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79 lines
2.8 KiB
79 lines
2.8 KiB
6 years ago
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// Copyright 2018, OpenCensus Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package exemplar implements support for exemplars. Exemplars are additional
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// data associated with each measurement.
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//
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// Their purpose it to provide an example of the kind of thing
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// (request, RPC, trace span, etc.) that resulted in that measurement.
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package exemplar
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import (
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"context"
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"time"
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)
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const (
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KeyTraceID = "trace_id"
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KeySpanID = "span_id"
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KeyPrefixTag = "tag:"
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)
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// Exemplar is an example data point associated with each bucket of a
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// distribution type aggregation.
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type Exemplar struct {
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Value float64 // the value that was recorded
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Timestamp time.Time // the time the value was recorded
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Attachments Attachments // attachments (if any)
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}
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// Attachments is a map of extra values associated with a recorded data point.
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// The map should only be mutated from AttachmentExtractor functions.
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type Attachments map[string]string
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// AttachmentExtractor is a function capable of extracting exemplar attachments
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// from the context used to record measurements.
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// The map passed to the function should be mutated and returned. It will
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// initially be nil: the first AttachmentExtractor that would like to add keys to the
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// map is responsible for initializing it.
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type AttachmentExtractor func(ctx context.Context, a Attachments) Attachments
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var extractors []AttachmentExtractor
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// RegisterAttachmentExtractor registers the given extractor associated with the exemplar
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// type name.
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//
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// Extractors will be used to attempt to extract exemplars from the context
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// associated with each recorded measurement.
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//
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// Packages that support exemplars should register their extractor functions on
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// initialization.
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//
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// RegisterAttachmentExtractor should not be called after any measurements have
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// been recorded.
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func RegisterAttachmentExtractor(e AttachmentExtractor) {
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extractors = append(extractors, e)
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}
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// NewFromContext extracts exemplars from the given context.
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// Each registered AttachmentExtractor (see RegisterAttachmentExtractor) is called in an
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// unspecified order to add attachments to the exemplar.
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func AttachmentsFromContext(ctx context.Context) Attachments {
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var a Attachments
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for _, extractor := range extractors {
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a = extractor(ctx, a)
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}
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return a
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}
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