使用HTTParty檢索JSON時出現「嵌套過深」錯誤

Question

我正在爲reddit api編寫一個非常簡單的代理包裝，因此我可以使跨域JSONP請求（reddit不允許JSONP調用我的知識）。

我使用HTTParty gem來調出並檢索響應，我立即將其顯示爲json。

我檢索版（Subreddit）JSON完美的罰款，到目前爲止這個作爲我的路線：

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

...這是我的控制器操作：

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

作爲一個例子，JSON回來是類似於這樣的：http://www.reddit.com/r/pics/.json

我的問題是當我試圖抓住特定線程的評論。

我的路線是這樣：

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

...和我的控制器操作是這樣的：

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

，我想回到這裏可以看到的JSON：http://www.reddit.com/r/pics/comments/rhzgc/.json

但是，當我將此操作稱爲此操作時，我收到以下錯誤消息：

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

完整的堆棧跟蹤如下：

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' 

什麼我錯在這裏做什麼？如果JSON太大而無法解析（我發現這種難以置信的信息！）我該怎麼辦？

編輯：

看起來像掉到了標準的Net :: HTTP的lib解決我的問題：

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! 

...但我還是很好奇，爲什麼我沒有這個相同的調用與HTTParty！

感謝您的幫助！

Answer 1

這並不是說JSON太大。它嵌套得太深了。 HTTParty嘗試解碼它自動獲得的結果。在您的堆棧跟蹤和HTTParty依賴關係之後，它依賴於使用json gem的multi_json。

json裏面有lib/json/pure/parser.rb。默認的最大深度設置在那裏設置，特別是在第79行。返回的JSON中的某些內容深度超過20 +，觸發異常。

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

Answer 2

切換到OJ JSON解析器通過添加以下到我的Gemfile：

gem 'oj' 

這個問題自行解決。

Answer 3

看起來這可以通過調用to_json和max_nesting選項設置來解決。

json = obj.to_json(max_nesting: 50)