V8039. Suspicious leading or trailing whitespace in the value used to identify an element.

The analyzer has detected a string with a potentially incorrect leading or trailing whitespace character.

Consider several examples that trigger this warning.

The example N1:

func buildRequestHeaders() {
  headers := map[string]string{
    "Content-Type": "application/json",
    "Accept ":      "application/json",
    "User-Agent":   "my-service/1.0",
    ....
  }
  ....
}

The "Accept " string key contains a trailing whitespace character. If a value is retrieved via the "Accept" key (without the whitespace), it will not be found.

To fix the issue, remove the whitespace:

"Accept":      "application/json"

The example N2:

func registerFlags() {
  debug := flag.Bool("debug", false, "enable debug logging")
  port := flag.Int(" port", 8080, "server port")

  flag.Parse()

  ....
}

The " port" flag name starts with the whitespace. As a result, the flag will be registered with this exact name, and users cannot pass it in the expected way (--port).

To fix the issue, remove the whitespace:

port := flag.Int("port", 8080, "server port")

The example N3:

func decodeUser() {
  type User struct {
    ID   int    `json:"id"`
    Name string `json:" name"`
  }

  u := User{
    ID:   1,
    Name: "Donald",
  }

  ....
}

The json:" name" tag value contains a leading whitespace character. During JSON serialization and deserialization, the " name" key will be used instead of the expected "name" key.

To fix the issue, remove the whitespace:

Name string `json:"name"`