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races.go
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races.go
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// Copyright 2018 Google LLC. All Rights Reserved.
//
// 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 submission
import (
"context"
"fmt"
"strings"
"sync"
"time"
ct "github.com/ctylim/certificate-transparency-go-p192"
"github.com/ctylim/certificate-transparency-go-p192/ctpolicy"
)
const (
// PostBatchInterval is duration between parallel batch call and subsequent
// requests to Logs within group.
// TODO(Mercurrent): optimize to avoid excessive requests.
PostBatchInterval = time.Second
)
// Submitter is interface wrapping Log-request-response cycle and any processing.
type Submitter interface {
SubmitToLog(ctx context.Context, logURL string, chain []ct.ASN1Cert, asPreChain bool) (*ct.SignedCertificateTimestamp, error)
}
// submissionResult holds outcome of a single-log submission.
type submissionResult struct {
sct *ct.SignedCertificateTimestamp
err error
}
type groupState struct {
Name string
Success bool
}
// safeSubmissionState is a submission state-machine for set of Log-groups.
// When some group is complete cancels all requests that are not needed by any
// group.
type safeSubmissionState struct {
mu sync.Mutex
logToGroups map[string]ctpolicy.GroupSet
groupNeeds map[string]int
results map[string]*submissionResult
cancels map[string]context.CancelFunc
}
func newSafeSubmissionState(groups ctpolicy.LogPolicyData) *safeSubmissionState {
var s safeSubmissionState
s.logToGroups = ctpolicy.GroupByLogs(groups)
s.groupNeeds = make(map[string]int)
for _, g := range groups {
s.groupNeeds[g.Name] = g.MinInclusions
}
s.results = make(map[string]*submissionResult)
s.cancels = make(map[string]context.CancelFunc)
return &s
}
// request includes empty submissionResult in the set, returns whether
// the entry is requested for the first time.
func (sub *safeSubmissionState) request(logURL string, cancel context.CancelFunc) bool {
sub.mu.Lock()
defer sub.mu.Unlock()
if sub.results[logURL] != nil {
// Already requested.
return false
}
sub.results[logURL] = &submissionResult{}
isAwaited := false
for g := range sub.logToGroups[logURL] {
if sub.groupNeeds[g] > 0 {
isAwaited = true
break
}
}
if !isAwaited {
// No groups expecting result from this Log.
return false
}
sub.cancels[logURL] = cancel
return true
}
// setResult processes SCT-result. Writes it down if it is error or awaited-SCT.
// Re-calculates group-completion and cancels any running but
// not-awaited-anymore Log-requests.
func (sub *safeSubmissionState) setResult(logURL string, sct *ct.SignedCertificateTimestamp, err error) {
sub.mu.Lock()
defer sub.mu.Unlock()
if sct == nil {
sub.results[logURL] = &submissionResult{sct: sct, err: err}
return
}
// If at least one group needs that SCT, result is set. Otherwise dumped.
for groupName := range sub.logToGroups[logURL] {
if sub.groupNeeds[groupName] > 0 {
sub.results[logURL] = &submissionResult{sct: sct, err: err}
}
sub.groupNeeds[groupName]--
}
// Cancel any pending Log-requests for which there're no more awaiting
// Log-groups.
for logURL, groupSet := range sub.logToGroups {
isAwaited := false
for g := range groupSet {
if sub.groupNeeds[g] > 0 {
isAwaited = true
break
}
}
if !isAwaited && sub.cancels[logURL] != nil {
sub.cancels[logURL]()
sub.cancels[logURL] = nil
}
}
}
// groupComplete returns true iff the specified group has all the SCTs it needs.
func (sub *safeSubmissionState) groupComplete(groupName string) bool {
sub.mu.Lock()
defer sub.mu.Unlock()
needs, ok := sub.groupNeeds[groupName]
if !ok {
return true
}
return needs <= 0
}
func (sub *safeSubmissionState) collectSCTs() []*AssignedSCT {
sub.mu.Lock()
defer sub.mu.Unlock()
scts := []*AssignedSCT{}
for logURL, r := range sub.results {
if r != nil && r.sct != nil {
scts = append(scts, &AssignedSCT{LogURL: logURL, SCT: r.sct})
}
}
return scts
}
// postInterval calculates duration for consequent call.
