├── .gitignore ├── message.go ├── network.go ├── paxos_test.go ├── leaner.go ├── acceptor.go ├── proposer.go └── LICENSE /.gitignore: -------------------------------------------------------------------------------- 1 | # Compiled Object files, Static and Dynamic libs (Shared Objects) 2 | *.o 3 | *.a 4 | *.so 5 | 6 | # Folders 7 | _obj 8 | _test 9 | 10 | # Architecture specific extensions/prefixes 11 | *.[568vq] 12 | [568vq].out 13 | 14 | *.cgo1.go 15 | *.cgo2.c 16 | _cgo_defun.c 17 | _cgo_gotypes.go 18 | _cgo_export.* 19 | 20 | _testmain.go 21 | 22 | *.exe 23 | *.test 24 | *.prof 25 | -------------------------------------------------------------------------------- /message.go: -------------------------------------------------------------------------------- 1 | package paxos 2 | 3 | type msgType int 4 | 5 | const ( 6 | Prepare msgType = iota + 1 7 | Propose 8 | Promise 9 | Accept 10 | ) 11 | 12 | type message struct { 13 | from, to int 14 | typ msgType 15 | n int 16 | prevn int 17 | value string 18 | } 19 | 20 | func (m message) number() int { 21 | return m.n 22 | } 23 | 24 | func (m message) proposalValue() string { 25 | switch m.typ { 26 | case Promise, Accept: 27 | return m.value 28 | default: 29 | panic("unexpected proposalV") 30 | } 31 | } 32 | 33 | func (m message) proposalNumber() int { 34 | switch m.typ { 35 | case Promise: 36 | return m.prevn 37 | case Accept: 38 | return m.n 39 | default: 40 | panic("unexpected proposalN") 41 | } 42 | } 43 | 44 | type promise interface { 45 | number() int 46 | } 47 | 48 | type accept interface { 49 | proposalValue() string 50 | proposalNumber() int 51 | } 52 | -------------------------------------------------------------------------------- /network.go: -------------------------------------------------------------------------------- 1 | package paxos 2 | 3 | import ( 4 | "log" 5 | "time" 6 | ) 7 | 8 | type network interface { 9 | send(m message) 10 | recv(timeout time.Duration) (message, bool) 11 | } 12 | 13 | type paxosNetwork struct { 14 | recvQueues map[int]chan message 15 | } 16 | 17 | func newPaxosNetwork(agents ...int) *paxosNetwork { 18 | pn := &paxosNetwork{ 19 | recvQueues: make(map[int]chan message, 0), 20 | } 21 | 22 | for _, a := range agents { 23 | pn.recvQueues[a] = make(chan message, 1024) 24 | } 25 | return pn 26 | } 27 | 28 | func (pn *paxosNetwork) agentNetwork(id int) *agentNetwork { 29 | return &agentNetwork{id: id, paxosNetwork: pn} 30 | } 31 | 32 | func (pn *paxosNetwork) send(m message) { 33 | log.Printf("nt: send %+v", m) 34 | pn.recvQueues[m.to] <- m 35 | } 36 | 37 | func (pn *paxosNetwork) empty() bool { 38 | var n int 39 | for i, q := range pn.recvQueues { 40 | log.Printf("nt: %d left %d", i, len(q)) 41 | n += len(q) 42 | } 43 | return n == 0 44 | } 45 | 46 | func (pn *paxosNetwork) recvFrom(from int, timeout time.Duration) (message, bool) { 47 | select { 48 | case m := <-pn.recvQueues[from]: 49 | log.Printf("nt: recv %+v", m) 50 | return m, true 51 | case <-time.After(timeout): 52 | return message{}, false 53 | } 54 | } 55 | 56 | type agentNetwork struct { 57 | id int 58 | *paxosNetwork 59 | } 60 | 61 | func (an *agentNetwork) send(m message) { 62 | an.paxosNetwork.send(m) 63 | } 64 | 65 | func (an *agentNetwork) recv(timeout time.Duration) (message, bool) { 66 | return an.recvFrom(an.id, timeout) 67 | } 68 | -------------------------------------------------------------------------------- /paxos_test.go: -------------------------------------------------------------------------------- 1 | package paxos 2 | 3 | import ( 4 | "testing" 5 | "time" 6 | ) 7 | 8 | func TestPaxosWithSingleProposer(t *testing.T) { 9 | // 1, 2, 3 are acceptors 10 | // 1001 is a proposer 11 | pn := newPaxosNetwork(1, 2, 3, 1001, 2001) 12 | 13 | as := make([]*acceptor, 0) 14 | for i := 1; i <= 3; i++ { 15 | as = append(as, newAcceptor(i, pn.agentNetwork(i), 2001)) 16 | } 17 | 18 | for _, a := range as { 19 | go a.run() 20 | } 21 | 22 | p := newProposer(1001, "hello world", pn.agentNetwork(1001), 1, 2, 3) 23 | go p.run() 24 | 25 | l := newLearner(2001, pn.agentNetwork(2001), 1, 2, 3) 26 | value := l.learn() 27 | if value != "hello world" { 28 | t.Errorf("value = %s, want %s", value, "hello world") 29 | } 30 | } 31 | 32 | func TestPaxosWithTwoProposers(t *testing.T) { 