Add support to bind to struct, interface, array, slices etc for multi…

…part form types (#986)

docs/references/context/page.md

@@ -50,6 +50,24 @@ parts of the request.
   ctx.Bind(&p)
   // the Bind() method will map the incoming request to variable p
   ```
+
+  ### Binding multipart-form data 
+  - To bind multipart-form data, you can use the Bind method similarly. The struct fields should be tagged appropriately 
+    to map the form fields to the struct fields.
+
+    ```go
+    type Data struct {
+    Name string `form:"name"`
+
+    Compressed file.Zip `file:"upload"`
+
+    FileHeader *multipart.FileHeader `file:"file_upload"`
+    }
+    ```
+
+  - The `form` tag is used to bind non-file fields.
+  - The `file` tag is used to bind file fields. If the tag is not present, the field name is used as the key.
+
 
 - `HostName()` - to access the host name for the incoming request
   ```go

examples/using-file-bind/README.md

@@ -8,7 +8,7 @@ it to the fields of the struct. GoFr currently supports zip file type and also b
 type Data struct {
     Compressed file.Zip `file:"upload"`
 
-    FileHeader *multipart.FileHeader `file:"a"`
+    FileHeader *multipart.FileHeader `file:"file_upload"`
 }
 
 func Handler (c *gofr.Context) (interface{}, error) {

examples/using-file-bind/main.go

@@ -30,7 +30,7 @@ type Data struct {
 
 	// The FileHeader determines the generic file format that we can get
 	// from the multipart form that gets parsed by the incoming HTTP request
-	FileHeader *multipart.FileHeader `file:"a"`
+	FileHeader *multipart.FileHeader `file:"file_upload"`
 }
 
 func UploadHandler(c *gofr.Context) (interface{}, error) {

examples/using-file-bind/main_test.go

@@ -56,7 +56,7 @@ func generateMultiPartBody(t *testing.T) (*bytes.Buffer, string) {
 		t.Fatalf("Failed to write file to form: %v", err)
 	}
 
-	fileHeader, err := writer.CreateFormFile("a", "hello.txt")
+	fileHeader, err := writer.CreateFormFile("file_upload", "hello.txt")
 	if err != nil {
 		t.Fatalf("Failed to create form file: %v", err)
 	}

