http.go

// Copyright (c) 2016, 2018, 2021, Oracle and/or its affiliates.  All rights reserved.
// This software is dual-licensed to you under the Universal Permissive License (UPL) 1.0 as shown at https://oss.oracle.com/licenses/upl or Apache License 2.0 as shown at http://www.apache.org/licenses/LICENSE-2.0. You may choose either license.

package common

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"net/url"
	"os"
	"reflect"
	"regexp"
	"strconv"
	"strings"
	"time"
)

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
//Request Marshaling
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////

func isNil(v reflect.Value) bool {
	return v.Kind() == reflect.Ptr && v.IsNil()
}

// Returns the string representation of a reflect.Value
// Only transforms primitive values
func toStringValue(v reflect.Value, field reflect.StructField) (string, error) {
	if v.Kind() == reflect.Ptr {
		if v.IsNil() {
			return "", fmt.Errorf("can not marshal a nil pointer")
		}
		v = v.Elem()
	}

	if v.Type() == timeType {
		t := v.Interface().(SDKTime)
		return formatTime(t), nil
	}

	if v.Type() == sdkDateType {
		t := v.Interface().(SDKDate)
		return formatDate(t), nil
	}

	switch v.Kind() {
	case reflect.Bool:
		return strconv.FormatBool(v.Bool()), nil
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return strconv.FormatInt(v.Int(), 10), nil
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return strconv.FormatUint(v.Uint(), 10), nil
	case reflect.String:
		return v.String(), nil
	case reflect.Float32:
		return strconv.FormatFloat(v.Float(), 'f', -1, 32), nil
	case reflect.Float64:
		return strconv.FormatFloat(v.Float(), 'f', -1, 64), nil
	default:
		return "", fmt.Errorf("marshaling structure to a http.Request does not support field named: %s of type: %v",
			field.Name, v.Type().String())
	}
}

func addBinaryBody(request *http.Request, value reflect.Value, field reflect.StructField) (e error) {
	readCloser, ok := value.Interface().(io.ReadCloser)
	isMandatory, err := strconv.ParseBool(field.Tag.Get("mandatory"))
	if err != nil {
		return fmt.Errorf("mandatory tag is not valid for field %s", field.Name)
	}

	if isMandatory && !ok {
		e = fmt.Errorf("body of the request is mandatory and needs to be an io.ReadCloser interface. Can not marshal body of binary request")
		return
	}

	request.Body = readCloser

	//Set the default content type to application/octet-stream if not set
	if request.Header.Get(requestHeaderContentType) == "" {
		request.Header.Set(requestHeaderContentType, "application/octet-stream")
	}
	return nil
}

// getTaggedNilFieldNameOrError, evaluates if a field with json and  non mandatory tags is nil
// returns the json tag name, or an error if the tags are incorrectly present
func getTaggedNilFieldNameOrError(field reflect.StructField, fieldValue reflect.Value) (bool, string, error) {
	currentTag := field.Tag
	jsonTag := currentTag.Get("json")

	if jsonTag == "" {
		return false, "", fmt.Errorf("json tag is not valid for field %s", field.Name)
	}

	partsJSONTag := strings.Split(jsonTag, ",")
	nameJSONField := partsJSONTag[0]

	if _, ok := currentTag.Lookup("mandatory"); !ok {
		//No mandatory field set, no-op
		return false, nameJSONField, nil
	}
	isMandatory, err := strconv.ParseBool(currentTag.Get("mandatory"))
	if err != nil {
		return false, "", fmt.Errorf("mandatory tag is not valid for field %s", field.Name)
	}

	// If the field is marked as mandatory, no-op
	if isMandatory {
		return false, nameJSONField, nil
	}

	Debugf("Adjusting tag: mandatory is false and json tag is valid on field: %s", field.Name)

	// If the field can not be nil, then no-op
	if !isNillableType(&fieldValue) {
		Debugf("WARNING json field is tagged with mandatory flags, but the type can not be nil, field name: %s", field.Name)
		return false, nameJSONField, nil
	}

	// If field value is nil, tag it as omitEmpty
	return fieldValue.IsNil(), nameJSONField, nil

}

// isNillableType returns true if the filed can be nil
func isNillableType(value *reflect.Value) bool {
	k := value.Kind()
	switch k {
	case reflect.Chan, reflect.Func, reflect.Map, reflect.Ptr, reflect.Interface, reflect.Slice:
		return true
	}
	return false
}