// For first parallelStart calls duration is 0, while every next one gets
// additional dur interval.
func postInterval(idx int, parallelStart int, dur time.Duration) time.Duration {
if idx < parallelStart {
return time.Duration(0)
}
return time.Duration(idx+1-parallelStart) * dur
}
// groupRace shuffles logs within the group, submits avoiding
// duplicate-requests and collects responses.
func groupRace(ctx context.Context, chain []ct.ASN1Cert, asPreChain bool,
group *ctpolicy.LogGroupInfo, parallelStart int,
state *safeSubmissionState, submitter Submitter) groupState {
// Randomize the order in which we send requests to the logs in a group
// so we maximize the distribution of logs we get SCTs from.
session := group.GetSubmissionSession()
type count struct{}
counter := make(chan count, len(session))
countCall := func() {
counter <- count{}
}
for i, logURL := range session {
subCtx, cancel := context.WithCancel(ctx)
go func(i int, logURL string) {
defer countCall()
timeoutchan := time.After(postInterval(i, parallelStart, PostBatchInterval))
select {
case <-subCtx.Done():
return
case <-timeoutchan:
}
if state.groupComplete(group.Name) {
cancel()
return
}
if firstRequested := state.request(logURL, cancel); !firstRequested {
return
}
sct, err := submitter.SubmitToLog(subCtx, logURL, chain, asPreChain)
// TODO(Mercurrent): verify SCT
state.setResult(logURL, sct, err)
}(i, logURL)
}
// Wait until either all logs within session are processed or context is
// cancelled.
for range session {
select {
case <-ctx.Done():
return groupState{Name: group.Name, Success: state.groupComplete(group.Name)}
case <-counter:
if state.groupComplete(group.Name) {
return groupState{Name: group.Name, Success: true}
}
}
}
return groupState{Name: group.Name, Success: state.groupComplete(group.Name)}
}
func parallelNums(groups ctpolicy.LogPolicyData) map[string]int {
nums := make(map[string]int)
var subsetSum int
for _, g := range groups {
nums[g.Name] = g.MinInclusions
if !g.IsBase {
subsetSum += g.MinInclusions
}
}
if _, hasBase := nums[ctpolicy.BaseName]; hasBase {
if nums[ctpolicy.BaseName] >= subsetSum {
nums[ctpolicy.BaseName] -= subsetSum
} else {
nums[ctpolicy.BaseName] = 0
}
}
return nums
}
// AssignedSCT represents SCT with logURL of log-producer.
type AssignedSCT struct {
LogURL string
SCT *ct.SignedCertificateTimestamp
}
func completenessError(groupComplete map[string]bool) error {
failedGroups := []string{}
for name, success := range groupComplete {
if !success {
failedGroups = append(failedGroups, name)
}
}
if len(failedGroups) > 0 {
return fmt.Errorf("log-group(s) %s didn't receive enough SCTs", strings.Join(failedGroups, ", "))
}
return nil
}
// GetSCTs picks required number of Logs according to policy-group logic and
// collects SCTs from them.
// Emits all collected SCTs even when any error produced.
func GetSCTs(ctx context.Context, submitter Submitter, chain []ct.ASN1Cert, asPreChain bool, groups ctpolicy.LogPolicyData) ([]*AssignedSCT, error) {
groupComplete := make(map[string]bool)
for _, g := range groups {
groupComplete[g.Name] = false
}
parallelNums := parallelNums(groups)
// channel listening to group-completion (failure) events from each single group-race.
groupEvents := make(chan groupState, len(groups))
submissions := newSafeSubmissionState(groups)
for _, g := range groups {
go func(g *ctpolicy.LogGroupInfo) {
groupEvents <- groupRace(ctx, chain, asPreChain, g, parallelNums[g.Name], submissions, submitter)
}(g)
}
// Terminates upon either all logs available are requested or required
// number of SCTs is collected or upon context timeout.
for i := 0; i < len(groups); i++ {
select {
case <-ctx.Done():
return submissions.collectSCTs(), completenessError(groupComplete)
case g := <-groupEvents:
groupComplete[g.Name] = g.Success
}
}
return submissions.collectSCTs(), completenessError(groupComplete)
}