forked from lix-project/lix
869 lines
32 KiB
C++
869 lines
32 KiB
C++
#include "filetransfer.hh"
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#include "util.hh"
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#include "globals.hh"
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#include "store-api.hh"
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#include "s3.hh"
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#include "compression.hh"
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#include "finally.hh"
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#include "callback.hh"
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#if ENABLE_S3
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#include <aws/core/client/ClientConfiguration.h>
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#endif
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#include <unistd.h>
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#include <fcntl.h>
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#include <curl/curl.h>
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#include <algorithm>
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#include <cmath>
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#include <cstring>
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#include <iostream>
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#include <queue>
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#include <random>
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#include <thread>
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#include <regex>
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using namespace std::string_literals;
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namespace nix {
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FileTransferSettings fileTransferSettings;
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static GlobalConfig::Register rFileTransferSettings(&fileTransferSettings);
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struct curlFileTransfer : public FileTransfer
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{
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CURLM * curlm = 0;
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std::random_device rd;
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std::mt19937 mt19937;
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struct TransferItem : public std::enable_shared_from_this<TransferItem>
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{
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curlFileTransfer & fileTransfer;
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FileTransferRequest request;
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FileTransferResult result;
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Activity act;
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bool done = false; // whether either the success or failure function has been called
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Callback<FileTransferResult> callback;
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CURL * req = 0;
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bool active = false; // whether the handle has been added to the multi object
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std::string statusMsg;
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unsigned int attempt = 0;
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/* Don't start this download until the specified time point
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has been reached. */
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std::chrono::steady_clock::time_point embargo;
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struct curl_slist * requestHeaders = 0;
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std::string encoding;
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bool acceptRanges = false;
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curl_off_t writtenToSink = 0;
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inline static const std::set<long> successfulStatuses {200, 201, 204, 206, 304, 0 /* other protocol */};
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/* Get the HTTP status code, or 0 for other protocols. */
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long getHTTPStatus()
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{
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long httpStatus = 0;
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long protocol = 0;
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curl_easy_getinfo(req, CURLINFO_PROTOCOL, &protocol);
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if (protocol == CURLPROTO_HTTP || protocol == CURLPROTO_HTTPS)
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curl_easy_getinfo(req, CURLINFO_RESPONSE_CODE, &httpStatus);
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return httpStatus;
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}
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TransferItem(curlFileTransfer & fileTransfer,
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const FileTransferRequest & request,
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Callback<FileTransferResult> && callback)
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: fileTransfer(fileTransfer)
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, request(request)
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, act(*logger, lvlTalkative, actFileTransfer,
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fmt(request.data ? "uploading '%s'" : "downloading '%s'", request.uri),
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{request.uri}, request.parentAct)
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, callback(std::move(callback))
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, finalSink([this](std::string_view data) {
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if (this->request.dataCallback) {
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auto httpStatus = getHTTPStatus();
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/* Only write data to the sink if this is a
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successful response. */
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if (successfulStatuses.count(httpStatus)) {
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writtenToSink += data.size();
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this->request.dataCallback(data);
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}
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} else
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this->result.data.append(data);
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})
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{
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if (!request.expectedETag.empty())
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requestHeaders = curl_slist_append(requestHeaders, ("If-None-Match: " + request.expectedETag).c_str());
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if (!request.mimeType.empty())
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requestHeaders = curl_slist_append(requestHeaders, ("Content-Type: " + request.mimeType).c_str());
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for (auto it = request.headers.begin(); it != request.headers.end(); ++it){
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requestHeaders = curl_slist_append(requestHeaders, fmt("%s: %s", it->first, it->second).c_str());
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}
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}
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~TransferItem()
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{
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if (req) {
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if (active)
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curl_multi_remove_handle(fileTransfer.curlm, req);
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curl_easy_cleanup(req);
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}
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if (requestHeaders) curl_slist_free_all(requestHeaders);
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try {
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if (!done)
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fail(FileTransferError(Interrupted, {}, "download of '%s' was interrupted", request.uri));
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} catch (...) {
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ignoreException();
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}
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}
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void failEx(std::exception_ptr ex)
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{
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assert(!done);
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done = true;
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callback.rethrow(ex);
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}
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template<class T>
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void fail(T && e)
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{
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failEx(std::make_exception_ptr(std::move(e)));
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}
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LambdaSink finalSink;
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std::shared_ptr<FinishSink> decompressionSink;
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std::optional<StringSink> errorSink;
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std::exception_ptr writeException;
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size_t writeCallback(void * contents, size_t size, size_t nmemb)
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{
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try {
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size_t realSize = size * nmemb;
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result.bodySize += realSize;
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if (!decompressionSink) {
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decompressionSink = makeDecompressionSink(encoding, finalSink);
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if (! successfulStatuses.count(getHTTPStatus())) {
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// In this case we want to construct a TeeSink, to keep
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// the response around (which we figure won't be big
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// like an actual download should be) to improve error
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// messages.
