How to Handle Nested Encoded Strings in JSON Websocket Data?

Decoding JSON with Nested Encoded Strings

Problem:

When parsing websocket data in JSON format, users may encounter errors due to nested encoded JSON strings that violate JSON syntax. For instance, the string value of a "text" field may contain HTML entities like "" and "<", causing the decoder to fail.

Solution:

To handle nested encoded strings in JSON, the application must decode the data in two steps:

1. First pass: Decode the outer JSON layer using a basic struct, which ignores the nested encoded strings and treats them as regular text.
2. Second pass: After obtaining the outer layer data, decode the nested JSON strings within the "args" field.

Here's an example code snippet demonstrating this approach:

type main struct {
  Name string   `json:"name"`
  Args []string `json:"args"`
}

type arg struct {
  Method string `json:"method"`
  Params par    `json:"params"`
}
type par struct {
  Channel   string `json:"channel,omitempty"`
  Name      string `json:"name,omitempty"`
  NameColor string `json:"nameColor,omitempty"`
  Text      string `json:"text,omitempty"`
  Time      int64  `json:"time,omitempty"`
}

// Input JSON string
str := `{"name":"message","args":["{\"method\":\"chatMsg\",\"params\":{\"channel\":\"channel\",\"name\":\"name\",\"nameColor\":\"B5B11E\",\"text\":\"https://play.spotify.com/browse\",\"time\":1455397119}}"]}`

var m main
if err := json.Unmarshal([]byte(str), &m); err != nil {
    log.Fatal(err)
}
var args arg
if err := json.Unmarshal([]byte(m.Args[0]), &args); err != nil {
    log.Fatal(err)
}
In this example, the first pass is performed by decoding the outer JSON string into the main struct, which contains the "name" and "args" fields. The "args" field is then parsed as a separate JSON string in the second pass, removing the HTML entities and restoring it to a valid arg object. This approach ensures that all JSON data is correctly processed and errors are avoided.
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