/
merging.go
199 lines (172 loc) · 4.56 KB
/
merging.go
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package proxy
import (
"context"
"strings"
"time"
"github.com/devopsfaith/krakend/config"
)
// NewMergeDataMiddleware creates proxy middleware for merging responses from several backends
func NewMergeDataMiddleware(endpointConfig *config.EndpointConfig) Middleware {
totalBackends := len(endpointConfig.Backend)
if totalBackends == 0 {
panic(ErrNoBackends)
}
if totalBackends == 1 {
return EmptyMiddleware
}
serviceTimeout := time.Duration(85*endpointConfig.Timeout.Nanoseconds()/100) * time.Nanosecond
combiner := getResponseCombiner(endpointConfig.ExtraConfig)
return func(next ...Proxy) Proxy {
if len(next) != totalBackends {
panic(ErrNotEnoughProxies)
}
return func(ctx context.Context, request *Request) (*Response, error) {
localCtx, cancel := context.WithTimeout(ctx, serviceTimeout)
parts := make(chan *Response, totalBackends)
failed := make(chan error, totalBackends)
for _, n := range next {
go requestPart(localCtx, n, request, parts, failed)
}
acc := newIncrementalMergeAccumulator(totalBackends, combiner)
for i := 0; i < totalBackends; i++ {
select {
case err := <-failed:
acc.Merge(nil, err)
case response := <-parts:
acc.Merge(response, nil)
}
}
result, err := acc.Result()
cancel()
return result, err
}
}
}
type incrementalMergeAccumulator struct {
pending int
data *Response
combiner ResponseCombiner
errs []error
}
func newIncrementalMergeAccumulator(total int, combiner ResponseCombiner) *incrementalMergeAccumulator {
return &incrementalMergeAccumulator{
pending: total,
combiner: combiner,
errs: []error{},
}
}
func (i *incrementalMergeAccumulator) Merge(res *Response, err error) {
i.pending--
if err != nil {
i.errs = append(i.errs, err)
if i.data != nil {
i.data.IsComplete = false
}
return
}
if res == nil {
i.errs = append(i.errs, errNullResult)
return
}
if i.data == nil {
i.data = res
return
}
i.data = i.combiner(2, []*Response{i.data, res})
}
func (i *incrementalMergeAccumulator) Result() (*Response, error) {
if i.data == nil {
return &Response{Data: make(map[string]interface{}, 0), IsComplete: false}, newMergeError(i.errs)
}
if i.pending != 0 || len(i.errs) != 0 {
i.data.IsComplete = false
}
return i.data, newMergeError(i.errs)
}
func requestPart(ctx context.Context, next Proxy, request *Request, out chan<- *Response, failed chan<- error) {
localCtx, cancel := context.WithCancel(ctx)
in, err := next(localCtx, request)
if err != nil {
failed <- err
cancel()
return
}
if in == nil {
failed <- errNullResult
cancel()
return
}
select {
case out <- in:
case <-ctx.Done():
failed <- ctx.Err()
}
cancel()
}
func newMergeError(errs []error) error {
if len(errs) == 0 {
return nil
}
return mergeError{errs}
}
type mergeError struct {
errs []error
}
func (m mergeError) Error() string {
msg := make([]string, len(m.errs))
for i, err := range m.errs {
msg[i] = err.Error()
}
return strings.Join(msg, "\n")
}
// ResponseCombiner func to merge the collected responses into a single one
type ResponseCombiner func(int, []*Response) *Response
// RegisterResponseCombiner adds a new response combiner into the internal register
func RegisterResponseCombiner(name string, f ResponseCombiner) {
responseCombiners.SetResponseCombiner(name, f)
}
const (
mergeKey = "combiner"
defaultCombinerName = "default"
)
var responseCombiners = initResponseCombiners()
func initResponseCombiners() *combinerRegister {
return newCombinerRegister(map[string]ResponseCombiner{defaultCombinerName: combineData}, combineData)
}
func getResponseCombiner(extra config.ExtraConfig) ResponseCombiner {
combiner, _ := responseCombiners.GetResponseCombiner(defaultCombinerName)
if v, ok := extra[Namespace]; ok {
if e, ok := v.(map[string]interface{}); ok {
if v, ok := e[mergeKey]; ok {
if c, ok := responseCombiners.GetResponseCombiner(v.(string)); ok {
combiner = c
}
}
}
}
return combiner
}
func combineData(total int, parts []*Response) *Response {
isComplete := len(parts) == total
var retResponse *Response
for _, part := range parts {
if part == nil || part.Data == nil {
isComplete = false
continue
}
isComplete = isComplete && part.IsComplete
if retResponse == nil {
retResponse = part
continue
}
for k, v := range part.Data {
retResponse.Data[k] = v
}
}
if nil == retResponse {
// do not allow nil data in the response:
return &Response{Data: make(map[string]interface{}, 0), IsComplete: isComplete}
}
retResponse.IsComplete = isComplete
return retResponse
}