text: // Copyright 2015 The Prometheus Authors
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  // http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  package expfmt
  
  import (
  	"fmt"
  	"io"
  	"net/http"
  
  	"github.com/golang/protobuf/proto"
  	"github.com/matttproud/golang_protobuf_extensions/pbutil"
  	"github.com/prometheus/common/internal/bitbucket.org/ww/goautoneg"
  
  	dto "github.com/prometheus/client_model/go"
  )
  
  // Encoder types encode metric families into an underlying wire protocol.
  type Encoder interface {
  	Encode(*dto.MetricFamily) error
  }
  
  // Closer is implemented by Encoders that need to be closed to finalize
  // encoding. (For example, OpenMetrics needs a final `# EOF` line.)
  //
  // Note that all Encoder implementations returned from this package implement
  // Closer, too, even if the Close call is a no-op. This happens in preparation
  // for adding a Close method to the Encoder interface directly in a (mildly
  // breaking) release in the future.
  type Closer interface {
  	Close() error
  }
  
  type encoderCloser struct {
  	encode func(*dto.MetricFamily) error
  	close  func() error
  }
  
  func (ec encoderCloser) Encode(v *dto.MetricFamily) error {
  	return ec.encode(v)
  }
  
  func (ec encoderCloser) Close() error {
  	return ec.close()
  }
  
  // Negotiate returns the Content-Type based on the given Accept header. If no
  // appropriate accepted type is found, FmtText is returned (which is the
  // Prometheus text format). This function will never negotiate FmtOpenMetrics,
  // as the support is still experimental. To include the option to negotiate
  // FmtOpenMetrics, use NegotiateOpenMetrics.
  func Negotiate(h http.Header) Format {
  	for _, ac := range goautoneg.ParseAccept(h.Get(hdrAccept)) {
  		ver := ac.Params["version"]
  		if ac.Type+"/"+ac.SubType == ProtoType && ac.Params["proto"] == ProtoProtocol {
  			switch ac.Params["encoding"] {
  			case "delimited":
  				return FmtProtoDelim
  			case "text":
  				return FmtProtoText
  			case "compact-text":
  				return FmtProtoCompact
  			}
  		}
  		if ac.Type == "text" && ac.SubType == "plain" && (ver == TextVersion || ver == "") {
  			return FmtText
  		}
  	}
  	return FmtText
  }
  
  // NegotiateIncludingOpenMetrics works like Negotiate but includes
  // FmtOpenMetrics as an option for the result. Note that this function is
  // temporary and will disappear once FmtOpenMetrics is fully supported and as
  // such may be negotiated by the normal Negotiate function.
  func NegotiateIncludingOpenMetrics(h http.Header) Format {
  	for _, ac := range goautoneg.ParseAccept(h.Get(hdrAccept)) {
  		ver := ac.Params["version"]
  		if ac.Type+"/"+ac.SubType == ProtoType && ac.Params["proto"] == ProtoProtocol {
  			switch ac.Params["encoding"] {
  			case "delimited":
  				return FmtProtoDelim
  			case "text":
  				return FmtProtoText
  			case "compact-text":
  				return FmtProtoCompact
  			}
  		}
  		if ac.Type == "text" && ac.SubType == "plain" && (ver == TextVersion || ver == "") {
  			return FmtText
  		}
  		if ac.Type+"/"+ac.SubType == OpenMetricsType && (ver == OpenMetricsVersion || ver == "") {
  			return FmtOpenMetrics
  		}
  	}
  	return FmtText
  }
  
  // NewEncoder returns a new encoder based on content type negotiation. All
  // Encoder implementations returned by NewEncoder also implement Closer, and
  // callers should always call the Close method. It is currently only required
  // for FmtOpenMetrics, but a future (breaking) release will add the Close method
  // to the Encoder interface directly. The current version of the Encoder
  // interface is kept for backwards compatibility.
  func NewEncoder(w io.Writer, format Format) Encoder {
  	switch format {
  	case FmtProtoDelim:
  		return encoderCloser{
  			encode: func(v *dto.MetricFamily) error {
  				_, err := pbutil.WriteDelimited(w, v)
  				return err
  			},
  			close: func() error { return nil },
  		}
  	case FmtProtoCompact:
  		return encoderCloser{
  			encode: func(v *dto.MetricFamily) error {
  				_, err := fmt.Fprintln(w, v.String())
  				return err
  			},
  			close: func() error { return nil },
  		}
  	case FmtProtoText:
  		return encoderCloser{
  			encode: func(v *dto.MetricFamily) error {
  				_, err := fmt.Fprintln(w, proto.MarshalTextString(v))
  				return err
  			},
  			close: func() error { return nil },
  		}
  	case FmtText:
  		return encoderCloser{
  			encode: func(v *dto.MetricFamily) error {
  				_, err := MetricFamilyToText(w, v)
  				return err
  			},
  			close: func() error { return nil },
  		}
  	case FmtOpenMetrics:
  		return encoderCloser{
  			encode: func(v *dto.MetricFamily) error {
  				_, err := MetricFamilyToOpenMetrics(w, v)
  				return err
  			},
  			close: func() error {
  				_, err := FinalizeOpenMetrics(w)
  				return err
  			},
  		}
  	}
  	panic(fmt.Errorf("expfmt.NewEncoder: unknown format %q", format))
  }
  