/
decode.go
646 lines (577 loc) · 15.1 KB
/
decode.go
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// Parses PG Arrays into Go arrays
package arrays
import (
"encoding/base64"
"errors"
"fmt"
"reflect"
"runtime"
"strconv"
"unicode"
"unicode/utf16"
"unicode/utf8"
)
var byteSliceType = reflect.TypeOf([]byte(nil))
// Unmarshal parses the PG Array data and stores the result
// in the value pointed to by v.
//
// Heavily lifted from the Go JSON decoder. Main difference is
// PG Arrays can contain unquoted strings if they're string arrays
// and the strings don't have whitespace or special characters.
func Unmarshal(data []byte, v interface{}) error {
var d decodeState
d.init(data)
return d.unmarshal(v)
}
// An UnmarshalTypeError describes a value that was
// not appropriate for a value of a specific Go type.
type UnmarshalTypeError struct {
Value string // description of value - "bool", "array", "number -5"
Type reflect.Type // type of Go value it could not be assigned to
}
func (e *UnmarshalTypeError) Error() string {
return "cannot unmarshal " + e.Value + " into Go value of type " + e.Type.String()
}
// An InvalidUnmarshalError describes an invalid argument passed to Unmarshal.
// (The argument to Unmarshal must be a non-nil pointer.)
type InvalidUnmarshalError struct {
Type reflect.Type
}
func (e *InvalidUnmarshalError) Error() string {
if e.Type == nil {
return "Unmarshal(nil)"
}
if e.Type.Kind() != reflect.Ptr {
return "Unmarshal(non-pointer " + e.Type.String() + ")"
}
return "Unmarshal(nil " + e.Type.String() + ")"
}
func (d *decodeState) unmarshal(v interface{}) (err error) {
defer func() {
if r := recover(); r != nil {
if _, ok := r.(runtime.Error); ok {
panic(r)
}
err = r.(error)
}
}()
rv := reflect.ValueOf(v)
if (rv.Kind() != reflect.Ptr) || rv.IsNil() {
return &InvalidUnmarshalError{reflect.TypeOf(v)}
}
d.scan.reset()
// We decode rv not rv.Elem because the Unmarshaler interface
// test must be applied at the top level of the value.
d.value(rv)
return d.savedError
}
// decodeState represents the state while decoding an array value.
type decodeState struct {
data []byte
off int // read offset in data
scan scanner
nextscan scanner // for calls to nextValue
savedError error
tempstr string // scratch space to avoid some allocations
}
// errPhase is used for errors that should not happen unless
// there is a bug in the decoder or something is editing
// the data slice while the decoder executes.
var errPhase = errors.New("decoder out of sync - data changing underfoot?")
func (d *decodeState) init(data []byte) *decodeState {
d.data = data
d.off = 0
d.savedError = nil
return d
}
// error aborts the decoding by panicking with err.
func (d *decodeState) error(err error) {
panic(err)
}
// saveError saves the first err it is called with,
// for reporting at the end of the unmarshal.
func (d *decodeState) saveError(err error) {
if d.savedError == nil {
d.savedError = err
}
}
// next cuts off and returns the next full value in d.data[d.off:].
// The next value is known to be an object or array, not a literal.
func (d *decodeState) next() []byte {
// c := d.data[d.off]
item, rest, err := nextValue(d.data[d.off:], &d.nextscan)
if err != nil {
d.error(err)
}
d.off = len(d.data) - len(rest)
return item
}
// scanWhile processes bytes in d.data[d.off:] until it
// receives a scan code not equal to op.
// It updates d.off and returns the new scan code.
func (d *decodeState) scanWhile(op opcode) opcode {
var newOp opcode
for {
if d.off >= len(d.data) {
newOp = d.scan.eof()
d.off = len(d.data) + 1 // mark processed EOF with len+1
} else {
c := int(d.data[d.off])
d.off++
newOp = d.scan.step(&d.scan, c)
}
if newOp != op {
break
}
}
return newOp
}
// value decodes a value from d.data[d.off:] into the value.
