閱讀理解FireFox瀏覽器插件開發文檔（一）

昨天白天用官方示例在主機安裝了FF插件，然而晚上回寢室用VS2013並沒有成功，不禁想起了那句話“程序員都是好男人，他們每天都會反省自己，我又錯在哪了”。

言歸正傳，今天的目標是閱讀理解FF插件官方文檔，我這菜雞一般的英語水平勉強能應付。

一、Initialization
當一個插件加載了，在創建第一個實例之前就會調用NPError NP_Initialize(void) {};分配內存資源給所有實例使用。
對應的NP_Shutdown函數是在最後一個實例銷燬糊調用，用來釋放NP_Initialize分配的內存資源

/* Define global variable to hold the user agent string. */
static char* userAgent = NULL;

/* Initialize function. */
NPError NP_Initialize(void)
{
  /* Get the user agent from the browser. */
  char* result = NPN_UserAgent();
  if (result == NULL) return NPERR_OUT_OF_MEMORY_ERROR;

  /* Allocate some memory so that you can keep a copy of it. */
  userAgent = (char*) NPN_MemAlloc(strlen(result) + 1);
  if (userAgent == NULL) return NPERR_OUT_OF_MEMORY_ERROR;

  /* Copy the string to your memory. */
  strcpy(userAgent, result);

  return NPERR_NO_ERROR;
}

/* Shutdown function */
NPError NP_Shutdown(void)
{
  /* Delete the memory you allocated. */
  if (userAgent != NULL)
    NPN_MemFree(userAgent);

  return NPERR_NO_ERROR;
}

userAgent 是什麼，“用戶代理”？算了暫時不管了，反正它是個全局靜態指針變量。指的是NPN_UserAgent（）得到的資源。

二、MIMEType
在初始化的時候，瀏覽器會去數MIMEType類型的已被註冊的插件。接着看看怎麼註冊插件吧。
“A MIME type is made up of a major type (such as application or image) and a minor type, for example, image/jpeg.If you define a new MIME type for a plug-in, you must register it with IETF (Internet Engineering Task Force). Until your new MIME type is registered, preface its name with “x-“, for example, image/x-nwim.”
IETF看不懂。我的FF瀏覽器application已經存在，所以我昨天修改的MIMEType沒有加“x-”。

緊接着往後看我就炸了！
When a Gecko-based browser starts up, it checks certain directories for plug-ins, in this order:

Windows
1、Directory pointed to by MOZ_PLUGIN_PATH environment variable.
2、%APPDATA%\Mozilla\plugins, where %APPDATA% denotes per-user Application Data directory.
3、Plug-ins within toolkit bundles.
4、Profile directory\plugins, where Profile directory is a user profile directory.
5、Directories pointed to by HKEY_CURRENT_USER\Software\MozillaPlugins*\Path registry value, where * can be replaced by any name.
6、Directories pointed to by HKEY_LOCAL_MACHINE\Software\MozillaPlugins*\Path registry value, where * can be replaced by any name.

奇怪啊，最開始我在
HKEY_LOCAL_MACHINE\Software\MozillaPlugins\添加@mozilla.com.cn/test可是瀏覽器並沒有檢測到我的插件啊，反而在HKEY_CURRENT_USER\Software\MozillaPlugins\添加時纔有效果。現在再試一次，還是如此！
算了不較真了，除了最後一條，其他的在我電腦上都好用。

Mac OS X
1、~/Library/Internet Plug-Ins.
2、/Library/Internet Plug-Ins.
3、/System/Library/Frameworks/JavaVM.framework/Versions/Current/Resources.
4、Plug-ins within toolkit bundles.
5、Profile directory/plugins, where Profile directory is a user profile directory.

Linux
1、 Directory pointed to by MOZ_PLUGIN_PATH environment variable. For example:

#!/bin/bash
export MOZ_PLUGIN_PATH=/usr/lib64/mozilla/plugins
exec /usr/lib64/firefox/firefox

Which /usr/lib64/mozilla/plugins this is path for folder with plugins,  /usr/lib64/firefox/firefox  this is path for firefox (binary file). 

2、 ~/.mozilla/plugins.
3、 /usr/lib/mozilla/plugins (on 64-bit systems, /usr/lib64/mozilla/plugins is used instead).