metadata.go

Documentation: github.com/grpc-ecosystem/go-grpc-middleware/tracing/opentracing

     1  // Copyright 2017 Michal Witkowski. All Rights Reserved.
     2  // See LICENSE for licensing terms.
     3  
     4  package grpc_opentracing
     5  
     6  import (
     7  	"encoding/base64"
     8  	"strings"
     9  
    10  	"google.golang.org/grpc/metadata"
    11  )
    12  
    13  const (
    14  	binHdrSuffix = "-bin"
    15  )
    16  
    17  // metadataTextMap extends a metadata.MD to be an opentracing textmap
    18  type metadataTextMap metadata.MD
    19  
    20  // Set is a opentracing.TextMapReader interface that extracts values.
    21  func (m metadataTextMap) Set(key, val string) {
    22  	// gRPC allows for complex binary values to be written.
    23  	encodedKey, encodedVal := encodeKeyValue(key, val)
    24  	// The metadata object is a multimap, and previous values may exist, but for opentracing headers, we do not append
    25  	// we just override.
    26  	m[encodedKey] = []string{encodedVal}
    27  }
    28  
    29  // ForeachKey is a opentracing.TextMapReader interface that extracts values.
    30  func (m metadataTextMap) ForeachKey(callback func(key, val string) error) error {
    31  	for k, vv := range m {
    32  		for _, v := range vv {
    33  			if err := callback(k, v); err != nil {
    34  				return err
    35  			}
    36  		}
    37  	}
    38  	return nil
    39  }
    40  
    41  // encodeKeyValue encodes key and value qualified for transmission via gRPC.
    42  // note: copy pasted from private values of grpc.metadata
    43  func encodeKeyValue(k, v string) (string, string) {
    44  	k = strings.ToLower(k)
    45  	if strings.HasSuffix(k, binHdrSuffix) {
    46  		val := base64.StdEncoding.EncodeToString([]byte(v))
    47  		v = string(val)
    48  	}
    49  	return k, v
    50  }
    51
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