Golang json Unmarshal "unexpected end of JSON input"

Question

I am working on some code to parse the JSON data from an HTTP response. The code I have looks something like this:

type ResultStruct struct {
    result []map[string]string
}

var jsonData ResultStruct
err = json.Unmarshal(respBytes, &jsonData)

The json in the respBytes variable looks like this:

{
 "result": [
  {
   "id": "ID 1"
  },
  {
   "id": "ID 2"
  }
 ]
}

However, err is not nil. When I print it out it says unexpected end of JSON input. What is causing this? The JSON seems to valid. Does this error have something to do with my custom struct?

Thanks in advance!

Also, note that lowercase indicates private visibility. You want the field name in your `ResultStruct` to be capitalized: otherwise the `json` decoder isn't allowed to touch the field. See: http://play.golang.org/p/bATT5uMPRT for an example that appears to work. So we need more information to see what your error is: the question as stated doesn't have enough to tell. — dyoo, Jan 16 '15 at 23:58
@dyoo `respBytes` is just an array of bytes (I take the response, do some processing and extract the body). I also capitalized the result field in the `ResultStruct`. Your Go playground example takes the JSON I receive and handles it correctly, so there must be something else wrong with my code... Thanks for your help! — Stratus3D, Jan 19 '15 at 18:32

score 25 · Accepted Answer · edited Mar 26 '16 at 23:31

25

The unexpected end of JSON input is the result of a syntax error in the JSON input (likely a missing ", }, or ]). The error does not depend on the type of the value that you are decoding to.

I ran the code with the example JSON input on the playground. It runs without error.

The code does not decode anything because the result field is not exported. If you export the result field:

type ResultStruct struct {
   Result []map[string]string
}

then the input is decoded as shown in this playground example.

I suspect that you are not reading the entire response body in your application. I suggest decoding the JSON input using:

err := json.NewDecoder(resp.Body).Decode(&jsonData)

The decoder reads directly from the response body.

edited Mar 26 '16 at 23:31

Wai Ha Lee

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answered Jan 17 '15 at 01:14

Charlie Tumahai

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I suspect that besides of what @3of3 said, you try to parse your JSON without last '}' character. – kopiczko Jan 17 '15 at 10:18
This makes sense, however I printed out the JSON and ran it through an online validator as well as through @dyoo's Go playground example and it succeeded. I must conclude that this error is due to an issue with another portion of my code. Thanks! – Stratus3D Jan 19 '15 at 18:51
1

JSON validator here https://jsonlint.com/ – Mark Mar 07 '22 at 17:20

score 6 · Answer 2 · answered Apr 01 '16 at 15:04

You can also get this error if you're using json.RawMessage in an unexported field. For example, the following code produces the same error:

package main

import (
    "encoding/json"
    "fmt"
)

type MyJson struct {
    Foo bool `json:"foo"`
    bar json.RawMessage `json:"bar"`
}

type Bar struct {
    X int `json:"x"`
}

var respBytes = []byte(`
{
  "foo": true,
  "bar": { "x": 10 }
}`)

func main() {
    var myJson MyJson
    err := json.Unmarshal(respBytes, &myJson)
    if err != nil {
        fmt.Println(err)
        return
    }
    myBar := new(Bar)
    err = json.Unmarshal(myJson.bar, myBar)
    fmt.Println(err)
}

If you export "MyJson.bar" field (e.g. -> "MyJson.Bar", then the code works.

you just saved my day. I wouldn't have thought that it would be this issue. Thank you! — Sam Stoelinga, Dec 06 '20 at 05:06

keepTrackOfYourStack · Answer 3 · 2021-11-30T23:22:34.533

it is not the case here; but if you are getting this error loading json from a file it Will occur if the byte slice for the buffer is not initialized the the byte size of the file. [when you're new like me that happens! ] Since this is the first search result I got it still took some digging to figure out. In this use case the error is a bit misleading.

type GenesisResultStruct []GenesisField

fileinfo, _ := genesis.Stat()
bs := make([]byte, fileinfo.Size())
//bs := []byte {} // wrong!!
_, error := genesis.Read(bs)

if error != nil {
    fmt.Println("genesis read error: ", error)
    os.Exit(1)
}

var jsonData GenesisResultStruct
eGen = json.Unmarshal(bs, &jsonData)

if eGen != nil {
    fmt.Println("genesis unmarshal error: ", eGen)
    os.Exit(1)
}

score 0 · Answer 4 · answered Aug 23 '22 at 14:57

Faced the same issue today.

You can also get this error if the respBytes is nil or there are no brackets [] if you are unmarshalling it to a slice. In that case, you need to explicitly set respBytes.

As you are unmarshalling it to a slice, brackets [] are expected in the byte-slice

if src == nil {
    src = []byte("[]")
}

Golang json Unmarshal "unexpected end of JSON input"

4 Answers4

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