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try.go
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try.go
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package processor
import (
"fmt"
"time"
"github.com/dafanshu/benthos/v3/internal/docs"
"github.com/dafanshu/benthos/v3/internal/interop"
"github.com/dafanshu/benthos/v3/lib/log"
"github.com/dafanshu/benthos/v3/lib/message"
"github.com/dafanshu/benthos/v3/lib/metrics"
"github.com/dafanshu/benthos/v3/lib/types"
)
//------------------------------------------------------------------------------
func init() {
Constructors[TypeTry] = TypeSpec{
constructor: NewTry,
Categories: []Category{
CategoryComposition,
},
Summary: `Executes a list of child processors on messages only if no prior processors have failed (or the errors have been cleared).`,
Description: `
This processor behaves similarly to the ` + "[`for_each`](/docs/components/processors/for_each)" + ` processor, where a list of child processors are applied to individual messages of a batch. However, if a message has failed any prior processor (before or during the try block) then that message will skip all following processors.
For example, with the following config:
` + "```yaml" + `
pipeline:
processors:
- resource: foo
- try:
- resource: bar
- resource: baz
- resource: buz
` + "```" + `
If the processor ` + "`bar`" + ` fails for a particular message, that message will skip the processors ` + "`baz` and `buz`" + `. Similarly, if ` + "`bar`" + ` succeeds but ` + "`baz`" + ` does not then ` + "`buz`" + ` will be skipped. If the processor ` + "`foo`" + ` fails for a message then none of ` + "`bar`, `baz` or `buz`" + ` are executed on that message.
This processor is useful for when child processors depend on the successful output of previous processors. This processor can be followed with a ` + "[catch](/docs/components/processors/catch)" + ` processor for defining child processors to be applied only to failed messages.
More information about error handing can be found [here](/docs/configuration/error_handling).
### Nesting within a catch block
In some cases it might be useful to nest a try block within a catch block, since the ` + "[`catch` processor](/docs/components/processors/catch)" + ` only clears errors _after_ executing its child processors this means a nested try processor will not execute unless the errors are explicitly cleared beforehand.
This can be done by inserting an empty catch block before the try block like as follows:
` + "```yaml" + `
pipeline:
processors:
- resource: foo
- catch:
- log:
level: ERROR
message: "Foo failed due to: ${! error() }"
- catch: [] # Clear prior error
- try:
- resource: bar
- resource: baz
` + "```" + `
`,
config: docs.FieldComponent().Array().HasType(docs.FieldTypeProcessor),
}
}
//------------------------------------------------------------------------------
// TryConfig is a config struct containing fields for the Try processor.
type TryConfig []Config
// NewTryConfig returns a default TryConfig.
func NewTryConfig() TryConfig {
return []Config{}
}
//------------------------------------------------------------------------------
// Try is a processor that applies a list of child processors to each message of
// a batch individually, where processors are skipped for messages that failed a
// previous processor step.
type Try struct {
children []types.Processor
log log.Modular
mCount metrics.StatCounter
mErr metrics.StatCounter
mSent metrics.StatCounter
mBatchSent metrics.StatCounter
}
// NewTry returns a Try processor.
func NewTry(
conf Config, mgr types.Manager, log log.Modular, stats metrics.Type,
) (Type, error) {
var children []types.Processor
for i, pconf := range conf.Try {
pMgr, pLog, pStats := interop.LabelChild(fmt.Sprintf("%v", i), mgr, log, stats)
proc, err := New(pconf, pMgr, pLog, pStats)
if err != nil {
return nil, err
}
children = append(children, proc)
}
return &Try{
children: children,
log: log,
mCount: stats.GetCounter("count"),
mErr: stats.GetCounter("error"),
mSent: stats.GetCounter("sent"),
mBatchSent: stats.GetCounter("batch.sent"),
}, nil
}
//------------------------------------------------------------------------------
// ProcessMessage applies the processor to a message, either creating >0
// resulting messages or a response to be sent back to the message source.
func (p *Try) ProcessMessage(msg types.Message) ([]types.Message, types.Response) {
p.mCount.Incr(1)
resultMsgs := make([]types.Message, msg.Len())
msg.Iter(func(i int, p types.Part) error {
tmpMsg := message.New(nil)
tmpMsg.SetAll([]types.Part{p})
resultMsgs[i] = tmpMsg
return nil
})
var res types.Response
if resultMsgs, res = ExecuteTryAll(p.children, resultMsgs...); res != nil {
return nil, res
}
resMsg := message.New(nil)
for _, m := range resultMsgs {
m.Iter(func(i int, p types.Part) error {
resMsg.Append(p)
return nil
})
}
p.mBatchSent.Incr(1)
p.mSent.Incr(int64(resMsg.Len()))
resMsgs := [1]types.Message{resMsg}
return resMsgs[:], nil
}
// CloseAsync shuts down the processor and stops processing requests.
func (p *Try) CloseAsync() {
for _, c := range p.children {
c.CloseAsync()
}
}
// WaitForClose blocks until the processor has closed down.
func (p *Try) WaitForClose(timeout time.Duration) error {
stopBy := time.Now().Add(timeout)
for _, c := range p.children {
if err := c.WaitForClose(time.Until(stopBy)); err != nil {
return err
}
}
return nil
}
//------------------------------------------------------------------------------