netty4 实现一个断点上传大文件功能

我本来以为文件断点续传功能很简单，不就是提供2个方法：

一个返回已经上传的文件的长度；另外一个负责上传文件呗（请求带上content-range 指明本次上传的内容在整个文件中的位置），然后根据请求提供的位置写呗，太简单了。

但是实际情况还是比较复杂的，关键问题是，上面的描述现在想想只能称作为文件分段上传，而不是断点续传。

断点意味着网络会断，然后断了之后，服务端根本获取不到本次上传的内容，于是下次又只能从头开始传文件。一种解决办法是客户端将文件分成很小的片段（单个片段丢了就整个片段重传），这个方案要求客户端做很多工作，服务端还得根据片段的编号组织文件，总之客户端和服务端都挺麻烦。

于是就想到用netty在写一个服务filestoreApdapterServer，文件上传提交给这个代理服务。这个做法有个前提就是，客户端上传的文件名称保证唯一，并且在请求头里面带着这个名字，以便服务端定位文件。利用的原理是一般长度比较大的消息体，netty会使用chunk传输，我们取得chunk写入临时文件，这样即使网络断了，服务端已经获取的文件内容还是保留在临时文件里面。

流程如下：

1. filestoreApdapterServer将请求的消息体写到临时文件（网络断了也不要紧，读到多少写多少）。

2. 客户端下次传之前先调用getSize获取上传传递的文件长度，我们就在这个getSize方法里面偷偷的将第一步保存的临时文件追加到正式文件里面，然后返回文件长度。

3. 客户端根据获取的服务端文件长度，定位未传的文件位置，读取上传。重复1，2步骤。直到文件上传完成。

看代码：FilestoreAdaptorServerInitializer

public class FilestoreAdaptorServerInitializer extends
ChannelInitializer<SocketChannel> {

@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast("decoder", new HttpRequestDecoder());
pipeline.addLast("aggregator", new StreamChunkAggregator(-1));
pipeline.addLast("encoder", new HttpResponseEncoder());
pipeline.addLast("handler", new FileUploadAdaptorHandler());
}
}

StreamChunkAggregator就是获取上传文件，写临时文件的：

public class StreamChunkAggregator extends MessageToMessageDecoder<HttpObject> {
private static final Logger log = LoggerFactory.getLogger(StreamChunkAggregator.class);

private volatile FullHttpMessage currentMessage;
private volatile OutputStream out;
private final int maxContentLength;
private volatile File file;

private ChannelHandlerContext ctx;

public static final int DEFAULT_MAX_COMPOSITEBUFFER_COMPONENTS = 1024;
private int maxCumulationBufferComponents = DEFAULT_MAX_COMPOSITEBUFFER_COMPONENTS;

/**
* Creates a new instance.
*/
public StreamChunkAggregator(int maxContentLength) {
this.maxContentLength = maxContentLength;
}

@Override
protected void decode(ChannelHandlerContext ctx, HttpObject msg,
List<Object> out) throws Exception {
FullHttpMessage currentMessage = this.currentMessage;

if (msg instanceof HttpMessage) {
HttpMessage m = (HttpMessage) msg;
if (msg instanceof HttpRequest) {
HttpRequest header = (HttpRequest) msg;
this.currentMessage = currentMessage = new DefaultFullHttpRequest(header.getProtocolVersion(),
header.getMethod(), header.getUri(), Unpooled.compositeBuffer(maxCumulationBufferComponents));

final String localName = m.headers().get("file"); // 取上传文件名
log.debug("upload file name is {}", localName);
if(null == localName || "".equals(localName.trim())) {
ctx.fireChannelRead(m);
}
File dir = new File(ServerHelper.getDestDir().getAbsolutePath() + File.separator + ServerHelper.getStorePath(localName));
if(!dir.exists())
dir.mkdirs();
log.debug("upload file path is {}", dir.getAbsolutePath());
File tempFile = new File(dir, localName + ".utmp");
if(tempFile.exists()) { // 文件已经存在可能是上次上传遗留的
tempFile.delete();
}
this.file = tempFile;
this.out = new FileOutputStream(file, true);
} else {
throw new Error();
}

currentMessage.headers().set(m.headers());
} else if (msg instanceof HttpContent) {
assert currentMessage != null;
HttpContent chunk = (HttpContent) msg;

if (chunk.content().isReadable()) {
chunk.retain();
IOUtils.copyLarge(new ByteBufInputStream(chunk.content()), this.out);
}

final boolean last;
if (!chunk.getDecoderResult().isSuccess()) {
currentMessage.setDecoderResult(
DecoderResult.failure(chunk.getDecoderResult().cause()));
last = true;
} else {
last = chunk instanceof LastHttpContent;
}

if (last) {
this.out.flush();
this.out.close();

this.out = null;
this.currentMessage = null;
this.file = null;
out.add(currentMessage);
}
} else {
throw new Error();
}
}

FileUploadAdaptorHandler 这个是最后传成功后通知真正的服务端，并且获取服务的返回，给客户端：

public class FileUploadAdaptorHandler extends SimpleChannelInboundHandler<DefaultFullHttpRequest> {
private static final Logger log = LoggerFactory.getLogger(FileUploadAdaptorHandler.class);