pkg/gofr/http/form_data_binder.go

@@ -0,0 +1,205 @@
+package http
+
+import (
+	"encoding/json"
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+func (*formData) setInterfaceValue(value reflect.Value, data any) (bool, error) {
+	if !value.CanSet() {
+		return false, fmt.Errorf("%w: %s", errUnsupportedInterfaceType, value.Kind())
+	}
+
+	value.Set(reflect.ValueOf(data))
+
+	return true, nil
+}
+
+func (uf *formData) setSliceOrArrayValue(value reflect.Value, data string) (bool, error) {
+	if value.Kind() != reflect.Slice && value.Kind() != reflect.Array {
+		return false, fmt.Errorf("%w: %s", errUnsupportedKind, value.Kind())
+	}
+
+	elemType := value.Type().Elem()
+
+	elements := strings.Split(data, ",")
+
+	// Create a new slice/array with appropriate length and capacity
+	var newSlice reflect.Value
+
+	if value.Kind() == reflect.Slice {
+		newSlice = reflect.MakeSlice(value.Type(), len(elements), len(elements))
+	} else if len(elements) > value.Len() {
+		return false, errDataLengthExceeded
+	} else {
+		newSlice = reflect.New(value.Type()).Elem()
+	}
+
+	// Create a reusable element value to avoid unnecessary allocations
+	elemValue := reflect.New(elemType).Elem()
+
+	// Set the elements of the slice/array
+	for i, strVal := range elements {
+		// Update the reusable element value
+		if _, err := uf.setFieldValue(elemValue, strVal); err != nil {
+			return false, fmt.Errorf("%w %d: %w", errSettingValueFailure, i, err)
+		}
+
+		newSlice.Index(i).Set(elemValue)
+	}
+
+	value.Set(newSlice)
+
+	return true, nil
+}
+
+func (*formData) setStructValue(value reflect.Value, data string) (bool, error) {
+	if value.Kind() != reflect.Struct {
+		return false, errNotAStruct
+	}
+
+	dataMap, err := parseStringToMap(data)
+	if err != nil {
+		return false, err
+	}
+
+	if len(dataMap) == 0 {
+		return false, errFieldsNotSet
+	}
+
+	numFieldsSet := 0
+
+	var multiErr error
+
+	// Create a map for case-insensitive lookups
+	caseInsensitiveMap := make(map[string]interface{})
+	for key, val := range dataMap {
+		caseInsensitiveMap[strings.ToLower(key)] = val
+	}
+
+	for i := 0; i < value.NumField(); i++ {
+		fieldType := value.Type().Field(i)
+		fieldValue := value.Field(i)
+		fieldName := fieldType.Name
+
+		// Perform case-insensitive lookup for the key in dataMap
+		val, exists := caseInsensitiveMap[strings.ToLower(fieldName)]
+		if !exists {
+			continue
+		}
+
+		if !fieldValue.CanSet() {
+			multiErr = fmt.Errorf("%w: %s", errUnexportedField, fieldName)
+			continue
+		}
+
+		if err := setFieldValueFromData(fieldValue, val); err != nil {
+			multiErr = fmt.Errorf("%w; %w", multiErr, err)
+			continue
+		}
+
+		numFieldsSet++
+	}
+
+	if numFieldsSet == 0 {
+		return false, errFieldsNotSet
+	}
+
+	return true, multiErr
+}
+
+// setFieldValueFromData sets the field's value based on the provided data.
+func setFieldValueFromData(field reflect.Value, data interface{}) error {
+	switch field.Kind() {
+	case reflect.String:
+		return setStringField(field, data)
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return setIntField(field, data)
+	case reflect.Float32, reflect.Float64:
+		return setFloatField(field, data)
+	case reflect.Bool:
+		return setBoolField(field, data)
+	case reflect.Invalid, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr,
+		reflect.Complex64, reflect.Complex128, reflect.Array, reflect.Chan, reflect.Func, reflect.Interface, reflect.Map,
+		reflect.Pointer, reflect.Slice, reflect.Struct, reflect.UnsafePointer:
+		return fmt.Errorf("%w: %s, %T", errUnsupportedFieldType, field.Type().Name(), data)
+	default:
+		return fmt.Errorf("%w: %s, %T", errUnsupportedFieldType, field.Type().Name(), data)
+	}
+}
+
+type customUnmarshaller struct {
+	dataMap map[string]interface{}
+}
+
+// UnmarshalJSON is a custom unmarshaller because json package in Go unmarshal numbers to float64 by default.
+func (c *customUnmarshaller) UnmarshalJSON(data []byte) error {
+	var rawData map[string]interface{}
+
+	err := json.Unmarshal(data, &rawData)
+	if err != nil {
+		return err
+	}
+
+	dataMap := make(map[string]any, len(rawData))
+
+	for key, val := range rawData {
+		if valFloat, ok := val.(float64); ok {
+			valInt := int(valFloat)
+			if valFloat == float64(valInt) {
+				val = valInt
+			}
+		}
+
+		dataMap[key] = val
+	}
+
+	*c = customUnmarshaller{dataMap}
+
+	return nil
+}
+
+func parseStringToMap(data string) (map[string]interface{}, error) {
+	var c customUnmarshaller
+	err := json.Unmarshal([]byte(data), &c)
+
+	return c.dataMap, err
+}
+
+func setStringField(field reflect.Value, data interface{}) error {
+	if val, ok := data.(string); ok {
+		field.SetString(val)
+		return nil
+	}
+
+	return fmt.Errorf("%w: expected string but got %T", errUnsupportedFieldType, data)
+}
+
+func setIntField(field reflect.Value, data interface{}) error {
+	if val, ok := data.(int); ok {
+		field.SetInt(int64(val))
+		return nil
+	}
+
+	return fmt.Errorf("%w: expected int but got %T", errUnsupportedFieldType, data)
+}
+
+func setFloatField(field reflect.Value, data interface{}) error {
+	if val, ok := data.(float64); ok {
+		field.SetFloat(val)
+		return nil
+	}
+
+	return fmt.Errorf("%w: expected float64 but got %T", errUnsupportedFieldType, data)
+}
+
+func setBoolField(field reflect.Value, data interface{}) error {
+	if val, ok := data.(bool); ok {
+		field.SetBool(val)
+		return nil
+	}
+
+	return fmt.Errorf("%w: expected bool but got %T", errUnsupportedFieldType, data)
+}

