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Enable HTTP/2 support

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The binary cache store can now use HTTP/2 to do lookups. This is much
more efficient than HTTP/1.1 due to multiplexing: we can issue many
requests in parallel over a single TCP connection. Thus it's no longer
necessary to use a bunch of concurrent TCP connections (25 by
default).

For example, downloading 802 .narinfo files from
https://cache.nixos.org/, using a single TCP connection, takes 11.8s
with HTTP/1.1, but only 0.61s with HTTP/2.

This did require a fairly substantial rewrite of the Downloader class
to use the curl multi interface, because otherwise curl wouldn't be
able to do multiplexing for us. As a bonus, we get connection reuse
even with HTTP/1.1. All downloads are now handled by a single worker
thread. Clients call Downloader::enqueueDownload() to tell the worker
thread to start the download, getting a std::future to the result.
This commit is contained in:
Eelco Dolstra 2016-09-14 16:00:40 +02:00
parent a75d11a7e6
commit 90ad02bf62
9 changed files with 433 additions and 210 deletions
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26
src/libstore/http-binary-cache-store.cc
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@ -13,17 +13,12 @@ private:
Path cacheUri;
Pool<Downloader> downloaders;
public:
HttpBinaryCacheStore(
const Params & params, const Path & _cacheUri)
: BinaryCacheStore(params)
, cacheUri(_cacheUri)
, downloaders(
std::numeric_limits<size_t>::max(),
[]() { return makeDownloader(); })
{
if (cacheUri.back() == '/')
cacheUri.pop_back();
@ -54,12 +49,11 @@ protected:
bool fileExists(const std::string & path) override
{
try {
auto downloader(downloaders.get());
DownloadOptions options;
options.showProgress = DownloadOptions::no;
options.head = true;
options.tries = 5;
downloader->download(cacheUri + "/" + path, options);
DownloadRequest request(cacheUri + "/" + path);
request.showProgress = DownloadRequest::no;
request.head = true;
request.tries = 5;
getDownloader()->download(request);
return true;
} catch (DownloadError & e) {
/* S3 buckets return 403 if a file doesn't exist and the
@ -77,13 +71,11 @@ protected:
std::shared_ptr<std::string> getFile(const std::string & path) override
{
auto downloader(downloaders.get());
DownloadOptions options;
options.showProgress = DownloadOptions::no;
options.tries = 5;
options.baseRetryTimeMs = 1000;
DownloadRequest request(cacheUri + "/" + path);
request.showProgress = DownloadRequest::no;
request.tries = 8;
try {
return downloader->download(cacheUri + "/" + path, options).data;
return getDownloader()->download(request).data;
} catch (DownloadError & e) {
if (e.error == Downloader::NotFound || e.error == Downloader::Forbidden)
return 0;