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view.go
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view.go
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// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0
package metric // import "go.opentelemetry.io/otel/sdk/metric"
import (
"errors"
"regexp"
"strings"
"go.opentelemetry.io/otel/internal/global"
)
var (
errMultiInst = errors.New("name replacement for multiple instruments")
errEmptyView = errors.New("no criteria provided for view")
emptyView = func(Instrument) (Stream, bool) { return Stream{}, false }
)
// View is an override to the default behavior of the SDK. It defines how data
// should be collected for certain instruments. It returns true and the exact
// Stream to use for matching Instruments. Otherwise, if the view does not
// match, false is returned.
type View func(Instrument) (Stream, bool)
// NewView returns a View that applies the Stream mask for all instruments that
// match criteria. The returned View will only apply mask if all non-zero-value
// fields of criteria match the corresponding Instrument passed to the view. If
// no criteria are provided, all field of criteria are their zero-values, a
// view that matches no instruments is returned. If you need to match a
// zero-value field, create a View directly.
//
// The Name field of criteria supports wildcard pattern matching. The "*"
// wildcard is recognized as matching zero or more characters, and "?" is
// recognized as matching exactly one character. For example, a pattern of "*"
// matches all instrument names.
//
// The Stream mask only applies updates for non-zero-value fields. By default,
// the Instrument the View matches against will be use for the Name,
// Description, and Unit of the returned Stream and no Aggregation or
// AttributeFilter are set. All non-zero-value fields of mask are used instead
// of the default. If you need to zero out an Stream field returned from a
// View, create a View directly.
func NewView(criteria Instrument, mask Stream) View {
if criteria.IsEmpty() {
global.Error(
errEmptyView, "dropping view",
"mask", mask,
)
return emptyView
}
var matchFunc func(Instrument) bool
if strings.ContainsAny(criteria.Name, "*?") {
if mask.Name != "" {
global.Error(
errMultiInst, "dropping view",
"criteria", criteria,
"mask", mask,
)
return emptyView
}
// Handle branching here in NewView instead of criteria.matches so
// criteria.matches remains inlinable for the simple case.
pattern := regexp.QuoteMeta(criteria.Name)
pattern = "^" + pattern + "$"
pattern = strings.ReplaceAll(pattern, `\?`, ".")
pattern = strings.ReplaceAll(pattern, `\*`, ".*")
re := regexp.MustCompile(pattern)
matchFunc = func(i Instrument) bool {
return re.MatchString(i.Name) &&
criteria.matchesDescription(i) &&
criteria.matchesKind(i) &&
criteria.matchesUnit(i) &&
criteria.matchesScope(i)
}
} else {
matchFunc = criteria.matches
}
var agg Aggregation
if mask.Aggregation != nil {
agg = mask.Aggregation.copy()
if err := agg.err(); err != nil {
global.Error(
err, "not using aggregation with view",
"criteria", criteria,
"mask", mask,
)
agg = nil
}
}
return func(i Instrument) (Stream, bool) {
if matchFunc(i) {
return Stream{
Name: nonZero(mask.Name, i.Name),
Description: nonZero(mask.Description, i.Description),
Unit: nonZero(mask.Unit, i.Unit),
Aggregation: agg,
AttributeFilter: mask.AttributeFilter,
}, true
}
return Stream{}, false
}
}
// nonZero returns v if it is non-zero-valued, otherwise alt.
func nonZero[T comparable](v, alt T) T {
var zero T
if v != zero {
return v
}
return alt
}