9

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": "juanperez@gmail.com",
        "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": "benancio@gmail.com"
            }
        }
    ]
}

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!

transistor
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    Echo or something called by Echo is reading the request body before your handler is invoked. Some frameworks automatically read url encoded forms. Print the content type on the server to confirm that it's set as you expect. If you use net/http directly, then `json.NewDecoder(r.Body).Decode(&v)` will do what you expect. – Charlie Tumahai Nov 08 '17 at 18:15
  • Can you show the full code of the handler? Also do you have any middleware that gets executed before your handler? As Cerise Limon already said, the error looks very much like the body reader's position is at its end when you try to read the json, that can happen when some other code read the body first without "rewinding" the reader back to the beginning. Or it could be that the request body is actually empty... – mkopriva Nov 08 '17 at 21:05
  • Thank you for your comments, you got me thinking and found a solution – transistor Nov 14 '17 at 21:39

2 Answers2

34

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

transistor
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-1

I believe you can do this:

m := make(map[string]interface{});
if err := context.Bind(&m); err != nil {
    return result, err
}
fmt.Println(m)
dave
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