good good study, day day up!

vendor/gopl.io/ch12/params/params.go

@@ -0,0 +1,90 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 349.
+
+// Package params provides a reflection-based parser for URL parameters.
+package params
+
+import (
+	"fmt"
+	"net/http"
+	"reflect"
+	"strconv"
+	"strings"
+)
+
+//!+Unpack
+
+// Unpack populates the fields of the struct pointed to by ptr
+// from the HTTP request parameters in req.
+func Unpack(req *http.Request, ptr interface{}) error {
+	if err := req.ParseForm(); err != nil {
+		return err
+	}
+
+	// Build map of fields keyed by effective name.
+	fields := make(map[string]reflect.Value)
+	v := reflect.ValueOf(ptr).Elem() // the struct variable
+	for i := 0; i < v.NumField(); i++ {
+		fieldInfo := v.Type().Field(i) // a reflect.StructField
+		tag := fieldInfo.Tag           // a reflect.StructTag
+		name := tag.Get("http")
+		if name == "" {
+			name = strings.ToLower(fieldInfo.Name)
+		}
+		fields[name] = v.Field(i)
+	}
+
+	// Update struct field for each parameter in the request.
+	for name, values := range req.Form {
+		f := fields[name]
+		if !f.IsValid() {
+			continue // ignore unrecognized HTTP parameters
+		}
+		for _, value := range values {
+			if f.Kind() == reflect.Slice {
+				elem := reflect.New(f.Type().Elem()).Elem()
+				if err := populate(elem, value); err != nil {
+					return fmt.Errorf("%s: %v", name, err)
+				}
+				f.Set(reflect.Append(f, elem))
+			} else {
+				if err := populate(f, value); err != nil {
+					return fmt.Errorf("%s: %v", name, err)
+				}
+			}
+		}
+	}
+	return nil
+}
+
+//!-Unpack
+
+//!+populate
+func populate(v reflect.Value, value string) error {
+	switch v.Kind() {
+	case reflect.String:
+		v.SetString(value)
+
+	case reflect.Int:
+		i, err := strconv.ParseInt(value, 10, 64)
+		if err != nil {
+			return err
+		}
+		v.SetInt(i)
+
+	case reflect.Bool:
+		b, err := strconv.ParseBool(value)
+		if err != nil {
+			return err
+		}
+		v.SetBool(b)
+
+	default:
+		return fmt.Errorf("unsupported kind %s", v.Type())
+	}
+	return nil
+}
+
+//!-populate