common.go

Documentation: encoding/asn1

		 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  		// This loop uses IndexByte and explicit slicing
		98  		// instead of strings.Split(str, ",") to reduce allocations.
		99  		i := strings.IndexByte(str, ',')
	 100  		if i < 0 {
	 101  			part, str = str, ""
	 102  		} else {
	 103  			part, str = str[:i], str[i+1:]
	 104  		}
	 105  		switch {
	 106  		case part == "optional":
	 107  			ret.optional = true
	 108  		case part == "explicit":
	 109  			ret.explicit = true
	 110  			if ret.tag == nil {
	 111  				ret.tag = new(int)
	 112  			}
	 113  		case part == "generalized":
	 114  			ret.timeType = TagGeneralizedTime
	 115  		case part == "utc":
	 116  			ret.timeType = TagUTCTime
	 117  		case part == "ia5":
	 118  			ret.stringType = TagIA5String
	 119  		case part == "printable":
	 120  			ret.stringType = TagPrintableString
	 121  		case part == "numeric":
	 122  			ret.stringType = TagNumericString
	 123  		case part == "utf8":
	 124  			ret.stringType = TagUTF8String
	 125  		case strings.HasPrefix(part, "default:"):
	 126  			i, err := strconv.ParseInt(part[8:], 10, 64)
	 127  			if err == nil {
	 128  				ret.defaultValue = new(int64)
	 129  				*ret.defaultValue = i
	 130  			}
	 131  		case strings.HasPrefix(part, "tag:"):
	 132  			i, err := strconv.Atoi(part[4:])
	 133  			if err == nil {
	 134  				ret.tag = new(int)
	 135  				*ret.tag = i
	 136  			}
	 137  		case part == "set":
	 138  			ret.set = true
	 139  		case part == "application":
	 140  			ret.application = true
	 141  			if ret.tag == nil {
	 142  				ret.tag = new(int)
	 143  			}
	 144  		case part == "private":
	 145  			ret.private = true
	 146  			if ret.tag == nil {
	 147  				ret.tag = new(int)
	 148  			}
	 149  		case part == "omitempty":
	 150  			ret.omitEmpty = true
	 151  		}
	 152  	}
	 153  	return
	 154  }
	 155  
	 156  // Given a reflected Go type, getUniversalType returns the default tag number
	 157  // and expected compound flag.
	 158  func getUniversalType(t reflect.Type) (matchAny bool, tagNumber int, isCompound, ok bool) {
	 159  	switch t {
	 160  	case rawValueType:
	 161  		return true, -1, false, true
	 162  	case objectIdentifierType:
	 163  		return false, TagOID, false, true
	 164  	case bitStringType:
	 165  		return false, TagBitString, false, true
	 166  	case timeType:
	 167  		return false, TagUTCTime, false, true
	 168  	case enumeratedType:
	 169  		return false, TagEnum, false, true
	 170  	case bigIntType:
	 171  		return false, TagInteger, false, true
	 172  	}
	 173  	switch t.Kind() {
	 174  	case reflect.Bool:
	 175  		return false, TagBoolean, false, true
	 176  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
	 177  		return false, TagInteger, false, true
	 178  	case reflect.Struct:
	 179  		return false, TagSequence, true, true
	 180  	case reflect.Slice:
	 181  		if t.Elem().Kind() == reflect.Uint8 {
	 182  			return false, TagOctetString, false, true
	 183  		}
	 184  		if strings.HasSuffix(t.Name(), "SET") {
	 185  			return false, TagSet, true, true
	 186  		}
	 187  		return false, TagSequence, true, true
	 188  	case reflect.String:
	 189  		return false, TagPrintableString, false, true
	 190  	}
	 191  	return false, 0, false, false
	 192  }
	 193
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