params.go - debian/gophercloud - Gitiles

 package gophercloud

 import (
 	"encoding/json"
 	"fmt"
 	"net/url"
 	"reflect"
 	"strconv"
 	"strings"
 	"time"
 )

 // BuildRequestBody builds a map[string]interface from the given `struct`. If
 // parent is not the empty string, the final map[string]interface returned will
 // encapsulate the built one
 //
 func BuildRequestBody(opts interface{}, parent string) (map[string]interface{}, error) {
 	optsValue := reflect.ValueOf(opts)
 	if optsValue.Kind() == reflect.Ptr {
 		optsValue = optsValue.Elem()
 	}

 	optsType := reflect.TypeOf(opts)
 	if optsType.Kind() == reflect.Ptr {
 		optsType = optsType.Elem()
 	}

 	optsMap := make(map[string]interface{})
 	if optsValue.Kind() == reflect.Struct {
 		//fmt.Printf("optsValue.Kind() is a reflect.Struct: %+v\n", optsValue.Kind())
 		for i := 0; i < optsValue.NumField(); i++ {
 			v := optsValue.Field(i)
 			f := optsType.Field(i)

 			if f.Name != strings.Title(f.Name) {
 				//fmt.Printf("Skipping field: %s...\n", f.Name)
 				continue
 			}

 			//fmt.Printf("Starting on field: %s...\n", f.Name)

 			zero := isZero(v)
 			//fmt.Printf("v is zero?: %v\n", zero)

 			// if the field has a required tag that's set to "true"
 			if requiredTag := f.Tag.Get("required"); requiredTag == "true" {
 				//fmt.Printf("Checking required field [%s]:\n\tv: %+v\n\tisZero:%v\n", f.Name, v.Interface(), zero)
 				// if the field's value is zero, return a missing-argument error
 				if zero {
 					// if the field has a 'required' tag, it can't have a zero-value
 					err := ErrMissingInput{}
 					err.Argument = f.Name
 					return nil, err
 				}
 			}

 			if xorTag := f.Tag.Get("xor"); xorTag != "" {
 				//fmt.Printf("Checking `xor` tag for field [%s] with value %+v:\n\txorTag: %s\n", f.Name, v, xorTag)
 				xorField := optsValue.FieldByName(xorTag)
 				var xorFieldIsZero bool
 				if reflect.ValueOf(xorField.Interface()) == reflect.Zero(xorField.Type()) {
 					xorFieldIsZero = true
 				} else {
 					if xorField.Kind() == reflect.Ptr {
 						xorField = xorField.Elem()
 					}
 					xorFieldIsZero = isZero(xorField)
 				}
 				if !(zero != xorFieldIsZero) {
 					err := ErrMissingInput{}
 					err.Argument = fmt.Sprintf("%s/%s", f.Name, xorTag)
 					err.Info = fmt.Sprintf("Exactly one of %s and %s must be provided", f.Name, xorTag)
 					return nil, err
 				}
 			}

 			if orTag := f.Tag.Get("or"); orTag != "" {
 				//fmt.Printf("Checking `or` tag for field with:\n\tname: %+v\n\torTag:%s\n", f.Name, orTag)
 				//fmt.Printf("field is zero?: %v\n", zero)
 				if zero {
 					orField := optsValue.FieldByName(orTag)
 					var orFieldIsZero bool
 					if reflect.ValueOf(orField.Interface()) == reflect.Zero(orField.Type()) {
 						orFieldIsZero = true
 					} else {
 						if orField.Kind() == reflect.Ptr {
 							orField = orField.Elem()
 						}
 						orFieldIsZero = isZero(orField)
 					}
 					if orFieldIsZero {
 						err := ErrMissingInput{}
 						err.Argument = fmt.Sprintf("%s/%s", f.Name, orTag)
 						err.Info = fmt.Sprintf("At least one of %s and %s must be provided", f.Name, orTag)
 						return nil, err
 					}
 				}
 			}

