| // 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. |
| |
| // The asn1 package implements parsing of DER-encoded ASN.1 data structures, |
| // as defined in ITU-T Rec X.690. |
| // |
| // See also ``A Layman's Guide to a Subset of ASN.1, BER, and DER,'' |
| // http://luca.ntop.org/Teaching/Appunti/asn1.html. |
| package asn1 |
| |
| // ASN.1 is a syntax for specifying abstract objects and BER, DER, PER, XER etc |
| // are different encoding formats for those objects. Here, we'll be dealing |
| // with DER, the Distinguished Encoding Rules. DER is used in X.509 because |
| // it's fast to parse and, unlike BER, has a unique encoding for every object. |
| // When calculating hashes over objects, it's important that the resulting |
| // bytes be the same at both ends and DER removes this margin of error. |
| // |
| // ASN.1 is very complex and this package doesn't attempt to implement |
| // everything by any means. |
| |
| import ( |
| "fmt" |
| "os" |
| "reflect" |
| "time" |
| ) |
| |
| // A StructuralError suggests that the ASN.1 data is valid, but the Go type |
| // which is receiving it doesn't match. |
| type StructuralError struct { |
| Msg string |
| } |
| |
| func (e StructuralError) String() string { return "ASN.1 structure error: " + e.Msg } |
| |
| // A SyntaxError suggests that the ASN.1 data is invalid. |
| type SyntaxError struct { |
| Msg string |
| } |
| |
| func (e SyntaxError) String() string { return "ASN.1 syntax error: " + e.Msg } |
| |
| // We start by dealing with each of the primitive types in turn. |
| |
| // BOOLEAN |
| |
| func parseBool(bytes []byte) (ret bool, err os.Error) { |
| if len(bytes) != 1 { |
| err = SyntaxError{"invalid boolean"} |
| return |
| } |
| |
| return bytes[0] != 0, nil |
| } |
| |
| // INTEGER |
| |
| // parseInt64 treats the given bytes as a big-endian, signed integer and |
| // returns the result. |
| func parseInt64(bytes []byte) (ret int64, err os.Error) { |
| if len(bytes) > 8 { |
| // We'll overflow an int64 in this case. |
| err = StructuralError{"integer too large"} |
| return |
| } |
| for bytesRead := 0; bytesRead < len(bytes); bytesRead++ { |
| ret <<= 8 |
| ret |= int64(bytes[bytesRead]) |
| } |
| |
| // Shift up and down in order to sign extend the result. |
| ret <<= 64 - uint8(len(bytes))*8 |
| ret >>= 64 - uint8(len(bytes))*8 |
| return |
| } |
| |
| // parseInt treats the given bytes as a big-endian, signed integer and returns |
| // the result. |
| func parseInt(bytes []byte) (int, os.Error) { |
| ret64, err := parseInt64(bytes) |
| if err != nil { |
| return 0, err |
| } |
| if ret64 != int64(int(ret64)) { |
| return 0, StructuralError{"integer too large"} |
| } |
| return int(ret64), nil |
| } |
| |
| // BIT STRING |
| |
| // BitString is the structure to use when you want an ASN.1 BIT STRING type. A |
| // bit string is padded up to the nearest byte in memory and the number of |
| // valid bits is recorded. Padding bits will be zero. |
| type BitString struct { |
| Bytes []byte // bits packed into bytes. |
| BitLength int // length in bits. |
| } |
| |
| // At returns the bit at the given index. If the index is out of range it |
| // returns false. |
| func (b BitString) At(i int) int { |
| if i < 0 || i >= b.BitLength { |
| return 0 |
| } |
| x := i / 8 |
| y := 7 - uint(i%8) |
| return int(b.Bytes[x]>>y) & 1 |
| } |
| |
| // RightAlign returns a slice where the padding bits are at the beginning. The |
