Gin Framework

Ref - https://github.com/gin-gonic/gin

package main

import (
  "fmt"
  "net/http"

  "github.com/gin-gonic/gin"
)

func hello(w http.ResponseWriter, req *http.Request) {
  fmt.Fprint(w, "hello")
}

func main() {
  r := gin.Default()
  r.GET("/ping", func(c *gin.Context) {
    c.JSON(http.StatusOK, gin.H{
      "message": "pong",
    })
  })
  r.Run("127.0.0.1:3000")
}

Receiving/Sending back custom JSON

package main

import (
  "net/http"

  "github.com/gin-gonic/gin"
)

// Define the input struct for incoming requests
type OrderRequest struct {
  Stock    string  `json:"stock" binding:"required"`
  Type     string  `json:"type" binding:"required,oneof=buy sell"` // Only allow "buy" or "sell"
  Price    float64 `json:"price" binding:"required"`
  Quantity int     `json:"quantity" binding:"required"`
}

// Define the response struct for outgoing responses
type OrderResponse struct {
  FilledQty int `json:"filledQty"`
}

func processOrder(c *gin.Context) {
  var order OrderRequest

  // Bind incoming JSON to the OrderRequest struct
  if err := c.ShouldBindJSON(&order); err != nil {
    // If there is an error, return a 400 Bad Request with the error message
    c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
    return
  }

  // Here you would implement your business logic to calculate filledQty
  // For demonstration, we'll just set it to the quantity received
  filledQty := order.Quantity // This is just a placeholder

  // Create the response
  response := OrderResponse{
    FilledQty: filledQty,
  }

  // Send the response as JSON
  c.JSON(http.StatusOK, response)
}

func main() {
  r := gin.Default()

  // Endpoint for the order processing
  r.POST("/order", processOrder)

  // Start the server
  r.Run("127.0.0.1:3000")
}

Some more examples - https://gin-gonic.com/docs/examples/