tracestate.go

Documentation: go.opencensus.io/trace/tracestate

     1  // Copyright 2018, OpenCensus Authors
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // Package tracestate implements support for the Tracestate header of the
    16  // W3C TraceContext propagation format.
    17  package tracestate
    18  
    19  import (
    20  	"fmt"
    21  	"regexp"
    22  )
    23  
    24  const (
    25  	keyMaxSize       = 256
    26  	valueMaxSize     = 256
    27  	maxKeyValuePairs = 32
    28  )
    29  
    30  const (
    31  	keyWithoutVendorFormat = `[a-z][_0-9a-z\-\*\/]{0,255}`
    32  	keyWithVendorFormat    = `[a-z][_0-9a-z\-\*\/]{0,240}@[a-z][_0-9a-z\-\*\/]{0,13}`
    33  	keyFormat              = `(` + keyWithoutVendorFormat + `)|(` + keyWithVendorFormat + `)`
    34  	valueFormat            = `[\x20-\x2b\x2d-\x3c\x3e-\x7e]{0,255}[\x21-\x2b\x2d-\x3c\x3e-\x7e]`
    35  )
    36  
    37  var keyValidationRegExp = regexp.MustCompile(`^(` + keyFormat + `)$`)
    38  var valueValidationRegExp = regexp.MustCompile(`^(` + valueFormat + `)$`)
    39  
    40  // Tracestate represents tracing-system specific context in a list of key-value pairs. Tracestate allows different
    41  // vendors propagate additional information and inter-operate with their legacy Id formats.
    42  type Tracestate struct {
    43  	entries []Entry
    44  }
    45  
    46  // Entry represents one key-value pair in a list of key-value pair of Tracestate.
    47  type Entry struct {
    48  	// Key is an opaque string up to 256 characters printable. It MUST begin with a lowercase letter,
    49  	// and can only contain lowercase letters a-z, digits 0-9, underscores _, dashes -, asterisks *, and
    50  	// forward slashes /.
    51  	Key string
    52  
    53  	// Value is an opaque string up to 256 characters printable ASCII RFC0020 characters (i.e., the
    54  	// range 0x20 to 0x7E) except comma , and =.
    55  	Value string
    56  }
    57  
    58  // Entries returns a slice of Entry.
    59  func (ts *Tracestate) Entries() []Entry {
    60  	if ts == nil {
    61  		return nil
    62  	}
    63  	return ts.entries
    64  }
    65  
    66  func (ts *Tracestate) remove(key string) *Entry {
    67  	for index, entry := range ts.entries {
    68  		if entry.Key == key {
    69  			ts.entries = append(ts.entries[:index], ts.entries[index+1:]...)
    70  			return &entry
    71  		}
    72  	}
    73  	return nil
    74  }
    75  
    76  func (ts *Tracestate) add(entries []Entry) error {
    77  	for _, entry := range entries {
    78  		ts.remove(entry.Key)
    79  	}
    80  	if len(ts.entries)+len(entries) > maxKeyValuePairs {
    81  		return fmt.Errorf("adding %d key-value pairs to current %d pairs exceeds the limit of %d",
    82  			len(entries), len(ts.entries), maxKeyValuePairs)
    83  	}
    84  	ts.entries = append(entries, ts.entries...)
    85  	return nil
    86  }
    87  
    88  func isValid(entry Entry) bool {
    89  	return keyValidationRegExp.MatchString(entry.Key) &&
    90  		valueValidationRegExp.MatchString(entry.Value)
    91  }
    92  
    93  func containsDuplicateKey(entries ...Entry) (string, bool) {
    94  	keyMap := make(map[string]int)
    95  	for _, entry := range entries {
    96  		if _, ok := keyMap[entry.Key]; ok {
    97  			return entry.Key, true
    98  		}
    99  		keyMap[entry.Key] = 1
   100  	}
   101  	return "", false
   102  }
   103  
   104  func areEntriesValid(entries ...Entry) (*Entry, bool) {
   105  	for _, entry := range entries {
   106  		if !isValid(entry) {
   107  			return &entry, false
   108  		}
   109  	}
   110  	return nil, true
   111  }
   112  
   113  // New creates a Tracestate object from a parent and/or entries (key-value pair).
   114  // Entries from the parent are copied if present. The entries passed to this function
   115  // are inserted in front of those copied from the parent. If an entry copied from the
   116  // parent contains the same key as one of the entry in entries then the entry copied
   117  // from the parent is removed. See add func.
   118  //
   119  // An error is returned with nil Tracestate if
   120  //  1. one or more entry in entries is invalid.
   121  //  2. two or more entries in the input entries have the same key.
   122  //  3. the number of entries combined from the parent and the input entries exceeds maxKeyValuePairs.
   123  //     (duplicate entry is counted only once).
   124  func New(parent *Tracestate, entries ...Entry) (*Tracestate, error) {
   125  	if parent == nil && len(entries) == 0 {
   126  		return nil, nil
   127  	}
   128  	if entry, ok := areEntriesValid(entries...); !ok {
   129  		return nil, fmt.Errorf("key-value pair {%s, %s} is invalid", entry.Key, entry.Value)
   130  	}
   131  
   132  	if key, duplicate := containsDuplicateKey(entries...); duplicate {
   133  		return nil, fmt.Errorf("contains duplicate keys (%s)", key)
   134  	}
   135  
   136  	tracestate := Tracestate{}
   137  
   138  	if parent != nil && len(parent.entries) > 0 {
   139  		tracestate.entries = append([]Entry{}, parent.entries...)
   140  	}
   141  
   142  	err := tracestate.add(entries)
   143  	if err != nil {
   144  		return nil, err
   145  	}
   146  	return &tracestate, nil
   147  }
   148
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