// it updates d.off to point past the decoded value.
func (d *decodeState) value(v reflect.Value) {
switch op := d.scanWhile(scanSkipSpace); op {
default:
d.error(errPhase)
case scanBeginArray:
d.array(v)
case scanBeginLiteral:
d.literal(v)
}
}
// indirect walks down v allocating pointers as needed,
// until it gets to a non-pointer.
// if decodingNull is true, indirect stops at the last pointer so it can be set to nil.
func (d *decodeState) indirect(v reflect.Value, decodingNull bool) reflect.Value {
// If v is a named type and is addressable,
// start with its address, so that if the type has pointer methods,
// we find them.
if v.Kind() != reflect.Ptr && v.Type().Name() != "" && v.CanAddr() {
v = v.Addr()
}
for {
// Load value from interface, but only if the result will be
// usefully addressable.
if v.Kind() == reflect.Interface && !v.IsNil() {
e := v.Elem()
if e.Kind() == reflect.Ptr && !e.IsNil() && (!decodingNull || e.Elem().Kind() == reflect.Ptr) {
v = e
continue
}
}
if v.Kind() != reflect.Ptr {
break
}
if v.Elem().Kind() != reflect.Ptr && decodingNull && v.CanSet() {
break
}
if v.IsNil() {
v.Set(reflect.New(v.Type().Elem()))
}
v = v.Elem()
}
return v
}
// array consumes an array from d.data[d.off-1:], decoding into the value v.
// the first byte of the array ('{') has been read already.
func (d *decodeState) array(v reflect.Value) {
v = d.indirect(v, false)
// Check type of target.
switch v.Kind() {
case reflect.Interface:
if v.NumMethod() == 0 {
// Decoding into nil interface? Switch to non-reflect code.
v.Set(reflect.ValueOf(d.arrayInterface()))
return
}
// Otherwise it's invalid.
fallthrough
default:
d.saveError(&UnmarshalTypeError{"array", v.Type()})
d.off--
d.next()
return
case reflect.Array:
case reflect.Slice:
break
}
i := 0
for {
// Look ahead for } - can only happen on first iteration.
op := d.scanWhile(scanSkipSpace)
if op == scanEndArray {
break
}
// Back up so d.value can have the byte we just read.
d.off--
d.scan.undo(op)
// Get element of array, growing if necessary.
if v.Kind() == reflect.Slice {
// Grow slice if necessary
if i >= v.Cap() {
newcap := v.Cap() + v.Cap()/2
if newcap < 4 {
newcap = 4
}
newv := reflect.MakeSlice(v.Type(), v.Len(), newcap)
reflect.Copy(newv, v)
v.Set(newv)
}
if i >= v.Len() {
v.SetLen(i + 1)
}
}
if i < v.Len() {
// Decode into element.
d.value(v.Index(i))
} else {
// Ran out of fixed array: skip.
d.value(reflect.Value{})
}
i++
// Next token must be , or }.
op = d.scanWhile(scanSkipSpace)
if op == scanEndArray {
break
}
if op == scanError {
d.error(d.scan.err)
} else if op != scanArrayValue {
d.error(errPhase)
}
}
if i < v.Len() {
if v.Kind() == reflect.Array {
// Array. Zero the rest.
z := reflect.Zero(v.Type().Elem())
for ; i < v.Len(); i++ {
v.Index(i).Set(z)
}
} else {
v.SetLen(i)
}
}
if i == 0 && v.Kind() == reflect.Slice {
v.Set(reflect.MakeSlice(v.Type(), 0, 0))
}
}
// literal consumes a literal from d.data[d.off-1:], decoding into the value v.
// The first byte of the literal has been read already
// (that's how the caller knows it's a literal).
func (d *decodeState) literal(v reflect.Value) {
// All bytes inside literal return scanContinue op code.
start := d.off - 1
op := d.scanWhile(scanContinue)
// Scan read one byte too far; back up.
d.off--
d.scan.undo(op)
d.literalStore(d.data[start:d.off], v, false)
}
// convertNumber converts the number literal s to a float64
func (d *decodeState) convertNumber(s string) (interface{}, error) {
f, err := strconv.ParseFloat(s, 64)
if err != nil {
return nil, &UnmarshalTypeError{"number " + s, reflect.TypeOf(0.0)}
}
return f, nil
}
// literalStore decodes a literal stored in item into v.
