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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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35
src/libstore/download.hh
View file

@ -4,24 +4,30 @@
#include "hash.hh"
#include <string>
#include <future>
namespace nix {
struct DownloadOptions
struct DownloadRequest
{
std::string uri;
std::string expectedETag;
bool verifyTLS = true;
enum { yes, no, automatic } showProgress = yes;
bool head = false;
size_t tries = 1;
unsigned int baseRetryTimeMs = 100;
unsigned int baseRetryTimeMs = 250;
DownloadRequest(const std::string & uri) : uri(uri) { }
};
struct DownloadResult
{
enum Status { Success, NotFound, Forbidden, Misc, Transient };
Status status;
bool cached;
string etag;
string effectiveUrl;
std::string etag;
std::string effectiveUrl;
std::shared_ptr<std::string> data;
};
@ -29,14 +35,29 @@ class Store;
struct Downloader
{
virtual DownloadResult download(string url, const DownloadOptions & options) = 0;
/* Enqueue a download request, returning a future to the result of
the download. The future may throw a DownloadError
exception. */
virtual std::future<DownloadResult> enqueueDownload(const DownloadRequest & request) = 0;
Path downloadCached(ref<Store> store, const string & url, bool unpack, string name = "",
const Hash & expectedHash = Hash(), string * effectiveUrl = nullptr);
/* Synchronously download a file. */
DownloadResult download(const DownloadRequest & request);
/* Check if the specified file is already in ~/.cache/nix/tarballs
and is more recent than ‘tarball-ttl’ seconds. Otherwise,
use the recorded ETag to verify if the server has a more
recent version, and if so, download it to the Nix store. */
Path downloadCached(ref<Store> store, const string & uri, bool unpack, string name = "",
const Hash & expectedHash = Hash(), string * effectiveUri = nullptr);
enum Error { NotFound, Forbidden, Misc, Transient };
};
/* Return a shared Downloader object. Using this object is preferred
because it enables connection reuse and HTTP/2 multiplexing. */
ref<Downloader> getDownloader();
/* Return a new Downloader object. */
ref<Downloader> makeDownloader();
class DownloadError : public Error