最近开发了一个firefox plugin，有点心得，决定将其写下来。因为plugin的一些规则比较死板，所以了解其中函数的关系和调用的先后顺序还要参考https://developer.mozilla.org/en/Plugins，本文主要讨论Windows，Linux，MAC OS X三个平台间的差异以及安装更新的过程。
plugin其实是一个可执行的文件（动态库），主要用于扩充浏览器对数据的解释能力，如flash，pdf格式，也可以用于与本机其他模块或对象进行通信，如具有脚本访问功能的plugin。因为我想开发一个具有脚本访问功能的plugin，所以从firefox源代码包中我选择了npruntime，因为这些结构都是比较固定的。
构建npruntime之前要安装SDK，新建工程或makefile，设置一些宏定义，如XP_WIN=1，这个是很容易成功的。要是npruntime跨平台还需要修改其代码，经多次摸索以及google，我提炼出完整的接口如下：
#include
"
npapi.h
"
#include
"
npupp.h
"
char
*
NPP_GetMIMEDescription();#ifdef XP_MACOSX
extern
"
C
"
{
NP_EXPORT(NPError) OSCALL NP_Initialize(NPNetscapeFuncs* pFuncs#ifdef XP_UNIX , NPPluginFuncs* pluginFuncs#endif // XP_UNIX ); NP_EXPORT(NPError) OSCALL NP_GetEntryPoints(NPPluginFuncs* pFuncs); NP_EXPORT(NPError) OSCALL NP_Shutdown(void); NP_EXPORT(int) main(NPNetscapeFuncs* nsTable, NPPluginFuncs* pluginFuncs, NPP_ShutdownUPP* unloadUpp);
}
#endif
//
XP_MACOSX
#ifndef HIBYTE
#define
HIBYTE(x) ((((uint32_t)(x)) & 0xff00) >> 8)
#endif
NPNetscapeFuncs NPNFuncs;
#if
defined(XP_WIN) || defined(XP_MACOSX)
NPError OSCALL NP_GetEntryPoints(NPPluginFuncs
*
pFuncs)
{ printf("GetEntryPoints\n"); if (pFuncs == NULL) return NPERR_INVALID_FUNCTABLE_ERROR; #ifdef XP_MACOSX // Webkit under OS X passes 0 in pFuncs->size, and Apple's sample code // (NetscapeMoviePlugIn) treats this as an output parameter. if (pFuncs->size == 0) pFuncs->size = sizeof(NPPluginFuncs);#endif // XP_MACOSX if (pFuncs->size < sizeof(NPPluginFuncs)) return NPERR_INVALID_FUNCTABLE_ERROR; pFuncs->version = (NP_VERSION_MAJOR << 8) | NP_VERSION_MINOR; pFuncs->newp = NPP_New; pFuncs->destroy = NPP_Destroy; pFuncs->setwindow = NPP_SetWindow; pFuncs->newstream = NPP_NewStream; pFuncs->destroystream = NPP_DestroyStream; pFuncs->asfile = NPP_StreamAsFile; pFuncs->writeready = NPP_WriteReady; pFuncs->write = NPP_Write; pFuncs->print = NPP_Print; pFuncs->event = NPP_HandleEvent; pFuncs->urlnotify = NPP_URLNotify; pFuncs->getvalue = NPP_GetValue; pFuncs->setvalue = NPP_SetValue; pFuncs->javaClass = NULL; return NPERR_NO_ERROR;}
#endif
//
defined(XP_WIN) || defined(XP_MACOSX)
char
*
NP_GetMIMEDescription()
{ printf("GetMIMEDescription\n"); return NPP_GetMIMEDescription();}
NPErrorNP_GetValue(
void
*
future, NPPVariable variable,
void
*
value)
{ return NPP_GetValue((NPP_t *)future, variable, value);}
//
Under OS X, we rely on NP_GetEntryPoints() to be called to set up
//
the NPPluginFuncs structure, and we do not use the second parameter
//
`pluginFuncs` here for the compatibility with Safari under OS X.
