如何从Go上的请求主体获取JSON

Question

I'm a newbie with Go, but so far I'm liking it very much.

I have a problem I can't figure out. I'm migrating an API from Node to Go and there is this log where I have to capture the Body of a POST AS IT IS and save it to a jsonb type column in a Postgresql database.

This means I can't use a struct or anything predetermined.

The POST is made with body raw Content-Type: application/json like so:

{
    "debug": false,
    "order_id_gea": 326064,
    "increment_id_gea": 200436102,
    "date": "2017-05-18T01:44:44+00:00",
    "total_amount": 10000.00,
    "currency": "MXN",
    "payment_method": "Referencia bancaria",
    "reference": "857374",
    "buyer": {
        "buyer_id_gea": 1234,
        "full_name": "Juan Perez Martinez",
        "email": "[e-mail]",
        "phone": "5512341234"
    },
    "products": [
        {
            "sku":"PEP16114",
            "price": 10000.00,
            "currency": "MXN",
            "student": {
                "school_id_gea": 172,
                "grade_id_gea": 119,
                "level_id_gea": 36,
                "name": "Benancio",
                "last_name": "Perez",
                "second_last_name": "Garcia",
                "email": "[e-mail]"
            }
        }
    ]
}

On Node + Hapi is quite simple:

const payload = request.payload

and then I can access the JSON from payload.

I am using Go with Echo, so context is a wrapper where I can find Request() *http.Request.

I have tried the following, but everytime the result is empty or an error because it is empty:

var v interface{}
err := json.NewDecoder(context.Request().Body).Decode(&v)
if err != nil {
    return result, err
}
fmt.Println(v)

Result: EOF

--

m := echo.Map{}
if err := context.Bind(&m); err != nil {
    return result, err
}
fmt.Println(m)

Result code 400, message EOF

--

body, error := ioutil.ReadAll(context.Request().Body)
if error != nil {
    return result, error
}
fmt.Println(body)

Result []

--

What am I missing and/or doing wrong? Thanks!

Answer 1

TIL that http.Response.Body is a buffer, which means that once it has been read, it cannot be read again.

It's like a stream of water, you can see it and measure it as it passes but once it's gone, it's gone.

However, knowing this, there is a workaround, you need to "catch" the body and restore it:

// Read the Body content
var bodyBytes []byte
if context.Request().Body != nil {
    bodyBytes, _ = ioutil.ReadAll(context.Request().Body)
}

// Restore the io.ReadCloser to its original state
context.Request().Body = ioutil.NopCloser(bytes.NewBuffer(bodyBytes))

// Continue to use the Body, like Binding it to a struct:
order := new(models.GeaOrder)
error := context.Bind(order)

Now, you can use context.Request().Body somewhere else.

Sources:

http://grokbase.com/t/gg/golang-nuts/12adq8a2ys/go-nuts-re-reading-http-response-body-or-any-reader

https://medium.com/@xoen/golang-read-from-an-io-readwriter-without-loosing-its-content-2c6911805361