//
// fromQuoted indicates whether this literal came from unwrapping a
// string from the ",string" struct tag option. this is used only to
// produce more helpful error messages.
func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool) {
// Check for unmarshaler.
if len(item) == 0 {
//Empty string given
d.saveError(fmt.Errorf("invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
return
}
wantptr := string(item) == "NULL"
v = d.indirect(v, wantptr)
// special cases for unquoted values (could be NULL or t/f)
switch str := string(item); str {
case "NULL":
switch v.Kind() {
case reflect.Interface, reflect.Ptr, reflect.Map, reflect.Slice:
v.Set(reflect.Zero(v.Type()))
// otherwise, ignore null for primitives/string
}
return
case "t", "f": // true, false
value := str == "t"
switch v.Kind() {
default:
if fromQuoted {
d.saveError(fmt.Errorf("invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
} else {
d.saveError(&UnmarshalTypeError{"bool", v.Type()})
}
case reflect.Bool:
v.SetBool(value)
case reflect.String:
v.SetString(str)
case reflect.Interface:
if v.NumMethod() == 0 {
v.Set(reflect.ValueOf(value))
} else {
d.saveError(&UnmarshalTypeError{"bool", v.Type()})
}
}
return
}
// handle the value as a literal, either a quoted string or some other value
switch c := item[0]; c {
case '"': // string
s, ok := unquoteBytes(item)
if !ok {
if fromQuoted {
d.error(fmt.Errorf("invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
} else {
d.error(errPhase)
}
}
switch v.Kind() {
default:
d.saveError(&UnmarshalTypeError{"string", v.Type()})
case reflect.Slice:
if v.Type() != byteSliceType {
d.saveError(&UnmarshalTypeError{"string", v.Type()})
break
}
b := make([]byte, base64.StdEncoding.DecodedLen(len(s)))
n, err := base64.StdEncoding.Decode(b, s)
if err != nil {
d.saveError(err)
break
}
v.Set(reflect.ValueOf(b[0:n]))
case reflect.String:
v.SetString(string(s))
case reflect.Interface:
if v.NumMethod() == 0 {
v.Set(reflect.ValueOf(string(s)))
} else {
d.saveError(&UnmarshalTypeError{"string", v.Type()})
}
}
default: // number or unquoted string
s := string(item)
switch v.Kind() {
default:
d.error(&UnmarshalTypeError{s, v.Type()})
case reflect.String:
v.SetString(string(s))
case reflect.Interface:
n, err := d.convertNumber(s)
if err != nil {
d.saveError(err)
break
}
if v.NumMethod() != 0 {
d.saveError(&UnmarshalTypeError{"number", v.Type()})
break
}
v.Set(reflect.ValueOf(n))
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
n, err := strconv.ParseInt(s, 10, 64)
if err != nil || v.OverflowInt(n) {
d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
break
}
v.SetInt(n)
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
n, err := strconv.ParseUint(s, 10, 64)
if err != nil || v.OverflowUint(n) {
d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
break
}
v.SetUint(n)
case reflect.Float32, reflect.Float64:
n, err := strconv.ParseFloat(s, v.Type().Bits())
if err != nil || v.OverflowFloat(n) {
d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
break
}
v.SetFloat(n)
}
}
}
// The xxxInterface routines build up a value to be stored
// in an empty interface. They are not strictly necessary,
// but they avoid the weight of reflection in this common case.