// omitNilFieldsInJSON, removes json keys whose struct value is nil, and the field is tagged with the json and
// mandatory:false tags
func omitNilFieldsInJSON(data interface{}, value reflect.Value) (interface{}, error) {
	switch value.Kind() {
	case reflect.Struct:
		jsonMap := data.(map[string]interface{})
		fieldType := value.Type()
		for i := 0; i < fieldType.NumField(); i++ {
			currentField := fieldType.Field(i)
			//unexported skip
			if currentField.PkgPath != "" {
				continue
			}

			//Does not have json tag, no-op
			if _, ok := currentField.Tag.Lookup("json"); !ok {
				continue
			}

			currentFieldValue := value.Field(i)
			ok, jsonFieldName, err := getTaggedNilFieldNameOrError(currentField, currentFieldValue)
			if err != nil {
				return nil, fmt.Errorf("can not omit nil fields for field: %s, due to: %s",
					currentField.Name, err.Error())
			}

			//Delete the struct field from the json representation
			if ok {
				delete(jsonMap, jsonFieldName)
				continue
			}

			// Check to make sure the field is part of the json representation of the value
			if _, contains := jsonMap[jsonFieldName]; !contains {
				Debugf("Field %s is not present in json, omitting", jsonFieldName)
				continue
			}

			if currentFieldValue.Type() == timeType || currentFieldValue.Type() == timeTypePtr ||
				currentField.Type == sdkDateType || currentField.Type == sdkDateTypePtr {
				continue
			}
			// does it need to be adjusted?
			var adjustedValue interface{}
			adjustedValue, err = omitNilFieldsInJSON(jsonMap[jsonFieldName], currentFieldValue)
			if err != nil {
				return nil, fmt.Errorf("can not omit nil fields for field: %s, due to: %s",
					currentField.Name, err.Error())
			}
			jsonMap[jsonFieldName] = adjustedValue
		}
		return jsonMap, nil
	case reflect.Slice, reflect.Array:
		// Special case: a []byte may have been marshalled as a string
		if data != nil && reflect.TypeOf(data).Kind() == reflect.String && value.Type().Elem().Kind() == reflect.Uint8 {
			return data, nil
		}
		jsonList, ok := data.([]interface{})
		if !ok {
			return nil, fmt.Errorf("can not omit nil fields, data was expected to be a not-nil list")
		}
		newList := make([]interface{}, len(jsonList))
		var err error
		for i, val := range jsonList {
			newList[i], err = omitNilFieldsInJSON(val, value.Index(i))
			if err != nil {
				return nil, err
			}
		}
		return newList, nil
	case reflect.Map:
		jsonMap, ok := data.(map[string]interface{})
		if !ok {
			return nil, fmt.Errorf("can not omit nil fields, data was expected to be a not-nil map")
		}
		newMap := make(map[string]interface{}, len(jsonMap))
		var err error
		for key, val := range jsonMap {
			newMap[key], err = omitNilFieldsInJSON(val, value.MapIndex(reflect.ValueOf(key)))
			if err != nil {
				return nil, err
			}
		}
		return newMap, nil
	case reflect.Ptr, reflect.Interface:
		valPtr := value.Elem()
		return omitNilFieldsInJSON(data, valPtr)
	default:
		//Otherwise no-op
		return data, nil
	}
}

// removeNilFieldsInJSONWithTaggedStruct remove struct fields tagged with json and mandatory false
// that are nil
func removeNilFieldsInJSONWithTaggedStruct(rawJSON []byte, value reflect.Value) ([]byte, error) {
	var rawInterface interface{}
	decoder := json.NewDecoder(bytes.NewBuffer(rawJSON))
	decoder.UseNumber()
	var err error
	if err = decoder.Decode(&rawInterface); err != nil {
		return nil, err
	}

	fixedMap, err := omitNilFieldsInJSON(rawInterface, value)
	if err != nil {
		return nil, err
	}
	return json.Marshal(fixedMap)
}

func addToBody(request *http.Request, value reflect.Value, field reflect.StructField, binaryBodySpecified *bool) (e error) {
	Debugln("Marshaling to body from field:", field.Name)
	if request.Body != nil {
		Logf("The body of the request is already set. Structure: %s will overwrite it\n", field.Name)
	}
	tag := field.Tag
	encoding := tag.Get("encoding")

	if encoding == "binary" {
		*binaryBodySpecified = true
		return addBinaryBody(request, value, field)
	}

	rawJSON, e := json.Marshal(value.Interface())
	if e != nil {
		return
	}
	marshaled, e := removeNilFieldsInJSONWithTaggedStruct(rawJSON, value)
	if e != nil {
		return
	}