 			if v.Kind() == reflect.Struct || (v.Kind() == reflect.Ptr && v.Elem().Kind() == reflect.Struct) {
 				if zero {
 					//fmt.Printf("value before change: %+v\n", optsValue.Field(i))
 					if jsonTag := f.Tag.Get("json"); jsonTag != "" {
 						jsonTagPieces := strings.Split(jsonTag, ",")
 						if len(jsonTagPieces) > 1 && jsonTagPieces[1] == "omitempty" {
 							if v.CanSet() {
 								if !v.IsNil() {
 									if v.Kind() == reflect.Ptr {
 										v.Set(reflect.Zero(v.Type()))
 									}
 								}
 								//fmt.Printf("value after change: %+v\n", optsValue.Field(i))
 							}
 						}
 					}
 					continue
 				}

 				//fmt.Printf("Calling BuildRequestBody with:\n\tv: %+v\n\tf.Name:%s\n", v.Interface(), f.Name)
 				_, err := BuildRequestBody(v.Interface(), f.Name)
 				if err != nil {
 					return nil, err
 				}
 			}
 		}

 		//fmt.Printf("opts: %+v \n", opts)

 		b, err := json.Marshal(opts)
 		if err != nil {
 			return nil, err
 		}

 		//fmt.Printf("string(b): %s\n", string(b))

 		err = json.Unmarshal(b, &optsMap)
 		if err != nil {
 			return nil, err
 		}

 		//fmt.Printf("optsMap: %+v\n", optsMap)

 		if parent != "" {
 			optsMap = map[string]interface{}{parent: optsMap}
 		}
 		//fmt.Printf("optsMap after parent added: %+v\n", optsMap)
 		return optsMap, nil
 	}
 	// Return an error if the underlying type of 'opts' isn't a struct.
 	return nil, fmt.Errorf("Options type is not a struct.")
 }

 // EnabledState is a convenience type, mostly used in Create and Update
 // operations. Because the zero value of a bool is FALSE, we need to use a
 // pointer instead to indicate zero-ness.
 type EnabledState *bool

 // Convenience vars for EnabledState values.
 var (
 	iTrue  = true
 	iFalse = false

 	Enabled  EnabledState = &iTrue
 	Disabled EnabledState = &iFalse
 )

 // IPVersion is a type for the possible IP address versions. Valid instances
 // are IPv4 and IPv6
 type IPVersion int

 const (
 	// IPv4 is used for IP version 4 addresses
 	IPv4 IPVersion = 4
 	// IPv6 is used for IP version 6 addresses
 	IPv6 IPVersion = 6
 )

 // IntToPointer is a function for converting integers into integer pointers.
 // This is useful when passing in options to operations.
 func IntToPointer(i int) *int {
 	return &i
 }

 /*
 MaybeString is an internal function to be used by request methods in individual
 resource packages.

 It takes a string that might be a zero value and returns either a pointer to its
 address or nil. This is useful for allowing users to conveniently omit values
 from an options struct by leaving them zeroed, but still pass nil to the JSON
 serializer so they'll be omitted from the request body.
 */
 func MaybeString(original string) *string {
 	if original != "" {
 		return &original
 	}
 	return nil
 }

 /*
 MaybeInt is an internal function to be used by request methods in individual
 resource packages.

 Like MaybeString, it accepts an int that may or may not be a zero value, and
 returns either a pointer to its address or nil. It's intended to hint that the
 JSON serializer should omit its field.
 */
 func MaybeInt(original int) *int {
 	if original != 0 {
 		return &original
 	}
 	return nil
 }

 /*
 func isUnderlyingStructZero(v reflect.Value) bool {
 	switch v.Kind() {
 	case reflect.Ptr:
 		return isUnderlyingStructZero(v.Elem())
 	default:
 		return isZero(v)
 	}
 }
 */