33 | // 1, 2, 3 are acceptors 34 | // 1001,1002 is a proposer 35 | pn := newPaxosNetwork(1, 2, 3, 1001, 1002, 2001) 36 | 37 | as := make([]*acceptor, 0) 38 | for i := 1; i <= 3; i++ { 39 | as = append(as, newAcceptor(i, pn.agentNetwork(i), 2001)) 40 | } 41 | 42 | for _, a := range as { 43 | go a.run() 44 | } 45 | 46 | p1 := newProposer(1001, "hello world", pn.agentNetwork(1001), 1, 2, 3) 47 | go p1.run() 48 | 49 | time.Sleep(time.Millisecond) 50 | p2 := newProposer(1002, "bad day", pn.agentNetwork(1002), 1, 2, 3) 51 | go p2.run() 52 | 53 | l := newLearner(2001, pn.agentNetwork(2001), 1, 2, 3) 54 | value := l.learn() 55 | if value != "hello world" { 56 | t.Errorf("value = %s, want %s", value, "hello world") 57 | } 58 | time.Sleep(time.Millisecond) 59 | } 60 | -------------------------------------------------------------------------------- /leaner.go: -------------------------------------------------------------------------------- 1 | package paxos 2 | 3 | import ( 4 | "log" 5 | "time" 6 | ) 7 | 8 | type learner struct { 9 | id int 10 | acceptors map[int]accept 11 | 12 | nt network 13 | } 14 | 15 | func newLearner(id int, nt network, acceptors ...int) *learner { 16 | l := &learner{id: id, nt: nt, acceptors: make(map[int]accept)} 17 | for _, a := range acceptors { 18 | l.acceptors[a] = message{typ: Accept} 19 | } 20 | return l 21 | } 22 | 23 | // A value is learned when a single proposal with that value has been accepted by 24 | // a majority of the acceptors. 25 | func (l *learner) learn() string { 26 | for { 27 | m, ok := l.nt.recv(time.Hour) 28 | if !ok { 29 | continue 30 | } 31 | if m.typ != Accept { 32 | log.Panicf("learner: %d received unexpected msg %+v", l.id, m) 33 | } 34 | l.receiveAccepted(m) 35 | accept, ok := l.chosen() 36 | if !ok { 37 | continue 38 | } 39 | log.Printf("learner: %d learned the chosen propose %+v", l.id, accept) 40 | return accept.proposalValue() 41 | } 42 | } 43 | 44 | func (l *learner) receiveAccepted(accepted message) { 45 | a := l.acceptors[accepted.from] 46 | if a.proposalNumber() < accepted.n { 47 | log.Printf("learner: %d received a new accepted proposal %+v", l.id, accepted) 48 | l.acceptors[accepted.from] = accepted 49 | } 50 | } 51 | 52 | func (l *learner) majority() int { return len(l.acceptors)/2 + 1 } 53 | 54 | // A proposal is chosen when it has been accepted by a majority of the 55 | // acceptors. 56 | // The leader might choose multiple proposals when it learns multiple times, 57 | // but we guarantee that all chosen proposals have the same value. 58 | func (l *learner) chosen() (accept, bool) { 59 | counts := make(map[int]int) 60 | accepteds := make(map[int]accept) 61 | 62 | for _, accepted := range l.acceptors { 63 | if accepted.proposalNumber() != 0 { 64 | counts[accepted.proposalNumber()]++ 65 | accepteds[accepted.proposalNumber()] = accepted 66 | } 67 | } 68 | 69 | for n, count := range counts { 70 | if count >= l.majority() { 71 | return accepteds[n], true 72 | } 73 | } 74 | return message{}, false 75 | } 76 | -------------------------------------------------------------------------------- /acceptor.go: -------------------------------------------------------------------------------- 1 | package paxos 2 | 3 | import ( 4 | "log" 5 | "time" 6 | ) 7 | 8 | // P1. An acceptor must accept the first proposal that it receives. 9 | // If a proposal with value v is chosen, then every higher-numbered proposal 10 | // accepted by any acceptor has value v. 11 | type acceptor struct { 12 | id int 13 | learners []int 14 | 15 | accept message 16 | promised promise 17 | 18 | nt network 19 | } 20 | 21 | func newAcceptor(id int, nt network, learners ...int) *acceptor { 22 | return &acceptor{id: id, nt: nt, promised: message{}, learners: learners} 23 | } 24 | 25 | func (a *acceptor) run() { 26 | for { 27 | m, ok := a.nt.recv(time.Hour) 28 | if !ok { 29 | continue 30 | } 31 | switch m.typ { 32 | case Propose: 33 | accepted := a.receivePropose(m) 34 | if accepted { 35 | for _, l := range a.learners { 36 | m := a.accept 37 | m.from = a.id 38 | m.to = l 39 | a.nt.send(m) 40 | } 41 | } 42 | case Prepare: 43 | promise, ok := a.receivePrepare(m) 44 | if ok { 45 | a.nt.send(promise) 46 | } 47 | default: 48 | log.Panicf("acceptor: %d unexpected message type: %v", a.id, m.typ) 49 | } 50 | } 51 | } 52 | 53 | // If an acceptor receives a prepare request with number n greater 54 | // than that of any prepare request to which it has already responded, 55 | // then it responds to the request with a promise not to accept any more 56 | // proposals numbered less than n and with the highest-numbered proposal 57 | // (if any) that it has accepted. 