	if defaultLogger.LogLevel() == verboseLogging {
		Debugf("Marshaled body is: %s\n", string(marshaled))
	}

	bodyBytes := bytes.NewReader(marshaled)
	request.ContentLength = int64(bodyBytes.Len())
	request.Header.Set(requestHeaderContentLength, strconv.FormatInt(request.ContentLength, 10))
	request.Header.Set(requestHeaderContentType, "application/json")
	request.Body = ioutil.NopCloser(bodyBytes)
	snapshot := *bodyBytes
	request.GetBody = func() (io.ReadCloser, error) {
		r := snapshot
		return ioutil.NopCloser(&r), nil
	}

	return
}

func checkBinaryBodyLength(request *http.Request) (contentLen int64, err error) {
	if reflect.TypeOf(request.Body) == reflect.TypeOf(ioutil.NopCloser(nil)) {
		ioReader := reflect.ValueOf(request.Body).Field(0).Interface().(io.Reader)
		switch t := ioReader.(type) {
		case *bytes.Reader:
			return int64(t.Len()), nil
		case *bytes.Buffer:
			return int64(t.Len()), nil
		case *strings.Reader:
			return int64(t.Len()), nil
		default:
			return getNormalBinaryBodyLength(request)
		}
	}
	if reflect.TypeOf(request.Body) == reflect.TypeOf((*os.File)(nil)) {
		fi, err := (request.Body.(*os.File)).Stat()
		if err != nil {
			return contentLen, err
		}
		return fi.Size(), nil
	}
	return getNormalBinaryBodyLength(request)
}

func getNormalBinaryBodyLength(request *http.Request) (contentLen int64, err error) {
	dumpRequestBody := ioutil.NopCloser(bytes.NewBuffer(nil))
	if dumpRequestBody, request.Body, err = drainBody(request.Body); err != nil {
		dumpRequestBody = ioutil.NopCloser(bytes.NewBuffer(nil))
		return contentLen, err
	}
	contentBody, err := ioutil.ReadAll(dumpRequestBody)
	if err != nil {
		return contentLen, err
	}
	return int64(len(contentBody)), nil
}

func addToQuery(request *http.Request, value reflect.Value, field reflect.StructField) (e error) {
	Debugln("Marshaling to query from field: ", field.Name)
	if request.URL == nil {
		request.URL = &url.URL{}
	}
	query := request.URL.Query()
	var queryParameterValue, queryParameterName string

	if queryParameterName = field.Tag.Get("name"); queryParameterName == "" {
		return fmt.Errorf("marshaling request to a query requires the 'name' tag for field: %s ", field.Name)
	}

	mandatory, _ := strconv.ParseBool(strings.ToLower(field.Tag.Get("mandatory")))

	//If mandatory and nil. Error out
	if mandatory && isNil(value) {
		return fmt.Errorf("marshaling request to a header requires not nil pointer for field: %s", field.Name)
	}

	//if not mandatory and nil. Omit
	if !mandatory && isNil(value) {
		Debugf("Query parameter value is not mandatory and is nil pointer in field: %s. Skipping query", field.Name)
		return
	}

	encoding := strings.ToLower(field.Tag.Get("collectionFormat"))
	var collectionFormatStringValues []string
	switch encoding {
	case "csv", "multi":
		if value.Kind() != reflect.Slice && value.Kind() != reflect.Array {
			e = fmt.Errorf("query parameter is tagged as csv or multi yet its type is neither an Array nor a Slice: %s", field.Name)
			break
		}

		numOfElements := value.Len()
		collectionFormatStringValues = make([]string, numOfElements)
		for i := 0; i < numOfElements; i++ {
			collectionFormatStringValues[i], e = toStringValue(value.Index(i), field)
			if e != nil {
				break
			}
		}
		queryParameterValue = strings.Join(collectionFormatStringValues, ",")
	case "":
		queryParameterValue, e = toStringValue(value, field)
	default:
		e = fmt.Errorf("encoding of type %s is not supported for query param: %s", encoding, field.Name)
	}

	if e != nil {
		return
	}

	//check for tag "omitEmpty", this is done to accomodate unset fields that do not
	//support an empty string: enums in query params
	if omitEmpty, present := field.Tag.Lookup("omitEmpty"); present {
		omitEmptyBool, _ := strconv.ParseBool(strings.ToLower(omitEmpty))
		if queryParameterValue != "" || !omitEmptyBool {
			addToQueryForEncoding(&query, encoding, queryParameterName, queryParameterValue, collectionFormatStringValues)
		} else {
			Debugf("Omitting %s, is empty and omitEmpty tag is set", field.Name)
		}
	} else {
		addToQueryForEncoding(&query, encoding, queryParameterName, queryParameterValue, collectionFormatStringValues)
	}

	request.URL.RawQuery = query.Encode()
	return
}

func addToQueryForEncoding(query *url.Values, encoding string, queryParameterName string, queryParameterValue string, collectionFormatStringValues []string) {
	if encoding == "multi" {
		for _, stringValue := range collectionFormatStringValues {
			query.Add(queryParameterName, stringValue)
		}
	} else {
		query.Set(queryParameterName, queryParameterValue)
	}
}

