mesh-sdk/go/delivery/answer_paths.go

package delivery

import (
	"bytes"
	"encoding/json"
	"sort"
	"strconv"
	"strings"
)

// DifferingPaths is every JSON path at which two bodies of one resource differ, sorted (issue 1126, T1: the shadow
// shows its work): object keys and list places joined by dots (`content.url`, `links.0`), a string that holds a JSON
// object or list read as that JSON and walked on (a runtime's config carried as text), a key or place one side alone
// holds named as it is. A key a secret could be under (secretWords) is named and not walked into. A body that is not
// JSON differs at "" (the whole), and a resource one side alone holds has none. At most MaxPaths: the last then says how many more there are. A path names keys
// alone, never a value, so it holds no secret.
func DifferingPaths(composed, running json.RawMessage) []string {
	if composed == nil || running == nil {
		return nil // one side alone holds it: its why says so
	}
	var a, b any
	okA := unmarshalNumbers(composed, &a) == nil
	okB := unmarshalNumbers(running, &b) == nil
	if !okA || !okB {
		if bytes.Equal(composed, running) {
			return nil
		}
		return []string{""}
	}
	var out []string
	walkDiffering(a, b, "", &out)
	sort.Strings(out)
	if len(out) > MaxPaths {
		more := len(out) - (MaxPaths - 1)
		out = append(out[:MaxPaths-1], "… "+strconv.Itoa(more)+" more")
	}
	return out
}

func unmarshalNumbers(raw []byte, into *any) error {
	d := json.NewDecoder(bytes.NewReader(raw))
	d.UseNumber()
	return d.Decode(into)
}

// asJSON is a string holding a JSON object or list read as that value; v itself otherwise.
func asJSON(v any) any {
	s, ok := v.(string)
	if !ok {
		return v
	}
	t := strings.TrimSpace(s)
	if t == "" || (t[0] != '{' && t[0] != '[') {
		return v
	}
	var parsed any
	if unmarshalNumbers([]byte(t), &parsed) != nil {
		return v
	}
	return parsed
}

func join(at, key string) string {
	if at == "" {
		return key
	}
	return at + "." + key
}

func walkDiffering(a, b any, at string, out *[]string) {
	a, b = asJSON(a), asJSON(b)
	ma, isMA := a.(map[string]any)
	mb, isMB := b.(map[string]any)
	if isMA && isMB {
		keys := map[string]bool{}
		for k := range ma {
			keys[k] = true
		}
		for k := range mb {
			keys[k] = true
		}
		for k := range keys {
			x, inA := ma[k]
			y, inB := mb[k]
			switch {
			case !inA || !inB:
				*out = append(*out, join(at, k))
			case secretKey(k):
				if !sameAny(x, y) {
					*out = append(*out, join(at, k))
				}
			default:
				walkDiffering(x, y, join(at, k), out)
			}
		}
		return
	}
	la, isLA := a.([]any)
	lb, isLB := b.([]any)
	if isLA && isLB {
		for i := range max(len(la), len(lb)) {
			if i >= len(la) || i >= len(lb) {
				*out = append(*out, join(at, strconv.Itoa(i)))
				continue
			}
			walkDiffering(la[i], lb[i], join(at, strconv.Itoa(i)), out)
		}
		return
	}
	if !sameAny(a, b) {
		*out = append(*out, at)
	}
}

func sameAny(a, b any) bool {
	x, errA := json.Marshal(a)
	y, errB := json.Marshal(b)
	return errA == nil && errB == nil && bytes.Equal(x, y)
}

// FitAnswer is a with its shown bodies cut until its JSON is within limit bytes (MaxAnswerBytes for the node's key):
// first the bodies' texts, from the last differing module back, keeping their paths; then the paths too. What is cut
// is said in the answer's note. The verdict and every list of modules are never cut.
func FitAnswer(a CandidateAnswer, limit int) CandidateAnswer {
	size := func() int {
		raw, err := json.Marshal(a)
		if err != nil {
			return 0
		}
		return len(raw)
	}
	if size() <= limit {
		return a
	}
	a.Differs = append([]ModuleDiffers(nil), a.Differs...)
	for i := range a.Differs {
		a.Differs[i].Bodies = append([]ResourceBodies(nil), a.Differs[i].Bodies...)
	}
	cutTexts, cutPaths := false, false
	for i := len(a.Differs) - 1; i >= 0 && size() > limit; i-- {
		for j := range a.Differs[i].Bodies {
			a.Differs[i].Bodies[j].Composed, a.Differs[i].Bodies[j].Running = "", ""
		}
		cutTexts = true
	}
	for i := len(a.Differs) - 1; i >= 0 && size() > limit; i-- {
		for j := range a.Differs[i].Bodies {
			a.Differs[i].Bodies[j].Paths = nil
		}
		cutPaths = true
	}
	why := "the bodies shown were cut to keep the answer within " + strconv.Itoa(limit>>10) + " KiB"
	if cutPaths {
		why += ", their paths too"
	}
	if cutTexts {
		a.Note = strings.TrimPrefix(a.Note+"; ", "; ") + why
	}
	return a
}