| // slice may share memory with the BitString. |
| func (b BitString) RightAlign() []byte { |
| shift := uint(8 - (b.BitLength % 8)) |
| if shift == 8 || len(b.Bytes) == 0 { |
| return b.Bytes |
| } |
| |
| a := make([]byte, len(b.Bytes)) |
| a[0] = b.Bytes[0] >> shift |
| for i := 1; i < len(b.Bytes); i++ { |
| a[i] = b.Bytes[i-1] << (8 - shift) |
| a[i] |= b.Bytes[i] >> shift |
| } |
| |
| return a |
| } |
| |
| // parseBitString parses an ASN.1 bit string from the given byte array and returns it. |
| func parseBitString(bytes []byte) (ret BitString, err os.Error) { |
| if len(bytes) == 0 { |
| err = SyntaxError{"zero length BIT STRING"} |
| return |
| } |
| paddingBits := int(bytes[0]) |
| if paddingBits > 7 || |
| len(bytes) == 1 && paddingBits > 0 || |
| bytes[len(bytes)-1]&((1<<bytes[0])-1) != 0 { |
| err = SyntaxError{"invalid padding bits in BIT STRING"} |
| return |
| } |
| ret.BitLength = (len(bytes)-1)*8 - paddingBits |
| ret.Bytes = bytes[1:] |
| return |
| } |
| |
| // OBJECT IDENTIFIER |
| |
| // An ObjectIdentifier represents an ASN.1 OBJECT IDENTIFIER. |
| type ObjectIdentifier []int |
| |
| // Equal returns true iff oi and other represent the same identifier. |
| func (oi ObjectIdentifier) Equal(other ObjectIdentifier) bool { |
| if len(oi) != len(other) { |
| return false |
| } |
| for i := 0; i < len(oi); i++ { |
| if oi[i] != other[i] { |
| return false |
| } |
| } |
| |
| return true |
| } |
| |
| // parseObjectIdentifier parses an OBJECT IDENTIFER from the given bytes and |
| // returns it. An object identifer is a sequence of variable length integers |
| // that are assigned in a hierarachy. |
| func parseObjectIdentifier(bytes []byte) (s []int, err os.Error) { |
| if len(bytes) == 0 { |
| err = SyntaxError{"zero length OBJECT IDENTIFIER"} |
| return |
| } |
| |
| // In the worst case, we get two elements from the first byte (which is |
| // encoded differently) and then every varint is a single byte long. |
| s = make([]int, len(bytes)+1) |
| |
| // The first byte is 40*value1 + value2: |
| s[0] = int(bytes[0]) / 40 |
| s[1] = int(bytes[0]) % 40 |
| i := 2 |
| for offset := 1; offset < len(bytes); i++ { |
| var v int |
| v, offset, err = parseBase128Int(bytes, offset) |
| if err != nil { |
| return |
| } |
| s[i] = v |
| } |
| s = s[0:i] |
| return |
| } |
| |
| // ENUMERATED |
| |
| // An Enumerated is represented as a plain int. |
| type Enumerated int |
| |
| |
| // FLAG |
| |
| // A Flag accepts any data and is set to true if present. |
| type Flag bool |
| |
| // parseBase128Int parses a base-128 encoded int from the given offset in the |
| // given byte array. It returns the value and the new offset. |
| func parseBase128Int(bytes []byte, initOffset int) (ret, offset int, err os.Error) { |
| offset = initOffset |
| for shifted := 0; offset < len(bytes); shifted++ { |
| if shifted > 4 { |
| err = StructuralError{"base 128 integer too large"} |
| return |
| } |
| ret <<= 7 |
| b := bytes[offset] |
| ret |= int(b & 0x7f) |
| offset++ |
| if b&0x80 == 0 { |
| return |
| } |
| } |
| err = SyntaxError{"truncated base 128 integer"} |
| return |
| } |
| |
| // UTCTime |
| |
| func parseUTCTime(bytes []byte) (ret *time.Time, err os.Error) { |
| s := string(bytes) |
| ret, err = time.Parse("0601021504Z0700", s) |
| if err == nil { |
| return |
| } |
| ret, err = time.Parse("060102150405Z0700", s) |
| return |
| } |
| |
| // parseGeneralizedTime parses the GeneralizedTime from the given byte array |
