wantPacket: &neighbors{
   327  			Nodes: []rpcNode{
   328  				{
   329  					ID:  MustHexID("3155e1427f85f10a5c9a7755877748041af1bcd8d474ec065eb33df57a97babf54bfd2103575fa829115d224c523596b401065a97f74010610fce76382c0bf32"),
   330  					IP:  net.ParseIP("99.33.22.55").To4(),
   331  					UDP: 4444,
   332  					TCP: 4445,
   333  				},
   334  				{
   335  					ID:  MustHexID("312c55512422cf9b8a4097e9a6ad79402e87a15ae909a4bfefa22398f03d20951933beea1e4dfa6f968212385e829f04c2d314fc2d4e255e0d3bc08792b069db"),
   336  					IP:  net.ParseIP("1.2.3.4").To4(),
   337  					UDP: 1,
   338  					TCP: 1,
   339  				},
   340  				{
   341  					ID:  MustHexID("38643200b172dcfef857492156971f0e6aa2c538d8b74010f8e140811d53b98c765dd2d96126051913f44582e8c199ad7c6d6819e9a56483f637feaac9448aac"),
   342  					IP:  net.ParseIP("2001:db8:3c4d:15::abcd:ef12"),
   343  					UDP: 3333,
   344  					TCP: 3333,
   345  				},
   346  				{
   347  					ID:  MustHexID("8dcab8618c3253b558d459da53bd8fa68935a719aff8b811197101a4b2b47dd2d47295286fc00cc081bb542d760717d1bdd6bec2c37cd72eca367d6dd3b9df73"),
   348  					IP:  net.ParseIP("2001:db8:85a3:8d3:1319:8a2e:370:7348"),
   349  					UDP: 999,
   350  					TCP: 1000,
   351  				},
   352  			},
   353  			Expiration: 1136239445,
   354  			Rest:       []rlp.RawValue{{0x01}, {0x02}, {0x03}},
   355  		},
   356  	},
   357  }
   358  
   359  func TestForwardCompatibility(t *testing.T) {
   360  	t.Skip("skipped while working on discovery v5")
   361  
   362  	testkey, _ := crypto.HexToECDSA("b71c71a67e1177ad4e901695e1b4b9ee17ae16c6668d313eac2f96dbcda3f291")
   363  	wantNodeID := PubkeyID(&testkey.PublicKey)
   364  
   365  	for _, test := range testPackets {
   366  		input, err := hex.DecodeString(test.input)
   367  		if err != nil {
   368  			t.Fatalf("invalid hex: %s", test.input)
   369  		}
   370  		var pkt ingressPacket
   371  		if err := decodePacket(input, &pkt); err != nil {
   372  			t.Errorf("did not accept packet %s\n%v", test.input, err)
   373  			continue
   374  		}
   375  		if !reflect.DeepEqual(pkt.data, test.wantPacket) {
   376  			t.Errorf("got %s\nwant %s", spew.Sdump(pkt.data), spew.Sdump(test.wantPacket))
   377  		}
   378  		if pkt.remoteID != wantNodeID {
   379  			t.Errorf("got id %v\nwant id %v", pkt.remoteID, wantNodeID)
   380  		}
   381  	}
   382  }
   383  
   384  //dgrampipe是一个假的udp套接字。它将所有发送的数据报排队。
   385  type dgramPipe struct {
   386  	mu      *sync.Mutex
   387  	cond    *sync.Cond
   388  	closing chan struct{}
   389  	closed  bool
   390  	queue   [][]byte
   391  }
   392  
   393  func newpipe() *dgramPipe {
   394  	mu := new(sync.Mutex)
   395  	return &dgramPipe{
   396  		closing: make(chan struct{}),
   397  		cond:    &sync.Cond{L: mu},
   398  		mu:      mu,
   399  	}
   400  }
   401  
   402  //writetoudp将数据报排队。
   403  func (c *dgramPipe) WriteToUDP(b []byte, to *net.UDPAddr) (n int, err error) {
   404  	msg := make([]byte, len(b))
   405  	copy(msg, b)
   406  	c.mu.Lock()
   407  	defer c.mu.Unlock()
   408  	if c.closed {
   409  		return 0, errors.New("closed")
   410  	}
   411  	c.queue = append(c.queue, msg)
   412  	c.cond.Signal()
   413  	return len(b), nil
   414  }
   415  
   416  //readfromudp只是挂起,直到管道关闭。
   417  func (c *dgramPipe) ReadFromUDP(b []byte) (n int, addr *net.UDPAddr, err error) {
   418  	<-c.closing
   419  	return 0, nil, io.EOF
   420  }
   421  
   422  func (c *dgramPipe) Close() error {
   423  	c.mu.Lock()
   424  	defer c.mu.Unlock()
   425  	if !c.closed {
   426  		close(c.closing)
   427  		c.closed = true
   428  	}
   429  	return nil
   430  }
   431  
   432  func (c *dgramPipe) LocalAddr() net.Addr {
   433  	return &net.UDPAddr{IP: testLocal.IP, Port: int(testLocal.UDP)}
   434  }
   435  
   436  func (c *dgramPipe) waitPacketOut() []byte {
   437  	c.mu.Lock()
   438  	defer c.mu.Unlock()
   439  	for len(c.queue) == 0 {
   440  		c.cond.Wait()
   441  	}
   442  	p := c.queue[0]
   443  	copy(c.queue, c.queue[1:])
   444  	c.queue = c.queue[:len(c.queue)-1]
   445  	return p
   446  }
   447