在Apache mod_lua中读取响应体

手册中对此有一些好的指导：

http://httpd.apache.org/docs/current/mod/mod_lua.html#modifying_buckets

通过 Lua 过滤器修改内容通过 LuaInputFilter 或 LuaOutputFilter 实现的过滤器函数被设计为使用协程挂起和恢复函数作为桶沿着过滤器链发送的三阶段非阻塞函数。这样的函数的核心结构是：

function filter(r)
    -- Our first yield is to signal that we are ready to receive buckets.
    -- Before this yield, we can set up our environment, check for conditions,
    -- and, if we deem it necessary, decline filtering a request alltogether:
    if something_bad then
        return -- This would skip this filter.
    end
    -- Regardless of whether we have data to prepend, a yield MUST be called here.
    -- Note that only output filters can prepend data. Input filters must use the
    -- final stage to append data to the content.
    coroutine.yield([optional header to be prepended to the content])

    -- After we have yielded, buckets will be sent to us, one by one, and we can
    -- do whatever we want with them and then pass on the result.
    -- Buckets are stored in the global variable 'bucket', so we create a loop
    -- that checks if 'bucket' is not nil:
    while bucket ~= nil do
        local output = mangle(bucket) -- Do some stuff to the content
        coroutine.yield(output) -- Return our new content to the filter chain
    end

    -- Once the buckets are gone, 'bucket' is set to nil, which will exit the
    -- loop and land us here. Anything extra we want to append to the content
    -- can be done by doing a final yield here. Both input and output filters
    -- can append data to the content in this phase.
    coroutine.yield([optional footer to be appended to the content])
end