 var t time.Time

 func isZero(v reflect.Value) bool {
 	//fmt.Printf("\n\nchecking isZero for value: %+v\n", v)
 	switch v.Kind() {
 	case reflect.Ptr:
 		if v.IsNil() {
 			return true
 		}
 		return false
 	case reflect.Func, reflect.Map, reflect.Slice:
 		return v.IsNil()
 	case reflect.Array:
 		z := true
 		for i := 0; i < v.Len(); i++ {
 			z = z && isZero(v.Index(i))
 		}
 		return z
 	case reflect.Struct:
 		if v.Type() == reflect.TypeOf(t) {
 			if v.Interface().(time.Time).IsZero() {
 				return true
 			}
 			return false
 		}
 		z := true
 		for i := 0; i < v.NumField(); i++ {
 			z = z && isZero(v.Field(i))
 		}
 		return z
 	}
 	// Compare other types directly:
 	z := reflect.Zero(v.Type())
 	//fmt.Printf("zero type for value: %+v\n\n\n", z)
 	return v.Interface() == z.Interface()
 }

 /*
 BuildQueryString is an internal function to be used by request methods in
 individual resource packages.

 It accepts a tagged structure and expands it into a URL struct. Field names are
 converted into query parameters based on a "q" tag. For example:

 	type struct Something {
 	   Bar string `q:"x_bar"`
 	   Baz int    `q:"lorem_ipsum"`
 	}

 	instance := Something{
 	   Bar: "AAA",
 	   Baz: "BBB",
 	}

 will be converted into "?x_bar=AAA&lorem_ipsum=BBB".

 The struct's fields may be strings, integers, or boolean values. Fields left at
 their type's zero value will be omitted from the query.
 */
 func BuildQueryString(opts interface{}) (*url.URL, error) {
 	optsValue := reflect.ValueOf(opts)
 	if optsValue.Kind() == reflect.Ptr {
 		optsValue = optsValue.Elem()
 	}

 	optsType := reflect.TypeOf(opts)
 	if optsType.Kind() == reflect.Ptr {
 		optsType = optsType.Elem()
 	}

 	params := url.Values{}

 	if optsValue.Kind() == reflect.Struct {
 		for i := 0; i < optsValue.NumField(); i++ {
 			v := optsValue.Field(i)
 			f := optsType.Field(i)
 			qTag := f.Tag.Get("q")

 			// if the field has a 'q' tag, it goes in the query string
 			if qTag != "" {
 				tags := strings.Split(qTag, ",")

 				// if the field is set, add it to the slice of query pieces
 				if !isZero(v) {
 				loop:
 					switch v.Kind() {
 					case reflect.Ptr:
 						v = v.Elem()
 						goto loop
 					case reflect.String:
 						params.Add(tags[0], v.String())
 					case reflect.Int:
 						params.Add(tags[0], strconv.FormatInt(v.Int(), 10))
 					case reflect.Bool:
 						params.Add(tags[0], strconv.FormatBool(v.Bool()))
 					case reflect.Slice:
 						switch v.Type().Elem() {
 						case reflect.TypeOf(0):
 							for i := 0; i < v.Len(); i++ {
 								params.Add(tags[0], strconv.FormatInt(v.Index(i).Int(), 10))
 							}
 						default:
 							for i := 0; i < v.Len(); i++ {
 								params.Add(tags[0], v.Index(i).String())
 							}
 						}
 					}
 				} else {
 					// Otherwise, the field is not set.
 					if len(tags) == 2 && tags[1] == "required" {
 						// And the field is required. Return an error.
 						return nil, fmt.Errorf("Required query parameter [%s] not set.", f.Name)
 					}
 				}
 			}
 		}

 		return &url.URL{RawQuery: params.Encode()}, nil
 	}
 	// Return an error if the underlying type of 'opts' isn't a struct.
 	return nil, fmt.Errorf("Options type is not a struct.")
 }

 /*
 BuildHeaders is an internal function to be used by request methods in
 individual resource packages.