| // and returns the resulting time. |
| func parseGeneralizedTime(bytes []byte) (ret *time.Time, err os.Error) { |
| return time.Parse("20060102150405Z0700", string(bytes)) |
| } |
| |
| // PrintableString |
| |
| // parsePrintableString parses a ASN.1 PrintableString from the given byte |
| // array and returns it. |
| func parsePrintableString(bytes []byte) (ret string, err os.Error) { |
| for _, b := range bytes { |
| if !isPrintable(b) { |
| err = SyntaxError{"PrintableString contains invalid character"} |
| return |
| } |
| } |
| ret = string(bytes) |
| return |
| } |
| |
| // isPrintable returns true iff the given b is in the ASN.1 PrintableString set. |
| func isPrintable(b byte) bool { |
| return 'a' <= b && b <= 'z' || |
| 'A' <= b && b <= 'Z' || |
| '0' <= b && b <= '9' || |
| '\'' <= b && b <= ')' || |
| '+' <= b && b <= '/' || |
| b == ' ' || |
| b == ':' || |
| b == '=' || |
| b == '?' || |
| // This is techincally not allowed in a PrintableString. |
| // However, x509 certificates with wildcard strings don't |
| // always use the correct string type so we permit it. |
| b == '*' |
| } |
| |
| // IA5String |
| |
| // parseIA5String parses a ASN.1 IA5String (ASCII string) from the given |
| // byte array and returns it. |
| func parseIA5String(bytes []byte) (ret string, err os.Error) { |
| for _, b := range bytes { |
| if b >= 0x80 { |
| err = SyntaxError{"IA5String contains invalid character"} |
| return |
| } |
| } |
| ret = string(bytes) |
| return |
| } |
| |
| // T61String |
| |
| // parseT61String parses a ASN.1 T61String (8-bit clean string) from the given |
| // byte array and returns it. |
| func parseT61String(bytes []byte) (ret string, err os.Error) { |
| return string(bytes), nil |
| } |
| |
| // A RawValue represents an undecoded ASN.1 object. |
| type RawValue struct { |
| Class, Tag int |
| IsCompound bool |
| Bytes []byte |
| FullBytes []byte // includes the tag and length |
| } |
| |
| // RawContent is used to signal that the undecoded, DER data needs to be |
| // preserved for a struct. To use it, the first field of the struct must have |
| // this type. It's an error for any of the other fields to have this type. |
| type RawContent []byte |
| |
| // Tagging |
| |
| // parseTagAndLength parses an ASN.1 tag and length pair from the given offset |
| // into a byte array. It returns the parsed data and the new offset. SET and |
| // SET OF (tag 17) are mapped to SEQUENCE and SEQUENCE OF (tag 16) since we |
| // don't distinguish between ordered and unordered objects in this code. |
| func parseTagAndLength(bytes []byte, initOffset int) (ret tagAndLength, offset int, err os.Error) { |
| offset = initOffset |
| b := bytes[offset] |
| offset++ |
| ret.class = int(b >> 6) |
| ret.isCompound = b&0x20 == 0x20 |
| ret.tag = int(b & 0x1f) |
| |
| // If the bottom five bits are set, then the tag number is actually base 128 |
| // encoded afterwards |
| if ret.tag == 0x1f { |
| ret.tag, offset, err = parseBase128Int(bytes, offset) |
| if err != nil { |
| return |
| } |
| } |
| if offset >= len(bytes) { |
| err = SyntaxError{"truncated tag or length"} |
| return |
| } |
| b = bytes[offset] |
| offset++ |
| if b&0x80 == 0 { |
| // The length is encoded in the bottom 7 bits. |
| ret.length = int(b & 0x7f) |
| } else { |
| // Bottom 7 bits give the number of length bytes to follow. |
| numBytes := int(b & 0x7f) |
