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// Package jsonutil provides a function for decoding JSON
// into a GraphQL query data structure.
package jsonutil
import (
"bytes"
"encoding/json"
"errors"
"fmt"
"io"
"reflect"
"strings"
)
// UnmarshalGraphQL parses the JSON-encoded GraphQL response data and stores
// the result in the GraphQL query data structure pointed to by v.
//
// The implementation is created on top of the JSON tokenizer available
// in "encoding/json".Decoder.
func UnmarshalGraphQL(data []byte, v interface{}) error {
dec := json.NewDecoder(bytes.NewReader(data))
dec.UseNumber()
err := (&decoder{tokenizer: dec}).Decode(v)
if err != nil {
return err
}
tok, err := dec.Token()
switch err {
case io.EOF:
// Expect to get io.EOF. There shouldn't be any more
// tokens left after we've decoded v successfully.
return nil
case nil:
return fmt.Errorf("invalid token '%v' after top-level value", tok)
default:
return err
}
}
// decoder is a JSON decoder that performs custom unmarshaling behavior
// for GraphQL query data structures. It's implemented on top of a JSON tokenizer.
type decoder struct {
tokenizer interface {
Token() (json.Token, error)
}
// Stack of what part of input JSON we're in the middle of - objects, arrays.
parseState []json.Delim
// Stacks of values where to unmarshal.
// The top of each stack is the reflect.Value where to unmarshal next JSON value.
//
// The reason there's more than one stack is because we might be unmarshaling
// a single JSON value into multiple GraphQL fragments or embedded structs, so
// we keep track of them all.
vs [][]reflect.Value
}
// Decode decodes a single JSON value from d.tokenizer into v.
func (d *decoder) Decode(v interface{}) error {
rv := reflect.ValueOf(v)
if rv.Kind() != reflect.Ptr {
return fmt.Errorf("cannot decode into non-pointer %T", v)
}
d.vs = [][]reflect.Value{{rv.Elem()}}
return d.decode()
}
// decode decodes a single JSON value from d.tokenizer into d.vs.
func (d *decoder) decode() error {
// The loop invariant is that the top of each d.vs stack
// is where we try to unmarshal the next JSON value we see.
for len(d.vs) > 0 {
tok, err := d.tokenizer.Token()
if err == io.EOF {
return errors.New("unexpected end of JSON input")
} else if err != nil {
return err
}
switch {
// Are we inside an object and seeing next key (rather than end of object)?
case d.state() == '{' && tok != json.Delim('}'):
key, ok := tok.(string)
if !ok {
return errors.New("unexpected non-key in JSON input")
}
someFieldExist := false
for i := range d.vs {
v := d.vs[i][len(d.vs[i])-1]
if v.Kind() == reflect.Ptr {
v = v.Elem()
}
var f reflect.Value
if v.Kind() == reflect.Struct {
f = fieldByGraphQLName(v, key)
if f.IsValid() {
someFieldExist = true
}
}
d.vs[i] = append(d.vs[i], f)
}
if !someFieldExist {
return fmt.Errorf("struct field for %q doesn't exist in any of %v places to unmarshal", key, len(d.vs))
}
// We've just consumed the current token, which was the key.
// Read the next token, which should be the value, and let the rest of code process it.
tok, err = d.tokenizer.Token()
if err == io.EOF {
return errors.New("unexpected end of JSON input")
} else if err != nil {
return err
}
// Are we inside an array and seeing next value (rather than end of array)?
case d.state() == '[' && tok != json.Delim(']'):
someSliceExist := false
for i := range d.vs {
v := d.vs[i][len(d.vs[i])-1]
if v.Kind() == reflect.Ptr {
v = v.Elem()
}
var f reflect.Value
if v.Kind() == reflect.Slice {
v.Set(reflect.Append(v, reflect.Zero(v.Type().Elem()))) // v = append(v, T).
f = v.Index(v.Len() - 1)
someSliceExist = true
}
d.vs[i] = append(d.vs[i], f)
}
if !someSliceExist {
return fmt.Errorf("slice doesn't exist in any of %v places to unmarshal", len(d.vs))
}
}
switch tok := tok.(type) {
case string, json.Number, bool, nil:
// Value.
for i := range d.vs {
v := d.vs[i][len(d.vs[i])-1]
if !v.IsValid() {
continue
}
err := unmarshalValue(tok, v)
if err != nil {
return err
}
}
d.popAllVs()
case json.Delim:
switch tok {
case '{':
// Start of object.
d.pushState(tok)
frontier := make([]reflect.Value, len(d.vs)) // Places to look for GraphQL fragments/embedded structs.
for i := range d.vs {
v := d.vs[i][len(d.vs[i])-1]
frontier[i] = v
// TODO: Do this recursively or not? Add a test case if needed.
if v.Kind() == reflect.Ptr && v.IsNil() {
v.Set(reflect.New(v.Type().Elem())) // v = new(T).
