Error getting the body with middleware in Golang

Question

I am creating an endpoint and I am using the JSONContentExtractor middleware to obtain the context, but if I use it I cannot obtain the Body in the handler.

package main

import (
"encoding/json"
"fmt"
"log"
"net/http"

    "github.com/gorilla/mux"
    "go.mnc.gt/middleware"

)

type RequestBody struct {
Id        int    `json:"id"`
FirstName string `json:"first_name"`
}

func main() {
log.Println("starting API server")

    //create a new router
    router := mux.NewRouter()
    log.Println("creating routes")
    
    // Add external routes wthout encryption
    middlewaresChainWithoutSessionAndWithoutEncryption := middleware.MiddlewaresChain(middleware.JSONContentExtractor)
    
    //specify endpoints
    router.HandleFunc("/personsMiddleware", middlewaresChainWithoutSessionAndWithoutEncryption(Persons)).Methods("POST")
    http.Handle("/", router)
    
    //start and listen to requests
    http.ListenAndServe(":8080", router)

}

func Persons(w http.ResponseWriter, r *http.Request) {
log.Println("entering persons end point")

    var requestBody RequestBody
    err := json.NewDecoder(r.Body).Decode(&requestBody)
    if err != nil {
        http.Error(w, "Error al decodificar el cuerpo de la petición", http.StatusBadRequest)
        return
    }
    
    fmt.Printf("Cuerpo de la petición: %+v\n", requestBody)

}

In the middleware it is possible to read the Body, and in the trace, it also appears, but I cannot take it from the Body again, I know it is possible because the middleware makes the body available again with the line r.Body = ioutil.NopCloser(bytes.NewBuffer(rawRequestBody))

This is the error I'm getting

2023/11/09 13:39:37 starting API server
2023/11/09 13:39:37 creating routes
2023-11-09T13:39:38.686-0600    DEBUG   [email protected]/json_content_extractor_middleware.go:34   request body: {
    "id": 1,
    "first_name": "first_name",
    "last_name": "last_name"
}
2023/11/09 13:39:38 entering persons end point
Cuerpo de la petición: {Id:0 FirstName: LastName:}
2023-11-09T13:39:38.686-0600    ERROR   [email protected]/event_publisher.go:27  
    Event publisher not configured. Event may be lost
        /Users/tribal/go/pkg/mod/go.mnc.gt/[email protected]/event_publisher.go:27   (go.mnc.gt/trace.publishEvent)
2023-11-09T13:39:38.687-0600    ERROR   [email protected]/event_publisher.go:37  Unsent event: {"traceID":":1699558778686647000 /personsMiddleware","httpMethod":"POST","host":"localhost:8080","ipAddress":"[::1]:52249","path":"/personsMiddleware","startTime":1699558778,"endTime":1699558778,"elapsedTime":0,"appVersion":"","request":{"id":1,"first_name":"first_name","last_name":"last_name"},"response":null,"status":"Ok","device":{"uuid":"","os":"","osVersion":""}}

I am trying to get the body of the request. I have tried to obtain the body of the context (maybe not ideal, but I have not succeeded either). Without the middleware I can obtain the body of the request without problem.

I'm thinking it may be the contents of the config.toml file, but I'm not sure what the contents should be, it's currently a blank file.

Answer 1

Your first middleware is reading from the request body. You need to provide a way to re-read the request body. See https://pkg.go.dev/net/http#Request

// GetBody defines an optional func to return a new copy of
// Body. It is used for client requests when a redirect requires
// reading the body more than once. Use of GetBody still
// requires setting Body.
//
// For server requests, it is unused.
GetBody func() (io.ReadCloser, error)

Answer 2

It seems like you're facing an issue with reading the request body in your handler after using the JSONContentExtractor middleware. The problem might be that the middleware is consuming the request body, and you need to reset it for your handler to read it again.

One solution is to use the ioutil.NopCloser and bytes.NewBuffer approach, but you might need to adjust where you place this code. Try moving the body reset code to the beginning of your Persons handler function, just before you attempt to decode the JSON:

func Persons(w http.ResponseWriter, r *http.Request) {
    log.Println("entering persons end point")

    // Reset the request body so it can be read again
    rawRequestBody, err := ioutil.ReadAll(r.Body)
    if err != nil {
        http.Error(w, "Error reading request body", http.StatusInternalServerError)
        return
    }
    r.Body = ioutil.NopCloser(bytes.NewBuffer(rawRequestBody))

    var requestBody RequestBody
    err = json.NewDecoder(r.Body).Decode(&requestBody)
    if err != nil {
        http.Error(w, "Error decoding the request body", http.StatusBadRequest)
        return
    }

    fmt.Printf("Cuerpo de la petición: %+v\n", requestBody)
}

This way, you capture the raw request body, reset the request body for your handler, and then proceed with decoding as usual. Make sure to handle errors appropriately for production code.