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errorSink = StringSink { };
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}
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}
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if (errorSink)
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(*errorSink)({(char *) contents, realSize});
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(*decompressionSink)({(char *) contents, realSize});
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return realSize;
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} catch (...) {
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writeException = std::current_exception();
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return 0;
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}
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}
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static size_t writeCallbackWrapper(void * contents, size_t size, size_t nmemb, void * userp)
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{
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return ((TransferItem *) userp)->writeCallback(contents, size, nmemb);
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}
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size_t headerCallback(void * contents, size_t size, size_t nmemb)
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{
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size_t realSize = size * nmemb;
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std::string line((char *) contents, realSize);
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printMsg(lvlVomit, format("got header for '%s': %s") % request.uri % trim(line));
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static std::regex statusLine("HTTP/[^ ]+ +[0-9]+(.*)", std::regex::extended | std::regex::icase);
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std::smatch match;
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if (std::regex_match(line, match, statusLine)) {
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result.etag = "";
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result.data.clear();
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result.bodySize = 0;
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statusMsg = trim(match.str(1));
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acceptRanges = false;
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encoding = "";
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} else {
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auto i = line.find(':');
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if (i != std::string::npos) {
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std::string name = toLower(trim(line.substr(0, i)));
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if (name == "etag") {
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result.etag = trim(line.substr(i + 1));
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/* Hack to work around a GitHub bug: it sends
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ETags, but ignores If-None-Match. So if we get
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the expected ETag on a 200 response, then shut
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down the connection because we already have the
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data. */
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long httpStatus = 0;
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curl_easy_getinfo(req, CURLINFO_RESPONSE_CODE, &httpStatus);
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if (result.etag == request.expectedETag && httpStatus == 200) {
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debug(format("shutting down on 200 HTTP response with expected ETag"));
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return 0;
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}
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} else if (name == "content-encoding")
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encoding = trim(line.substr(i + 1));
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else if (name == "accept-ranges" && toLower(trim(line.substr(i + 1))) == "bytes")
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acceptRanges = true;
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}
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}
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return realSize;
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}
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static size_t headerCallbackWrapper(void * contents, size_t size, size_t nmemb, void * userp)
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{
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return ((TransferItem *) userp)->headerCallback(contents, size, nmemb);
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}
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int progressCallback(double dltotal, double dlnow)
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{
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try {
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act.progress(dlnow, dltotal);
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} catch (nix::Interrupted &) {
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assert(_isInterrupted);
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}
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return _isInterrupted;
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}
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static int progressCallbackWrapper(void * userp, double dltotal, double dlnow, double ultotal, double ulnow)
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{
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return ((TransferItem *) userp)->progressCallback(dltotal, dlnow);
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}
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static int debugCallback(CURL * handle, curl_infotype type, char * data, size_t size, void * userptr)
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{
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if (type == CURLINFO_TEXT)
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vomit("curl: %s", chomp(std::string(data, size)));
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return 0;
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}
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size_t readOffset = 0;
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size_t readCallback(char *buffer, size_t size, size_t nitems)
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{
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if (readOffset == request.data->length())
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return 0;
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auto count = std::min(size * nitems, request.data->length() - readOffset);
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assert(count);
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memcpy(buffer, request.data->data() + readOffset, count);
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readOffset += count;
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return count;
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}
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static size_t readCallbackWrapper(char *buffer, size_t size, size_t nitems, void * userp)
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{
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return ((TransferItem *) userp)->readCallback(buffer, size, nitems);
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}
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void init()
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{
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if (!req) req = curl_easy_init();
