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base.go
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base.go
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package actions
import (
"bytes"
"context"
"crypto/sha256"
"encoding/json"
"net/http"
"time"
horizonContext "github.com/stellar/go/services/horizon/internal/context"
"github.com/stellar/go/services/horizon/internal/ledger"
"github.com/stellar/go/services/horizon/internal/render"
hProblem "github.com/stellar/go/services/horizon/internal/render/problem"
"github.com/stellar/go/services/horizon/internal/render/sse"
"github.com/stellar/go/support/errors"
"github.com/stellar/go/support/render/problem"
)
// Base is a helper struct you can use as part of a custom action via
// composition.
//
// TODO: example usage
type Base struct {
W http.ResponseWriter
R *http.Request
Err error
appCtx context.Context
sseUpdateFrequency time.Duration
isSetup bool
}
// Prepare established the common attributes that get used in nearly every
// action. "Child" actions may override this method to extend action, but it
// is advised you also call this implementation to maintain behavior.
func (base *Base) Prepare(w http.ResponseWriter, r *http.Request, appCtx context.Context, sseUpdateFrequency time.Duration) {
base.W = w
base.R = r
base.sseUpdateFrequency = sseUpdateFrequency
base.appCtx = appCtx
}
// Execute trigger content negotiation and the actual execution of one of the
// action's handlers.
func (base *Base) Execute(action interface{}) {
ctx := base.R.Context()
contentType := render.Negotiate(base.R)
switch contentType {
case render.MimeHal, render.MimeJSON:
action, ok := action.(JSONer)
if !ok {
goto NotAcceptable
}
err := action.JSON()
if err != nil {
problem.Render(ctx, base.W, err)
return
}
case render.MimeEventStream:
switch action.(type) {
case EventStreamer, SingleObjectStreamer:
default:
goto NotAcceptable
}
stream := sse.NewStream(ctx, base.W)
var oldHash [32]byte
for {
lastLedgerState := ledger.CurrentState()
// Rate limit the request if it's a call to stream since it queries the DB every second. See
// https://github.com/stellar/go/issues/715 for more details.
app := base.R.Context().Value(&horizonContext.AppContextKey)
rateLimiter := app.(RateLimiterProvider).GetRateLimiter()
if rateLimiter != nil {
limited, _, err := rateLimiter.RateLimiter.RateLimit(rateLimiter.VaryBy.Key(base.R), 1)
if err != nil {
stream.Err(errors.Wrap(err, "RateLimiter error"))
return
}
if limited {
stream.Err(sse.ErrRateLimited)
return
}
}
switch ac := action.(type) {
case EventStreamer:
err := ac.SSE(stream)
if err != nil {
stream.Err(err)
return
}
case SingleObjectStreamer:
newEvent, err := ac.LoadEvent()
if err != nil {
stream.Err(err)
return
}
resource, err := json.Marshal(newEvent.Data)
if err != nil {
stream.Err(errors.Wrap(err, "unable to marshal next action resource"))
return
}
nextHash := sha256.Sum256(resource)
if bytes.Equal(nextHash[:], oldHash[:]) {
break
}
oldHash = nextHash
stream.SetLimit(10)
stream.Send(newEvent)
}
// Manually send the preamble in case there are no data events in SSE to trigger a stream.Send call.
// This method is called every iteration of the loop, but is protected by a sync.Once variable so it's
// only executed once.
stream.Init()
if stream.IsDone() {
return
}
// Make sure this is buffered channel of size 1. Otherwise, the go routine below
// will never return if `newLedgers` channel is not read. From Effective Go:
// > If the channel is unbuffered, the sender blocks until the receiver has received the value.
newLedgers := make(chan bool, 1)
go func() {
for {
time.Sleep(base.sseUpdateFrequency)
currentLedgerState := ledger.CurrentState()
if currentLedgerState.HistoryLatest >= lastLedgerState.HistoryLatest+1 {
newLedgers <- true
return
}
}
}()
select {
case <-newLedgers:
continue
case <-ctx.Done():
case <-base.appCtx.Done():
}
stream.Done()
return
}
case render.MimeRaw:
action, ok := action.(RawDataResponder)
if !ok {
goto NotAcceptable
}
err := action.Raw()
if err != nil {
problem.Render(ctx, base.W, err)
return
}
default:
goto NotAcceptable
}
return
NotAcceptable:
problem.Render(ctx, base.W, hProblem.NotAcceptable)
return
}
// Do executes the provided func iff there is no current error for the action.
// Provides a nicer way to invoke a set of steps that each may set `action.Err`
// during execution
func (base *Base) Do(fns ...func()) {
for _, fn := range fns {
if base.Err != nil {
return
}
fn()
}
}
// Setup runs the provided funcs if and only if no call to Setup() has been
// made previously on this action.
func (base *Base) Setup(fns ...func()) {
if base.isSetup {
return
}
base.Do(fns...)
base.isSetup = true
}