iOS 记录一处alamofire源码

/// Returns a percent-escaped string following RFC 3986 for a query string key or value.
///
/// RFC 3986 states that the following characters are "reserved" characters.
///
/// - General Delimiters: ":", "#", "[", "]", "@", "?", "/"
/// - Sub-Delimiters: "!", "$", "&", "'", "(", ")", "*", "+", ",", ";", "="
///
/// In RFC 3986 - Section 3.4, it states that the "?" and "/" characters should not be escaped to allow
/// query strings to include a URL. Therefore, all "reserved" characters with the exception of "?" and "/"
/// should be percent-escaped in the query string.
///
/// - parameter string: The string to be percent-escaped.
///
/// - returns: The percent-escaped string.
public func escape(_ string: String) -> String {
    let generalDelimitersToEncode = ":#[]@" // does not include "?" or "/" due to RFC 3986 - Section 3.4
    let subDelimitersToEncode = "!$&'()*+,;="

    var allowedCharacterSet = CharacterSet.urlQueryAllowed
    allowedCharacterSet.remove(charactersIn: "\(generalDelimitersToEncode)\(subDelimitersToEncode)")

    var escaped = ""

    //==========================================================================================================
    //
    //  Batching is required for escaping due to an internal bug in iOS 8.1 and 8.2. Encoding more than a few
    //  hundred Chinese characters causes various malloc error crashes. To avoid this issue until iOS 8 is no
    //  longer supported, batching MUST be used for encoding. This introduces roughly a 20% overhead. For more
    //  info, please refer to:
    //
    //      - https://github.com/Alamofire/Alamofire/issues/206
    //
    //==========================================================================================================

    if #available(iOS 8.3, *) {
        escaped = string.addingPercentEncoding(withAllowedCharacters: allowedCharacterSet) ?? string
    } else {
        let batchSize = 50
        var index = string.startIndex
        while index != string.endIndex {
            let startIndex = index
            let endIndex = string.index(index, offsetBy: batchSize, limitedBy: string.endIndex) ?? string.endIndex
            let range = startIndex..<endIndex
            let substring = string[range]
            escaped += substring.addingPercentEncoding(withAllowedCharacters: allowedCharacterSet) ?? String(substring)
            index = endIndex
        }
    }

    return escaped
}

上面的方法中有一段urlencode是用while一段一段处理的，看了上面的解释，大概意思是在iOS 8.1和iOS8.2有BUG，超过100个汉字处理时在分配内存有错误。

现在的应用基本都iOS 10起步了，直接一次性处理就可以了。