@Override
protected void channelRead0(final ChannelHandlerContext ctx, DefaultFullHttpRequest msg) throws Exception {
if(log.isDebugEnabled()) {
log.debug("message received: begin");
}

final String filename = msg.headers().get("file");
if(filename == null || "".equals(filename.trim())) { //没有文件名 直接返回4001 参数错误
String responseBody = "{\"result_code\": 4001,\"result_msg\": \"请求参数错误\"}";
response(responseBody.getBytes(), HttpResponseStatus.BAD_REQUEST, ctx);

} else {
// 转发给play服务处理
final CloseableHttpAsyncClient httpclient = HttpAsyncClients.createDefault();
httpclient.start();
try {
HttpGet request1 = new HttpGet(ServerHelper.getPlayServer());
request1.setHeader("Client-Session", msg.headers().get("client-session"));
request1.setHeader("Content-Range", msg.headers().get("content-range"));
request1.setHeader("file", msg.headers().get("file"));
httpclient.start();
httpclient.execute(request1, new FutureCallback<org.apache.http.HttpResponse>() {
@Override
public void failed(Exception e) {
try {
httpclient.close();
} catch (IOException e1) {
log.error(e1.getMessage(), e1);
}
serve500(ctx, filename);
}

@Override
public void completed(org.apache.http.HttpResponse playResonse) {
log.debug("HttpAsyncClient callback");
int status = playResonse.getStatusLine().getStatusCode();
log.debug("HttpAsyncClient callback playResonse status is {}", status);
if(status != 200) {
ServerHelper.deleteTmpFile(filename);
}
HttpEntity entity = playResonse.getEntity();
byte[] bytes = new byte[(int) entity.getContentLength()];
try {
IOUtils.read(entity.getContent(), bytes);

response(bytes, new HttpResponseStatus(status, ""), ctx);
} catch (Exception e) {
log.error(e.getMessage(), e);
serve500(ctx, filename);
} finally {
try {
httpclient.close();
} catch (IOException e1) {
log.error(e1.getMessage(), e1);
}
}
}

@Override
public void cancelled() {
try {
httpclient.close();
} catch (IOException e1) {
log.error(e1.getMessage(), e1);
}
serve500(ctx, filename);
}
});
} catch (Exception e) {
httpclient.close();
log.error(e.getMessage(), e);
serve500(ctx, filename);
}
}

if(log.isDebugEnabled()) {
log.debug("message received: end");
}

}

真正服务提供2个方法，一个是获取长度，一个是接收filestoreAapterServer请求的方法：

public static void getFileLength(String name) {
Logger.debug("getFileLength path is " + FileHelper.getStorgePath(name));
File file = new File(FileHelper.getStorgePath(name));
long length = file.length();
response.status = StatusCode.OK;
response.setHeader("Content-Size", String.valueOf(length));
LocalFile file = LocalFile .find(。。。).first();
if(file != null){ // 如果数据中有记录则认为文件已经保存完整
Logger.debug("getFileLength file has been in database");
FileResult result = new FileResult();
。。。
throw new CustomJsonResult(result);
}

File fileTmp = new File(FileHelper.getStorgePath(name) + FileHelper.TMP_SUFFIX);
if(Logger.isDebugEnabled())
Logger.debug("getFileLength temp path is " + fileTmp.getAbsolutePath() + ", existed is: " + fileTmp.exists());
if(fileTmp.exists()) {
// 临时文件存在，则保存临时文件
Logger.debug("getFileLength save tmp file");
try {
FileHelper.saveFileFromTmp(fileTmp, file);
} catch (IOException ingore) {
Logger.error(ingore.getMessage(), ingore);
}
length = file.length();
}
response.setHeader("Content-Size", String.valueOf(length));
}

public static void saveUploadFile() {
String filename = getFileName();
Logger.debug("saveUploadFile name is %s", filename);
long total = getFileTotal(); // 整个文件的大小
File tempFile = new File(FileHelper.getStorgePath(filename) + FileHelper.TMP_SUFFIX);
if(Logger.isDebugEnabled()) {
Logger.debug("saveUploadFile upload tmp file is: " + tempFile.getAbsolutePath());
}
if(!tempFile.exists()) {
ApiResult result = new ApiResult();
result.resultCode = ApiResultCode.UPLOAD_FILE_FAIL;
response.status = Http.StatusCode.INTERNAL_ERROR;
throw new CustomJsonResult(result);
}
File destFile = new File(FileHelper.getStorgePath(filename));
if(destFile.length() >= total) {
// 已经上传成功了 需要删除临时文件
FileUtils.deleteQuietly(tempFile);

if(Logger.isDebugEnabled()) {
Logger.debug("saveUploadFile video has upload completely");
}
// 已经完整了，如果数据库不存在保存数据库
....

FileResult result = new FileResult();
result.resultCode = ApiResultCode.SUCCESS;
result.videoUrl = video.videoUrl;
result.shortUrl = video.shortUrl;
throw new CustomJsonResult(result);
}
try {
FileHelper.saveFileFromTmp(tempFile, destFile);
} catch (IOException e) {
Logger.error("saveUploadFile " + e.getMessage(), e);
ApiResult result = new ApiResult();
result.resultCode = ApiResultCode.UPLOAD_FILE_FAIL;
response.status = Http.StatusCode.INTERNAL_ERROR;
throw new CustomJsonResult(result);
}

afterWrite(filename, destFile, total); //一些后续工作，如果文件保存完整，保存数据库返回成功结果给客户端
}

这个解决方法，和我们的服务绑定的比较紧，不能解决较为通用的问题 只是提出一种思路。