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curl_easy_reset(req);
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if (verbosity >= lvlVomit) {
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curl_easy_setopt(req, CURLOPT_VERBOSE, 1);
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curl_easy_setopt(req, CURLOPT_DEBUGFUNCTION, TransferItem::debugCallback);
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}
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curl_easy_setopt(req, CURLOPT_URL, request.uri.c_str());
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curl_easy_setopt(req, CURLOPT_FOLLOWLOCATION, 1L);
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curl_easy_setopt(req, CURLOPT_MAXREDIRS, 10);
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curl_easy_setopt(req, CURLOPT_NOSIGNAL, 1);
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curl_easy_setopt(req, CURLOPT_USERAGENT,
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("curl/" LIBCURL_VERSION " Nix/" + nixVersion +
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(fileTransferSettings.userAgentSuffix != "" ? " " + fileTransferSettings.userAgentSuffix.get() : "")).c_str());
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#if LIBCURL_VERSION_NUM >= 0x072b00
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curl_easy_setopt(req, CURLOPT_PIPEWAIT, 1);
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#endif
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#if LIBCURL_VERSION_NUM >= 0x072f00
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if (fileTransferSettings.enableHttp2)
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curl_easy_setopt(req, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);
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else
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curl_easy_setopt(req, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
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#endif
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curl_easy_setopt(req, CURLOPT_WRITEFUNCTION, TransferItem::writeCallbackWrapper);
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curl_easy_setopt(req, CURLOPT_WRITEDATA, this);
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curl_easy_setopt(req, CURLOPT_HEADERFUNCTION, TransferItem::headerCallbackWrapper);
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curl_easy_setopt(req, CURLOPT_HEADERDATA, this);
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curl_easy_setopt(req, CURLOPT_PROGRESSFUNCTION, progressCallbackWrapper);
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curl_easy_setopt(req, CURLOPT_PROGRESSDATA, this);
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curl_easy_setopt(req, CURLOPT_NOPROGRESS, 0);
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curl_easy_setopt(req, CURLOPT_HTTPHEADER, requestHeaders);
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if (settings.downloadSpeed.get() > 0)
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curl_easy_setopt(req, CURLOPT_MAX_RECV_SPEED_LARGE, (curl_off_t) (settings.downloadSpeed.get() * 1024));
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if (request.head)
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curl_easy_setopt(req, CURLOPT_NOBODY, 1);
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if (request.data) {
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curl_easy_setopt(req, CURLOPT_UPLOAD, 1L);
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curl_easy_setopt(req, CURLOPT_READFUNCTION, readCallbackWrapper);
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curl_easy_setopt(req, CURLOPT_READDATA, this);
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curl_easy_setopt(req, CURLOPT_INFILESIZE_LARGE, (curl_off_t) request.data->length());
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}
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if (request.verifyTLS) {
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if (settings.caFile != "")
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curl_easy_setopt(req, CURLOPT_CAINFO, settings.caFile.c_str());
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} else {
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curl_easy_setopt(req, CURLOPT_SSL_VERIFYPEER, 0);
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curl_easy_setopt(req, CURLOPT_SSL_VERIFYHOST, 0);
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}
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curl_easy_setopt(req, CURLOPT_CONNECTTIMEOUT, fileTransferSettings.connectTimeout.get());
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curl_easy_setopt(req, CURLOPT_LOW_SPEED_LIMIT, 1L);
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curl_easy_setopt(req, CURLOPT_LOW_SPEED_TIME, fileTransferSettings.stalledDownloadTimeout.get());
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/* If no file exist in the specified path, curl continues to work
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anyway as if netrc support was disabled. */
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curl_easy_setopt(req, CURLOPT_NETRC_FILE, settings.netrcFile.get().c_str());
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curl_easy_setopt(req, CURLOPT_NETRC, CURL_NETRC_OPTIONAL);
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if (writtenToSink)
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curl_easy_setopt(req, CURLOPT_RESUME_FROM_LARGE, writtenToSink);
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result.data.clear();
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result.bodySize = 0;
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}
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void finish(CURLcode code)
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{
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auto httpStatus = getHTTPStatus();
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char * effectiveUriCStr;
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curl_easy_getinfo(req, CURLINFO_EFFECTIVE_URL, &effectiveUriCStr);
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if (effectiveUriCStr)
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result.effectiveUri = effectiveUriCStr;
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debug("finished %s of '%s'; curl status = %d, HTTP status = %d, body = %d bytes",
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request.verb(), request.uri, code, httpStatus, result.bodySize);
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if (decompressionSink) {
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try {
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decompressionSink->finish();
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} catch (...) {
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writeException = std::current_exception();
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}
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}
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if (code == CURLE_WRITE_ERROR && result.etag == request.expectedETag) {
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code = CURLE_OK;
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httpStatus = 304;
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}
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if (writeException)
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failEx(writeException);
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else if (code == CURLE_OK && successfulStatuses.count(httpStatus))
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{
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result.cached = httpStatus == 304;
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// In 2021, GitHub responds to If-None-Match with 304,
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// but omits ETag. We just use the If-None-Match etag
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// since 304 implies they are the same.
