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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2025 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
#if canImport(CollectionsInternal)
internal import CollectionsInternal
#elseif canImport(OrderedCollections)
internal import OrderedCollections
#elseif canImport(_FoundationCollections)
internal import _FoundationCollections
#endif
extension URL {
/// A template for constructing a URL from variable expansions.
///
/// This is an template that can be expanded into
/// a ``URL`` by calling ``URL(template:variables:)``.
///
/// Templating has a rich set of options for substituting various parts of URLs. See
/// [RFC 6570](https://datatracker.ietf.org/doc/html/rfc6570) for
/// details.
///
/// ### Example 1
///
/// ```swift
/// let template = URL.Template("http://www.example.com/foo{?query,number}")!
/// let url = URL(
/// template: template,
/// variables: [
/// .query: "bar baz",
/// .number: "234",
/// ]
/// )
///
/// extension URL.Template.VariableName {
/// static var query: URL.Template.VariableName { .init("query") }
/// static var number: URL.Template.VariableName { .init("number") }
/// }
/// ```
/// The resulting URL will be
/// ```text
/// http://www.example.com/foo?query=bar%20baz&number=234
/// ```
///
/// ### Usage
///
/// Templates provide a description of a URL space and define how URLs can
/// be constructed given specific variable values. Their intended use is,
/// for example, to allow a server to communicate to a client how to
/// construct URLs for particular resources.
///
/// For each specific resource, an API contract is required to clearly
/// define the variables applicable to that resource and its associated
/// template. For example, such an API contract might specify that the
/// variable `query` is mandatory and must be an alphanumeric string
/// while the variable `number` is optional and must be a positive integer
/// if provided. The server could then provide the client with a template
/// such as `http://www.example.com/foo{?query,number}`, which the client
/// can subsequently use to substitute variables accordingly.
///
/// An API contract is necessary to define which substitutions are valid
/// within a given URL space. There is no guarantee that every possible
/// expansion of variable expressions corresponds to an existing resource
/// URL; indeed, some expansions may not even produce a valid URL. Only
/// the API specification itself can determine which expansions are
/// expected to yield valid URLs corresponding to existing resources.
///
/// ### Example 2
///
/// Here’s an example, that illustrates how to define a specific set of variables:
/// ```swift
/// struct MyQueryTemplate: Sendable, Hashable {
/// var template: URL.Template
///
/// init?(_ template: String) {
/// guard let t = URL.Template(template) else { return nil }
/// self.template = t
/// }
/// }
///
/// struct MyQuery: Sendable, Hashable {
/// var query: String
/// var number: Int?
///
/// var variables: [URL.Template.VariableName: URL.Template.Value] {
/// var result: [URL.Template.VariableName: URL.Template.Value] = [
/// .query: .text(query)
/// ]
/// if let number {
/// result[.number] = .text("\(number)")
/// }
/// return result
/// }
/// }
///
/// extension URL.Template.VariableName {
/// static var query: URL.Template.VariableName { .init("query") }
/// static var number: URL.Template.VariableName { .init("number") }
/// }
///
/// extension URL {
/// init?(
/// template: MyQueryTemplate,
/// query: MyQuery
/// ) {
/// self.init(
/// template: template.template,
/// variables: query.variables
/// )
/// }
/// }
/// ```
@available(FoundationPreview 6.2, *)
public struct Template: Sendable, Hashable {
var elements: [Element] = []
enum Element: Sendable, Hashable {
case literal(String)
case expression(Expression)
}
}
}
// MARK: - Parse
@available(FoundationPreview 6.2, *)
extension URL.Template {
/// Creates a new template from its text form.
///
/// The template string needs to be a valid RFC 6570 template.
///
/// This will parse the template and return `nil` if the template is invalid.
public init?(_ template: String) {
do {
self.init()
var remainder = template[...]
func copyLiteral(upTo end: String.Index) {
guard remainder.startIndex < end else { return }
let literal = remainder[remainder.startIndex..<end]
let escaped = String(literal).normalizedAddingPercentEncoding(
withAllowedCharacters: .unreservedReserved
)
elements.append(.literal(escaped))
}
while let match = remainder.firstMatch(of: URL.Template.Global.shared.uriTemplateRegex) {
copyLiteral(upTo: match.range.lowerBound)
let expression = try Expression(String(match.output.1))
elements.append(.expression(expression))
remainder = remainder[match.range.upperBound..<remainder.endIndex]
}
copyLiteral(upTo: remainder.endIndex)
} catch {
return nil
}
}
}
// MARK: -
@available(FoundationPreview 6.2, *)
extension URL.Template: CustomStringConvertible {
public var description: String {
elements.reduce(into: "") {
$0.append("\($1)")
}
}
}
@available(FoundationPreview 6.2, *)
extension URL.Template.Element: CustomStringConvertible {
var description: String {
switch self {
case .literal(let l): l
case .expression(let e): "{\(e)}"
}
}
}
|