58 | func (a *acceptor) receivePrepare(prepare message) (message, bool) { 59 | if a.promised.number() >= prepare.number() { 60 | log.Printf("acceptor: %d [promised: %+v] ignored prepare %+v", a.id, a.promised, prepare) 61 | return message{}, false 62 | } 63 | log.Printf("acceptor: %d [promised: %+v] promised %+v", a.id, a.promised, prepare) 64 | a.promised = prepare 65 | m := message{ 66 | typ: Promise, 67 | from: a.id, to: prepare.from, 68 | n: a.promised.number(), 69 | // previously accepted proposal 70 | prevn: a.accept.n, value: a.accept.value, 71 | } 72 | return m, true 73 | } 74 | 75 | // If an acceptor receives an accept request for a proposal numbered 76 | // n, it accepts the proposal unless it has already responded to a prepare 77 | // request having a number greater than n. 78 | func (a *acceptor) receivePropose(propose message) bool { 79 | if a.promised.number() > propose.number() { 80 | log.Printf("acceptor: %d [promised: %+v] ignored proposal %+v", a.id, a.promised, propose) 81 | return false 82 | } 83 | if a.promised.number() < propose.number() { 84 | log.Panicf("acceptor: %d received unexpected proposal %+v", a.id, propose) 85 | } 86 | log.Printf("acceptor: %d [promised: %+v, accept: %+v] accepted proposal %+v", a.id, a.promised, a.accept, propose) 87 | a.accept = propose 88 | a.accept.typ = Accept 89 | return true 90 | } 91 | 92 | func (a *acceptor) restart() {} 93 | func (a *acceptor) delay() {} 94 | -------------------------------------------------------------------------------- /proposer.go: -------------------------------------------------------------------------------- 1 | package paxos 2 | 3 | import ( 4 | "log" 5 | "time" 6 | ) 7 | 8 | type proposer struct { 9 | id int 10 | // stable 11 | lastSeq int 12 | 13 | value string 14 | valueN int 15 | 16 | acceptors map[int]promise 17 | nt network 18 | } 19 | 20 | func newProposer(id int, value string, nt network, acceptors ...int) *proposer { 21 | p := &proposer{id: id, nt: nt, lastSeq: 0, value: value, acceptors: make(map[int]promise)} 22 | for _, a := range acceptors { 23 | p.acceptors[a] = message{} 24 | } 25 | return p 26 | } 27 | 28 | func (p *proposer) run() { 29 | var ok bool 30 | var m message 31 | 32 | // stage 1: do prepare until reach the majority 33 | for !p.majorityReached() { 34 | if !ok { 35 | ms := p.prepare() 36 | for i := range ms { 37 | p.nt.send(ms[i]) 38 | } 39 | } 40 | m, ok = p.nt.recv(time.Second) 41 | if !ok { 42 | // the previous prepare is failed 43 | // continue to do another prepare 44 | continue 45 | } 46 | 47 | switch m.typ { 48 | case Promise: 49 | p.receivePromise(m) 50 | default: 51 | log.Panicf("proposer: %d unexpected message type: %v", p.id, m.typ) 52 | } 53 | } 54 | log.Printf("proposer: %d promise %d reached majority %d", p.id, p.n(), p.majority()) 55 | 56 | // stage 2: do propose 57 | log.Printf("proposer: %d starts to propose [%d: %s]", p.id, p.n(), p.value) 58 | ms := p.propose() 59 | for i := range ms { 60 | p.nt.send(ms[i]) 61 | } 62 | } 63 | 64 | // If the proposer receives the requested responses from a majority of 65 | // the acceptors, then it can issue a proposal with number n and value 66 | // v, where v is the value of the highest-numbered proposal among the 67 | // responses, or is any value selected by the proposer if the responders 68 | // reported no proposals. 