 It accepts an arbitrary tagged structure and produces a string map that's
 suitable for use as the HTTP headers of an outgoing request. Field names are
 mapped to header names based in "h" tags.

   type struct Something {
     Bar string `h:"x_bar"`
     Baz int    `h:"lorem_ipsum"`
   }

   instance := Something{
     Bar: "AAA",
     Baz: "BBB",
   }

 will be converted into:

   map[string]string{
     "x_bar": "AAA",
     "lorem_ipsum": "BBB",
   }

 Untagged fields and fields left at their zero values are skipped. Integers,
 booleans and string values are supported.
 */
 func BuildHeaders(opts interface{}) (map[string]string, error) {
 	optsValue := reflect.ValueOf(opts)
 	if optsValue.Kind() == reflect.Ptr {
 		optsValue = optsValue.Elem()
 	}

 	optsType := reflect.TypeOf(opts)
 	if optsType.Kind() == reflect.Ptr {
 		optsType = optsType.Elem()
 	}

 	optsMap := make(map[string]string)
 	if optsValue.Kind() == reflect.Struct {
 		for i := 0; i < optsValue.NumField(); i++ {
 			v := optsValue.Field(i)
 			f := optsType.Field(i)
 			hTag := f.Tag.Get("h")

 			// if the field has a 'h' tag, it goes in the header
 			if hTag != "" {
 				tags := strings.Split(hTag, ",")

 				// if the field is set, add it to the slice of query pieces
 				if !isZero(v) {
 					switch v.Kind() {
 					case reflect.String:
 						optsMap[tags[0]] = v.String()
 					case reflect.Int:
 						optsMap[tags[0]] = strconv.FormatInt(v.Int(), 10)
 					case reflect.Bool:
 						optsMap[tags[0]] = strconv.FormatBool(v.Bool())
 					}
 				} else {
 					// Otherwise, the field is not set.
 					if len(tags) == 2 && tags[1] == "required" {
 						// And the field is required. Return an error.
 						return optsMap, fmt.Errorf("Required header not set.")
 					}
 				}
 			}

 		}
 		return optsMap, nil
 	}
 	// Return an error if the underlying type of 'opts' isn't a struct.
 	return optsMap, fmt.Errorf("Options type is not a struct.")
 }

 // IDSliceToQueryString takes a slice of elements and converts them into a query
 // string. For example, if name=foo and slice=[]int{20, 40, 60}, then the
 // result would be `?name=20&name=40&name=60'
 func IDSliceToQueryString(name string, ids []int) string {
 	str := ""
 	for k, v := range ids {
 		if k == 0 {
 			str += "?"
 		} else {
 			str += "&"
 		}
 		str += fmt.Sprintf("%s=%s", name, strconv.Itoa(v))
 	}
 	return str
 }

 // IntWithinRange returns TRUE if an integer falls within a defined range, and
 // FALSE if not.
 func IntWithinRange(val, min, max int) bool {
 	return val > min && val < max
 }
	package gophercloud

	import (
	"encoding/json"
	"fmt"
	"net/url"
	"reflect"
	"strconv"
	"strings"
	"time"
	)

	// BuildRequestBody builds a map[string]interface from the given `struct`. If
	// parent is not the empty string, the final map[string]interface returned will
	// encapsulate the built one
	//
	func BuildRequestBody(opts interface{}, parent string) (map[string]interface{}, error) {
	optsValue := reflect.ValueOf(opts)
	if optsValue.Kind() == reflect.Ptr {
	optsValue = optsValue.Elem()
	}

	optsType := reflect.TypeOf(opts)
	if optsType.Kind() == reflect.Ptr {
	optsType = optsType.Elem()
	}

	optsMap := make(map[string]interface{})
	if optsValue.Kind() == reflect.Struct {
	//fmt.Printf("optsValue.Kind() is a reflect.Struct: %+v\n", optsValue.Kind())
	for i := 0; i < optsValue.NumField(); i++ {
	v := optsValue.Field(i)
	f := optsType.Field(i)

	if f.Name != strings.Title(f.Name) {
	//fmt.Printf("Skipping field: %s...\n", f.Name)
	continue
	}

	//fmt.Printf("Starting on field: %s...\n", f.Name)

	zero := isZero(v)
	//fmt.Printf("v is zero?: %v\n", zero)

