88 lines
2.8 KiB
Go
88 lines
2.8 KiB
Go
package signature
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import (
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"bytes"
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"encoding/json"
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"fmt"
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"io"
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)
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// jsonFormatError is returned when JSON does not match expected format.
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type jsonFormatError string
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func (err jsonFormatError) Error() string {
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return string(err)
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}
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// paranoidUnmarshalJSONObject unmarshals data as a JSON object, but failing on the slightest unexpected aspect
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// (including duplicated keys, unrecognized keys, and non-matching types). Uses fieldResolver to
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// determine the destination for a field value, which should return a pointer to the destination if valid, or nil if the key is rejected.
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//
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// The fieldResolver approach is useful for decoding the Policy.Transports map; using it for structs is a bit lazy,
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// we could use reflection to automate this. Later?
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func paranoidUnmarshalJSONObject(data []byte, fieldResolver func(string) interface{}) error {
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seenKeys := map[string]struct{}{}
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dec := json.NewDecoder(bytes.NewReader(data))
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t, err := dec.Token()
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if err != nil {
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return jsonFormatError(err.Error())
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}
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if t != json.Delim('{') {
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return jsonFormatError(fmt.Sprintf("JSON object expected, got \"%s\"", t))
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}
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for {
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t, err := dec.Token()
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if err != nil {
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return jsonFormatError(err.Error())
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}
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if t == json.Delim('}') {
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break
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}
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key, ok := t.(string)
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if !ok {
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// Coverage: This should never happen, dec.Token() rejects non-string-literals in this state.
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return jsonFormatError(fmt.Sprintf("Key string literal expected, got \"%s\"", t))
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}
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if _, ok := seenKeys[key]; ok {
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return jsonFormatError(fmt.Sprintf("Duplicate key \"%s\"", key))
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}
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seenKeys[key] = struct{}{}
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valuePtr := fieldResolver(key)
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if valuePtr == nil {
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return jsonFormatError(fmt.Sprintf("Unknown key \"%s\"", key))
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}
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// This works like json.Unmarshal, in particular it allows us to implement UnmarshalJSON to implement strict parsing of the field value.
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if err := dec.Decode(valuePtr); err != nil {
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return jsonFormatError(err.Error())
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}
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}
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if _, err := dec.Token(); err != io.EOF {
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return jsonFormatError("Unexpected data after JSON object")
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}
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return nil
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}
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// paranoidUnmarshalJSONObject unmarshals data as a JSON object, but failing on the slightest unexpected aspect
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// (including duplicated keys, unrecognized keys, and non-matching types). Each of the fields in exactFields
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// must be present exactly once, and none other fields are accepted.
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func paranoidUnmarshalJSONObjectExactFields(data []byte, exactFields map[string]interface{}) error {
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seenKeys := map[string]struct{}{}
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if err := paranoidUnmarshalJSONObject(data, func(key string) interface{} {
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if valuePtr, ok := exactFields[key]; ok {
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seenKeys[key] = struct{}{}
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return valuePtr
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}
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return nil
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}); err != nil {
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return err
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}
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for key := range exactFields {
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if _, ok := seenKeys[key]; !ok {
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return jsonFormatError(fmt.Sprintf(`Key "%s" missing in a JSON object`, key))
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}
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}
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return nil
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}
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