| 1 | package suite |
| 2 | |
| 3 | import ( |
| 4 | "bytes" |
| 5 | "encoding/json" |
| 6 | "fmt" |
| 7 | "strings" |
| 8 | ) |
| 9 | |
| 10 | // rejectAmbiguousJSON refuses a body whose meaning depends on which duplicate |
| 11 | // wins. |
| 12 | // |
| 13 | // encoding/json resolves a duplicate object key by keeping the last one, and |
| 14 | // matches field names case-insensitively, so a sibling can send |
| 15 | // `{"result":"NOT_VISIBLE","result":"VISIBLE"}` — or spell the second one |
| 16 | // `RESULT` — and the value that survives is not the one a reader of the bytes |
| 17 | // would expect. That defeats every check made *after* decoding, including S2's |
| 18 | // duplicate-row rule: the duplicate is gone before the rule can see it. |
| 19 | // |
| 20 | // Keys are folded to lower case before comparison because that is how |
| 21 | // encoding/json matches them. Two keys differing only in case are therefore |
| 22 | // treated as the same key, which is the safe reading and costs nothing: no |
| 23 | // call in this contract has two fields whose names differ only by case. |
| 24 | func rejectAmbiguousJSON(data []byte) error { |
| 25 | dec := json.NewDecoder(bytes.NewReader(data)) |
| 26 | if err := scanUnique(dec); err != nil { |
| 27 | return err |
| 28 | } |
| 29 | // Anything after the first complete value means the body is two documents |
| 30 | // wearing one Content-Length, and which one is "the" answer is a guess. |
| 31 | if dec.More() { |
| 32 | return fmt.Errorf("suite: trailing content after the JSON document") |
| 33 | } |
| 34 | return nil |
| 35 | } |
| 36 | |
| 37 | func scanUnique(dec *json.Decoder) error { |
| 38 | tok, err := dec.Token() |
| 39 | if err != nil { |
| 40 | return err |
| 41 | } |
| 42 | |
| 43 | delim, isDelim := tok.(json.Delim) |
| 44 | if !isDelim { |
| 45 | return nil // a scalar; nothing nested to check |
| 46 | } |
| 47 | |
| 48 | switch delim { |
| 49 | case '{': |
| 50 | seen := make(map[string]bool) |
| 51 | for dec.More() { |
| 52 | keyTok, err := dec.Token() |
| 53 | if err != nil { |
| 54 | return err |
| 55 | } |
| 56 | key, ok := keyTok.(string) |
| 57 | if !ok { |
| 58 | return fmt.Errorf("suite: object key is not a string") |
| 59 | } |
| 60 | folded := strings.ToLower(key) |
| 61 | if seen[folded] { |
| 62 | return fmt.Errorf("suite: duplicate object key %q", key) |
| 63 | } |
| 64 | seen[folded] = true |
| 65 | |
| 66 | if err := scanUnique(dec); err != nil { |
| 67 | return err |
| 68 | } |
| 69 | } |
| 70 | case '[': |
| 71 | for dec.More() { |
| 72 | if err := scanUnique(dec); err != nil { |
| 73 | return err |
| 74 | } |
| 75 | } |
| 76 | } |
| 77 | |
| 78 | _, err = dec.Token() // the matching close |
| 79 | return err |
| 80 | } |
| 81 | |
amadan