// Adds to the path of the url in the order they appear in the structure
func addToPath(request *http.Request, value reflect.Value, field reflect.StructField) (e error) {
	var additionalURLPathPart string
	if additionalURLPathPart, e = toStringValue(value, field); e != nil {
		return fmt.Errorf("can not marshal to path in request for field %s. Due to %s", field.Name, e.Error())
	}

	// path should not be empty for any operations
	if len(additionalURLPathPart) == 0 {
		return fmt.Errorf("value cannot be empty for field %s in path", field.Name)
	}

	if request.URL == nil {
		request.URL = &url.URL{}
		request.URL.Path = ""
	}
	var currentURLPath = request.URL.Path

	var templatedPathRegex, _ = regexp.Compile(".*{.+}.*")
	if !templatedPathRegex.MatchString(currentURLPath) {
		Debugln("Marshaling request to path by appending field:", field.Name)
		allPath := []string{currentURLPath, additionalURLPathPart}
		request.URL.Path = strings.Join(allPath, "/")
	} else {
		var fieldName string
		if fieldName = field.Tag.Get("name"); fieldName == "" {
			e = fmt.Errorf("marshaling request to path name and template requires a 'name' tag for field: %s", field.Name)
			return
		}
		urlTemplate := currentURLPath
		Debugln("Marshaling to path from field: ", field.Name, " in template: ", urlTemplate)
		request.URL.Path = strings.Replace(urlTemplate, "{"+fieldName+"}", additionalURLPathPart, -1)
	}
	return
}

func setWellKnownHeaders(request *http.Request, headerName, headerValue string, contentLenSpecified *bool) (e error) {
	switch strings.ToLower(headerName) {
	case "content-length":
		var len int
		len, e = strconv.Atoi(headerValue)
		if e != nil {
			return
		}
		request.ContentLength = int64(len)
		*contentLenSpecified = true
	}
	return nil
}

func addToHeader(request *http.Request, value reflect.Value, field reflect.StructField, contentLenSpecified *bool) (e error) {
	Debugln("Marshaling to header from field: ", field.Name)
	if request.Header == nil {
		request.Header = http.Header{}
	}

	var headerName, headerValue string
	if headerName = field.Tag.Get("name"); headerName == "" {
		return fmt.Errorf("marshaling request to a header requires the 'name' tag for field: %s", field.Name)
	}

	mandatory, _ := strconv.ParseBool(strings.ToLower(field.Tag.Get("mandatory")))
	//If mandatory and nil. Error out
	if mandatory && isNil(value) {
		return fmt.Errorf("marshaling request to a header requires not nil pointer for field: %s", field.Name)
	}

	// generate opc-request-id if header value is nil and header name matches
	value = generateOpcRequestID(headerName, value)

	//if not mandatory and nil. Omit
	if !mandatory && isNil(value) {
		Debugf("Header value is not mandatory and is nil pointer in field: %s. Skipping header", field.Name)
		return
	}

	//Otherwise get value and set header
	if headerValue, e = toStringValue(value, field); e != nil {
		return
	}

	if e = setWellKnownHeaders(request, headerName, headerValue, contentLenSpecified); e != nil {
		return
	}

	if isUniqueHeaderRequired(headerName) {
		request.Header.Set(headerName, headerValue)
	} else {
		request.Header.Add(headerName, headerValue)
	}
	return
}

// Check if the header is required to be unique
func isUniqueHeaderRequired(headerName string) bool {
	return strings.EqualFold(headerName, requestHeaderContentType) || strings.EqualFold(headerName, requestHeaderContentLength)
}

// Header collection is a map of string to string that gets rendered as individual headers with a given prefix
func addToHeaderCollection(request *http.Request, value reflect.Value, field reflect.StructField) (e error) {
	Debugln("Marshaling to header-collection from field:", field.Name)
	if request.Header == nil {
		request.Header = http.Header{}
	}

	var headerPrefix string
	if headerPrefix = field.Tag.Get("prefix"); headerPrefix == "" {
		return fmt.Errorf("marshaling request to a header requires the 'prefix' tag for field: %s", field.Name)
	}

	mandatory, _ := strconv.ParseBool(strings.ToLower(field.Tag.Get("mandatory")))
	//If mandatory and nil. Error out
	if mandatory && isNil(value) {
		return fmt.Errorf("marshaling request to a header requires not nil pointer for field: %s", field.Name)
	}