69 | func (p *proposer) propose() []message { 70 | ms := make([]message, p.majority()) 71 | 72 | i := 0 73 | for to, promise := range p.acceptors { 74 | if promise.number() == p.n() { 75 | ms[i] = message{from: p.id, to: to, typ: Propose, n: p.n(), value: p.value} 76 | i++ 77 | } 78 | if i == p.majority() { 79 | break 80 | } 81 | } 82 | return ms 83 | } 84 | 85 | // A proposer chooses a new proposal number n and sends a request to 86 | // each member of some set of acceptors, asking it to respond with: 87 | // (a) A promise never again to accept a proposal numbered less than n, and 88 | // (b) The proposal with the highest number less than n that it has accepted, if any. 89 | func (p *proposer) prepare() []message { 90 | p.lastSeq++ 91 | 92 | ms := make([]message, p.majority()) 93 | i := 0 94 | for to := range p.acceptors { 95 | ms[i] = message{from: p.id, to: to, typ: Prepare, n: p.n()} 96 | i++ 97 | if i == p.majority() { 98 | break 99 | } 100 | } 101 | return ms 102 | } 103 | 104 | func (p *proposer) receivePromise(promise message) { 105 | prevPromise := p.acceptors[promise.from] 106 | 107 | if prevPromise.number() < promise.number() { 108 | log.Printf("proposer: %d received a new promise %+v", p.id, promise) 109 | p.acceptors[promise.from] = promise 110 | 111 | //update value to the value with a larger N 112 | if promise.proposalNumber() > p.valueN { 113 | log.Printf("proposer: %d updated the value [%s] to %s", p.id, p.value, promise.proposalValue()) 114 | p.valueN = promise.proposalNumber() 115 | p.value = promise.proposalValue() 116 | } 117 | } 118 | } 119 | 120 | func (p *proposer) majority() int { return len(p.acceptors)/2 + 1 } 121 | 122 | func (p *proposer) majorityReached() bool { 123 | m := 0 124 | for _, promise := range p.acceptors { 125 | if promise.number() == p.n() { 126 | m++ 127 | } 128 | } 129 | if m >= p.majority() { 130 | return true 131 | } 132 | return false 133 | } 134 | 135 | func (p *proposer) n() int { return p.lastSeq<<16 | p.id } 136 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | Apache License 2 | Version 2.0, January 2004 3 | http://www.apache.org/licenses/ 4 | 5 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 6 | 7 | 1. Definitions. 8 | 9 | "License" shall mean the terms and conditions for use, reproduction, 10 | and distribution as defined by Sections 1 through 9 of this document. 11 | 12 | "Licensor" shall mean the copyright owner or entity authorized by 13 | the copyright owner that is granting the License. 14 | 15 | "Legal Entity" shall mean the union of the acting entity and all 16 | other entities that control, are controlled by, or are under common 17 | control with that entity. For the purposes of this definition, 18 | "control" means (i) the power, direct or indirect, to cause the 19 | direction or management of such entity, whether by contract or 20 | otherwise, or (ii) ownership of fifty percent (50%) or more of the 21 | outstanding shares, or (iii) beneficial ownership of such entity. 22 | 23 | "You" (or "Your") shall mean an individual or Legal Entity 24 | exercising permissions granted by this License. 25 | 26 | "Source" form shall mean the preferred form for making modifications, 27 | including but not limited to software source code, documentation 28 | source, and configuration files. 29 | 30 | "Object" form shall mean any form resulting from mechanical 31 | transformation or translation of a Source form, including but 32 | not limited to compiled object code, generated documentation, 33 | and conversions to other media types. 34 | 35 | "Work" shall mean the work of authorship, whether in Source or 36 | Object form, made available under the License, as indicated by a 37 | copyright notice that is included in or attached to the work 38 | (an example is provided in the Appendix below). 39 | 40 | "Derivative Works" shall mean any work, whether in Source or Object 41 | form, that is based on (or derived from) the Work and for which the 42 | editorial revisions, annotations, elaborations, or other modifications 43 | represent, as a whole, an original work of authorship. For the purposes 44 | of this License, Derivative Works shall not include works that remain 45 | separable from, or merely link (or bind by name) to the interfaces of, 46 | the Work and Derivative Works thereof. 47 | 48 | "Contribution" shall mean any work of authorship, including 49 | the original version of the Work and any modifications or additions 50 | to that Work or Derivative Works thereof, that is intentionally 51 | submitted to Licensor for inclusion in the Work by the copyright owner 52 | or by an individual or Legal Entity authorized to submit on behalf of 53 | the copyright owner. For the purposes of this definition, "submitted" 54 | means any form of electronic, verbal, or written communication sent 55 | to the Licensor or its representatives, including but not limited to 56 | communication on electronic mailing lists, source code control systems, 57 | and issue tracking systems that are managed by, or on behalf of, the 58 | Licensor for the purpose of discussing and improving the Work, but 59 | excluding communication that is conspicuously marked or otherwise 60 | designated in writing by the copyright owner as "Not a Contribution." 