	// if the field has a required tag that's set to "true"
	if requiredTag := f.Tag.Get("required"); requiredTag == "true" {
	//fmt.Printf("Checking required field [%s]:\n\tv: %+v\n\tisZero:%v\n", f.Name, v.Interface(), zero)
	// if the field's value is zero, return a missing-argument error
	if zero {
	// if the field has a 'required' tag, it can't have a zero-value
	err := ErrMissingInput{}
	err.Argument = f.Name
	return nil, err
	}
	}

	if xorTag := f.Tag.Get("xor"); xorTag != "" {
	//fmt.Printf("Checking `xor` tag for field [%s] with value %+v:\n\txorTag: %s\n", f.Name, v, xorTag)
	xorField := optsValue.FieldByName(xorTag)
	var xorFieldIsZero bool
	if reflect.ValueOf(xorField.Interface()) == reflect.Zero(xorField.Type()) {
	xorFieldIsZero = true
	} else {
	if xorField.Kind() == reflect.Ptr {
	xorField = xorField.Elem()
	}
	xorFieldIsZero = isZero(xorField)
	}
	if !(zero != xorFieldIsZero) {
	err := ErrMissingInput{}
	err.Argument = fmt.Sprintf("%s/%s", f.Name, xorTag)
	err.Info = fmt.Sprintf("Exactly one of %s and %s must be provided", f.Name, xorTag)
	return nil, err
	}
	}

	if orTag := f.Tag.Get("or"); orTag != "" {
	//fmt.Printf("Checking `or` tag for field with:\n\tname: %+v\n\torTag:%s\n", f.Name, orTag)
	//fmt.Printf("field is zero?: %v\n", zero)
	if zero {
	orField := optsValue.FieldByName(orTag)
	var orFieldIsZero bool
	if reflect.ValueOf(orField.Interface()) == reflect.Zero(orField.Type()) {
	orFieldIsZero = true
	} else {
	if orField.Kind() == reflect.Ptr {
	orField = orField.Elem()
	}
	orFieldIsZero = isZero(orField)
	}
	if orFieldIsZero {
	err := ErrMissingInput{}
	err.Argument = fmt.Sprintf("%s/%s", f.Name, orTag)
	err.Info = fmt.Sprintf("At least one of %s and %s must be provided", f.Name, orTag)
	return nil, err
	}
	}
	}

	if v.Kind() == reflect.Struct \|\| (v.Kind() == reflect.Ptr && v.Elem().Kind() == reflect.Struct) {
	if zero {
	//fmt.Printf("value before change: %+v\n", optsValue.Field(i))
	if jsonTag := f.Tag.Get("json"); jsonTag != "" {
	jsonTagPieces := strings.Split(jsonTag, ",")
	if len(jsonTagPieces) > 1 && jsonTagPieces[1] == "omitempty" {
	if v.CanSet() {
	if !v.IsNil() {
	if v.Kind() == reflect.Ptr {
	v.Set(reflect.Zero(v.Type()))
	}
	}
	//fmt.Printf("value after change: %+v\n", optsValue.Field(i))
	}
	}
	}
	continue
	}

	//fmt.Printf("Calling BuildRequestBody with:\n\tv: %+v\n\tf.Name:%s\n", v.Interface(), f.Name)
	_, err := BuildRequestBody(v.Interface(), f.Name)
	if err != nil {
	return nil, err
	}
	}
	}

	//fmt.Printf("opts: %+v \n", opts)

	b, err := json.Marshal(opts)
	if err != nil {
	return nil, err
	}

	//fmt.Printf("string(b): %s\n", string(b))

	err = json.Unmarshal(b, &optsMap)
	if err != nil {
	return nil, err
	}

	//fmt.Printf("optsMap: %+v\n", optsMap)

	if parent != "" {
	optsMap = map[string]interface{}{parent: optsMap}
	}
	//fmt.Printf("optsMap after parent added: %+v\n", optsMap)
	return optsMap, nil
	}
	// Return an error if the underlying type of 'opts' isn't a struct.
	return nil, fmt.Errorf("Options type is not a struct.")
	}

	// EnabledState is a convenience type, mostly used in Create and Update
	// operations. Because the zero value of a bool is FALSE, we need to use a
	// pointer instead to indicate zero-ness.
	type EnabledState *bool

	// Convenience vars for EnabledState values.
	var (
	iTrue = true
	iFalse = false

