我正在尝试为以下定义执行 ASN.1 编码/解码:

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
...
}

对应的go结构体是:

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"`
}

我正在填充结构，编码它们，然后将它们转换为十六进制。 当我这样做时，获得的十六进制序列 (seqA) 是:

302e300f020101020204d2020215b302021a0a040430413042300b02019c020200be020200c80404304330440202309c

当我在 http://asn1-playground.oss.com/ 上做同样的事情时，我得到以下十六进制序列 (seqB):

302AA00F 80010181 0204D282 0215B383 021A0A81 020A0BA2 0B80019C 810200BE 820200C8 83020C0D 8402309C

我将这两个十六进制序列都输入到 unmarshal 函数中；虽然 seqA 已正确解码，但解码 seqB 会出现以下错误:

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

这是编码/解码的代码:

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
}

1. 为什么相同定义的十六进制序列不同？
2. 如何更正在解码 seqB 期间遇到的错误？

编辑:相反，将 go 代码序列 (seqA) 馈送到 http://asn1-playground.oss.com/ 时给我这个错误:

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'.

编辑 2:根据@YaFred 的建议编辑结构后，我的结构现在看起来像这样:

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"`
}

使用这些结构编码给我的十六进制代码与从 asn Playground 获得的代码相同。但是，解码失败并出现以下错误:

Hex code: 302aa00f800101810204d2820215b383021a0a81020a0ba20b80019c810200be820200c883020c0d8402309c

错误(与我之前尝试使用 go 代码解码十六进制代码(来自 asn playground)时遇到的错误相同):

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

编辑 3:从结构中删除“应用程序”标签有助于我按预期解码十六进制代码。

最佳答案

在您输入类型的地方(使用您的工具以及 http://asn1-playground.oss.com/ )，您必须使用模块。如果不是，则它不是有效的 asn1 规范(并且您的工具和 oss.com 应该拒绝它)。

My-module DEFINITIONS ::= 
BEGIN 

ACEI    ::= SEQUENCE {
etc ...

END

工具接受在不知道模块标记上下文的情况下对类型进行编码这一事实是关于 https://stackoverflow.com/questions/tagged/asn.1 的许多问题的原因。

要回答第二个问题(关于长度的差异)，你应该显示你给 oss.com 的值..它可能是:

neRegNumber  '0A0B'H
siteInfo     '0C0D'H    

它们都是2字节长

但是当您编写 []byte("0A0B") 时，您肯定要求 Go 为您提供字符串“0A0B”的字节(实际上是 ASCII 中的 30 41 30 42)

我认为 []byte{10,11} 应该为您提供 '0A0B'H

已编辑

如果您的工具不采用 asn.1 模块，您仍然可以自己进行自动标记

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
...
}

编辑 2(基于与@Aarvi 的聊天)

我刚刚想到https://golang.org/pkg/encoding/asn1/不涉及 ASN.1 编译器。

相反，Go 结构是手动编写和注释的。

所以遵循 ASN.1 类型(在选择了 AUTOMATICS TAGS 的模块中)

GpsInfo         ::= SEQUENCE {
   gpsLat      INTEGER(-900000000..900000000) OPTIONAL,
   gpsLong     INTEGER(-1800000000..1800000000) OPTIONAL,
   gpsAlt      INTEGER OPTIONAL,
   ...
}

必须这样手动写

type GPSInfo struct {
    GpsLatitude  int `asn1:"tag:0,implicit,optional"`
    GpsLongitude int `asn1:"tag:1,implicit,optional"`
    GpsAltitude int `asn1:"tag:2,implicit,optional"`
}

关于go - ASN.1 Unmarshalling using go structs 给出标签不匹配错误，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/49665475/