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if (httpStatus == 304 && result.etag == "")
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result.etag = request.expectedETag;
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act.progress(result.bodySize, result.bodySize);
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done = true;
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callback(std::move(result));
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}
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else {
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// We treat most errors as transient, but won't retry when hopeless
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Error err = Transient;
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if (httpStatus == 404 || httpStatus == 410 || code == CURLE_FILE_COULDNT_READ_FILE) {
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// The file is definitely not there
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err = NotFound;
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} else if (httpStatus == 401 || httpStatus == 403 || httpStatus == 407) {
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// Don't retry on authentication/authorization failures
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err = Forbidden;
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} else if (httpStatus >= 400 && httpStatus < 500 && httpStatus != 408 && httpStatus != 429) {
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// Most 4xx errors are client errors and are probably not worth retrying:
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// * 408 means the server timed out waiting for us, so we try again
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// * 429 means too many requests, so we retry (with a delay)
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err = Misc;
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} else if (httpStatus == 501 || httpStatus == 505 || httpStatus == 511) {
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// Let's treat most 5xx (server) errors as transient, except for a handful:
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// * 501 not implemented
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// * 505 http version not supported
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// * 511 we're behind a captive portal
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err = Misc;
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} else {
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// Don't bother retrying on certain cURL errors either
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switch (code) {
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case CURLE_FAILED_INIT:
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case CURLE_URL_MALFORMAT:
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case CURLE_NOT_BUILT_IN:
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case CURLE_REMOTE_ACCESS_DENIED:
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case CURLE_FILE_COULDNT_READ_FILE:
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case CURLE_FUNCTION_NOT_FOUND:
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case CURLE_ABORTED_BY_CALLBACK:
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case CURLE_BAD_FUNCTION_ARGUMENT:
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case CURLE_INTERFACE_FAILED:
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case CURLE_UNKNOWN_OPTION:
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case CURLE_SSL_CACERT_BADFILE:
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case CURLE_TOO_MANY_REDIRECTS:
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case CURLE_WRITE_ERROR:
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case CURLE_UNSUPPORTED_PROTOCOL:
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err = Misc;
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break;
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default: // Shut up warnings
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break;
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}
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}
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attempt++;
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std::optional<std::string> response;
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if (errorSink)
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response = std::move(errorSink->s);
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auto exc =
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code == CURLE_ABORTED_BY_CALLBACK && _isInterrupted
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? FileTransferError(Interrupted, std::move(response), "%s of '%s' was interrupted", request.verb(), request.uri)
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: httpStatus != 0
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? FileTransferError(err,
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std::move(response),
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"unable to %s '%s': HTTP error %d%s",
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request.verb(), request.uri, httpStatus,
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code == CURLE_OK ? "" : fmt(" (curl error: %s)", curl_easy_strerror(code)))
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: FileTransferError(err,
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std::move(response),
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"unable to %s '%s': %s (%d)",
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request.verb(), request.uri, curl_easy_strerror(code), code);
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/* If this is a transient error, then maybe retry the
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download after a while. If we're writing to a
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sink, we can only retry if the server supports
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ranged requests. */
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if (err == Transient
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&& attempt < request.tries
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&& (!this->request.dataCallback
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|| writtenToSink == 0
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|| (acceptRanges && encoding.empty())))
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{
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int ms = request.baseRetryTimeMs * std::pow(2.0f, attempt - 1 + std::uniform_real_distribution<>(0.0, 0.5)(fileTransfer.mt19937));
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if (writtenToSink)
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warn("%s; retrying from offset %d in %d ms", exc.what(), writtenToSink, ms);
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else
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warn("%s; retrying in %d ms", exc.what(), ms);
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embargo = std::chrono::steady_clock::now() + std::chrono::milliseconds(ms);
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fileTransfer.enqueueItem(shared_from_this());
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}
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else
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fail(std::move(exc));
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}
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}
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};
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struct State
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{
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struct EmbargoComparator {
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bool operator() (const std::shared_ptr<TransferItem> & i1, const std::shared_ptr<TransferItem> & i2) {
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return i1->embargo > i2->embargo;
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}
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};
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bool quit = false;
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std::priority_queue<std::shared_ptr<TransferItem>, std::vector<std::shared_ptr<TransferItem>>, EmbargoComparator> incoming;
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};
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Sync<State> state_;
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/* We can't use a std::condition_variable to wake up the curl
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thread, because it only monitors file descriptors. So use a
