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downloader: Support resuming from failed downloads #152

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19 changes: 14 additions & 5 deletions src/downloader.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -160,6 +160,12 @@ std::optional<std::chrono::system_clock::time_point> Downloader::downloadInterna
WriteCallbackData writeData{&dest, nullptr};
HeaderCallbackData headerData{url.starts_with("https"), &lastModified};

// Get current position if resuming download
long long currentFileSize = 0;
if (dest.good()) {
currentFileSize = dest.tellp();
}

curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writeCallback);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, &writeData);
Expand All @@ -170,6 +176,11 @@ std::optional<std::chrono::system_clock::time_point> Downloader::downloadInterna
curl_easy_setopt(curl, CURLOPT_TIMEOUT, 30L);
curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 30L);

if (currentFileSize > 0) {
logDebug("Resuming download of {} from offset {}", url, currentFileSize);
curl_easy_setopt(curl, CURLOPT_RESUME_FROM_LARGE, currentFileSize);
}

if (!caInfo.empty())
curl_easy_setopt(curl, CURLOPT_CAINFO, caInfo.c_str());

Expand All @@ -183,8 +194,6 @@ std::optional<std::chrono::system_clock::time_point> Downloader::downloadInterna
url,
maxTryCount,
maxTryCount > 1 ? "times" : "time");
// Reset file position to beginning before retry to avoid appending to partial data
dest.seekp(0);
return downloadInternal(url, dest, maxTryCount - 1);
} else {
throw DownloadException(std::format("curl_easy_perform() failed: {}", curl_easy_strerror(res)));
Expand All @@ -194,7 +203,7 @@ std::optional<std::chrono::system_clock::time_point> Downloader::downloadInterna
long responseCode;
curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &responseCode);

if (responseCode != 200 && responseCode != 301 && responseCode != 302) {
if (responseCode != 200 && responseCode != 301 && responseCode != 302 && responseCode != 206) {
curl_easy_cleanup(curl);
if (responseCode == 0) {
// with some recent update of the D runtime or Curl, the status line isn't set anymore
Expand Down Expand Up @@ -289,7 +298,7 @@ std::vector<std::uint8_t> Downloader::download(const std::string &url, std::uint
long responseCode;
curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &responseCode);

if (responseCode != 200 && responseCode != 301 && responseCode != 302) {
if (responseCode != 200 && responseCode != 301 && responseCode != 302 && responseCode != 206) {
curl_easy_cleanup(curl);
if (responseCode == 0) {
if (buffer.empty()) {
Expand Down Expand Up @@ -333,7 +342,7 @@ void Downloader::downloadFile(const std::string &url, const std::string &dest, s

fs::create_directories(fs::path(dest).parent_path());

std::ofstream file(dest, std::ios::binary);
std::ofstream file(dest, std::ios::binary | std::ios::app);
if (!file.is_open())
throw DownloadException(std::format("Failed to open destination file: {}", dest));

Expand Down