pkg/gofr/http/multipart_file_bind.go

@@ -1,6 +1,7 @@
 package http
 
 import (
+	"errors"
 	"io"
 	"mime/multipart"
 	"reflect"
@@ -9,6 +10,17 @@ import (
 	"gofr.dev/pkg/gofr/file"
 )
 
+var (
+	errUnsupportedInterfaceType = errors.New("unsupported interface value type")
+	errDataLengthExceeded       = errors.New("data length exceeds array capacity")
+	errUnsupportedKind          = errors.New("unsupported kind")
+	errSettingValueFailure      = errors.New("error setting value at index")
+	errNotAStruct               = errors.New("provided value is not a struct")
+	errUnexportedField          = errors.New("cannot set field; it might be unexported")
+	errUnsupportedFieldType     = errors.New("unsupported type for field")
+	errFieldsNotSet             = errors.New("no fields were set")
+)
+
 type formData struct {
 	fields map[string][]string
 	files  map[string][]*multipart.FileHeader
@@ -134,6 +146,8 @@ func (*formData) setFile(value reflect.Value, header []*multipart.FileHeader) (b
 }
 
 func (uf *formData) setFieldValue(value reflect.Value, data string) (bool, error) {
+	value = dereferencePointerType(value)
+
 	kind := value.Kind()
 	switch kind {
 	case reflect.String:
@@ -146,13 +160,31 @@ func (uf *formData) setFieldValue(value reflect.Value, data string) (bool, error
 		return uf.setFloatValue(value, data)
 	case reflect.Bool:
 		return uf.setBoolValue(value, data)
-	case reflect.Invalid, reflect.Complex64, reflect.Complex128, reflect.Array, reflect.Chan, reflect.Func, reflect.Interface,
-		reflect.Map, reflect.Pointer, reflect.Slice, reflect.Struct, reflect.UnsafePointer:
-		// These types are not supported for setting via form data
-		return false, nil
-	default:
+	case reflect.Slice, reflect.Array:
+		return uf.setSliceOrArrayValue(value, data)
+	case reflect.Interface:
+		return uf.setInterfaceValue(value, data)
+	case reflect.Struct:
+		return uf.setStructValue(value, data)
+	case reflect.Invalid, reflect.Complex64, reflect.Complex128, reflect.Chan, reflect.Func,
+		reflect.Map, reflect.Pointer, reflect.UnsafePointer:
 		return false, nil
 	}
+
+	return false, nil
+}
+
+func dereferencePointerType(value reflect.Value) reflect.Value {
+	if value.Kind() == reflect.Ptr {
+		if value.IsNil() {
+			// Initialize the pointer to a new value if it's nil
+			value.Set(reflect.New(value.Type().Elem()))
+		}
+
+		value = value.Elem() // Dereference the pointer
+	}
+
+	return value
 }
 
 func (*formData) setStringValue(value reflect.Value, data string) (bool, error) {