	Enabled EnabledState = &iTrue
	Disabled EnabledState = &iFalse
	)

	// IPVersion is a type for the possible IP address versions. Valid instances
	// are IPv4 and IPv6
	type IPVersion int

	const (
	// IPv4 is used for IP version 4 addresses
	IPv4 IPVersion = 4
	// IPv6 is used for IP version 6 addresses
	IPv6 IPVersion = 6
	)

	// IntToPointer is a function for converting integers into integer pointers.
	// This is useful when passing in options to operations.
	func IntToPointer(i int) *int {
	return &i
	}

	/*
	MaybeString is an internal function to be used by request methods in individual
	resource packages.

	It takes a string that might be a zero value and returns either a pointer to its
	address or nil. This is useful for allowing users to conveniently omit values
	from an options struct by leaving them zeroed, but still pass nil to the JSON
	serializer so they'll be omitted from the request body.
	*/
	func MaybeString(original string) *string {
	if original != "" {
	return &original
	}
	return nil
	}

	/*
	MaybeInt is an internal function to be used by request methods in individual
	resource packages.

	Like MaybeString, it accepts an int that may or may not be a zero value, and
	returns either a pointer to its address or nil. It's intended to hint that the
	JSON serializer should omit its field.
	*/
	func MaybeInt(original int) *int {
	if original != 0 {
	return &original
	}
	return nil
	}

	/*
	func isUnderlyingStructZero(v reflect.Value) bool {
	switch v.Kind() {
	case reflect.Ptr:
	return isUnderlyingStructZero(v.Elem())
	default:
	return isZero(v)
	}
	}
	*/

	var t time.Time

	func isZero(v reflect.Value) bool {
	//fmt.Printf("\n\nchecking isZero for value: %+v\n", v)
	switch v.Kind() {
	case reflect.Ptr:
	if v.IsNil() {
	return true
	}
	return false
	case reflect.Func, reflect.Map, reflect.Slice:
	return v.IsNil()
	case reflect.Array:
	z := true
	for i := 0; i < v.Len(); i++ {
	z = z && isZero(v.Index(i))
	}
	return z
	case reflect.Struct:
	if v.Type() == reflect.TypeOf(t) {
	if v.Interface().(time.Time).IsZero() {
	return true
	}
	return false
	}
	z := true
	for i := 0; i < v.NumField(); i++ {
	z = z && isZero(v.Field(i))
	}
	return z
	}
	// Compare other types directly:
	z := reflect.Zero(v.Type())
	//fmt.Printf("zero type for value: %+v\n\n\n", z)
	return v.Interface() == z.Interface()
	}

	/*
	BuildQueryString is an internal function to be used by request methods in
	individual resource packages.

	It accepts a tagged structure and expands it into a URL struct. Field names are
	converted into query parameters based on a "q" tag. For example:

	type struct Something {
	Bar string `q:"x_bar"`
	Baz int `q:"lorem_ipsum"`
	}

	instance := Something{
	Bar: "AAA",
	Baz: "BBB",
	}

	will be converted into "?x_bar=AAA&lorem_ipsum=BBB".

	The struct's fields may be strings, integers, or boolean values. Fields left at
	their type's zero value will be omitted from the query.
	*/
	func BuildQueryString(opts interface{}) (*url.URL, error) {
	optsValue := reflect.ValueOf(opts)
	if optsValue.Kind() == reflect.Ptr {
	optsValue = optsValue.Elem()
	}

	optsType := reflect.TypeOf(opts)
	if optsType.Kind() == reflect.Ptr {
	optsType = optsType.Elem()
	}

	params := url.Values{}

	if optsValue.Kind() == reflect.Struct {
	for i := 0; i < optsValue.NumField(); i++ {
	v := optsValue.Field(i)
	f := optsType.Field(i)
	qTag := f.Tag.Get("q")

	// if the field has a 'q' tag, it goes in the query string
	if qTag != "" {
	tags := strings.Split(qTag, ",")