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pipe instead. */
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Pipe wakeupPipe;
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|
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std::thread workerThread;
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|
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curlFileTransfer()
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: mt19937(rd())
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{
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static std::once_flag globalInit;
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std::call_once(globalInit, curl_global_init, CURL_GLOBAL_ALL);
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curlm = curl_multi_init();
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#if LIBCURL_VERSION_NUM >= 0x072b00 // Multiplex requires >= 7.43.0
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curl_multi_setopt(curlm, CURLMOPT_PIPELINING, CURLPIPE_MULTIPLEX);
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#endif
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#if LIBCURL_VERSION_NUM >= 0x071e00 // Max connections requires >= 7.30.0
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curl_multi_setopt(curlm, CURLMOPT_MAX_TOTAL_CONNECTIONS,
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fileTransferSettings.httpConnections.get());
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#endif
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wakeupPipe.create();
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fcntl(wakeupPipe.readSide.get(), F_SETFL, O_NONBLOCK);
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workerThread = std::thread([&]() { workerThreadEntry(); });
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}
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~curlFileTransfer()
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{
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stopWorkerThread();
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workerThread.join();
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if (curlm) curl_multi_cleanup(curlm);
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}
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void stopWorkerThread()
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{
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/* Signal the worker thread to exit. */
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{
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auto state(state_.lock());
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state->quit = true;
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}
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writeFull(wakeupPipe.writeSide.get(), " ", false);
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}
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void workerThreadMain()
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{
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/* Cause this thread to be notified on SIGINT. */
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auto callback = createInterruptCallback([&]() {
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stopWorkerThread();
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});
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unshareFilesystem();
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std::map<CURL *, std::shared_ptr<TransferItem>> items;
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bool quit = false;
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std::chrono::steady_clock::time_point nextWakeup;
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while (!quit) {
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checkInterrupt();
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/* Let curl do its thing. */
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int running;
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CURLMcode mc = curl_multi_perform(curlm, &running);
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if (mc != CURLM_OK)
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throw nix::Error("unexpected error from curl_multi_perform(): %s", curl_multi_strerror(mc));
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/* Set the promises of any finished requests. */
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CURLMsg * msg;
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int left;
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while ((msg = curl_multi_info_read(curlm, &left))) {
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if (msg->msg == CURLMSG_DONE) {
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auto i = items.find(msg->easy_handle);
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assert(i != items.end());
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i->second->finish(msg->data.result);
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curl_multi_remove_handle(curlm, i->second->req);
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i->second->active = false;
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items.erase(i);
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}
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}
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/* Wait for activity, including wakeup events. */
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int numfds = 0;
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struct curl_waitfd extraFDs[1];
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extraFDs[0].fd = wakeupPipe.readSide.get();
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extraFDs[0].events = CURL_WAIT_POLLIN;
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extraFDs[0].revents = 0;
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long maxSleepTimeMs = items.empty() ? 10000 : 100;
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auto sleepTimeMs =
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nextWakeup != std::chrono::steady_clock::time_point()
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? std::max(0, (int) std::chrono::duration_cast<std::chrono::milliseconds>(nextWakeup - std::chrono::steady_clock::now()).count())
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: maxSleepTimeMs;
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vomit("download thread waiting for %d ms", sleepTimeMs);
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mc = curl_multi_wait(curlm, extraFDs, 1, sleepTimeMs, &numfds);
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if (mc != CURLM_OK)
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throw nix::Error("unexpected error from curl_multi_wait(): %s", curl_multi_strerror(mc));
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nextWakeup = std::chrono::steady_clock::time_point();
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/* Add new curl requests from the incoming requests queue,
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except for requests that are embargoed (waiting for a
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retry timeout to expire). */
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if (extraFDs[0].revents & CURL_WAIT_POLLIN) {
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char buf[1024];
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auto res = read(extraFDs[0].fd, buf, sizeof(buf));
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if (res == -1 && errno != EINTR)
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throw SysError("reading curl wakeup socket");
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}
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std::vector<std::shared_ptr<TransferItem>> incoming;
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auto now = std::chrono::steady_clock::now();
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{
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auto state(state_.lock());
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while (!state->incoming.empty()) {
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auto item = state->incoming.top();
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if (item->embargo <= now) {
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incoming.push_back(item);
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state->incoming.pop();
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} else {
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if (nextWakeup == std::chrono::steady_clock::time_point()
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|| item->embargo < nextWakeup)
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nextWakeup = item->embargo;