61 | 62 | "Contributor" shall mean Licensor and any individual or Legal Entity 63 | on behalf of whom a Contribution has been received by Licensor and 64 | subsequently incorporated within the Work. 65 | 66 | 2. Grant of Copyright License. Subject to the terms and conditions of 67 | this License, each Contributor hereby grants to You a perpetual, 68 | worldwide, non-exclusive, no-charge, royalty-free, irrevocable 69 | copyright license to reproduce, prepare Derivative Works of, 70 | publicly display, publicly perform, sublicense, and distribute the 71 | Work and such Derivative Works in Source or Object form. 72 | 73 | 3. Grant of Patent License. Subject to the terms and conditions of 74 | this License, each Contributor hereby grants to You a perpetual, 75 | worldwide, non-exclusive, no-charge, royalty-free, irrevocable 76 | (except as stated in this section) patent license to make, have made, 77 | use, offer to sell, sell, import, and otherwise transfer the Work, 78 | where such license applies only to those patent claims licensable 79 | by such Contributor that are necessarily infringed by their 80 | Contribution(s) alone or by combination of their Contribution(s) 81 | with the Work to which such Contribution(s) was submitted. If You 82 | institute patent litigation against any entity (including a 83 | cross-claim or counterclaim in a lawsuit) alleging that the Work 84 | or a Contribution incorporated within the Work constitutes direct 85 | or contributory patent infringement, then any patent licenses 86 | granted to You under this License for that Work shall terminate 87 | as of the date such litigation is filed. 88 | 89 | 4. Redistribution. You may reproduce and distribute copies of the 90 | Work or Derivative Works thereof in any medium, with or without 91 | modifications, and in Source or Object form, provided that You 92 | meet the following conditions: 93 | 94 | (a) You must give any other recipients of the Work or 95 | Derivative Works a copy of this License; and 96 | 97 | (b) You must cause any modified files to carry prominent notices 98 | stating that You changed the files; and 99 | 100 | (c) You must retain, in the Source form of any Derivative Works 101 | that You distribute, all copyright, patent, trademark, and 102 | attribution notices from the Source form of the Work, 103 | excluding those notices that do not pertain to any part of 104 | the Derivative Works; and 105 | 106 | (d) If the Work includes a "NOTICE" text file as part of its 107 | distribution, then any Derivative Works that You distribute must 108 | include a readable copy of the attribution notices contained 109 | within such NOTICE file, excluding those notices that do not 110 | pertain to any part of the Derivative Works, in at least one 111 | of the following places: within a NOTICE text file distributed 112 | as part of the Derivative Works; within the Source form or 113 | documentation, if provided along with the Derivative Works; or, 114 | within a display generated by the Derivative Works, if and 115 | wherever such third-party notices normally appear. The contents 116 | of the NOTICE file are for informational purposes only and 117 | do not modify the License. You may add Your own attribution 118 | notices within Derivative Works that You distribute, alongside 119 | or as an addendum to the NOTICE text from the Work, provided 120 | that such additional attribution notices cannot be construed 121 | as modifying the License. 122 | 123 | You may add Your own copyright statement to Your modifications and 124 | may provide additional or different license terms and conditions 125 | for use, reproduction, or distribution of Your modifications, or 126 | for any such Derivative Works as a whole, provided Your use, 127 | reproduction, and distribution of the Work otherwise complies with 128 | the conditions stated in this License. 