swift-mirror/stdlib/private/OSLog/OSLog.swift

//===----------------- OSLog.swift ----------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2019 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
//
//===-----------------------------------------------------------------------===//

// This file contains the new swift APIs for OS log that accept string
// interpolations. This is a prototype meant for experimentation and testing.
// Do not use it outside of tests.

@_exported import os

@available(macOS 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *)
public struct Logger {
  @usableFromInline
  internal let logObject: OSLog

  /// Create a custom OS log object.
  public init(subsystem: String, category: String) {
    logObject = OSLog(subsystem: subsystem, category: category)
  }

  /// Return the default OS log object.
  public init() {
    logObject = OSLog.default
  }

  // Functions defined below are marked @_optimize(none) to prevent inlining
  // of string internals (such as String._StringGuts) which will interfere with
  // constant evaluation and folding. Note that these functions will be inlined,
  // constant evaluated/folded and optimized in the context of a caller.

  /// Log a string interpolation at a given level. The level is `default` if
  /// it is not specified.
  @_transparent
  @_optimize(none)
  public func log(level: OSLogType = .default, _ message: OSLogMessage) {
    osLog(logObject, level, message)
  }

  // TODO: define overloads for logging at specific levels: debug, info, notice,
  // error, fault based on the Swift forum "logging-levels" discussion.
}

/// Given an instance of the custom string interpolation type: `OSLogMessage`,
/// extract the format string, serialize the arguments to a byte buffer,
/// and pass them to the OS logging system.
@available(macOS 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *)
@usableFromInline
@_transparent
@_optimize(none)
internal func osLog(
  _ logObject: OSLog,
  _ logLevel: OSLogType,
  _ message: OSLogMessage
) {
  // Compute static constants first so that they can be folded by
  // OSLogOptimization pass.
  let formatString = message.interpolation.formatString
  let preamble = message.interpolation.preamble
  let argumentCount = message.interpolation.argumentCount
  let bufferSize = message.bufferSize

  // Code that will execute at runtime.
  let arguments = message.interpolation.arguments
  formatString.withCString { cFormatString in

    guard logObject.isEnabled(type: logLevel) else { return }

    // Ideally, we could stack allocate the buffer as it is local to this
    // function and also its size is a compile-time constant.
    let bufferMemory =
      UnsafeMutablePointer<UInt8>.allocate(capacity: bufferSize)
    var builder = OSLogByteBufferBuilder(bufferMemory)

    builder.serialize(preamble)
    builder.serialize(argumentCount)
    arguments.serialize(into: &builder)

    ___os_log_impl(UnsafeMutableRawPointer(mutating: #dsohandle),
                   logObject,
                   logLevel,
                   cFormatString,
                   bufferMemory,
                   UInt32(bufferSize))

    bufferMemory.deallocate()
  }
}

/// A test helper that constructs a byte buffer and a format string from an
/// instance of `OSLogMessage` using the same logic as the function `osLog`,
/// and applies a given `assertion` to the constructed format string and
/// byte buffer. This function should be used only in tests.
/// - Parameters:
///   - message: An instance of `OSLogMessage` created from string interpolation
///   - assertion: A closure that takes a format string and a pointer to a
///     byte buffer and asserts a condition.
@_transparent
@_optimize(none)
public // @testable
func _checkFormatStringAndBuffer(
  _ message: OSLogMessage,
  with assertion: (String, UnsafeBufferPointer<UInt8>) -> Void
) {
  // Compute static constants first so that they can be folded by
  // OSLogOptimization pass.
  let formatString = message.interpolation.formatString
  let preamble = message.interpolation.preamble
  let argumentCount = message.interpolation.argumentCount
  let bufferSize = message.bufferSize

  // Code that will execute at runtime.
  let bufferMemory = UnsafeMutablePointer<UInt8>.allocate(capacity: bufferSize)
  var builder = OSLogByteBufferBuilder(bufferMemory)

  builder.serialize(preamble)
  builder.serialize(argumentCount)
  message.interpolation.arguments.serialize(into: &builder)

  assertion(
    formatString,
    UnsafeBufferPointer(start: UnsafePointer(bufferMemory), count: bufferSize))

  bufferMemory.deallocate()
}