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iterator.go
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/
iterator.go
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package servicebus
import (
"context"
"errors"
"sort"
"time"
"github.com/Azure/azure-amqp-common-go/log"
"github.com/Azure/azure-amqp-common-go/rpc"
"pack.ag/amqp"
)
type (
// MessageIterator offers a simple mechanism for iterating over a list of
MessageIterator interface {
Done() bool
Next(context.Context) (*Message, error)
}
// MessageSliceIterator is a wrapper, which lets any slice of Message pointers be used as a MessageIterator.
MessageSliceIterator struct {
Target []*Message
Cursor int
}
peekIterator struct {
entity entityConnector
buffer chan *Message
lastSequenceNumber int64
}
// PeekOption allows customization of parameters when querying a Service Bus entity for messages without committing
// to processing them.
PeekOption func(*peekIterator) error
)
const (
defaultPeekPageSize = 10
)
// AsMessageSliceIterator wraps a slice of Message pointers to allow it to be made into a MessageIterator.
func AsMessageSliceIterator(target []*Message) *MessageSliceIterator {
return &MessageSliceIterator{
Target: target,
}
}
// Done communicates whether there are more messages remaining to be iterated over.
func (ms MessageSliceIterator) Done() bool {
return ms.Cursor >= len(ms.Target)
}
// Next fetches the Message in the slice at a position one larger than the last one accessed.s
func (ms *MessageSliceIterator) Next(_ context.Context) (*Message, error) {
if ms.Done() {
return nil, ErrNoMessages{}
}
retval := ms.Target[ms.Cursor]
ms.Cursor++
return retval, nil
}
func newPeekIterator(entityConnector entityConnector, options ...PeekOption) (*peekIterator, error) {
retval := &peekIterator{
entity: entityConnector,
}
foundPageSize := false
for i := range options {
if err := options[i](retval); err != nil {
return nil, err
}
if retval.buffer != nil {
foundPageSize = true
}
}
if !foundPageSize {
err := PeekWithPageSize(defaultPeekPageSize)(retval)
if err != nil {
return nil, err
}
}
return retval, nil
}
// PeekWithPageSize adjusts how many messages are fetched at once while peeking from the server.
func PeekWithPageSize(pageSize int) PeekOption {
return func(pi *peekIterator) error {
if pageSize < 0 {
return errors.New("page size must not be less than zero")
}
if pi.buffer != nil {
return errors.New("cannot modify an existing peekIterator's buffer")
}
pi.buffer = make(chan *Message, pageSize)
return nil
}
}
// PeekFromSequenceNumber adds a filter to the Peek operation, so that no messages with a Sequence Number less than
// 'seq' are returned.
func PeekFromSequenceNumber(seq int64) PeekOption {
return func(pi *peekIterator) error {
pi.lastSequenceNumber = seq + 1
return nil
}
}
func (pi peekIterator) Done() bool {
return false
}
func (pi *peekIterator) Next(ctx context.Context) (*Message, error) {
span, ctx := startConsumerSpanFromContext(ctx, "sb.peekIterator.Next")
defer span.Finish()
if len(pi.buffer) == 0 {
if err := pi.getNextPage(ctx); err != nil {
return nil, err
}
}
select {
case next := <-pi.buffer:
return next, nil
case <-ctx.Done():
return nil, ctx.Err()
}
}
func (pi *peekIterator) getNextPage(ctx context.Context) error {
span, ctx := startConsumerSpanFromContext(ctx, "sb.peekIterator.getNextPage")
defer span.Finish()
const messagesField, messageField = "messages", "message"
msg := &amqp.Message{
ApplicationProperties: map[string]interface{}{
operationFieldName: peekMessageOperationID,
},
Value: map[string]interface{}{
"from-sequence-number": pi.lastSequenceNumber,
"message-count": int32(cap(pi.buffer)),
},
}
if deadline, ok := ctx.Deadline(); ok {
msg.ApplicationProperties["server-timeout"] = uint(time.Until(deadline) / time.Millisecond)
}
conn, err := pi.entity.connection(ctx)
if err != nil {
log.For(ctx).Error(err)
return err
}
link, err := rpc.NewLink(conn, pi.entity.ManagementPath())
if err != nil {
log.For(ctx).Error(err)
return err
}
rsp, err := link.RetryableRPC(ctx, 5, 5*time.Second, msg)
if err != nil {
log.For(ctx).Error(err)
return err
}
if rsp.Code == 204 {
return ErrNoMessages{}
}
// Peeked messages come back in a relatively convoluted manner:
// a map (always with one key: "messages")
// of arrays
// of maps (always with one key: "message")
// of an array with raw encoded Service Bus messages
val, ok := rsp.Message.Value.(map[string]interface{})
if !ok {
err = newErrIncorrectType(messageField, map[string]interface{}{}, rsp.Message.Value)
log.For(ctx).Error(err)
return err
}
rawMessages, ok := val[messagesField]
if !ok {
err = ErrMissingField(messagesField)
log.For(ctx).Error(err)
return err
}
messages, ok := rawMessages.([]interface{})
if !ok {
err = newErrIncorrectType(messagesField, []interface{}{}, rawMessages)
log.For(ctx).Error(err)
return err
}
transformedMessages := make([]*Message, len(messages))
for i := range messages {
rawEntry, ok := messages[i].(map[string]interface{})
if !ok {
err = newErrIncorrectType(messageField, map[string]interface{}{}, messages[i])
log.For(ctx).Error(err)
return err
}
rawMessage, ok := rawEntry[messageField]
if !ok {
err = ErrMissingField(messageField)
log.For(ctx).Error(err)
return err
}
marshaled, ok := rawMessage.([]byte)
if !ok {
err = new(ErrMalformedMessage)
log.For(ctx).Error(err)
return err
}
var rehydrated amqp.Message
err = rehydrated.UnmarshalBinary(marshaled)
if err != nil {
log.For(ctx).Error(err)
return err
}
transformedMessages[i], err = messageFromAMQPMessage(&rehydrated)
if err != nil {
log.For(ctx).Error(err)
return err
}
}
// This sort is done to ensure that folks wanting to peek messages in sequence order may do so.
sort.Slice(transformedMessages, func(i, j int) bool {
iSeq := *transformedMessages[i].SystemProperties.SequenceNumber
jSeq := *transformedMessages[j].SystemProperties.SequenceNumber
return iSeq < jSeq
})
for i := range transformedMessages {
select {
case pi.buffer <- transformedMessages[i]:
// Intentionally Left Blank
case <-ctx.Done():
return ctx.Err()
}
}
// Update last seen sequence number so that the next read starts from where this ended.
pi.lastSequenceNumber = *transformedMessages[len(transformedMessages)-1].SystemProperties.SequenceNumber + 1
return nil
}