	// if the field is set, add it to the slice of query pieces
	if !isZero(v) {
	loop:
	switch v.Kind() {
	case reflect.Ptr:
	v = v.Elem()
	goto loop
	case reflect.String:
	params.Add(tags[0], v.String())
	case reflect.Int:
	params.Add(tags[0], strconv.FormatInt(v.Int(), 10))
	case reflect.Bool:
	params.Add(tags[0], strconv.FormatBool(v.Bool()))
	case reflect.Slice:
	switch v.Type().Elem() {
	case reflect.TypeOf(0):
	for i := 0; i < v.Len(); i++ {
	params.Add(tags[0], strconv.FormatInt(v.Index(i).Int(), 10))
	}
	default:
	for i := 0; i < v.Len(); i++ {
	params.Add(tags[0], v.Index(i).String())
	}
	}
	}
	} else {
	// Otherwise, the field is not set.
	if len(tags) == 2 && tags[1] == "required" {
	// And the field is required. Return an error.
	return nil, fmt.Errorf("Required query parameter [%s] not set.", f.Name)
	}
	}
	}
	}

	return &url.URL{RawQuery: params.Encode()}, nil
	}
	// Return an error if the underlying type of 'opts' isn't a struct.
	return nil, fmt.Errorf("Options type is not a struct.")
	}

	/*
	BuildHeaders is an internal function to be used by request methods in
	individual resource packages.

	It accepts an arbitrary tagged structure and produces a string map that's
	suitable for use as the HTTP headers of an outgoing request. Field names are
	mapped to header names based in "h" tags.

	type struct Something {
	Bar string `h:"x_bar"`
	Baz int `h:"lorem_ipsum"`
	}

	instance := Something{
	Bar: "AAA",
	Baz: "BBB",
	}

	will be converted into:

	map[string]string{
	"x_bar": "AAA",
	"lorem_ipsum": "BBB",
	}

	Untagged fields and fields left at their zero values are skipped. Integers,
	booleans and string values are supported.
	*/
	func BuildHeaders(opts interface{}) (map[string]string, error) {
	optsValue := reflect.ValueOf(opts)
	if optsValue.Kind() == reflect.Ptr {
	optsValue = optsValue.Elem()
	}

	optsType := reflect.TypeOf(opts)
	if optsType.Kind() == reflect.Ptr {
	optsType = optsType.Elem()
	}

	optsMap := make(map[string]string)
	if optsValue.Kind() == reflect.Struct {
	for i := 0; i < optsValue.NumField(); i++ {
	v := optsValue.Field(i)
	f := optsType.Field(i)
	hTag := f.Tag.Get("h")

	// if the field has a 'h' tag, it goes in the header
	if hTag != "" {
	tags := strings.Split(hTag, ",")

	// if the field is set, add it to the slice of query pieces
	if !isZero(v) {
	switch v.Kind() {
	case reflect.String:
	optsMap[tags[0]] = v.String()
	case reflect.Int:
	optsMap[tags[0]] = strconv.FormatInt(v.Int(), 10)
	case reflect.Bool:
	optsMap[tags[0]] = strconv.FormatBool(v.Bool())
	}
	} else {
	// Otherwise, the field is not set.
	if len(tags) == 2 && tags[1] == "required" {
	// And the field is required. Return an error.
	return optsMap, fmt.Errorf("Required header not set.")
	}
	}
	}

	}
	return optsMap, nil
	}
	// Return an error if the underlying type of 'opts' isn't a struct.
	return optsMap, fmt.Errorf("Options type is not a struct.")
	}

	// IDSliceToQueryString takes a slice of elements and converts them into a query
	// string. For example, if name=foo and slice=[]int{20, 40, 60}, then the
	// result would be `?name=20&name=40&name=60'
	func IDSliceToQueryString(name string, ids []int) string {
	str := ""
	for k, v := range ids {
	if k == 0 {
	str += "?"
	} else {
	str += "&"
	}
	str += fmt.Sprintf("%s=%s", name, strconv.Itoa(v))
	}
	return str
	}

	// IntWithinRange returns TRUE if an integer falls within a defined range, and
	// FALSE if not.
	func IntWithinRange(val, min, max int) bool {
	return val > min && val < max
	}