使用 HTTParty 检索 JSON 时出现“嵌套太深”错误答案

【问题标题】：'Nesting too deep' error while retrieving JSON using HTTParty使用 HTTParty 检索 JSON 时出现“嵌套太深”错误
【发布时间】：2012-03-29 00:39:07
【问题描述】：

我正在为 reddit api 编写一个非常简单的代理包装器，因此我可以发出跨域 JSONP 请求（据我所知，reddit 不允许 JSONP 调用）。

我正在使用 HTTParty gem 发出调用并检索响应，我立即将其呈现为 json。

到目前为止，我正在检索 subreddit json 作为我的路线：

  match "r/:name" => "api#subreddit"

...这是我的控制器操作：

def subreddit
    render :json => HTTParty.get("http://www.reddit.com/r/" + params[:name] + "/.json"), :callback => params[:callback]
end

例如，返回的 JSON 是这样的：http://www.reddit.com/r/pics/.json

我的问题是当我尝试获取特定线程的 cmets 时。

我的路线是这样的：

match "r/:name/comments/:id" => "api#comments"

...我的控制器操作是这样的：

  def comments
    render :json => HTTParty.get("http://www.reddit.com/r/" + params[:name] + "/comments/" + params[:id] + "/.json"), :callback => params[:callback]    
  end

我想要返回的 JSON 可以在这里看到：http://www.reddit.com/r/pics/comments/rhzgc/.json

但是，当我调用此操作时，我收到以下错误消息：

MultiJson::DecodeError in ApiController#comments
Nesting of 20 is too deep

完整的堆栈跟踪如下：

json (1.6.6) lib/json/common.rb:148:in `parse'
json (1.6.6) lib/json/common.rb:148:in `parse'
multi_json (1.2.0) lib/multi_json/engines/json_common.rb:9:in `decode'
multi_json (1.2.0) lib/multi_json.rb:81:in `decode'
httparty (0.8.1) lib/httparty/parser.rb:116:in `json'
httparty (0.8.1) lib/httparty/parser.rb:136:in `parse_supported_format'
httparty (0.8.1) lib/httparty/parser.rb:103:in `parse'
httparty (0.8.1) lib/httparty/parser.rb:66:in `call'
httparty (0.8.1) lib/httparty/request.rb:222:in `parse_response'
httparty (0.8.1) lib/httparty/request.rb:192:in `handle_response'
httparty (0.8.1) lib/httparty/request.rb:75:in `perform'
httparty (0.8.1) lib/httparty.rb:391:in `perform_request'
httparty (0.8.1) lib/httparty.rb:343:in `get'
httparty (0.8.1) lib/httparty.rb:423:in `get'
app/controllers/api_controller.rb:12:in `comments'
actionpack (3.1.1) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (3.1.1) lib/abstract_controller/base.rb:167:in `process_action'
actionpack (3.1.1) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (3.1.1) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (3.1.1) lib/active_support/callbacks.rb:416:in `_run__2872109728488784816__process_action__2261783022290592822__callbacks'
activesupport (3.1.1) lib/active_support/callbacks.rb:386:in `_run_process_action_callbacks'
activesupport (3.1.1) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.1.1) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (3.1.1) lib/action_controller/metal/rescue.rb:17:in `process_action'
actionpack (3.1.1) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
activesupport (3.1.1) lib/active_support/notifications.rb:53:in `block in instrument'
activesupport (3.1.1) lib/active_support/notifications/instrumenter.rb:21:in `instrument'
activesupport (3.1.1) lib/active_support/notifications.rb:53:in `instrument'
actionpack (3.1.1) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
actionpack (3.1.1) lib/action_controller/metal/params_wrapper.rb:201:in `process_action'
activerecord (3.1.1) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (3.1.1) lib/abstract_controller/base.rb:121:in `process'
actionpack (3.1.1) lib/abstract_controller/rendering.rb:45:in `process'
actionpack (3.1.1) lib/action_controller/metal.rb:193:in `dispatch'
actionpack (3.1.1) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
actionpack (3.1.1) lib/action_controller/metal.rb:236:in `block in action'
actionpack (3.1.1) lib/action_dispatch/routing/route_set.rb:65:in `call'
actionpack (3.1.1) lib/action_dispatch/routing/route_set.rb:65:in `dispatch'
actionpack (3.1.1) lib/action_dispatch/routing/route_set.rb:29:in `call'
rack-mount (0.8.3) lib/rack/mount/route_set.rb:152:in `block in call'
rack-mount (0.8.3) lib/rack/mount/code_generation.rb:96:in `block in recognize'
rack-mount (0.8.3) lib/rack/mount/code_generation.rb:89:in `optimized_each'
rack-mount (0.8.3) lib/rack/mount/code_generation.rb:95:in `recognize'
rack-mount (0.8.3) lib/rack/mount/route_set.rb:141:in `call'
actionpack (3.1.1) lib/action_dispatch/routing/route_set.rb:532:in `call'
actionpack (3.1.1) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
rack (1.3.6) lib/rack/etag.rb:23:in `call'
rack (1.3.6) lib/rack/conditionalget.rb:25:in `call'
actionpack (3.1.1) lib/action_dispatch/middleware/head.rb:14:in `call'
actionpack (3.1.1) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.1.1) lib/action_dispatch/middleware/flash.rb:243:in `call'
rack (1.3.6) lib/rack/session/abstract/id.rb:195:in `context'
rack (1.3.6) lib/rack/session/abstract/id.rb:190:in `call'
actionpack (3.1.1) lib/action_dispatch/middleware/cookies.rb:331:in `call'
activerecord (3.1.1) lib/active_record/query_cache.rb:62:in `call'
activerecord (3.1.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:477:in `call'
actionpack (3.1.1) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (3.1.1) lib/active_support/callbacks.rb:392:in `_run_call_callbacks'
activesupport (3.1.1) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.1.1) lib/action_dispatch/middleware/callbacks.rb:28:in `call'
actionpack (3.1.1) lib/action_dispatch/middleware/reloader.rb:68:in `call'
rack (1.3.6) lib/rack/sendfile.rb:101:in `call'
actionpack (3.1.1) lib/action_dispatch/middleware/remote_ip.rb:48:in `call'
actionpack (3.1.1) lib/action_dispatch/middleware/show_exceptions.rb:47:in `call'
railties (3.1.1) lib/rails/rack/logger.rb:13:in `call'
rack (1.3.6) lib/rack/methodoverride.rb:24:in `call'
rack (1.3.6) lib/rack/runtime.rb:17:in `call'
activesupport (3.1.1) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.3.6) lib/rack/lock.rb:15:in `call'
actionpack (3.1.1) lib/action_dispatch/middleware/static.rb:53:in `call'
railties (3.1.1) lib/rails/engine.rb:456:in `call'
railties (3.1.1) lib/rails/rack/content_length.rb:16:in `call'
railties (3.1.1) lib/rails/rack/log_tailer.rb:14:in `call'
rack (1.3.6) lib/rack/handler/webrick.rb:59:in `service'
/Users/emcummings/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/webrick/httpserver.rb:111:in `service'
/Users/emcummings/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/webrick/httpserver.rb:70:in `run'
/Users/emcummings/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/webrick/server.rb:183:in `block in start_thread'

