Generic REST API Golang - postgresql

Question

Searching SO for Generic REST API Golang gives 0 results. Searching Google gives 2 results. So this question is maybe not correctly formulated or it is impossible to achieve in Golang.
My goal is to avoid repeating similar code over and over again. So I am trying to make the code in Golang as generic as possible. Write once, use many.
This is my first attempt to create a generic REST API for select in Golang. The code below gives almost what I want:
But the result is presented in the Terminal. I have no idea how to redirect the result to the browser.
package main
import (
"fmt"
"log"
"net/http"
"database/sql"
"time"
_ "github.com/lib/pq"
)
var db *sql.DB
func main() {
Connect()
http.HandleFunc("/", Query)
log.Fatal(http.ListenAndServe(":8080", nil))
}
func Connect() {
const (
host = "127.0.0.1"
port = 5432
user = "test"
password = "test"
dbname = "Test")
login := fmt.Sprintf("host=%s port=%d user=%s "+"password=%s dbname=%s sslmode=require", host, port, user, password, dbname)
var err error
db, err = sql.Open("postgres", login)
if err != nil {
log.Fatalln(err)
}
err = db.Ping()
if err != nil {
panic(err)
}
func Query(w http.ResponseWriter, r *http.Request) {
var query string
switch r.URL.String() {
case "/getuser":
query = "select * from getuser()"
case "/getco":
query = "select * from getco()"
case "/etc"
query = "select * from etc"
default:
query = ""
}
var err error
var rows *sql.Rows
rows, err = db.Query(query)
if err != nil {
http.Error(w, http.StatusText(500), 500)
return
}
defer rows.Close()
cols, err := rows.Columns()
vals := make([]interface{}, len(cols))
for i := 0; i < len(cols); i++ {
vals[i] = new(interface{})
if i != 0 {
fmt.Print("\t")
}
fmt.Print(cols[i])
}
fmt.Println()
for rows.Next() {
err = rows.Scan(vals...)
if err != nil {
fmt.Println(err)
continue
}
for i := 0; i < len(vals); i++ {
if i != 0 {
fmt.Print("\t")
}
printValue(vals[i].(*interface{}))
}
fmt.Println()
}
func printValue(pval *interface{}) {
switch v := (*pval).(type) {
case nil:
fmt.Print("NULL")
case bool:
if v {
fmt.Print("1")
} else {
fmt.Print("0")
}
case []byte:
fmt.Print(string(v))
case time.Time:
fmt.Print(v.Format("2006-01-02"))
default:
fmt.Print(v)
}
}
Every attempt to write to the browser gives various type of errors:
fmt.Printf("%s\n", vals...)
My questions are
How do I redirect the result to the browser?
Is there any better way to achieve this? (reuse generic code)

Answer 1

My recommendation would be to look at using existing packages like "mux" for calling REST APIs in browser. As a quick demo how you would do it as as follows:
your restapi.go cound have APIs as follows:
func SampleAPI(w http.ResponseWriter, r *http.Request) { //Assuming this is a POST request
var example SomeSruct
_ = json.NewDecoder(r.Body).Decode(&example) //Decode the POST body
result := someLogicFunction(example) //call your generic function
json.NewEncoder(w).Encode(result) //encode the result to pass it back to browser
}
Now say you write a main.go and you are using mux package here is an example of how you would call this
main.go
func main() {
router := mux.NewRouter()
router.HandleFunc("/testFunc",restapi.SampleAPI).Methods("POST") //This creates the route for your http request
handler := cros.Default().Handler(router) //You will need this if you plan to deploy it in a server and call it externally for testing locally you don't need this
log.Fatal(http.ListenAndServe(":8080", handler)) //Port that the router is listening to
}
Now note that you will have to import the "github.com/gorilla/mux" and the "github.com/rs/cors" packages to use these but this way you can create REST APIs whic can be accessed by te browser. Similarly you could create a GET method and use parameters which you can grab in your function and perform any logical step.
If you build and install the above code you can POST to localhost:8080/testFunc over http using any web app and get results i your browser. If you had a GET request you could directly type the Url in the browser and see the result.

Answer 2

write response with appropriahe HTTP hearers && status code
import "net/http"
func writeResponse(w http.ResponseWriter, contents []byte) {
w.Header().Set("Content-Type", "text/plain; charset=utf-8")
w.Header().Set("X-Content-Type-Options", "nosniff")
w.WriteHeader(http.StatusOK)
fmt.Fprintln(w, contents)
}
sounds a little unclear, sorry