笔者的公司搭建了一个Nexus服务器,用来管理我们自己的项目Release构件和Site文档.
今天的问题是当用户访问一个Site里的PDF文件的时候，报错说“detected that the network has been closed.”
但是用右键点击，然后另存为，却每次都能成功下载下来.本来这几天公司的网络确实是不稳定，刚开始还真的以为是网络问题.
后来仔细观察了http请求后发现，每次报错后浏览器都还在不停的发送 http range 请求. 我们用的是Adbobe的PDF插件.
- Chrome问题
Chrome里有一个自带的plugin，可以通过 chrome://plugins 进入plugin配置页面，找到自带的Chrome PDF viewer.
这个Chrome插件发现提供PDF的Nexus服务器支持range请求后，在读取完response的header后会主动abort response.
然后改为通过XHR分批发送Http Range 请求，此时Adbobe的PDF插件就报network已经关闭了。这里的主要原因是两个插件互相冲突，
而且chrome自带的PDF viewer有bug，不能正确组装返回的range response. 解决办法可以是禁用Chrome PDF viewer。
- Firefox问题/IE问题
老版本的IE和Firefox都没问题，有问题的是IE10，Firefox25. 原因是老版本的IE/Firefox里的adobe插件不会发生http range 请求.
新版的IE/Firefox发生了range请求后，服务器也正常的给了response，结果可笑的是adobe 插件不能正确组装，悲剧。
最后想到的就是禁用range请求.但是在流浪器上是做不到的，因为是插件自己发送的.而Nexus服务器2.7.1是hard code支持这个特性的。
range request是http1.1标准里的特性，支持是理所应当的。 下面是NexusContextServlet.Java的部分代码.红色部分显示了这个特性。
protected void doGetFile(final HttpServletRequest request, final HttpServletResponse response,
final StorageFileItem file) throws IOException
{
// ETag, in "shaved" form of {SHA1{e5c244520e897865709c730433f8b0c44ef271f1}} (without quotes)
// or null if file does not have SHA1 (like Virtual) or generated items (as their SHA1 would correspond to template,
// not to actual generated content).
final String etag;
if (!file.isContentGenerated() && !file.isVirtual()
&& file.getRepositoryItemAttributes().containsKey(StorageFileItem.DIGEST_SHA1_KEY)) {
etag = "{SHA1{" + file.getRepositoryItemAttributes().get(StorageFileItem.DIGEST_SHA1_KEY) + "}}";
// tag header ETag: "{SHA1{e5c244520e897865709c730433f8b0c44ef271f1}}", quotes are must by RFC
response.setHeader("ETag", "\"" + etag + "\"");
}
else {
etag = null;
}
// content-type
response.setHeader("Content-Type", file.getMimeType()); // last-modified
response.setDateHeader("Last-Modified", file.getModified()); // content-length, if known
if (file.getLength() != ContentLocator.UNKNOWN_LENGTH) {
// Note: response.setContentLength Servlet API method uses ints (max 2GB file)!
// TODO: apparently, some Servlet containers follow serlvet API and assume
// contents can have 2GB max, so even this workaround below in inherently unsafe.
// Jetty is checked, and supports this (uses long internally), but unsure for other containers
response.setHeader("Content-Length", String.valueOf(file.getLength()));
} // handle conditional GETs only for "static" content, actual content stored, not generated
if (!file.isContentGenerated() && file.getResourceStoreRequest().getIfModifiedSince() != 0
&& file.getModified() <= file.getResourceStoreRequest().getIfModifiedSince()) {
// this is a conditional GET using time-stamp
response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
}
else if (!file.isContentGenerated() && file.getResourceStoreRequest().getIfNoneMatch() != null && etag != null
&& file.getResourceStoreRequest().getIfNoneMatch().equals(etag)) {
// this is a conditional GET using ETag
response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
}
else {
// NEXUS-5023 disable IE for sniffing into response content
response.setHeader("X-Content-Type-Options", "nosniff"); final List<Range<Long>> ranges = getRequestedRanges(request, file.getLength()); // pour the content, but only if needed (this method will be called even for HEAD reqs, but with content tossed
// away), so be conservative as getting input stream involves locking etc, is expensive
final boolean contentNeeded = "GET".equalsIgnoreCase(request.getMethod());
if (ranges.isEmpty()) {
if (contentNeeded) {
try (final InputStream in = file.getInputStream()) {
sendContent(in, response);
}
}
}
else if (ranges.size() > 1) {
response.setStatus(HttpServletResponse.SC_NOT_IMPLEMENTED);
renderer.renderErrorPage(request, response, file.getResourceStoreRequest(), new UnsupportedOperationException(
"Multiple ranges not yet supported!"));
}
else {
final Range<Long> range = ranges.get(0);
if (!isRequestedRangeSatisfiable(file, range)) {
response.setStatus(HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE);
response.setHeader("Content-Length", "0");
response.setHeader("Content-Range", "bytes */" + file.getLength());
return;
}
final long bodySize = range.upperEndpoint() - range.lowerEndpoint();
response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);
response.setHeader("Content-Length", String.valueOf(bodySize));
response.setHeader("Content-Range",
range.lowerEndpoint() + "-" + range.upperEndpoint() + "/" + file.getLength());
if (contentNeeded) {
try (final InputStream in = file.getInputStream()) {
in.skip(range.lowerEndpoint());
sendContent(limit(in, bodySize), response);
}
}
}
}
}
最后幸好我们的请求在到Nexus之前有一个Apache proxy,根据http1.1标准，range request必须是client先发送range 请求，如果服务器支持
那么才返回状态嘛206和部分数据。所以最后我在proxy中把range header 强行去掉。这样服务器就不会返回206，而是返回200了.
也没有content-range header返回了，所以插件就会按照老实的方式，等待下载完成，然后渲染打开PDF文件.
最后的解决方案就是在Apache中增加如下配置.
LoadModule headers_module modules/mod_headers.so
RequestHeader unset Range