我在这里做错了什么？如果 JSON 太大而无法解析（我觉得很难相信！）我该怎么办？

编辑：

看起来回到标准的 NET::HTTP 库解决了我的问题：

uri = URI.parse("http://www.reddit.com/r/pics/comments/rhzgc/.json")    
response = Net::HTTP.get_response(uri)
render :json => response.body, :callback => params[:callback]
#OK!

...但我仍然很好奇为什么我在 HTTParty 的同一次调用中失败了！

感谢您的帮助！

【问题讨论】：

标签： ruby-on-rails ruby json httparty

【解决方案1】：

不是 JSON 太大。嵌套太深了。 HTTParty 尝试解码它自动获得的结果。在您的堆栈跟踪和HTTParty 依赖项之后，它依赖于使用json gem 的multi_json。

在json 内部有lib/json/pure/parser.rb。在那里设置了默认的最大深度集，特别是在第 79 行。返回的 JSON 中有 20 多个级别的深度，触发了异常。

 if !opts.key?(:max_nesting) # defaults to 19
   @max_nesting = 19

【讨论】：

有趣 - 我认为这与 HTTParty 内部某处的 json 解析器有关 - 是否有任意限制的原因？
我很确定 JSON gem 与几乎所有其他默认使用的 gem 相同，包括 Rails。 HTTParty 只是通过 multi_json 间接要求它。至于他们为什么选择 19 作为默认限制，我不知道。这是一个可以设置的选项，但我不确定 HTTParty 是否容易暴露。
HTTParty 似乎没有公开在底层 json 解析器上设置任何选项 - [它没有将选项哈希 (github.com/jnunemaker/httparty/blob/master/lib/httparty/…) 传递给加载或解码方法。

【解决方案2】：

通过将以下内容添加到我的 Gemfile 来切换到 OJ JSON 解析器：

gem 'oj'

这个问题自己解决了。

【讨论】：

这对我也很有效；这应该是公认的答案。

【解决方案3】：

看来这可以通过设置max_nesting 选项集调用to_json 来解决。

json = obj.to_json(max_nesting: 50)

【讨论】：