| // We risk overflowing a signed 32-bit number if we accept more than 3 bytes. |
| if numBytes > 3 { |
| err = StructuralError{"length too large"} |
| return |
| } |
| if numBytes == 0 { |
| err = SyntaxError{"indefinite length found (not DER)"} |
| return |
| } |
| ret.length = 0 |
| for i := 0; i < numBytes; i++ { |
| if offset >= len(bytes) { |
| err = SyntaxError{"truncated tag or length"} |
| return |
| } |
| b = bytes[offset] |
| offset++ |
| ret.length <<= 8 |
| ret.length |= int(b) |
| } |
| } |
| |
| return |
| } |
| |
| // parseSequenceOf is used for SEQUENCE OF and SET OF values. It tries to parse |
| // a number of ASN.1 values from the given byte array and returns them as a |
| // slice of Go values of the given type. |
| func parseSequenceOf(bytes []byte, sliceType *reflect.SliceType, elemType reflect.Type) (ret *reflect.SliceValue, err os.Error) { |
| expectedTag, compoundType, ok := getUniversalType(elemType) |
| if !ok { |
| err = StructuralError{"unknown Go type for slice"} |
| return |
| } |
| |
| // First we iterate over the input and count the number of elements, |
| // checking that the types are correct in each case. |
| numElements := 0 |
| for offset := 0; offset < len(bytes); { |
| var t tagAndLength |
| t, offset, err = parseTagAndLength(bytes, offset) |
| if err != nil { |
| return |
| } |
| if t.class != classUniversal || t.isCompound != compoundType || t.tag != expectedTag { |
| err = StructuralError{"sequence tag mismatch"} |
| return |
| } |
| if invalidLength(offset, t.length, len(bytes)) { |
| err = SyntaxError{"truncated sequence"} |
| return |
| } |
| offset += t.length |
| numElements++ |
| } |
| ret = reflect.MakeSlice(sliceType, numElements, numElements) |
| params := fieldParameters{} |
| offset := 0 |
| for i := 0; i < numElements; i++ { |
| offset, err = parseField(ret.Elem(i), bytes, offset, params) |
| if err != nil { |
| return |
| } |
| } |
| return |
| } |
| |
| var ( |
| bitStringType = reflect.Typeof(BitString{}) |
| objectIdentifierType = reflect.Typeof(ObjectIdentifier{}) |
| enumeratedType = reflect.Typeof(Enumerated(0)) |
| flagType = reflect.Typeof(Flag(false)) |
| timeType = reflect.Typeof(&time.Time{}) |
| rawValueType = reflect.Typeof(RawValue{}) |
| rawContentsType = reflect.Typeof(RawContent(nil)) |
| ) |
| |
| // invalidLength returns true iff offset + length > sliceLength, or if the |
| // addition would overflow. |
| func invalidLength(offset, length, sliceLength int) bool { |
| return offset+length < offset || offset+length > sliceLength |
| } |
| |
| // parseField is the main parsing function. Given a byte array and an offset |
| // into the array, it will try to parse a suitable ASN.1 value out and store it |
| // in the given Value. |
| func parseField(v reflect.Value, bytes []byte, initOffset int, params fieldParameters) (offset int, err os.Error) { |
| offset = initOffset |
| fieldType := v.Type() |
| |
| // If we have run out of data, it may be that there are optional elements at the end. |
| if offset == len(bytes) { |
| if !setDefaultValue(v, params) { |
| err = SyntaxError{"sequence truncated"} |
| } |
| return |
| } |
| |
| // Deal with raw values. |
| if fieldType == rawValueType { |
| var t tagAndLength |
| t, offset, err = parseTagAndLength(bytes, offset) |
| if err != nil { |
| return |
| } |
| if invalidLength(offset, t.length, len(bytes)) { |
| err = SyntaxError{"data truncated"} |
| return |
| } |
