Cocoapods核心组件：cocoapods-downloader

Cocoapods

介绍

Cocoapods-Downloader 是用于下载源码的小工具，它支持各种类型的版本管理工具，包括 HTTP / SVN / Git / Mercurial。它可以提供tags、commites，revisions，branches以及zips文件的下载和解压缩操作。

文件构成

我们先通过入口文件 lib/cocoapods-downloader.rb 来一窥cocoapods-downloader项目的主要文件：

module Pod
  module Downloader
    require 'cocoapods-downloader/gem_version'
    require 'cocoapods-downloader/api'
    require 'cocoapods-downloader/api_exposable'
    require 'cocoapods-downloader/base'
    # 下载方式
    autoload :Bazaar,      'cocoapods-downloader/bazaar'
    autoload :Git,         'cocoapods-downloader/git'
    autoload :Http,        'cocoapods-downloader/http'
    autoload :Mercurial,   'cocoapods-downloader/mercurial'
    autoload :Scp,         'cocoapods-downloader/scp'
    # 下载方式对于的版本，比如tag等
    autoload :Subversion,  'cocoapods-downloader/subversion'
    # 支持的下载方式
    def self.downloader_class_by_key
      {
        :bzr  => Bazaar,
        :git  => Git,
        :hg   => Mercurial,
        :http => Http,
        :scp  => Scp,
        :svn  => Subversion,
      }
  end
end

下载流程

查找缓存

# lib/cocoapods/downloader/cache.rb
def download_pod(request)
  # 如果缓存中不存在，则进入无缓存下载
  cached_pod(request) || uncached_pod(request)
rescue Informative
  raise
rescue
  UI.puts("\n[!] Error installing #{request.name}".red)
  raise
end
# requeset对象包括podname，git地址和tag，以及spec对象
def uncached_pod(request)
  in_tmpdir do |target|
    # 下载完成之后会返回一个result(response)，和对应的podspec对象
    result, podspecs = download(request, target)
    result.location = nil
    podspecs.each do |name, spec|
      # 获取对应pod的缓存路径
      destination = path_for_pod(request, :name => name, :params => result.checkout_options)
      # 从下载目录复制到缓存目录中
      copy_and_clean(target, destination, spec)
      # podspec转成json类型存入缓存中
      write_spec(spec, path_for_spec(request, :name => name, :params => result.checkout_options))
      if request.name == name
        result.location = destination
      end
    end
    result
  end
end
# 准备下载
def download(request, target)
  Downloader.download_request(request, target)
end

初始化Downloader对象

# lib/cocoapods/downloader.rb
def self.download_request(request, target)
  result = Response.new
  result.checkout_options = download_source(target, request.params)
  result.location = target
  if request.released_pod?
    result.spec = request.spec
    podspecs = { request.name => request.spec }
  else
    podspecs = Sandbox::PodspecFinder.new(target).podspecs
    podspecs[request.name] = request.spec if request.spec
    podspecs.each do |name, spec|
      if request.name == name
        result.spec = spec
      end
    end
  end
  [result, podspecs]
end
# target是下载目录，params存的是git地址和tag
def self.download_source(target, params)
  FileUtils.rm_rf(target)
  # 根据目录和下载地址生成Downloader对象
  downloader = Downloader.for_target(target, params)
  downloader.download
  target.mkpath
  if downloader.options_specific?
    params
  else
    downloader.checkout_options
  end
end

Downloader对象开始下载

根据对应的下载类型，会生成对应的下载类型的对象：

def self.for_target(target_path, options)
  options = options_to_sym(options)
  if target_path.nil?
    raise DownloaderError, 'No target path provided.'
  end
  # 这里的options为{git:'',tag:''}，下载类型为git，则这里生成的klass为Pod::Downloader::Git
  strategy, klass = class_for_options(options)
  url = options[strategy]
  sub_options = options.dup
  sub_options.delete(strategy)
  # Pod::Downloader::Git类初始化
  klass.new(target_path, url, sub_options)
end

下载类型git、mercurial、remote_file、bazaar等的基类是base，初始化方法会走入基类里面：

# lib/cocoapods-downloader/base.rb
# 初始化对象，保存url，options，创建下载目录
def initialize(target_path, url, options)
  require 'pathname'
  @target_path = Pathname.new(target_path)
  @url = url
  @options = options
  unrecognized_options = options.keys - self.class.options
  unless unrecognized_options.empty?
    raise DownloaderError, "Unrecognized options `#{unrecognized_options}`"
  end
end
# name就是对应的子类的class名
def download
  ui_action("#{name} download") do
    target_path.mkpath
    download!
  end
end

最后进入子类的执行下载的函数：

# lib/cocoapods-downloader/git.rb
module Pod
  module Downloader
    class Git < Base
      def download!
        clone
        checkout_commit if options[:commit]
      end
      def clone(force_head = false, shallow_clone = true)
        ui_sub_action('Git download') do
          begin
            git! clone_arguments(force_head, shallow_clone)
            update_submodules
          rescue DownloaderError => e
            if e.message =~ /^fatal:.*does not support (--depth|shallow capabilities)$/im
              clone(force_head, false)
            else
              raise
            end
          end
        end
      end
      .
      .
      .
    end
  end
end