}
}
// Find GraphQL fragments/embedded structs recursively, adding to frontier
// as new ones are discovered and exploring them further.
for len(frontier) > 0 {
v := frontier[0]
frontier = frontier[1:]
if v.Kind() == reflect.Ptr {
v = v.Elem()
}
if v.Kind() != reflect.Struct {
continue
}
for i := 0; i < v.NumField(); i++ {
if isGraphQLFragment(v.Type().Field(i)) || v.Type().Field(i).Anonymous {
// Add GraphQL fragment or embedded struct.
d.vs = append(d.vs, []reflect.Value{v.Field(i)})
frontier = append(frontier, v.Field(i))
}
}
}
case '[':
// Start of array.
d.pushState(tok)
for i := range d.vs {
v := d.vs[i][len(d.vs[i])-1]
// TODO: Confirm this is needed, write a test case.
//if v.Kind() == reflect.Ptr && v.IsNil() {
// v.Set(reflect.New(v.Type().Elem())) // v = new(T).
//}
// Reset slice to empty (in case it had non-zero initial value).
if v.Kind() == reflect.Ptr {
v = v.Elem()
}
if v.Kind() != reflect.Slice {
continue
}
v.Set(reflect.MakeSlice(v.Type(), 0, 0)) // v = make(T, 0, 0).
}
case '}', ']':
// End of object or array.
d.popAllVs()
d.popState()
default:
return errors.New("unexpected delimiter in JSON input")
}
default:
return errors.New("unexpected token in JSON input")
}
}
return nil
}
// pushState pushes a new parse state s onto the stack.
func (d *decoder) pushState(s json.Delim) {
d.parseState = append(d.parseState, s)
}
// popState pops a parse state (already obtained) off the stack.
// The stack must be non-empty.
func (d *decoder) popState() {
d.parseState = d.parseState[:len(d.parseState)-1]
}
// state reports the parse state on top of stack, or 0 if empty.
func (d *decoder) state() json.Delim {
if len(d.parseState) == 0 {
return 0
}
return d.parseState[len(d.parseState)-1]
}
// popAllVs pops from all d.vs stacks, keeping only non-empty ones.
func (d *decoder) popAllVs() {
var nonEmpty [][]reflect.Value
for i := range d.vs {
d.vs[i] = d.vs[i][:len(d.vs[i])-1]
if len(d.vs[i]) > 0 {
nonEmpty = append(nonEmpty, d.vs[i])
}
}
d.vs = nonEmpty
}
// fieldByGraphQLName returns an exported struct field of struct v
// that matches GraphQL name, or invalid reflect.Value if none found.
func fieldByGraphQLName(v reflect.Value, name string) reflect.Value {
for i := 0; i < v.NumField(); i++ {
if v.Type().Field(i).PkgPath != "" {
// Skip unexported field.
continue
}
if hasGraphQLName(v.Type().Field(i), name) {
return v.Field(i)
}
}
return reflect.Value{}
}
// hasGraphQLName reports whether struct field f has GraphQL name.
func hasGraphQLName(f reflect.StructField, name string) bool {
value, ok := f.Tag.Lookup("graphql")
if !ok {
// TODO: caseconv package is relatively slow. Optimize it, then consider using it here.
//return caseconv.MixedCapsToLowerCamelCase(f.Name) == name
return strings.EqualFold(f.Name, name)
}
value = strings.TrimSpace(value) // TODO: Parse better.
if strings.HasPrefix(value, "...") {
// GraphQL fragment. It doesn't have a name.
return false
}
if i := strings.Index(value, "("); i != -1 {
value = value[:i]
}
if i := strings.Index(value, ":"); i != -1 {
value = value[:i]
}
return strings.TrimSpace(value) == name
}
// isGraphQLFragment reports whether struct field f is a GraphQL fragment.
func isGraphQLFragment(f reflect.StructField) bool {
value, ok := f.Tag.Lookup("graphql")
if !ok {
return false
}
value = strings.TrimSpace(value) // TODO: Parse better.
return strings.HasPrefix(value, "...")
}
// unmarshalValue unmarshals JSON value into v.
// v must be addressable and not obtained by the use of unexported
// struct fields, otherwise unmarshalValue will panic.
func unmarshalValue(value json.Token, v reflect.Value) error {
b, err := json.Marshal(value) // TODO: Short-circuit (if profiling says it's worth it).
if err != nil {
return err
}
return json.Unmarshal(b, v.Addr().Interface())
}
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