common.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package asn1
     6  
     7  import (
     8  	"reflect"
     9  	"strconv"
    10  	"strings"
    11  )
    12  
    13  // ASN.1 objects have metadata preceding them:
    14  //   the tag: the type of the object
    15  //   a flag denoting if this object is compound or not
    16  //   the class type: the namespace of the tag
    17  //   the length of the object, in bytes
    18  
    19  // Here are some standard tags and classes
    20  
    21  // ASN.1 tags represent the type of the following object.
    22  const (
    23  	TagBoolean         = 1
    24  	TagInteger         = 2
    25  	TagBitString       = 3
    26  	TagOctetString     = 4
    27  	TagNull            = 5
    28  	TagOID             = 6
    29  	TagEnum            = 10
    30  	TagUTF8String      = 12
    31  	TagSequence        = 16
    32  	TagSet             = 17
    33  	TagNumericString   = 18
    34  	TagPrintableString = 19
    35  	TagT61String       = 20
    36  	TagIA5String       = 22
    37  	TagUTCTime         = 23
    38  	TagGeneralizedTime = 24
    39  	TagGeneralString   = 27
    40  	TagBMPString       = 30
    41  )
    42  
    43  // ASN.1 class types represent the namespace of the tag.
    44  const (
    45  	ClassUniversal       = 0
    46  	ClassApplication     = 1
    47  	ClassContextSpecific = 2
    48  	ClassPrivate         = 3
    49  )
    50  
    51  type tagAndLength struct {
    52  	class, tag, length int
    53  	isCompound         bool
    54  }
    55  
    56  // ASN.1 has IMPLICIT and EXPLICIT tags, which can be translated as "instead
    57  // of" and "in addition to". When not specified, every primitive type has a
    58  // default tag in the UNIVERSAL class.
    59  //
    60  // For example: a BIT STRING is tagged [UNIVERSAL 3] by default (although ASN.1
    61  // doesn't actually have a UNIVERSAL keyword). However, by saying [IMPLICIT
    62  // CONTEXT-SPECIFIC 42], that means that the tag is replaced by another.
    63  //
    64  // On the other hand, if it said [EXPLICIT CONTEXT-SPECIFIC 10], then an
    65  // /additional/ tag would wrap the default tag. This explicit tag will have the
    66  // compound flag set.
    67  //
    68  // (This is used in order to remove ambiguity with optional elements.)
    69  //
    70  // You can layer EXPLICIT and IMPLICIT tags to an arbitrary depth, however we
    71  // don't support that here. We support a single layer of EXPLICIT or IMPLICIT
    72  // tagging with tag strings on the fields of a structure.
    73  
    74  // fieldParameters is the parsed representation of tag string from a structure field.
    75  type fieldParameters struct {
    76  	optional     bool   // true iff the field is OPTIONAL
    77  	explicit     bool   // true iff an EXPLICIT tag is in use.
    78  	application  bool   // true iff an APPLICATION tag is in use.
    79  	private      bool   // true iff a PRIVATE tag is in use.
    80  	defaultValue *int64 // a default value for INTEGER typed fields (maybe nil).
    81  	tag          *int   // the EXPLICIT or IMPLICIT tag (maybe nil).
    82  	stringType   int    // the string tag to use when marshaling.
    83  	timeType     int    // the time tag to use when marshaling.
    84  	set          bool   // true iff this should be encoded as a SET
    85  	omitEmpty    bool   // true iff this should be omitted if empty when marshaling.
    86  
    87  	// Invariants:
    88  	//   if explicit is set, tag is non-nil.
    89  }
    90  
    91  // Given a tag string with the format specified in the package comment,
    92  // parseFieldParameters will parse it into a fieldParameters structure,
    93  // ignoring unknown parts of the string.
    94  func parseFieldParameters(str string) (ret fieldParameters) {
    95  	var part string
    96  	for len(str) > 0 {
    97  		part, str, _ = strings.Cut(str, ",")
    98  		switch {
    99  		case part == "optional":
   100  			ret.optional = true
   101  		case part == "explicit":
   102  			ret.explicit = true
   103  			if ret.tag == nil {
   104  				ret.tag = new(int)
   105  			}
   106  		case part == "generalized":
   107  			ret.timeType = TagGeneralizedTime
   108  		case part == "utc":
   109  			ret.timeType = TagUTCTime
   110  		case part == "ia5":
   111  			ret.stringType = TagIA5String
   112  		case part == "printable":
   113  			ret.stringType = TagPrintableString
   114  		case part == "numeric":
   115  			ret.stringType = TagNumericString
   116  		case part == "utf8":
   117  			ret.stringType = TagUTF8String
   118  		case strings.HasPrefix(part, "default:"):
   119  			i, err := strconv.ParseInt(part[8:], 10, 64)
   120  			if err == nil {
   121  				ret.defaultValue = new(int64)
   122  				*ret.defaultValue = i
   123  			}
   124  		case strings.HasPrefix(part, "tag:"):
   125  			i, err := strconv.Atoi(part[4:])
   126  			if err == nil {
   127  				ret.tag = new(int)
   128  				*ret.tag = i
   129  			}
   130  		case part == "set":
   131  			ret.set = true
   132  		case part == "application":
   133  			ret.application = true
   134  			if ret.tag == nil {
   135  				ret.tag = new(int)
   136  			}
   137  		case part == "private":
   138  			ret.private = true
   139  			if ret.tag == nil {
   140  				ret.tag = new(int)
   141  			}
   142  		case part == "omitempty":
   143  			ret.omitEmpty = true
   144  		}
   145  	}
   146  	return
   147  }
   148  
   149  // Given a reflected Go type, getUniversalType returns the default tag number
   150  // and expected compound flag.
   151  func getUniversalType(t reflect.Type) (matchAny bool, tagNumber int, isCompound, ok bool) {
   152  	switch t {
   153  	case rawValueType:
   154  		return true, -1, false, true
   155  	case objectIdentifierType:
   156  		return false, TagOID, false, true
   157  	case bitStringType:
   158  		return false, TagBitString, false, true
   159  	case timeType:
   160  		return false, TagUTCTime, false, true
   161  	case enumeratedType:
   162  		return false, TagEnum, false, true
   163  	case bigIntType:
   164  		return false, TagInteger, false, true
   165  	}
   166  	switch t.Kind() {
   167  	case reflect.Bool:
   168  		return false, TagBoolean, false, true
   169  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   170  		return false, TagInteger, false, true
   171  	case reflect.Struct:
   172  		return false, TagSequence, true, true
   173  	case reflect.Slice:
   174  		if t.Elem().Kind() == reflect.Uint8 {
   175  			return false, TagOctetString, false, true
   176  		}
   177  		if strings.HasSuffix(t.Name(), "SET") {
   178  			return false, TagSet, true, true
   179  		}
   180  		return false, TagSequence, true, true
   181  	case reflect.String:
   182  		return false, TagPrintableString, false, true
   183  	}
   184  	return false, 0, false, false
   185  }
   186
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