| result := RawValue{t.class, t.tag, t.isCompound, bytes[offset : offset+t.length], bytes[initOffset : offset+t.length]} |
| offset += t.length |
| v.(*reflect.StructValue).Set(reflect.NewValue(result).(*reflect.StructValue)) |
| return |
| } |
| |
| // Deal with the ANY type. |
| if ifaceType, ok := fieldType.(*reflect.InterfaceType); ok && ifaceType.NumMethod() == 0 { |
| ifaceValue := v.(*reflect.InterfaceValue) |
| var t tagAndLength |
| t, offset, err = parseTagAndLength(bytes, offset) |
| if err != nil { |
| return |
| } |
| if invalidLength(offset, t.length, len(bytes)) { |
| err = SyntaxError{"data truncated"} |
| return |
| } |
| var result interface{} |
| if !t.isCompound && t.class == classUniversal { |
| innerBytes := bytes[offset : offset+t.length] |
| switch t.tag { |
| case tagPrintableString: |
| result, err = parsePrintableString(innerBytes) |
| case tagIA5String: |
| result, err = parseIA5String(innerBytes) |
| case tagT61String: |
| result, err = parseT61String(innerBytes) |
| case tagInteger: |
| result, err = parseInt64(innerBytes) |
| case tagBitString: |
| result, err = parseBitString(innerBytes) |
| case tagOID: |
| result, err = parseObjectIdentifier(innerBytes) |
| case tagUTCTime: |
| result, err = parseUTCTime(innerBytes) |
| case tagOctetString: |
| result = innerBytes |
| default: |
| // If we don't know how to handle the type, we just leave Value as nil. |
| } |
| } |
| offset += t.length |
| if err != nil { |
| return |
| } |
| if result != nil { |
| ifaceValue.Set(reflect.NewValue(result)) |
| } |
| return |
| } |
| universalTag, compoundType, ok1 := getUniversalType(fieldType) |
| if !ok1 { |
| err = StructuralError{fmt.Sprintf("unknown Go type: %v", fieldType)} |
| return |
| } |
| |
| t, offset, err := parseTagAndLength(bytes, offset) |
| if err != nil { |
| return |
| } |
| if params.explicit { |
| if t.class == classContextSpecific && t.tag == *params.tag && (t.length == 0 || t.isCompound) { |
| if t.length > 0 { |
| t, offset, err = parseTagAndLength(bytes, offset) |
| if err != nil { |
| return |
| } |
| } else { |
| if fieldType != flagType { |
| err = StructuralError{"Zero length explicit tag was not an asn1.Flag"} |
| return |
| } |
| |
| flagValue := v.(*reflect.BoolValue) |
| flagValue.Set(true) |
| return |
| } |
| } else { |
| // The tags didn't match, it might be an optional element. |
| ok := setDefaultValue(v, params) |
| if ok { |
| offset = initOffset |
| } else { |
| err = StructuralError{"explicitly tagged member didn't match"} |
| } |
| return |
| } |
| } |
| |
| // Special case for strings: PrintableString and IA5String both map to |
| // the Go type string. getUniversalType returns the tag for |
| // PrintableString when it sees a string so, if we see an IA5String on |
| // the wire, we change the universal type to match. |
| if universalTag == tagPrintableString && t.tag == tagIA5String { |
| universalTag = tagIA5String |
| } |
| |
| // Special case for time: UTCTime and GeneralizedTime both map to the |
| // Go type time.Time. |
| if universalTag == tagUTCTime && t.tag == tagGeneralizedTime { |
| universalTag = tagGeneralizedTime |
| } |
| |
| expectedClass := classUniversal |
| expectedTag := universalTag |
| |
| if !params.explicit && params.tag != nil { |
| expectedClass = classContextSpecific |
| expectedTag = *params.tag |
| } |
| |
| // We have unwrapped any explicit tagging at this point. |
| if t.class != expectedClass || t.tag != expectedTag || t.isCompound != compoundType { |
