api: Add go files

I know this is a huge commit, but I can't be bothered to check
this in part by part.

api/utils_http.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"net/http"
+	"reflect"
+)
+
+type response map[string]interface{}
+
+// TODO: Add tests in utils_http_test.go
+
+func unmarshalBody(r *http.Request, x interface{}) error {
+	b, err := ioutil.ReadAll(r.Body)
+	if err != nil {
+		logger.Errorf("cannot read POST body: %v\n", err)
+		return errorInternal
+	}
+
+	if err = json.Unmarshal(b, x); err != nil {
+		return errorInvalidJSONBody
+	}
+
+	xv := reflect.Indirect(reflect.ValueOf(x))
+	for i := 0; i < xv.NumField(); i++ {
+		if xv.Field(i).IsNil() {
+			return errorMissingField
+		}
+	}
+
+	return nil
+}
+
+func writeBody(w http.ResponseWriter, x map[string]interface{}) error {
+	resp, err := json.Marshal(x)
+	if err != nil {
+		w.Write([]byte(`{"success":false,"message":"Some internal error occurred"}`))
+		logger.Errorf("cannot marshal response: %v\n")
+		return errorInternal
+	}
+
+	w.Write(resp)
+	return nil
+}