	//if not mandatory and nil. Omit
	if !mandatory && isNil(value) {
		Debugf("Header value is not mandatory and is nil pointer in field: %s. Skipping header", field.Name)
		return
	}

	//cast to map
	headerValues, ok := value.Interface().(map[string]string)
	if !ok {
		e = fmt.Errorf("header fields need to be of type map[string]string")
		return
	}

	for k, v := range headerValues {
		headerName := fmt.Sprintf("%s%s", headerPrefix, k)
		request.Header.Set(headerName, v)
	}
	return
}

// Makes sure the incoming structure is able to be marshalled
// to a request
func checkForValidRequestStruct(s interface{}) (*reflect.Value, error) {
	val := reflect.ValueOf(s)
	for val.Kind() == reflect.Ptr {
		if val.IsNil() {
			return nil, fmt.Errorf("can not marshal to request a pointer to structure")
		}
		val = val.Elem()
	}

	if s == nil {
		return nil, fmt.Errorf("can not marshal to request a nil structure")
	}

	if val.Kind() != reflect.Struct {
		return nil, fmt.Errorf("can not marshal to request, expects struct input. Got %v", val.Kind())
	}

	return &val, nil
}

// Populates the parts of a request by reading tags in the passed structure
// nested structs are followed recursively depth-first.
func structToRequestPart(request *http.Request, val reflect.Value) (err error) {
	typ := val.Type()
	contentLenSpecified := false
	binaryBodySpecified := false
	for i := 0; i < typ.NumField(); i++ {
		if err != nil {
			return
		}

		sf := typ.Field(i)
		//unexported
		if sf.PkgPath != "" && !sf.Anonymous {
			continue
		}

		sv := val.Field(i)
		tag := sf.Tag.Get("contributesTo")
		switch tag {
		case "header":
			err = addToHeader(request, sv, sf, &contentLenSpecified)
		case "header-collection":
			err = addToHeaderCollection(request, sv, sf)
		case "path":
			err = addToPath(request, sv, sf)
		case "query":
			err = addToQuery(request, sv, sf)
		case "body":
			err = addToBody(request, sv, sf, &binaryBodySpecified)
		case "":
			Debugln(sf.Name, " does not contain contributes tag. Skipping.")
		default:
			err = fmt.Errorf("can not marshal field: %s. It needs to contain valid contributesTo tag", sf.Name)
		}
	}

	// if content-length is not specified but with binary body, calculate the content length according to request body
	if !contentLenSpecified && binaryBodySpecified && request.Body != nil && request.Body != http.NoBody {
		contentLen, err := checkBinaryBodyLength(request)
		if err == nil {
			request.Header.Set(requestHeaderContentLength, strconv.FormatInt(contentLen, 10))
			request.ContentLength = contentLen
		}
	}

	//If content length is zero, to avoid sending transfer-coding: chunked header, need to explicitly set the body to nil/Nobody.
	if request.Header != nil && request.Body != nil && request.Body != http.NoBody &&
		parseContentLength(request.Header.Get(requestHeaderContentLength)) == 0 {
		request.Body = http.NoBody
	}
	//If headers are and the content type was not set, we default to application/json
	if request.Header != nil && request.Header.Get(requestHeaderContentType) == "" {
		request.Header.Set(requestHeaderContentType, "application/json")
	}

	return
}

// HTTPRequestMarshaller marshals a structure to an http request using tag values in the struct
// The marshaller tag should like the following
// type A struct {
// 		 ANumber string `contributesTo="query" name="number"`
//		 TheBody `contributesTo="body"`
// }
// where the contributesTo tag can be: header, path, query, body
// and the 'name' tag is the name of the value used in the http request(not applicable for path)
// If path is specified as part of the tag, the values are appened to the url path
// in the order they appear in the structure
// The current implementation only supports primitive types, except for the body tag, which needs a struct type.
// The body of a request will be marshaled using the tags of the structure
func HTTPRequestMarshaller(requestStruct interface{}, httpRequest *http.Request) (err error) {
	var val *reflect.Value
	if val, err = checkForValidRequestStruct(requestStruct); err != nil {
		return
	}

