CODEWITHSUNDEEP
mongodbgobson
ryknow
ryknow

Reputation: 181

Unmarshalling BSON data using Gobson/Mgo

I am receiving different BSON documents, an example seen here:

{ "group" : { "id": ObjectId("11a123456bc345d452d32c0b5"), "name": "SomeName" }, "count1": 6, "count2": 33, "totalCount": 39 }

I am trying to use mgo/gobson to unmarshal this data into a map[string]interface{}, but keep getting an error. The unmarshalling code is

var record map[string]interface{}

err := bson.Unmarshal(data, &record)

This resulted in a error saying the document was corrupted. Looking into the code I saw that it expected the length of the byte array to be the first few bytes so I added code similar to what is found in the tests.

rec := make([]byte, len(data)+6)
binary.LittleEndian.PutUint32(rec, uint32(len(rec)))
copy(rec[4:], data)

This got me past the corrupt document error, but now I am getting 

Unknown element kind (0x7B)

What am I doing wrong that I can't easily unmarshal the above BSON document into a map? Is there a problem with the BSON document itself? I am not the creator of the BSON document, but am able to provide feedback to them if necessary.

Upvotes: 3

Views: 5102

Answers (1)

foecum
foecum

Reputation: 568

I tried out your code above and I managed to get it to "work". The reason you are getting 

Unknown element kind (0x7B)

is because there is no element of kind 0x7B in the BSON specification. See here http://bsonspec.org/spec.html. The particular unknow element I was getting was the byte value for the first curly bracket({) in your document

{ "group" : { "id": ObjectId("11a123456bc345d452d32c0b5"), "name": "SomeName" }, "count1": 6, "count2": 33, "totalCount": 39 }

after tweaking the code a bit I was able to get it working with out the unknown kind error.

package main

import (
    "encoding/binary"
    "fmt"

    "gopkg.in/mgo.v2/bson"
)

func main() {
    bsonData := `{ "group" : { "id": ObjectId("11a123456bc345d452d32c0b5"), "name": "SomeName" }, "count1": 6, "count2": 33, "totalCount": 39 }`

    var record map[string]interface{}

    rec := make([]byte, len(bsonData)+6)
    binary.LittleEndian.PutUint32(rec, uint32(len(rec)))
    copy(rec[4:], bsonData)
    //Adding a new line to the front of the rec byte variable seems to do the trick
    r := []byte("\n")
    rec[4] = r[0]
    err := bson.Unmarshal(rec, &record)
    if err != nil {
        panic(err)
    }
    fmt.Println(record)
}

I also found this answer to be of great use https://stackoverflow.com/a/33129119/2627768

Upvotes: 2

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