| // Tags don't match. Again, it could be an optional element. |
| ok := setDefaultValue(v, params) |
| if ok { |
| offset = initOffset |
| } else { |
| err = StructuralError{fmt.Sprintf("tags don't match (%d vs %+v) %+v %s @%d", expectedTag, t, params, fieldType.Name(), offset)} |
| } |
| return |
| } |
| if invalidLength(offset, t.length, len(bytes)) { |
| err = SyntaxError{"data truncated"} |
| return |
| } |
| innerBytes := bytes[offset : offset+t.length] |
| offset += t.length |
| |
| // We deal with the structures defined in this package first. |
| switch fieldType { |
| case objectIdentifierType: |
| newSlice, err1 := parseObjectIdentifier(innerBytes) |
| sliceValue := v.(*reflect.SliceValue) |
| sliceValue.Set(reflect.MakeSlice(sliceValue.Type().(*reflect.SliceType), len(newSlice), len(newSlice))) |
| if err1 == nil { |
| reflect.Copy(sliceValue, reflect.NewValue(newSlice).(reflect.ArrayOrSliceValue)) |
| } |
| err = err1 |
| return |
| case bitStringType: |
| structValue := v.(*reflect.StructValue) |
| bs, err1 := parseBitString(innerBytes) |
| if err1 == nil { |
| structValue.Set(reflect.NewValue(bs).(*reflect.StructValue)) |
| } |
| err = err1 |
| return |
| case timeType: |
| ptrValue := v.(*reflect.PtrValue) |
| var time *time.Time |
| var err1 os.Error |
| if universalTag == tagUTCTime { |
| time, err1 = parseUTCTime(innerBytes) |
| } else { |
| time, err1 = parseGeneralizedTime(innerBytes) |
| } |
| if err1 == nil { |
| ptrValue.Set(reflect.NewValue(time).(*reflect.PtrValue)) |
| } |
| err = err1 |
| return |
| case enumeratedType: |
| parsedInt, err1 := parseInt(innerBytes) |
| enumValue := v.(*reflect.IntValue) |
| if err1 == nil { |
| enumValue.Set(int64(parsedInt)) |
| } |
| err = err1 |
| return |
| case flagType: |
| flagValue := v.(*reflect.BoolValue) |
| flagValue.Set(true) |
| return |
| } |
| switch val := v.(type) { |
| case *reflect.BoolValue: |
| parsedBool, err1 := parseBool(innerBytes) |
| if err1 == nil { |
| val.Set(parsedBool) |
| } |
| err = err1 |
| return |
| case *reflect.IntValue: |
| switch val.Type().Kind() { |
| case reflect.Int: |
| parsedInt, err1 := parseInt(innerBytes) |
| if err1 == nil { |
| val.Set(int64(parsedInt)) |
| } |
| err = err1 |
| return |
| case reflect.Int64: |
| parsedInt, err1 := parseInt64(innerBytes) |
| if err1 == nil { |
| val.Set(parsedInt) |
| } |
| err = err1 |
| return |
| } |
| case *reflect.StructValue: |
| structType := fieldType.(*reflect.StructType) |
| |
| if structType.NumField() > 0 && |
| structType.Field(0).Type == rawContentsType { |
| bytes := bytes[initOffset:offset] |
| val.Field(0).SetValue(reflect.NewValue(RawContent(bytes))) |
| } |
| |
| innerOffset := 0 |
| for i := 0; i < structType.NumField(); i++ { |
| field := structType.Field(i) |
| if i == 0 && field.Type == rawContentsType { |
| continue |
| } |
| innerOffset, err = parseField(val.Field(i), innerBytes, innerOffset, parseFieldParameters(field.Tag)) |
| if err != nil { |
| return |
| } |
| } |
| // We allow extra bytes at the end of the SEQUENCE because |
| // adding elements to the end has been used in X.509 as the |
| // version numbers have increased. |
| return |
| case *reflect.SliceValue: |
| sliceType := fieldType.(*reflect.SliceType) |
| if sliceType.Elem().Kind() == reflect.Uint8 { |
| val.Set(reflect.MakeSlice(sliceType, len(innerBytes), len(innerBytes))) |
| reflect.Copy(val, reflect.NewValue(innerBytes).(reflect.ArrayOrSliceValue)) |