	Debugln("Marshaling to Request: ", val.Type().Name())
	err = structToRequestPart(httpRequest, *val)
	return
}

// MakeDefaultHTTPRequest creates the basic http request with the necessary headers set
func MakeDefaultHTTPRequest(method, path string) (httpRequest http.Request) {
	httpRequest = http.Request{
		Proto:      "HTTP/1.1",
		ProtoMajor: 1,
		ProtoMinor: 1,
		Header:     make(http.Header),
		URL:        &url.URL{},
	}

	httpRequest.Header.Set(requestHeaderContentLength, "0")
	httpRequest.Header.Set(requestHeaderDate, time.Now().UTC().Format(http.TimeFormat))
	httpRequest.Header.Set(requestHeaderOpcClientInfo, strings.Join([]string{defaultSDKMarker, Version()}, "/"))
	httpRequest.Header.Set(requestHeaderAccept, "*/*")
	httpRequest.Method = method
	httpRequest.URL.Path = path
	return
}

// MakeDefaultHTTPRequestWithTaggedStruct creates an http request from an struct with tagged fields, see HTTPRequestMarshaller
// for more information
func MakeDefaultHTTPRequestWithTaggedStruct(method, path string, requestStruct interface{}) (httpRequest http.Request, err error) {
	httpRequest = MakeDefaultHTTPRequest(method, path)
	err = HTTPRequestMarshaller(requestStruct, &httpRequest)
	return
}

// UpdateRequestBinaryBody updates the http request's body once it is binary request and the request body is seekable
// if the content length is zero, no need to update request body(since it's already been set to http.Nody)
func UpdateRequestBinaryBody(httpRequest *http.Request, rsc *OCIReadSeekCloser) {
	if parseContentLength(httpRequest.Header.Get(requestHeaderContentLength)) == 0 {
		return
	}
	httpRequest.Body = rsc
	return
}

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
//Request UnMarshaling
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////

// Makes sure the incoming structure is able to be unmarshaled
// to a request
func checkForValidResponseStruct(s interface{}) (*reflect.Value, error) {
	val := reflect.ValueOf(s)
	for val.Kind() == reflect.Ptr {
		if val.IsNil() {
			return nil, fmt.Errorf("can not unmarshal to response a pointer to nil structure")
		}
		val = val.Elem()
	}

	if s == nil {
		return nil, fmt.Errorf("can not unmarshal to response a nil structure")
	}

	if val.Kind() != reflect.Struct {
		return nil, fmt.Errorf("can not unmarshal to response, expects struct input. Got %v", val.Kind())
	}

	return &val, nil
}

func intSizeFromKind(kind reflect.Kind) int {
	switch kind {
	case reflect.Int8, reflect.Uint8:
		return 8
	case reflect.Int16, reflect.Uint16:
		return 16
	case reflect.Int32, reflect.Uint32:
		return 32
	case reflect.Int64, reflect.Uint64:
		return 64
	case reflect.Int, reflect.Uint:
		return strconv.IntSize
	default:
		Debugf("The type is not valid: %v. Returing int size for arch\n", kind.String())
		return strconv.IntSize
	}

}

func analyzeValue(stringValue string, kind reflect.Kind, field reflect.StructField) (val reflect.Value, valPointer reflect.Value, err error) {
	switch kind {
	case timeType.Kind():
		var t time.Time
		t, err = tryParsingTimeWithValidFormatsForHeaders([]byte(stringValue), field.Name)
		if err != nil {
			return
		}
		sdkTime := sdkTimeFromTime(t)
		val = reflect.ValueOf(sdkTime)
		valPointer = reflect.ValueOf(&sdkTime)
		return
	case sdkDateType.Kind():
		var t time.Time
		t, err = tryParsingTimeWithValidFormatsForHeaders([]byte(stringValue), field.Name)
		if err != nil {
			return
		}
		sdkDate := sdkDateFromTime(t)
		val = reflect.ValueOf(sdkDate)
		valPointer = reflect.ValueOf(&sdkDate)
		return
	case reflect.Bool:
		var bVal bool
		if bVal, err = strconv.ParseBool(stringValue); err != nil {
			return
		}
		val = reflect.ValueOf(bVal)
		valPointer = reflect.ValueOf(&bVal)
		return
	case reflect.Int:
		size := intSizeFromKind(kind)
		var iVal int64
		if iVal, err = strconv.ParseInt(stringValue, 10, size); err != nil {
			return
		}
		var iiVal int
		iiVal = int(iVal)
		val = reflect.ValueOf(iiVal)
		valPointer = reflect.ValueOf(&iiVal)
		return
	case reflect.Int64:
		size := intSizeFromKind(kind)
		var iVal int64
		if iVal, err = strconv.ParseInt(stringValue, 10, size); err != nil {
			return
		}
		val = reflect.ValueOf(iVal)
		valPointer = reflect.ValueOf(&iVal)
		return
	case reflect.Uint:
		size := intSizeFromKind(kind)
		var iVal uint64
		if iVal, err = strconv.ParseUint(stringValue, 10, size); err != nil {
			return
		}
		var uiVal uint
		uiVal = uint(iVal)
		val = reflect.ValueOf(uiVal)
		valPointer = reflect.ValueOf(&uiVal)
		return
	case reflect.String:
		val = reflect.ValueOf(stringValue)
		valPointer = reflect.ValueOf(&stringValue)
	case reflect.Float32:
		var fVal float64
		if fVal, err = strconv.ParseFloat(stringValue, 32); err != nil {
			return
		}
		var ffVal float32
		ffVal = float32(fVal)
		val = reflect.ValueOf(ffVal)
		valPointer = reflect.ValueOf(&ffVal)
		return
	case reflect.Float64:
		var fVal float64
		if fVal, err = strconv.ParseFloat(stringValue, 64); err != nil {
			return
		}
		val = reflect.ValueOf(fVal)
		valPointer = reflect.ValueOf(&fVal)
		return
	default:
		err = fmt.Errorf("value for kind: %s not supported", kind)
	}
	return
}