// valueInterface is like value but returns interface{}
func (d *decodeState) valueInterface() interface{} {
switch d.scanWhile(scanSkipSpace) {
default:
d.error(errPhase)
panic("unreachable")
case scanBeginArray:
return d.arrayInterface()
case scanBeginLiteral:
return d.literalInterface()
}
}
// arrayInterface is like array but returns []interface{}.
func (d *decodeState) arrayInterface() []interface{} {
var v = make([]interface{}, 0)
for {
// Look ahead for ] - can only happen on first iteration.
op := d.scanWhile(scanSkipSpace)
if op == scanEndArray {
break
}
// Back up so d.value can have the byte we just read.
d.off--
d.scan.undo(op)
v = append(v, d.valueInterface())
// Next token must be , or ].
op = d.scanWhile(scanSkipSpace)
if op == scanEndArray {
break
}
if op != scanArrayValue {
d.error(errPhase)
}
}
return v
}
// literalInterface is like literal but returns an interface value.
func (d *decodeState) literalInterface() interface{} {
// All bytes inside literal return scanContinue op code.
start := d.off - 1
op := d.scanWhile(scanContinue)
// Scan read one byte too far; back up.
d.off--
d.scan.undo(op)
item := d.data[start:d.off]
switch string(item) {
case "NULL":
return nil
case "t":
return true
case "f":
return false
}
switch c := item[0]; c {
case '"': // string
s, ok := unquote(item)
if !ok {
d.error(errPhase)
}
return s
default: // number
if c != '-' && (c < '0' || c > '9') {
d.error(errPhase)
}
n, err := d.convertNumber(string(item))
if err != nil {
d.saveError(err)
}
return n
}
}
// getu4 decodes \uXXXX from the beginning of s, returning the hex value,
// or it returns -1.
func getu4(s []byte) rune {
if len(s) < 6 || s[0] != '\\' || s[1] != 'u' {
return -1
}
r, err := strconv.ParseUint(string(s[2:6]), 16, 64)
if err != nil {
return -1
}
return rune(r)
}
// unquote converts a quoted string literal s into an actual string t.
// The rules are different than for Go, so cannot use strconv.Unquote.
func unquote(s []byte) (t string, ok bool) {
s, ok = unquoteBytes(s)
t = string(s)
return
}
func unquoteBytes(s []byte) (t []byte, ok bool) {
if len(s) < 2 || s[0] != '"' || s[len(s)-1] != '"' {
return
}
s = s[1 : len(s)-1]
// Check for unusual characters. If there are none,
// then no unquoting is needed, so return a slice of the
// original bytes.
r := 0
for r < len(s) {
c := s[r]
if c == '\\' || c == '"' || c < ' ' {
break
}
if c < utf8.RuneSelf {
r++
continue
}
rr, size := utf8.DecodeRune(s[r:])
if rr == utf8.RuneError && size == 1 {
break
}
r += size
}
if r == len(s) {
return s, true
}
b := make([]byte, len(s)+2*utf8.UTFMax)
w := copy(b, s[0:r])
for r < len(s) {
// Out of room? Can only happen if s is full of
// malformed UTF-8 and we're replacing each
// byte with RuneError.
if w >= len(b)-2*utf8.UTFMax {
nb := make([]byte, (len(b)+utf8.UTFMax)*2)
copy(nb, b[0:w])
b = nb
}
switch c := s[r]; {
case c == '\\':
r++
if r >= len(s) {
return
}
switch s[r] {
default:
b[w] = s[r]
r++
w++
case 'u':
r--
rr := getu4(s[r:])
if rr < 0 {
return
}
r += 6
if utf16.IsSurrogate(rr) {
rr1 := getu4(s[r:])
if dec := utf16.DecodeRune(rr, rr1); dec != unicode.ReplacementChar {
// A valid pair; consume.
r += 6
w += utf8.EncodeRune(b[w:], dec)
break
}
// Invalid surrogate; fall back to replacement rune.
rr = unicode.ReplacementChar
}
w += utf8.EncodeRune(b[w:], rr)
}
// Quote, control characters are invalid.
case c == '"', c < ' ':
return
// ASCII
case c < utf8.RuneSelf:
b[w] = c
r++
w++
// Coerce to well-formed UTF-8.
default:
rr, size := utf8.DecodeRune(s[r:])
r += size
w += utf8.EncodeRune(b[w:], rr)
}
}
return b[0:w], true
}