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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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8
src/nix-channel/nix-channel.cc
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@ -85,7 +85,7 @@ static void update(const StringSet & channelNames)
// got redirected in the process, so that we can grab the various parts of a nix channel
// definition from a consistent location if the redirect changes mid-download.
auto effectiveUrl = string{};
auto dl = makeDownloader();
auto dl = getDownloader();
auto filename = dl->downloadCached(store, url, false, "", Hash(), &effectiveUrl);
url = chomp(std::move(effectiveUrl));
@ -114,10 +114,10 @@ static void update(const StringSet & channelNames)
if (!unpacked) {
// The URL doesn't unpack directly, so let's try treating it like a full channel folder with files in it
// Check if the channel advertises a binary cache.
DownloadOptions opts;
opts.showProgress = DownloadOptions::no;
DownloadRequest request(url + "/binary-cache-url");
request.showProgress = DownloadRequest::no;
try {
auto dlRes = dl->download(url + "/binary-cache-url", opts);
auto dlRes = dl->download(request);
extraAttrs = "binaryCacheURL = \"" + *dlRes.data + "\";";
} catch (DownloadError & e) {
}