NPError OSCALLNP_Initialize(NPNetscapeFuncs
*
pFuncs#ifdef XP_UNIX , NPPluginFuncs
*
pluginFuncs
#endif
//
XP_UNIX
)
{ printf("Initialize\n"); if(pFuncs == NULL) return NPERR_INVALID_FUNCTABLE_ERROR; if(HIBYTE(pFuncs->version) > NP_VERSION_MAJOR) return NPERR_INCOMPATIBLE_VERSION_ERROR; NPNFuncs.size = pFuncs->size; NPNFuncs.version = pFuncs->version; NPNFuncs.geturlnotify = pFuncs->geturlnotify; NPNFuncs.geturl = pFuncs->geturl; NPNFuncs.posturlnotify = pFuncs->posturlnotify; NPNFuncs.posturl = pFuncs->posturl; NPNFuncs.requestread = pFuncs->requestread; NPNFuncs.newstream = pFuncs->newstream; NPNFuncs.write = pFuncs->write; NPNFuncs.destroystream = pFuncs->destroystream; NPNFuncs.status = pFuncs->status; NPNFuncs.uagent = pFuncs->uagent; NPNFuncs.memalloc = pFuncs->memalloc; NPNFuncs.memfree = pFuncs->memfree; NPNFuncs.memflush = pFuncs->memflush; NPNFuncs.reloadplugins = pFuncs->reloadplugins; NPNFuncs.getJavaEnv = pFuncs->getJavaEnv; NPNFuncs.getJavaPeer = pFuncs->getJavaPeer; NPNFuncs.getvalue = pFuncs->getvalue; NPNFuncs.setvalue = pFuncs->setvalue; NPNFuncs.invalidaterect = pFuncs->invalidaterect; NPNFuncs.invalidateregion = pFuncs->invalidateregion; NPNFuncs.forceredraw = pFuncs->forceredraw; NPNFuncs.getstringidentifier = pFuncs->getstringidentifier; NPNFuncs.getstringidentifiers = pFuncs->getstringidentifiers; NPNFuncs.getintidentifier = pFuncs->getintidentifier; NPNFuncs.identifierisstring = pFuncs->identifierisstring; NPNFuncs.utf8fromidentifier = pFuncs->utf8fromidentifier; NPNFuncs.intfromidentifier = pFuncs->intfromidentifier; NPNFuncs.createobject = pFuncs->createobject; NPNFuncs.retainobject = pFuncs->retainobject; NPNFuncs.releaseobject = pFuncs->releaseobject; NPNFuncs.invoke = pFuncs->invoke; NPNFuncs.invokeDefault = pFuncs->invokeDefault; NPNFuncs.evaluate = pFuncs->evaluate; NPNFuncs.getproperty = pFuncs->getproperty; NPNFuncs.setproperty = pFuncs->setproperty; NPNFuncs.removeproperty = pFuncs->removeproperty; NPNFuncs.hasproperty = pFuncs->hasproperty; NPNFuncs.hasmethod = pFuncs->hasmethod; NPNFuncs.releasevariantvalue = pFuncs->releasevariantvalue; NPNFuncs.setexception = pFuncs->setexception; // NPNFuncs.pluginthreadasynccall = pFuncs->pluginthreadasynccall; #if defined(XP_UNIX) && !defined(XP_MACOSX)
/**//* * Set up the plugin function table that Netscape will use to * call us. Netscape needs to know about our version and size * and have a UniversalProcPointer for every function we * implement.
