I am trying to do ASN.1 marshal/unmarshal for the following definition:
ACEI ::= SEQUENCE {
message MessageFields,
neRegNumber OCTET STRING OPTIONAL,
gpsInfo GpsInfo OPTIONAL,
siteInfo OCTET STRING OPTIONAL,
nlementID INTEGER(0..16777216) OPTIONAL,
...
}
GpsInfo ::= SEQUENCE {
gpsLat INTEGER(-900000000..900000000) OPTIONAL,
gpsLong INTEGER(-1800000000..1800000000) OPTIONAL,
gpsAlt INTEGER OPTIONAL,
...
}
MessageFields ::= SEQUENCE {
messageSequence INTEGER (1..65535),
bsId INTEGER (1..65535) OPTIONAL,
neID INTEGER(0..16777216) OPTIONAL, -- unsigned int
nelementID INTEGER(0..16777216) OPTIONAL, -- unsigned int
...
}
The corresponding go structs are:
type ACEI struct {
Message MessageFields
NeRegNumber []byte `asn1:"optional"`
GPSInfo GPSInfo `asn1:"optional"`
SiteInfo []byte `asn1:"optional"`
NElementID int `asn1:"optional"`
}
type GPSInfo struct {
GpsLatitude int `asn1:"optional"`
GpsLongitude int `asn1:"optional"`
GpsAltitude int `asn1:"optional"`
}
type MessageFields struct {
MessageSequence int
BsId int `asn1:"optional"`
NeID int `asn1:"optional"`
NElementID int `asn1:"optional"`
}
I am filling in the structs, marshalling them and then converting them to hex. When I do that, the hex sequence (seqA) obtained is:
302e300f020101020204d2020215b302021a0a040430413042300b02019c020200be020200c80404304330440202309c
When I do the same on http://asn1-playground.oss.com/, I get the following hex sequence (seqB):
302AA00F 80010181 0204D282 0215B383 021A0A81 020A0BA2 0B80019C 810200BE 820200C8 83020C0D 8402309C
I fed in both these hex sequences to the unmarshal function; while the seqA is correctly unmarshalled, unmarshalling seqB gives me the following error:
Error while unmarshalling: asn1: structure error: tags don't match (16 vs {class:2 tag:0 length:15 isCompound:true}) {optional:false explicit:false application:false defaultValue: tag: stringType:0 timeType:0 set:false omitEmpty:false} MessageFields @2
This is the code that marshals/unmarshals:
func main() {
//Marshalling
messageSequence := structs.MessageFields{1, 1234, 5555, 6666}
gpsInfo := structs.GPSInfo{-100, 190, 200}
val := structs.ACEI{messageSequence, []byte("0A0B"), gpsInfo, []byte("0C0D"), 12444}
hexmdata := asn1Marshal(val)
//Unmarshalling hex sequence (seqA) generated by go code
res1, _ := asn1Unmarshal(hexmdata)
fmt.Println(res1)
//Unmarshalling hex sequence (seqB) generated by http://asn1-playground.oss.com/
res2, _ := asn1Unmarshal(strings.ToLower("302AA00F800101810204D2820215B383021A0A81020A0BA20B80019C810200BE820200C883020C0D8402309C"))
fmt.Println(res2)
}
func asn1Unmarshal(hexmdata string) (structs.ACEI, error){
fmt.Println(hexmdata)
s, _ := hex.DecodeString(hexmdata)
res := structs.ACEI{}
_, err := asn1.Unmarshal(s, &res)
if err != nil {
fmt.Println("Error while unmarshalling: ", err)
}
return res, err
}
func asn1Marshal(data structs.ACEI) string {
mdata, _ := asn1.Marshal(data)
hexmdata := hex.EncodeToString(mdata)
return hexmdata
}
EDIT: Conversely, the go code sequence (seqA) when fed to http://asn1-playground.oss.com/ gives me this error:
ACEI SEQUENCE: tag = [UNIVERSAL 16] constructed; length = 46
D0033E: Tag mismatch or tag not expected: [UNIVERSAL 16] (expected tag [0]); check field 'message' (type: MessageFields) of PDU #1 'ACEI'.
*SKIPPED*: tag = [UNIVERSAL 16] constructed; length = 15
<skipped>
D0033E: Tag mismatch or tag not expected: [UNIVERSAL 4] (expected tag [0]); check field 'message' (type: MessageFields) of PDU #1 'ACEI'.
*SKIPPED*: tag = [UNIVERSAL 4] primitive; length = 4
<skipped>
D0033E: Tag mismatch or tag not expected: [UNIVERSAL 16] (expected tag [0]); check field 'message' (type: MessageFields) of PDU #1 'ACEI'.
*SKIPPED*: tag = [UNIVERSAL 16] constructed; length = 11
<skipped>
D0033E: Tag mismatch or tag not expected: [UNIVERSAL 4] (expected tag [0]); check field 'message' (type: MessageFields) of PDU #1 'ACEI'.