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break;
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}
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}
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quit = state->quit;
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}
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for (auto & item : incoming) {
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debug("starting %s of %s", item->request.verb(), item->request.uri);
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item->init();
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curl_multi_add_handle(curlm, item->req);
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item->active = true;
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items[item->req] = item;
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}
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}
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debug("download thread shutting down");
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}
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void workerThreadEntry()
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{
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try {
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workerThreadMain();
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} catch (nix::Interrupted & e) {
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} catch (std::exception & e) {
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printError("unexpected error in download thread: %s", e.what());
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}
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{
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auto state(state_.lock());
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while (!state->incoming.empty()) state->incoming.pop();
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state->quit = true;
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}
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}
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void enqueueItem(std::shared_ptr<TransferItem> item)
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{
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if (item->request.data
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&& !hasPrefix(item->request.uri, "http://")
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&& !hasPrefix(item->request.uri, "https://"))
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throw nix::Error("uploading to '%s' is not supported", item->request.uri);
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{
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auto state(state_.lock());
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if (state->quit)
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throw nix::Error("cannot enqueue download request because the download thread is shutting down");
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state->incoming.push(item);
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}
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writeFull(wakeupPipe.writeSide.get(), " ");
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}
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#if ENABLE_S3
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std::tuple<std::string, std::string, Store::Params> parseS3Uri(std::string uri)
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{
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auto [path, params] = splitUriAndParams(uri);
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auto slash = path.find('/', 5); // 5 is the length of "s3://" prefix
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if (slash == std::string::npos)
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throw nix::Error("bad S3 URI '%s'", path);
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std::string bucketName(path, 5, slash - 5);
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std::string key(path, slash + 1);
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return {bucketName, key, params};
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}
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#endif
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void enqueueFileTransfer(const FileTransferRequest & request,
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Callback<FileTransferResult> callback) override
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{
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/* Ugly hack to support s3:// URIs. */
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if (hasPrefix(request.uri, "s3://")) {
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// FIXME: do this on a worker thread
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try {
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#if ENABLE_S3
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auto [bucketName, key, params] = parseS3Uri(request.uri);
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std::string profile = getOr(params, "profile", "");
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std::string region = getOr(params, "region", Aws::Region::US_EAST_1);
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std::string scheme = getOr(params, "scheme", "");
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std::string endpoint = getOr(params, "endpoint", "");
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S3Helper s3Helper(profile, region, scheme, endpoint);
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// FIXME: implement ETag
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auto s3Res = s3Helper.getObject(bucketName, key);
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FileTransferResult res;
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if (!s3Res.data)
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throw FileTransferError(NotFound, "S3 object '%s' does not exist", request.uri);
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res.data = std::move(*s3Res.data);
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callback(std::move(res));
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#else
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throw nix::Error("cannot download '%s' because Nix is not built with S3 support", request.uri);
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#endif
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} catch (...) { callback.rethrow(); }
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return;
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}
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enqueueItem(std::make_shared<TransferItem>(*this, request, std::move(callback)));
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}
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};
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ref<curlFileTransfer> makeCurlFileTransfer()
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{
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return make_ref<curlFileTransfer>();
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}
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ref<FileTransfer> getFileTransfer()
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{
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static ref<curlFileTransfer> fileTransfer = makeCurlFileTransfer();
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if (fileTransfer->state_.lock()->quit)
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fileTransfer = makeCurlFileTransfer();
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return fileTransfer;
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}
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ref<FileTransfer> makeFileTransfer()
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{
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return makeCurlFileTransfer();
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}
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std::future<FileTransferResult> FileTransfer::enqueueFileTransfer(const FileTransferRequest & request)
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{
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auto promise = std::make_shared<std::promise<FileTransferResult>>();
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enqueueFileTransfer(request,
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{[promise](std::future<FileTransferResult> fut) {
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try {
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promise->set_value(fut.get());
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} catch (...) {