// Sets the field of a struct, with the appropriate value of the string
// Only sets basic types
func fromStringValue(newValue string, val *reflect.Value, field reflect.StructField) (err error) {

	if !val.CanSet() {
		err = fmt.Errorf("can not set field name: %s of type: %v", field.Name, val.Type().String())
		return
	}

	kind := val.Kind()
	isPointer := false
	if val.Kind() == reflect.Ptr {
		isPointer = true
		kind = field.Type.Elem().Kind()
	}

	value, valPtr, err := analyzeValue(newValue, kind, field)
	valueType := val.Type()
	if err != nil {
		return
	}
	if !isPointer {
		val.Set(value.Convert(valueType))
	} else {
		val.Set(valPtr)
	}
	return
}

// PolymorphicJSONUnmarshaler is the interface to unmarshal polymorphic json payloads
type PolymorphicJSONUnmarshaler interface {
	UnmarshalPolymorphicJSON(data []byte) (interface{}, error)
}

func valueFromPolymorphicJSON(content []byte, unmarshaler PolymorphicJSONUnmarshaler) (val interface{}, err error) {
	err = json.Unmarshal(content, unmarshaler)
	if err != nil {
		return
	}
	val, err = unmarshaler.UnmarshalPolymorphicJSON(content)
	return
}

func valueFromJSONBody(response *http.Response, value *reflect.Value, unmarshaler PolymorphicJSONUnmarshaler) (val interface{}, err error) {
	//Consumes the body, consider implementing it
	//without body consumption
	var content []byte
	content, err = ioutil.ReadAll(response.Body)
	if err != nil {
		return
	}

	if unmarshaler != nil {
		val, err = valueFromPolymorphicJSON(content, unmarshaler)
		return
	}

	val = reflect.New(value.Type()).Interface()
	err = json.Unmarshal(content, &val)
	return
}

func addFromBody(response *http.Response, value *reflect.Value, field reflect.StructField, unmarshaler PolymorphicJSONUnmarshaler) (err error) {
	Debugln("Unmarshaling from body to field: ", field.Name)
	if response.Body == nil {
		Debugln("Unmarshaling body skipped due to nil body content for field: ", field.Name)
		return nil
	}

	tag := field.Tag
	encoding := tag.Get("encoding")
	var iVal interface{}
	switch encoding {
	case "binary":
		value.Set(reflect.ValueOf(response.Body))
		return
	case "plain-text":
		//Expects UTF-8
		byteArr, e := ioutil.ReadAll(response.Body)
		if e != nil {
			return e
		}
		str := string(byteArr)
		value.Set(reflect.ValueOf(&str))
		return
	default: //If the encoding is not set. we'll decode with json
		iVal, err = valueFromJSONBody(response, value, unmarshaler)
		if err != nil {
			return
		}

		newVal := reflect.ValueOf(iVal)
		if newVal.Kind() == reflect.Ptr {
			newVal = newVal.Elem()
		}
		value.Set(newVal)
		return
	}
}