129 | 130 | 5. Submission of Contributions. Unless You explicitly state otherwise, 131 | any Contribution intentionally submitted for inclusion in the Work 132 | by You to the Licensor shall be under the terms and conditions of 133 | this License, without any additional terms or conditions. 134 | Notwithstanding the above, nothing herein shall supersede or modify 135 | the terms of any separate license agreement you may have executed 136 | with Licensor regarding such Contributions. 137 | 138 | 6. Trademarks. This License does not grant permission to use the trade 139 | names, trademarks, service marks, or product names of the Licensor, 140 | except as required for reasonable and customary use in describing the 141 | origin of the Work and reproducing the content of the NOTICE file. 142 | 143 | 7. Disclaimer of Warranty. Unless required by applicable law or 144 | agreed to in writing, Licensor provides the Work (and each 145 | Contributor provides its Contributions) on an "AS IS" BASIS, 146 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 147 | implied, including, without limitation, any warranties or conditions 148 | of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A 149 | PARTICULAR PURPOSE. You are solely responsible for determining the 150 | appropriateness of using or redistributing the Work and assume any 151 | risks associated with Your exercise of permissions under this License. 152 | 153 | 8. Limitation of Liability. In no event and under no legal theory, 154 | whether in tort (including negligence), contract, or otherwise, 155 | unless required by applicable law (such as deliberate and grossly 156 | negligent acts) or agreed to in writing, shall any Contributor be 157 | liable to You for damages, including any direct, indirect, special, 158 | incidental, or consequential damages of any character arising as a 159 | result of this License or out of the use or inability to use the 160 | Work (including but not limited to damages for loss of goodwill, 161 | work stoppage, computer failure or malfunction, or any and all 162 | other commercial damages or losses), even if such Contributor 163 | has been advised of the possibility of such damages. 164 | 165 | 9. Accepting Warranty or Additional Liability. While redistributing 166 | the Work or Derivative Works thereof, You may choose to offer, 167 | and charge a fee for, acceptance of support, warranty, indemnity, 168 | or other liability obligations and/or rights consistent with this 169 | License. However, in accepting such obligations, You may act only 170 | on Your own behalf and on Your sole responsibility, not on behalf 171 | of any other Contributor, and only if You agree to indemnify, 172 | defend, and hold each Contributor harmless for any liability 173 | incurred by, or claims asserted against, such Contributor by reason 174 | of your accepting any such warranty or additional liability. 175 | 176 | END OF TERMS AND CONDITIONS 177 | 178 | APPENDIX: How to apply the Apache License to your work. 179 | 180 | To apply the Apache License to your work, attach the following 181 | boilerplate notice, with the fields enclosed by brackets "{}" 182 | replaced with your own identifying information. (Don't include 183 | the brackets!) The text should be enclosed in the appropriate 184 | comment syntax for the file format. We also recommend that a 185 | file or class name and description of purpose be included on the 186 | same "printed page" as the copyright notice for easier 187 | identification within third-party archives. 188 | 189 | Copyright {yyyy} {name of copyright owner} 190 | 191 | Licensed under the Apache License, Version 2.0 (the "License"); 192 | you may not use this file except in compliance with the License. 193 | You may obtain a copy of the License at 194 | 195 | http://www.apache.org/licenses/LICENSE-2.0 196 | 197 | Unless required by applicable law or agreed to in writing, software 198 | distributed under the License is distributed on an "AS IS" BASIS, 199 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 200 | See the License for the specific language governing permissions and 201 | limitations under the License. 202 | 203 | --------------------------------------------------------------------------------