*SKIPPED*: tag = [UNIVERSAL 4] primitive; length = 4
<skipped>
D0033E: Tag mismatch or tag not expected: [UNIVERSAL 2] (expected tag [0]); check field 'message' (type: MessageFields) of PDU #1 'ACEI'.
*SKIPPED*: tag = [UNIVERSAL 2] primitive; length = 2
<skipped>
D0049E: Field omitted: "message"; check PDU #1 'ACEI'.
S0012E: Decoding of PDU #1 failed with the return code '5'.
EDIT 2: After editing the structs according to @YaFred's suggestion, my structs look like this now:
type ACEI struct {
Message MessageFields `asn1:"application,tag:0,implicit"`
NeRegNumber []byte `asn1:"application,tag:1,implicit,optional"`
GPSInfo GPSInfo `asn1:"application,tag:2,implicit,optional"`
SiteInfo []byte `asn1:"application,tag:3,implicit,optional"`
NElementID int `asn1:"application,tag:4,implicit,optional"`
}
type GPSInfo struct {
GpsLatitude int `asn1:"application,tag:0,implicit,optional"`
GpsLongitude int `asn1:"application,tag:1,implicit,optional"`
GpsAltitude int `asn1:"application,tag:2,implicit,optional"`
}
type MessageFields struct {
MessageSequence int `asn1:"application,tag:0,implicit"`
BsId int `asn1:"application,tag:1,implicit,optional"`
NeID int `asn1:"application,tag:2,implicit,optional"`
NElementID int `asn1:"application,tag:3,implicit,optional"`
}
Marshalling using these structs gives me the same hex code as that obtained from asn playground. But, the unmarshalling fails with the following error:
Hex code: 302aa00f800101810204d2820215b383021a0a81020a0ba20b80019c810200be820200c883020c0d8402309c
Error (the same error I was getting before when I tried to unmarshall hex code (from asn playground) using go code):
Error while unmarshalling: asn1: structure error: tags don't match (0 vs {class:2 tag:0 length:15 isCompound:true}) {optional:false explicit:false application:true defaultValue: tag:0xc042008348 stringType:0 timeType:0 set:false omitEmpty:false} MessageFields @2
EDIT 3: Removing the "application" tag from the structs helps me unmarshal the hex code as expected.
Where you input your types (with your tool as well as with http://asn1-playground.oss.com/), you must use a module. If not, it is not a valid asn1 specification (and your tool as well as oss.com should reject it).
My-module DEFINITIONS ::=
BEGIN
ACEI ::= SEQUENCE {
etc ...
END
The fact that tools accept to encode types without knowing the module tagging context is the reason for many questions on https://stackoverflow.com/questions/tagged/asn.1
To answer the second question (about the difference of length), you should show what values you gave to oss.com .. it's likely:
neRegNumber '0A0B'H
siteInfo '0C0D'H
They are both 2 bytes long
But when you write []byte("0A0B") you are certainly asking Go to give you the bytes of the string "0A0B" (indeed 30 41 30 42 in ASCII)
I think []byte{10,11} should give you the bytes for '0A0B'H
EDITED
If your tool does not take an asn.1 module, you can still do the automatic tagging yourself
ACEI ::= SEQUENCE {
message [0] IMPLICIT MessageFields,
neRegNumber [1] IMPLICIT OCTET STRING OPTIONAL,
gpsInfo [2] IMPLICIT GpsInfo OPTIONAL,
siteInfo [3] IMPLICIT OCTET STRING OPTIONAL,
nlementID [4] IMPLICIT INTEGER(0..16777216) OPTIONAL,
...
}
GpsInfo ::= SEQUENCE {
gpsLat [0] IMPLICIT INTEGER(-900000000..900000000) OPTIONAL,
gpsLong [1] IMPLICIT INTEGER(-1800000000..1800000000) OPTIONAL,
gpsAlt [2] IMPLICIT INTEGER OPTIONAL,
...
}
MessageFields ::= SEQUENCE {
messageSequence [0] IMPLICIT INTEGER (1..65535),
bsId [1] IMPLICIT INTEGER (1..65535) OPTIONAL,
neID [2] IMPLICIT INTEGER(0..16777216) OPTIONAL, -- unsigned int
nelementID [3] IMPLICIT INTEGER(0..16777216) OPTIONAL, -- unsigned int
...
}
EDITED 2 (based on chat with @Aarvi)
It just occurred to me that https://golang.org/pkg/encoding/asn1/ does not involve an ASN.1 compiler.
Instead a Go struct is manually written and annotated.
So following ASN.1 type (in a module with AUTOMATICS TAGS selected)
GpsInfo ::= SEQUENCE {
gpsLat INTEGER(-900000000..900000000) OPTIONAL,
gpsLong INTEGER(-1800000000..1800000000) OPTIONAL,
gpsAlt INTEGER OPTIONAL,
...
}
has to be written manually like this
type GPSInfo struct {
GpsLatitude int `asn1:"tag:0,implicit,optional"`
GpsLongitude int `asn1:"tag:1,implicit,optional"`
GpsAltitude int `asn1:"tag:2,implicit,optional"`
}