Alamofire/Source/ParameterEncoding.swift

//
//  ParameterEncoding.swift
//
//  Copyright (c) 2014-2016 Alamofire Software Foundation (http://alamofire.org/)
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.
//

import Foundation

/// HTTP method definitions.
///
/// See https://tools.ietf.org/html/rfc7231#section-4.3
public enum HTTPMethod: String {
    case options = "OPTIONS"
    case get     = "GET"
    case head    = "HEAD"
    case post    = "POST"
    case put     = "PUT"
    case patch   = "PATCH"
    case delete  = "DELETE"
    case trace   = "TRACE"
    case connect = "CONNECT"
}

// MARK: -

/// Used to specify the way in which a set of parameters are applied to a URL request.
///
/// - url:             Creates a query string to be set as or appended to any existing URL query for `GET`, `HEAD`,
///                    and `DELETE` requests, or set as the body for requests with any other HTTP method. The
///                    `Content-Type` HTTP header field of an encoded request with HTTP body is set to
///                    `application/x-www-form-urlencoded; charset=utf-8`. Since there is no published specification
///                    for how to encode collection types, the convention of appending `[]` to the key for array
///                    values (`foo[]=1&foo[]=2`), and appending the key surrounded by square brackets for nested
///                    dictionary values (`foo[bar]=baz`).
///
/// - urlEncodedInURL: Creates query string to be set as or appended to any existing URL query. Uses the same
///                    implementation as the `.url` case, but always applies the encoded result to the URL.
///
/// - json:            Uses `JSONSerialization` to create a JSON representation of the parameters object, which is
///                    set as the body of the request. The `Content-Type` HTTP header field of an encoded request is
///                    set to `application/json`.
///
/// - propertyList:    Uses `PropertyListSerialization` to create a plist representation of the parameters object,
///                    according to the associated format and write options values, which is set as the body of the
///                    request. The `Content-Type` HTTP header field of an encoded request is set to
///                    `application/x-plist`.
///
/// - custom:          Uses the associated closure value to construct a new request given an existing request and
///                    parameters.
public enum ParameterEncoding {
    case url
    case urlEncodedInURL
    case json
    case propertyList(PropertyListSerialization.PropertyListFormat, PropertyListSerialization.WriteOptions)
    case custom((URLRequestConvertible, [String: Any]?) -> (URLRequest, Error?))

    /// Creates a URL request by encoding parameters and applying them onto an existing request.
    ///
    /// - parameter urlRequest: The request to have parameters applied.
    /// - parameter parameters: The parameters to apply.
    ///
    /// - returns: A tuple containing the constructed request and the error that occurred during parameter encoding,
    ///            if any.
    public func encode(
        _ urlRequest: URLRequestConvertible,
        parameters: [String: Any]?)
        -> (URLRequest, Error?)
    {
        var urlRequest = urlRequest.urlRequest

        guard let parameters = parameters else { return (urlRequest, nil) }

        var encodingError: Error? = nil

        switch self {
        case .url, .urlEncodedInURL:
            func query(_ parameters: [String: Any]) -> String {
                var components: [(String, String)] = []

                for key in parameters.keys.sorted(by: <) {
                    let value = parameters[key]!
                    components += queryComponents(fromKey: key, value: value)
                }

                return components.map { "\($0)=\($1)" }.joined(separator: "&")
            }

            func encodesParametersInURL(with method: HTTPMethod) -> Bool {
                switch self {
                case .urlEncodedInURL:
                    return true
                default:
                    break
                }

                switch method {
                case .get, .head, .delete:
                    return true
                default:
                    return false
                }
            }

            if let method = HTTPMethod(rawValue: urlRequest.httpMethod!), encodesParametersInURL(with: method) {
                if
                    var URLComponents = URLComponents(url: urlRequest.url!, resolvingAgainstBaseURL: false),
                    !parameters.isEmpty
                {
                    let percentEncodedQuery = (URLComponents.percentEncodedQuery.map { $0 + "&" } ?? "") + query(parameters)
                    URLComponents.percentEncodedQuery = percentEncodedQuery
                    urlRequest.url = URLComponents.url
                }
            } else {
                if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
                    urlRequest.setValue(
                        "application/x-www-form-urlencoded; charset=utf-8",
                        forHTTPHeaderField: "Content-Type"
                    )
                }

                urlRequest.httpBody = query(parameters).data(
                    using: String.Encoding.utf8,
                    allowLossyConversion: false
                )
            }
        case .json:
            do {
                let data = try JSONSerialization.data(withJSONObject: parameters, options: [])

                if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
                    urlRequest.setValue("application/json", forHTTPHeaderField: "Content-Type")
                }

                urlRequest.httpBody = data
            } catch {
                encodingError = error
            }
        case .propertyList(let format, let options):
            do {
                let data = try PropertyListSerialization.data(
                    fromPropertyList: parameters,
                    format: format,
                    options: options
                )

                if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
                    urlRequest.setValue("application/x-plist", forHTTPHeaderField: "Content-Type")
                }

                urlRequest.httpBody = data
            } catch {
                encodingError = error
            }
        case .custom(let closure):
            (urlRequest, encodingError) = closure(urlRequest, parameters)
        }

        return (urlRequest, encodingError)
    }

    /// Creates percent-escaped, URL encoded query string components from the given key-value pair using recursion.
    ///
    /// - parameter key:   The key of the query component.
    /// - parameter value: The value of the query component.
    ///
    /// - returns: The percent-escaped, URL encoded query string components.
    public func queryComponents(fromKey key: String, value: Any) -> [(String, String)] {
        var components: [(String, String)] = []

        if let dictionary = value as? [String: Any] {
            for (nestedKey, value) in dictionary {
                components += queryComponents(fromKey: "\(key)[\(nestedKey)]", value: value)
            }
        } else if let array = value as? [Any] {
            for value in array {
                components += queryComponents(fromKey: "\(key)[]", value: value)
            }
        } else if let bool = value as? Bool {
            components.append((escape(key), escape((bool ? "1" : "0"))))
        } else {
            components.append((escape(key), escape("\(value)")))
        }

        return components
    }

    /// 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)")

        return string.addingPercentEncoding(withAllowedCharacters: allowedCharacterSet) ?? string
    }
}