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promise->set_exception(std::current_exception());
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}
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}});
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return promise->get_future();
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}
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FileTransferResult FileTransfer::download(const FileTransferRequest & request)
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{
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return enqueueFileTransfer(request).get();
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}
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FileTransferResult FileTransfer::upload(const FileTransferRequest & request)
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{
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/* Note: this method is the same as download, but helps in readability */
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return enqueueFileTransfer(request).get();
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}
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void FileTransfer::download(FileTransferRequest && request, Sink & sink)
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{
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/* Note: we can't call 'sink' via request.dataCallback, because
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that would cause the sink to execute on the fileTransfer
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thread. If 'sink' is a coroutine, this will fail. Also, if the
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sink is expensive (e.g. one that does decompression and writing
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to the Nix store), it would stall the download thread too much.
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Therefore we use a buffer to communicate data between the
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download thread and the calling thread. */
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struct State {
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bool quit = false;
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std::exception_ptr exc;
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std::string data;
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std::condition_variable avail, request;
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};
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auto _state = std::make_shared<Sync<State>>();
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/* In case of an exception, wake up the download thread. FIXME:
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abort the download request. */
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Finally finally([&]() {
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auto state(_state->lock());
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state->quit = true;
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state->request.notify_one();
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});
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request.dataCallback = [_state](std::string_view data) {
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auto state(_state->lock());
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if (state->quit) return;
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/* If the buffer is full, then go to sleep until the calling
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thread wakes us up (i.e. when it has removed data from the
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buffer). We don't wait forever to prevent stalling the
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download thread. (Hopefully sleeping will throttle the
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sender.) */
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if (state->data.size() > 1024 * 1024) {
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debug("download buffer is full; going to sleep");
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state.wait_for(state->request, std::chrono::seconds(10));
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}
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/* Append data to the buffer and wake up the calling
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thread. */
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state->data.append(data);
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state->avail.notify_one();
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};
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enqueueFileTransfer(request,
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{[_state](std::future<FileTransferResult> fut) {
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auto state(_state->lock());
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state->quit = true;
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try {
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fut.get();
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} catch (...) {
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state->exc = std::current_exception();
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}
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state->avail.notify_one();
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state->request.notify_one();
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}});
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while (true) {
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checkInterrupt();
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std::string chunk;
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/* Grab data if available, otherwise wait for the download
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thread to wake us up. */
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{
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auto state(_state->lock());
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while (state->data.empty()) {
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if (state->quit) {
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if (state->exc) std::rethrow_exception(state->exc);
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return;
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}
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state.wait(state->avail);
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}
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chunk = std::move(state->data);
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state->request.notify_one();
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}
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/* Flush the data to the sink and wake up the download thread
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if it's blocked on a full buffer. We don't hold the state
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lock while doing this to prevent blocking the download
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thread if sink() takes a long time. */
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sink(chunk);
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}
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}
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template<typename... Args>
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FileTransferError::FileTransferError(FileTransfer::Error error, std::optional<std::string> response, const Args & ... args)
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: Error(args...), error(error), response(response)
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{
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const auto hf = hintfmt(args...);
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// FIXME: Due to https://github.com/NixOS/nix/issues/3841 we don't know how
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// to print different messages for different verbosity levels. For now
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// we add some heuristics for detecting when we want to show the response.
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if (response && (response->size() < 1024 || response->find("<html>") != std::string::npos))
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err.msg = hintfmt("%1%\n\nresponse body:\n\n%2%", normaltxt(hf.str()), chomp(*response));
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else
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err.msg = hf;
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}
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}
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