Johannes 'fish' Ziemke
8 years ago
3 changed files with 212 additions and 5 deletions
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// Copyright 2016 The Prometheus Authors
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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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// Copyright (c) 2013, The Prometheus Authors
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// All rights reserved.
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//
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// Use of this source code is governed by a BSD-style license that can be found
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// in the LICENSE file.
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// Package promhttp contains functions to create http.Handler instances to
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// expose Prometheus metrics via HTTP. In later versions of this package, it
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// will also contain tooling to instrument instances of http.Handler and
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// http.RoundTripper.
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//
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// promhttp.Handler acts on the prometheus.DefaultGatherer. With HandlerFor,
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// you can create a handler for a custom registry or anything that implements
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// the Gatherer interface. It also allows to create handlers that act
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// differently on errors or allow to log errors.
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package promhttp |
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import ( |
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"bytes" |
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"compress/gzip" |
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"fmt" |
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"io" |
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"net/http" |
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"strings" |
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"sync" |
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"github.com/prometheus/common/expfmt" |
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"github.com/prometheus/client_golang/prometheus" |
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) |
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const ( |
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contentTypeHeader = "Content-Type" |
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contentLengthHeader = "Content-Length" |
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contentEncodingHeader = "Content-Encoding" |
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acceptEncodingHeader = "Accept-Encoding" |
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) |
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var bufPool sync.Pool |
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func getBuf() *bytes.Buffer { |
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buf := bufPool.Get() |
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if buf == nil { |
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return &bytes.Buffer{} |
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} |
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return buf.(*bytes.Buffer) |
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} |
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func giveBuf(buf *bytes.Buffer) { |
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buf.Reset() |
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bufPool.Put(buf) |
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} |
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// Handler returns an HTTP handler for the prometheus.DefaultGatherer. The
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// Handler uses the default HandlerOpts, i.e. report the first error as an HTTP
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// error, no error logging, and compression if requested by the client.
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//
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// If you want to create a Handler for the DefaultGatherer with different
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// HandlerOpts, create it with HandlerFor with prometheus.DefaultGatherer and
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// your desired HandlerOpts.
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func Handler() http.Handler { |
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return HandlerFor(prometheus.DefaultGatherer, HandlerOpts{}) |
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} |
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// HandlerFor returns an http.Handler for the provided Gatherer. The behavior
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// of the Handler is defined by the provided HandlerOpts.
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func HandlerFor(reg prometheus.Gatherer, opts HandlerOpts) http.Handler { |
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return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) { |
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mfs, err := reg.Gather() |
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if err != nil { |
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if opts.ErrorLog != nil { |
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opts.ErrorLog.Println("error gathering metrics:", err) |
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} |
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switch opts.ErrorHandling { |
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case PanicOnError: |
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panic(err) |
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case ContinueOnError: |
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if len(mfs) == 0 { |
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http.Error(w, "No metrics gathered, last error:\n\n"+err.Error(), http.StatusInternalServerError) |
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return |
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} |
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case HTTPErrorOnError: |
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http.Error(w, "An error has occurred during metrics gathering:\n\n"+err.Error(), http.StatusInternalServerError) |
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return |
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} |
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} |
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contentType := expfmt.Negotiate(req.Header) |
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buf := getBuf() |
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defer giveBuf(buf) |
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writer, encoding := decorateWriter(req, buf, opts.DisableCompression) |
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enc := expfmt.NewEncoder(writer, contentType) |
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var lastErr error |
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for _, mf := range mfs { |
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if err := enc.Encode(mf); err != nil { |
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lastErr = err |
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if opts.ErrorLog != nil { |
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opts.ErrorLog.Println("error encoding metric family:", err) |
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} |
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switch opts.ErrorHandling { |
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case PanicOnError: |
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panic(err) |
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case ContinueOnError: |
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// Handled later.
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case HTTPErrorOnError: |
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http.Error(w, "An error has occurred during metrics encoding:\n\n"+err.Error(), http.StatusInternalServerError) |
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return |
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} |
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} |
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} |
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if closer, ok := writer.(io.Closer); ok { |
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closer.Close() |
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} |
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if lastErr != nil && buf.Len() == 0 { |
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http.Error(w, "No metrics encoded, last error:\n\n"+err.Error(), http.StatusInternalServerError) |
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return |
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} |
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header := w.Header() |
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header.Set(contentTypeHeader, string(contentType)) |
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header.Set(contentLengthHeader, fmt.Sprint(buf.Len())) |
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if encoding != "" { |
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header.Set(contentEncodingHeader, encoding) |
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} |
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w.Write(buf.Bytes()) |
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// TODO(beorn7): Consider streaming serving of metrics.
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}) |
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} |
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// HandlerErrorHandling defines how a Handler serving metrics will handle
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// errors.
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type HandlerErrorHandling int |
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// These constants cause handlers serving metrics to behave as described if
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// errors are encountered.
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const ( |
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// Serve an HTTP status code 500 upon the first error
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// encountered. Report the error message in the body.
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HTTPErrorOnError HandlerErrorHandling = iota |
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// Ignore errors and try to serve as many metrics as possible. However,
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// if no metrics can be served, serve an HTTP status code 500 and the
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// last error message in the body. Only use this in deliberate "best
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// effort" metrics collection scenarios. It is recommended to at least
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// log errors (by providing an ErrorLog in HandlerOpts) to not mask
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// errors completely.
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ContinueOnError |
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// Panic upon the first error encountered (useful for "crash only" apps).
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PanicOnError |
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) |
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// Logger is the minimal interface HandlerOpts needs for logging. Note that
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// log.Logger from the standard library implements this interface, and it is
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// easy to implement by custom loggers, if they don't do so already anyway.
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type Logger interface { |
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Println(v ...interface{}) |
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} |
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// HandlerOpts specifies options how to serve metrics via an http.Handler. The
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// zero value of HandlerOpts is a reasonable default.
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type HandlerOpts struct { |
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// ErrorLog specifies an optional logger for errors collecting and
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// serving metrics. If nil, errors are not logged at all.
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ErrorLog Logger |
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// ErrorHandling defines how errors are handled. Note that errors are
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// logged regardless of the configured ErrorHandling provided ErrorLog
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// is not nil.
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ErrorHandling HandlerErrorHandling |
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// If DisableCompression is true, the handler will never compress the
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// response, even if requested by the client.
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DisableCompression bool |
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} |
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// decorateWriter wraps a writer to handle gzip compression if requested. It
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// returns the decorated writer and the appropriate "Content-Encoding" header
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// (which is empty if no compression is enabled).
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func decorateWriter(request *http.Request, writer io.Writer, compressionDisabled bool) (io.Writer, string) { |
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if compressionDisabled { |
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return writer, "" |
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} |
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header := request.Header.Get(acceptEncodingHeader) |
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parts := strings.Split(header, ",") |
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for _, part := range parts { |
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part := strings.TrimSpace(part) |
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if part == "gzip" || strings.HasPrefix(part, "gzip;") { |
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return gzip.NewWriter(writer), "gzip" |
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} |
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} |
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return writer, "" |
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} |
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