*/ pluginFuncs->version = (NP_VERSION_MAJOR << 8) + NP_VERSION_MINOR; pluginFuncs->size = sizeof(NPPluginFuncs); pluginFuncs->newp = NewNPP_NewProc(NPP_New); pluginFuncs->destroy = NewNPP_DestroyProc(NPP_Destroy); pluginFuncs->setwindow = NewNPP_SetWindowProc(NPP_SetWindow); pluginFuncs->newstream = NewNPP_NewStreamProc(NPP_NewStream); pluginFuncs->destroystream = NewNPP_DestroyStreamProc(NPP_DestroyStream); pluginFuncs->asfile = NewNPP_StreamAsFileProc(NPP_StreamAsFile); pluginFuncs->writeready = NewNPP_WriteReadyProc(NPP_WriteReady); pluginFuncs->write = NewNPP_WriteProc(NPP_Write); pluginFuncs->print = NewNPP_PrintProc(NPP_Print); pluginFuncs->urlnotify = NewNPP_URLNotifyProc(NPP_URLNotify); pluginFuncs->event = NewNPP_HandleEventProc(NPP_HandleEvent); pluginFuncs->getvalue = NewNPP_GetValueProc(NPP_GetValue);#ifdef OJI pluginFuncs->javaClass = NPP_GetJavaClass();#endif // OJI#endif // defined(XP_UNIX) && !defined(XP_MACOSX) return NPP_Initialize();}
NPError OSCALL NP_Shutdown()
{ NPP_Shutdown(); return NPERR_NO_ERROR;}
#ifdef XP_MACOSX
int
main(NPNetscapeFuncs
*
nsTable, NPPluginFuncs
*
pluginFuncs, NPP_ShutdownUPP
*
unloadUpp)
{ NPError err = NPERR_NO_ERROR; printf("main\n"); // // Ensure that everything Netscape passed us is valid! // if ((nsTable == NULL) || (pluginFuncs == NULL) || (unloadUpp == NULL)) err = NPERR_INVALID_FUNCTABLE_ERROR; // // Check the "major" version passed in Netscape's function table. // We won't load if the major version is newer than what we expect. // Also check that the function tables passed in are big enough for // all the functions we need (they could be bigger, if Netscape added // new APIs, but that's OK with us -- we'll just ignore them). // if (err == NPERR_NO_ERROR) { if (HIBYTE(nsTable->version) > NP_VERSION_MAJOR) err = NPERR_INCOMPATIBLE_VERSION_ERROR; } if (err == NPERR_NO_ERROR) { err = NP_Initialize(nsTable, NULL); } if (err == NPERR_NO_ERROR) { err = NP_GetEntryPoints(pluginFuncs); *unloadUpp = NewNPP_ShutdownProc(NP_Shutdown); } return err;}
#endif
//
XP_MACOSX
这三个平台接口实现的功能都一样，但firefox硬把他们写的这么复杂。仔细对比一下npruntime原来的接口就会明白这三个平台到底有什么不同，这里多出了一个main函数，这个main函数是在MAC OS X的firefox 2里面才有的，在firefox 3中已经取消了，但为了插件的可移植性还是把这个函数加了进来，里面调用了了其他的三个接口函数来实现，本质上没有任何区别。
这3个平台的声明plugin信息的方式也是不一样的。Windows的plugin信息都存放在资源的Version中，可以用VC或记事本打开进行编辑，Linux上的MIMEType需要通过导出函数NP_GetMIMEDescription来获取，而其他的信息则通过NPP_GetValue来获取，firefox通过这个函数向plugin请求插件名称和插件描述。在MAC OS X上plugin信息是放在资源脚本里，要先定义.r 文件，添加到XCode中，.r文件的一个范例如下
#include <CoreServices/CoreServices.r>
resource 'STR#' (127)
{{
"myplugins"
}};
resource 'STR#' (128)
{{
"application/myscriptable-plugin",
"*"
}};
resource 'STR#' (126)
{{
"<a href=\"http://www.mypage.com\">MyPlugin 1.0.0 </a> "
"can do something",
"my discription。"
}};
然后将这个文件和源文件一起编译成一个Bundle（相当于一个DLL），在XCode中还需要将CFBundlePackageType改为BRPL。因为MAC OS X还可运行在ppc架构上，所以最好能编写成universal版，这样就不用考虑平台问题了。
至此，这个接口就算完成了，能够在三个平台上工作。