func addFromHeader(response *http.Response, value *reflect.Value, field reflect.StructField) (err error) {
	Debugln("Unmarshaling from header to field: ", field.Name)
	var headerName string
	if headerName = field.Tag.Get("name"); headerName == "" {
		return fmt.Errorf("unmarshaling response to a header requires the 'name' tag for field: %s", field.Name)
	}

	headerValue := response.Header.Get(headerName)
	if headerValue == "" {
		Debugf("Unmarshalling did not find header with name:%s", headerName)
		return nil
	}

	if err = fromStringValue(headerValue, value, field); err != nil {
		return fmt.Errorf("unmarshaling response to a header failed for field %s, due to %s", field.Name,
			err.Error())
	}
	return
}

func addFromHeaderCollection(response *http.Response, value *reflect.Value, field reflect.StructField) error {
	Debugln("Unmarshaling from header-collection to field:", field.Name)
	var headerPrefix string
	if headerPrefix = field.Tag.Get("prefix"); headerPrefix == "" {
		return fmt.Errorf("Unmarshaling response to a header-collection requires the 'prefix' tag for field: %s", field.Name)
	}

	mapCollection := make(map[string]string)
	for name, value := range response.Header {
		nameLowerCase := strings.ToLower(name)
		if strings.HasPrefix(nameLowerCase, headerPrefix) {
			headerNoPrefix := strings.TrimPrefix(nameLowerCase, headerPrefix)
			mapCollection[headerNoPrefix] = value[0]
		}
	}

	Debugln("Marshalled header collection is:", mapCollection)
	value.Set(reflect.ValueOf(mapCollection))
	return nil
}

// Populates a struct from parts of a request by reading tags of the struct
func responseToStruct(response *http.Response, val *reflect.Value, unmarshaler PolymorphicJSONUnmarshaler) (err error) {
	typ := val.Type()
	for i := 0; i < typ.NumField(); i++ {
		if err != nil {
			return
		}

		sf := typ.Field(i)

		//unexported
		if sf.PkgPath != "" {
			continue
		}

		sv := val.Field(i)
		tag := sf.Tag.Get("presentIn")
		switch tag {
		case "header":
			err = addFromHeader(response, &sv, sf)
		case "header-collection":
			err = addFromHeaderCollection(response, &sv, sf)
		case "body":
			err = addFromBody(response, &sv, sf, unmarshaler)
		case "":
			Debugln(sf.Name, " does not contain presentIn tag. Skipping")
		default:
			err = fmt.Errorf("can not unmarshal field: %s. It needs to contain valid presentIn tag", sf.Name)
		}
	}
	return
}

// UnmarshalResponse hydrates the fields of a struct with the values of a http response, guided
// by the field tags. The directive tag is "presentIn" and it can be either
//  - "header": Will look for the header tagged as "name" in the headers of the struct and set it value to that
//  - "body": It will try to marshal the body from a json string to a struct tagged with 'presentIn: "body"'.
// Further this method will consume the body it should be safe to close it after this function
// Notice the current implementation only supports native types:int, strings, floats, bool as the field types
func UnmarshalResponse(httpResponse *http.Response, responseStruct interface{}) (err error) {

	var val *reflect.Value
	if val, err = checkForValidResponseStruct(responseStruct); err != nil {
		return
	}

	if err = responseToStruct(httpResponse, val, nil); err != nil {
		return
	}

	return nil
}

// UnmarshalResponseWithPolymorphicBody similar to UnmarshalResponse but assumes the body of the response
// contains polymorphic json. This function will use the unmarshaler argument to unmarshal json content
func UnmarshalResponseWithPolymorphicBody(httpResponse *http.Response, responseStruct interface{}, unmarshaler PolymorphicJSONUnmarshaler) (err error) {

	var val *reflect.Value
	if val, err = checkForValidResponseStruct(responseStruct); err != nil {
		return
	}

	if err = responseToStruct(httpResponse, val, unmarshaler); err != nil {
		return
	}

	return nil
}

// generate request id if user not provided and for each retry operation re-gen a new request id
func generateOpcRequestID(headerName string, value reflect.Value) (newValue reflect.Value) {
	newValue = value
	isNilValue := isNil(newValue)
	isOpcRequestIDHeader := headerName == requestHeaderOpcRequestID || headerName == requestHeaderOpcClientRequestID

	if isNilValue && isOpcRequestIDHeader {
		requestID, err := generateRandUUID()

		if err != nil {
			// this will not fail the request, just skip add opc-request-id
			Debugf("unable to generate opc-request-id. %s", err.Error())
		} else {
			newValue = reflect.ValueOf(String(requestID))
			Debugf("add request id for header: %s, with value: %s", headerName, requestID)
		}
	}

	return
}