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Diffstat (limited to 'src/encoding/asn1/common.go')
| -rw-r--r-- | src/encoding/asn1/common.go | 185 |
1 files changed, 185 insertions, 0 deletions
diff --git a/src/encoding/asn1/common.go b/src/encoding/asn1/common.go new file mode 100644 index 0000000..40115df --- /dev/null +++ b/src/encoding/asn1/common.go @@ -0,0 +1,185 @@ +// Copyright 2009 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package asn1 + +import ( + "reflect" + "strconv" + "strings" +) + +// ASN.1 objects have metadata preceding them: +// the tag: the type of the object +// a flag denoting if this object is compound or not +// the class type: the namespace of the tag +// the length of the object, in bytes + +// Here are some standard tags and classes + +// ASN.1 tags represent the type of the following object. +const ( + TagBoolean = 1 + TagInteger = 2 + TagBitString = 3 + TagOctetString = 4 + TagNull = 5 + TagOID = 6 + TagEnum = 10 + TagUTF8String = 12 + TagSequence = 16 + TagSet = 17 + TagNumericString = 18 + TagPrintableString = 19 + TagT61String = 20 + TagIA5String = 22 + TagUTCTime = 23 + TagGeneralizedTime = 24 + TagGeneralString = 27 + TagBMPString = 30 +) + +// ASN.1 class types represent the namespace of the tag. +const ( + ClassUniversal = 0 + ClassApplication = 1 + ClassContextSpecific = 2 + ClassPrivate = 3 +) + +type tagAndLength struct { + class, tag, length int + isCompound bool +} + +// ASN.1 has IMPLICIT and EXPLICIT tags, which can be translated as "instead +// of" and "in addition to". When not specified, every primitive type has a +// default tag in the UNIVERSAL class. +// +// For example: a BIT STRING is tagged [UNIVERSAL 3] by default (although ASN.1 +// doesn't actually have a UNIVERSAL keyword). However, by saying [IMPLICIT +// CONTEXT-SPECIFIC 42], that means that the tag is replaced by another. +// +// On the other hand, if it said [EXPLICIT CONTEXT-SPECIFIC 10], then an +// /additional/ tag would wrap the default tag. This explicit tag will have the +// compound flag set. +// +// (This is used in order to remove ambiguity with optional elements.) +// +// You can layer EXPLICIT and IMPLICIT tags to an arbitrary depth, however we +// don't support that here. We support a single layer of EXPLICIT or IMPLICIT +// tagging with tag strings on the fields of a structure. + +// fieldParameters is the parsed representation of tag string from a structure field. +type fieldParameters struct { + optional bool // true iff the field is OPTIONAL + explicit bool // true iff an EXPLICIT tag is in use. + application bool // true iff an APPLICATION tag is in use. + private bool // true iff a PRIVATE tag is in use. + defaultValue *int64 // a default value for INTEGER typed fields (maybe nil). + tag *int // the EXPLICIT or IMPLICIT tag (maybe nil). + stringType int // the string tag to use when marshaling. + timeType int // the time tag to use when marshaling. + set bool // true iff this should be encoded as a SET + omitEmpty bool // true iff this should be omitted if empty when marshaling. + + // Invariants: + // if explicit is set, tag is non-nil. +} + +// Given a tag string with the format specified in the package comment, +// parseFieldParameters will parse it into a fieldParameters structure, +// ignoring unknown parts of the string. +func parseFieldParameters(str string) (ret fieldParameters) { + var part string + for len(str) > 0 { + part, str, _ = strings.Cut(str, ",") + switch { + case part == "optional": + ret.optional = true + case part == "explicit": + ret.explicit = true + if ret.tag == nil { + ret.tag = new(int) + } + case part == "generalized": + ret.timeType = TagGeneralizedTime + case part == "utc": + ret.timeType = TagUTCTime + case part == "ia5": + ret.stringType = TagIA5String + case part == "printable": + ret.stringType = TagPrintableString + case part == "numeric": + ret.stringType = TagNumericString + case part == "utf8": + ret.stringType = TagUTF8String + case strings.HasPrefix(part, "default:"): + i, err := strconv.ParseInt(part[8:], 10, 64) + if err == nil { + ret.defaultValue = new(int64) + *ret.defaultValue = i + } + case strings.HasPrefix(part, "tag:"): + i, err := strconv.Atoi(part[4:]) + if err == nil { + ret.tag = new(int) + *ret.tag = i + } + case part == "set": + ret.set = true + case part == "application": + ret.application = true + if ret.tag == nil { + ret.tag = new(int) + } + case part == "private": + ret.private = true + if ret.tag == nil { + ret.tag = new(int) + } + case part == "omitempty": + ret.omitEmpty = true + } + } + return +} + +// Given a reflected Go type, getUniversalType returns the default tag number +// and expected compound flag. +func getUniversalType(t reflect.Type) (matchAny bool, tagNumber int, isCompound, ok bool) { + switch t { + case rawValueType: + return true, -1, false, true + case objectIdentifierType: + return false, TagOID, false, true + case bitStringType: + return false, TagBitString, false, true + case timeType: + return false, TagUTCTime, false, true + case enumeratedType: + return false, TagEnum, false, true + case bigIntType: + return false, TagInteger, false, true + } + switch t.Kind() { + case reflect.Bool: + return false, TagBoolean, false, true + case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64: + return false, TagInteger, false, true + case reflect.Struct: + return false, TagSequence, true, true + case reflect.Slice: + if t.Elem().Kind() == reflect.Uint8 { + return false, TagOctetString, false, true + } + if strings.HasSuffix(t.Name(), "SET") { + return false, TagSet, true, true + } + return false, TagSequence, true, true + case reflect.String: + return false, TagPrintableString, false, true + } + return false, 0, false, false +} |