| return |
| } |
| newSlice, err1 := parseSequenceOf(innerBytes, sliceType, sliceType.Elem()) |
| if err1 == nil { |
| val.Set(newSlice) |
| } |
| err = err1 |
| return |
| case *reflect.StringValue: |
| var v string |
| switch universalTag { |
| case tagPrintableString: |
| v, err = parsePrintableString(innerBytes) |
| case tagIA5String: |
| v, err = parseIA5String(innerBytes) |
| case tagT61String: |
| v, err = parseT61String(innerBytes) |
| default: |
| err = SyntaxError{fmt.Sprintf("internal error: unknown string type %d", universalTag)} |
| } |
| if err == nil { |
| val.Set(v) |
| } |
| return |
| } |
| err = StructuralError{"unknown Go type"} |
| return |
| } |
| |
| // setDefaultValue is used to install a default value, from a tag string, into |
| // a Value. It is successful is the field was optional, even if a default value |
| // wasn't provided or it failed to install it into the Value. |
| func setDefaultValue(v reflect.Value, params fieldParameters) (ok bool) { |
| if !params.optional { |
| return |
| } |
| ok = true |
| if params.defaultValue == nil { |
| return |
| } |
| switch val := v.(type) { |
| case *reflect.IntValue: |
| val.Set(*params.defaultValue) |
| } |
| return |
| } |
| |
| // Unmarshal parses the DER-encoded ASN.1 data structure b |
| // and uses the reflect package to fill in an arbitrary value pointed at by val. |
| // Because Unmarshal uses the reflect package, the structs |
| // being written to must use upper case field names. |
| // |
| // An ASN.1 INTEGER can be written to an int or int64. |
| // If the encoded value does not fit in the Go type, |
| // Unmarshal returns a parse error. |
| // |
| // An ASN.1 BIT STRING can be written to a BitString. |
| // |
| // An ASN.1 OCTET STRING can be written to a []byte. |
| // |
| // An ASN.1 OBJECT IDENTIFIER can be written to an |
| // ObjectIdentifier. |
| // |
| // An ASN.1 ENUMERATED can be written to an Enumerated. |
| // |
| // An ASN.1 UTCTIME or GENERALIZEDTIME can be written to a *time.Time. |
| // |
| // An ASN.1 PrintableString or IA5String can be written to a string. |
| // |
| // Any of the above ASN.1 values can be written to an interface{}. |
| // The value stored in the interface has the corresponding Go type. |
| // For integers, that type is int64. |
| // |
| // An ASN.1 SEQUENCE OF x or SET OF x can be written |
| // to a slice if an x can be written to the slice's element type. |
| // |
| // An ASN.1 SEQUENCE or SET can be written to a struct |
| // if each of the elements in the sequence can be |
| // written to the corresponding element in the struct. |
| // |
| // The following tags on struct fields have special meaning to Unmarshal: |
| // |
| // optional marks the field as ASN.1 OPTIONAL |
| // [explicit] tag:x specifies the ASN.1 tag number; implies ASN.1 CONTEXT SPECIFIC |
| // default:x sets the default value for optional integer fields |
| // |
| // If the type of the first field of a structure is RawContent then the raw |
| // ASN1 contents of the struct will be stored in it. |
| // |
| // Other ASN.1 types are not supported; if it encounters them, |
| // Unmarshal returns a parse error. |
| func Unmarshal(b []byte, val interface{}) (rest []byte, err os.Error) { |
| v := reflect.NewValue(val).(*reflect.PtrValue).Elem() |
| offset, err := parseField(v, b, 0, fieldParameters{}) |
| if err != nil { |
| return nil, err |
| } |
| return b[offset:], nil |
| } |