Web服务图片压缩，nginx+lua生成缩略图

背景

目前而言，用移动端访问Web站点的用户越来越多，图片对流量的消耗是比较大的，之前一个用户用我们网站的app浏览的时候，2个小时耗去了2个G的流量，这是个很严重的问题，需要对图片进行压缩，减少对用户带宽的损耗。

方法

用户访问网站，上传图片，app端一律使用jpg格式压缩，不用png格式。

Niginx+lua+graphicsmagick

NIGINX配置：

      location  /images{
                        #图片防盗链配置
                        #valid_referers none blocked localhost *.mydomain.com;
                            #if ($invalid_referer)
                                #{
                                #       return 403;
                                #}

                        set $image_root /home/images;
                        set $file "$image_root$uri";
                        if (!-f $request_filename) {
                                rewrite_by_lua '
                                local index = string.find(ngx.var.uri, "([0-9]+)x([0-9]+)");
                                local originalUri = string.sub(ngx.var.uri, 0, index-2);
                                local area = string.sub(ngx.var.uri, index);
                                index = string.find(area, "([.])");
                                area = string.sub(area, 0, index-1);
                                function Split(szFullString, szSeparator)
                                        local nFindStartIndex = 1
                                        local nSplitIndex = 1
                                        local nSplitArray = {}
                                while true do
                                        local nFindLastIndex = string.find(szFullString, szSeparator, nFindStartIndex)
                                                if not nFindLastIndex then
                                                        nSplitArray[nSplitIndex] = string.sub(szFullString, nFindStartIndex, string.len(szFullString))
                                                                break
                                                                end
                                                                nSplitArray[nSplitIndex] = string.sub(szFullString, nFindStartIndex, nFindLastIndex - 1)
                                                                nFindStartIndex = nFindLastIndex + string.len(szSeparator)
                                                                nSplitIndex = nSplitIndex + 1
                                                                end
                                                                return nSplitArray
                                                                end
                                                                local size_list = Split(area, "x");

                                function table.isLegal(table)
                                        for _, value in pairs(table) do
                                                if value % 10 ~= 0 then
                                                        return false
                                                                end
                                                                end
                                                                return true
                                                                end
                                                                local extend = string.sub(ngx.var.uri, -3,-1);

                                if table.isLegal(size_list) and extend == "png" then
                                        local command = [[/usr/local/GraphicsMagick-1.3.24/bin/gm convert -compress Lossless -quality 90  -density 72  -background none  +profile "*"  ]] .. ngx.var.image_root ..  originalUri  .. " -geometry  " .. area .. "^ -gravity center -extent " .. area .. " " .. ngx.var.file;
                                os.execute(command);

                                elseif table.isLegal(size_list) and extend ~= "png" then
	                                local command = [[/usr/local/GraphicsMagick-1.3.24/bin/gm convert -compress Lossless -quality 90  -density 72 +profile "*"  ]] .. ngx.var.image_root ..  originalUri  .. " -resize " .. area .. "^ -gravity center -extent " .. area .. " " .. ngx.var.file;
                                os.execute(command);

                                else
                                        ngx.exit(404);
                                end;
                                ';
                        }}

/usr/local/GraphicsMagick-1.3.24/bin/gm convert -compress Lossless -quality 50 -background none  +profile "*" /home/image/1.png  -geometry  400^ -gravity center -extent 400 /home/image/2.jpg

用这种方法，可以将2M的png格式的大图片，压缩成为200KB的大小，非常有效。

之后我又对程序进行了优化，图片后面加上后缀.200x200.png，图片则会被压缩成200x200的png格式图片，如果加上.x.jpg，则会压缩成等比的jpg格式图片。

同时，nginx配置修改为

location  /images {
        set $image_root /home;
        set $file "$image_root$uri";
                 if (!-f $request_filename) {
                        rewrite_by_lua_file /home/software/nginx-server/conf/image.lua;
                 }
                alias /home/images;
                expires max;
        }

下面附上image.lua优化后的代码：

local extend = tostring(string.sub(ngx.var.uri, -3,-1));
local index = string.find(ngx.var.uri, "([0-9]+)x([0-9]+)");
local command;
if index == nil then
        index = string.find(ngx.var.uri, "(%.x%.)")
        if index == nil then
                ngx.exit(404);
                return;
        end
        local originalUri = string.sub(ngx.var.uri, 0, index-1);
        if extend == "png" then
                ngx.header.b="rr";
                ngx.exit(404);
        return;
        elseif entend ~= "png" then
          command = [[/usr/local/GraphicsMagick-1.3.24/bin/gm convert -quality 50 -density 72  +profile "*"  ]] .. ngx.var.image_root ..  originalUri  .. " -gravity center " .. ngx.var.file;
        end
        ngx.header.a=command;
        os.execute(command)
        return
end
originalUri = string.sub(ngx.var.uri, 0, index-2);
local area = string.sub(ngx.var.uri, index);
index = string.find(area, "([.])");
area = string.sub(area, 0, index-1);
function Split(szFullString, szSeparator)
        local nFindStartIndex = 1
        local nSplitIndex = 1
        local nSplitArray = {}
        while true do
                local nFindLastIndex = string.find(szFullString, szSeparator, nFindStartIndex)
                if not nFindLastIndex then
                        nSplitArray[nSplitIndex] = string.sub(szFullString, nFindStartIndex, string.len(szFullString))
                        break
                end
                nSplitArray[nSplitIndex] = string.sub(szFullString, nFindStartIndex, nFindLastIndex - 1)
                nFindStartIndex = nFindLastIndex + string.len(szSeparator)
                nSplitIndex = nSplitIndex + 1
        end
        return nSplitArray
end
local size_list = Split(area, "x");
function table.isLegal(table)
        for _, value in pairs(table) do
                if value % 10 ~= 0 then
                        return false
                end
        end
        return true
end
if table.isLegal(size_list) and extend == "png" then
        command = [[/usr/local/GraphicsMagick-1.3.24/bin/gm convert -quality 50 -density 72  -background none  +profile "*"  ]] .. ngx.var.image_root ..  originalUri  .. " -geometry  " .. area .. "^ -gravity center -extent " .. area .. " " .. ngx.var.file;
        os.execute(command);
elseif table.isLegal(size_list) and extend ~= "png" then
        command = [[/usr/local/GraphicsMagick-1.3.24/bin/gm convert -quality 50 -density 72 +profile "*"  ]] .. ngx.var.image_root ..  originalUri  .. " -resize " .. area .. "^ -gravity center -extent " .. area .. " " .. ngx.var.file;
        os.execute(command);
else
        ngx.exit(404);
end;