284 lines
7.1 KiB
Go
284 lines
7.1 KiB
Go
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// This code is based on encoding/json and gorilla/schema
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package encoding
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import (
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"reflect"
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"sort"
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"sync"
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"time"
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)
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// A field represents a single field found in a struct.
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type field struct {
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name string
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nameBytes []byte // []byte(name)
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equalFold func(s, t []byte) bool
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tag bool
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index []int
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typ reflect.Type
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omitEmpty bool
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quoted bool
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reference bool
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refName string
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compound bool
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compoundIndex int
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}
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func fillField(f field) field {
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f.nameBytes = []byte(f.name)
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f.equalFold = foldFunc(f.nameBytes)
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return f
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}
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// byName sorts field by name, breaking ties with depth,
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// then breaking ties with "name came from tag", then
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// breaking ties with index sequence.
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type byName []field
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func (x byName) Len() int { return len(x) }
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func (x byName) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
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func (x byName) Less(i, j int) bool {
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if x[i].name != x[j].name {
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return x[i].name < x[j].name
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}
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if len(x[i].index) != len(x[j].index) {
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return len(x[i].index) < len(x[j].index)
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}
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if x[i].tag != x[j].tag {
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return x[i].tag
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}
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return byIndex(x).Less(i, j)
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}
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// byIndex sorts field by index sequence.
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type byIndex []field
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func (x byIndex) Len() int { return len(x) }
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func (x byIndex) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
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func (x byIndex) Less(i, j int) bool {
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for k, xik := range x[i].index {
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if k >= len(x[j].index) {
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return false
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}
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if xik != x[j].index[k] {
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return xik < x[j].index[k]
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}
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}
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return len(x[i].index) < len(x[j].index)
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}
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// typeFields returns a list of fields that should be recognized for the given type.
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// The algorithm is breadth-first search over the set of structs to include - the top struct
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// and then any reachable anonymous structs.
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func typeFields(t reflect.Type) []field {
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// Anonymous fields to explore at the current level and the next.
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current := []field{}
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next := []field{{typ: t}}
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// Count of queued names for current level and the next.
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count := map[reflect.Type]int{}
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nextCount := map[reflect.Type]int{}
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// Types already visited at an earlier level.
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visited := map[reflect.Type]bool{}
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// Fields found.
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var fields []field
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for len(next) > 0 {
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current, next = next, current[:0]
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count, nextCount = nextCount, map[reflect.Type]int{}
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for _, f := range current {
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if visited[f.typ] {
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continue
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}
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visited[f.typ] = true
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// Scan f.typ for fields to include.
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for i := 0; i < f.typ.NumField(); i++ {
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sf := f.typ.Field(i)
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if sf.PkgPath != "" && !sf.Anonymous { // unexported
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continue
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}
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// Extract field name from tag
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tag := getTag(sf)
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if tag == "-" {
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continue
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}
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name, opts := parseTag(tag)
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name, compoundIndex, isCompound := parseCompoundIndex(name)
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if !isValidTag(name) {
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name = ""
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}
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// Extract referenced field from tags
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refTag := getRefTag(sf)
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ref, _ := parseTag(refTag)
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if !isValidTag(ref) {
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ref = ""
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}
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index := make([]int, len(f.index)+1)
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copy(index, f.index)
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index[len(f.index)] = i
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ft := sf.Type
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if ft.Name() == "" && ft.Kind() == reflect.Ptr {
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// Follow pointer.
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ft = ft.Elem()
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}
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// Record found field and index sequence.
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if name != "" || !sf.Anonymous || ft.Kind() != reflect.Struct || isPseudoType(ft) {
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tagged := name != ""
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if name == "" {
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name = sf.Name
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}
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fields = append(fields, fillField(field{
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name: name,
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tag: tagged,
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index: index,
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typ: ft,
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omitEmpty: opts.Contains("omitempty"),
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reference: opts.Contains("reference"),
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refName: ref,
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compound: isCompound,
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compoundIndex: compoundIndex,
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}))
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if count[f.typ] > 1 {
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// If there were multiple instances, add a second,
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// so that the annihilation code will see a duplicate.
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// It only cares about the distinction between 1 or 2,
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// so don't bother generating any more copies.
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fields = append(fields, fields[len(fields)-1])
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}
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continue
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}
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// Record new anonymous struct to explore in next round.
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nextCount[ft]++
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if nextCount[ft] == 1 {
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next = append(next, fillField(field{name: ft.Name(), index: index, typ: ft}))
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}
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}
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}
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}
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sort.Sort(byName(fields))
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// Delete all fields that are hidden by the Go rules for embedded fields,
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// except that fields with valid tags are promoted.
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// The fields are sorted in primary order of name, secondary order
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// of field index length. Loop over names; for each name, delete
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// hidden fields by choosing the one dominant field that survives.
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out := fields[:0]
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for advance, i := 0, 0; i < len(fields); i += advance {
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// One iteration per name.
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// Find the sequence of fields with the name of this first field.
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fi := fields[i]
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for advance = 1; i+advance < len(fields); advance++ {
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fj := fields[i+advance]
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if fj.name != fi.name {
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break
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}
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if fi.compound && fj.compound && fi.compoundIndex != fj.compoundIndex {
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break
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}
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}
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if advance == 1 { // Only one field with this name
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out = append(out, fi)
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continue
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}
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dominant, ok := dominantField(fields[i : i+advance])
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if ok {
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out = append(out, dominant)
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}
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}
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fields = out
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sort.Sort(byIndex(fields))
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return fields
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}
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func isPseudoType(t reflect.Type) bool {
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return t == reflect.TypeOf(time.Time{})
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}
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// dominantField looks through the fields, all of which are known to
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// have the same name, to find the single field that dominates the
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// others using Go's embedding rules, modified by the presence of
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// valid tags. If there are multiple top-level fields, the boolean
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// will be false: This condition is an error in Go and we skip all
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// the fields.
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func dominantField(fields []field) (field, bool) {
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// The fields are sorted in increasing index-length order. The winner
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// must therefore be one with the shortest index length. Drop all
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// longer entries, which is easy: just truncate the slice.
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length := len(fields[0].index)
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tagged := -1 // Index of first tagged field.
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for i, f := range fields {
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if len(f.index) > length {
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fields = fields[:i]
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break
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}
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if f.tag {
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if tagged >= 0 {
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// Multiple tagged fields at the same level: conflict.
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// Return no field.
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return field{}, false
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}
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tagged = i
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}
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}
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if tagged >= 0 {
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return fields[tagged], true
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}
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// All remaining fields have the same length. If there's more than one,
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// we have a conflict (two fields named "X" at the same level) and we
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// return no field.
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if len(fields) > 1 {
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return field{}, false
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}
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return fields[0], true
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}
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var fieldCache struct {
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sync.RWMutex
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m map[reflect.Type][]field
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}
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// cachedTypeFields is like typeFields but uses a cache to avoid repeated work.
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func cachedTypeFields(t reflect.Type) []field {
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fieldCache.RLock()
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f := fieldCache.m[t]
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fieldCache.RUnlock()
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if f != nil {
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return f
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}
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// Compute fields without lock.
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// Might duplicate effort but won't hold other computations back.
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f = typeFields(t)
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if f == nil {
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f = []field{}
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}
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fieldCache.Lock()
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if fieldCache.m == nil {
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fieldCache.m = map[reflect.Type][]field{}
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}
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fieldCache.m[t] = f
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fieldCache.Unlock()
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return f
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}
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