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libstore: check that transfer headers don't change during retries

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etag changing implies with high probability that the content of the
resource changed. immutable url changing implies that the immutable
url we got previously was wrong, which is probably a server bug. if
the encoding changes our decoding will break completely, so that is
also very illegal. one notable change we still allow is etags going
away completely, mostly since this does not imply any data changes.

Change-Id: I0220ceddc3fd732cd1b3bb39b40021cc631baadc
This commit is contained in:
eldritch horrors 2024-10-27 18:27:11 +01:00
parent 7c716b9716
commit 212a14bb1f
1 changed files with 36 additions and 20 deletions
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56
src/libstore/filetransfer.cc
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@ -159,6 +159,14 @@ struct curlFileTransfer : public FileTransfer
failEx(std::make_exception_ptr(std::forward<T>(e)));
}
[[noreturn]]
void throwChangedTarget(std::string_view what, std::string_view from, std::string_view to)
{
throw FileTransferError(
Misc, {}, "uri %s changed %s from %s to %s during transfer", uri, what, from, to
);
}
void maybeFinishSetup()
{
if (phase > retrySetup) {
@ -169,14 +177,7 @@ struct curlFileTransfer : public FileTransfer
curl_easy_getinfo(req, CURLINFO_EFFECTIVE_URL, &effectiveUriCStr);
if (effectiveUriCStr) {
if (!result.effectiveUri.empty() && result.effectiveUri != effectiveUriCStr) {
throw FileTransferError(
Misc,
{},
"uri %s changed final destination from %s to %s during transfer",
uri,
result.effectiveUri,
effectiveUriCStr
);
throwChangedTarget("final destination", result.effectiveUri, effectiveUriCStr);
}
result.effectiveUri = effectiveUriCStr;
}
@ -186,7 +187,7 @@ struct curlFileTransfer : public FileTransfer
phase = transferring;
}
std::exception_ptr writeException;
std::exception_ptr callbackException;
size_t writeCallback(void * contents, size_t size, size_t nmemb)
{
@ -206,7 +207,7 @@ struct curlFileTransfer : public FileTransfer
return realSize;
} catch (...) {
writeException = std::current_exception();
callbackException = std::current_exception();
return CURL_WRITEFUNC_ERROR;
}
}
@ -217,30 +218,39 @@ struct curlFileTransfer : public FileTransfer
}
size_t headerCallback(void * contents, size_t size, size_t nmemb)
{
try {
size_t realSize = size * nmemb;
std::string line(static_cast<char *>(contents), realSize);
printMsg(lvlVomit, "got header for '%s': %s", uri, trim(line));
static std::regex statusLine("HTTP/[^ ]+ +[0-9]+(.*)", std::regex::extended | std::regex::icase);
if (std::smatch match; std::regex_match(line, match, statusLine)) {
result.etag = "";
downloadData.clear();
bodySize = 0;
statusMsg = trim(match.str(1));
acceptRanges = false;
encoding = "";
} else {
auto i = line.find(':');
if (i != std::string::npos) {
std::string name = toLower(trim(line.substr(0, i)));
if (name == "etag") {
result.etag = trim(line.substr(i + 1));
// NOTE we don't check that the etag hasn't gone *missing*. technically
// this is not an error as long as we get the same data from the remote.
auto etag = trim(line.substr(i + 1));
if (!result.etag.empty() && result.etag != etag) {
throwChangedTarget("ETag", result.etag, etag);
}
result.etag = std::move(etag);
}
else if (name == "content-encoding")
encoding = trim(line.substr(i + 1));
else if (name == "content-encoding") {
auto encoding = trim(line.substr(i + 1));
if (!this->encoding.empty() && this->encoding != encoding) {
throwChangedTarget("encoding", this->encoding, encoding);
}
this->encoding = std::move(encoding);
}
else if (name == "accept-ranges" && toLower(trim(line.substr(i + 1))) == "bytes")
acceptRanges = true;
@ -248,14 +258,20 @@ struct curlFileTransfer : public FileTransfer
else if (name == "link" || name == "x-amz-meta-link") {
auto value = trim(line.substr(i + 1));
static std::regex linkRegex("<([^>]*)>; rel=\"immutable\"", std::regex::extended | std::regex::icase);
if (std::smatch match; std::regex_match(value, match, linkRegex))
if (std::smatch match; std::regex_match(value, match, linkRegex)) {
if (result.immutableUrl && result.immutableUrl != match.str(1)) {
throwChangedTarget("immutable url", *result.immutableUrl, match.str(1));
}
result.immutableUrl = match.str(1);
else
} else
debug("got invalid link header '%s'", value);
}
}
}
return realSize;
} catch (...) {
callbackException = std::current_exception();
return CURL_WRITEFUNC_ERROR;
}
static size_t headerCallbackWrapper(void * contents, size_t size, size_t nmemb, void * userp)
@ -397,8 +413,8 @@ struct curlFileTransfer : public FileTransfer
downloadData = decompress(encoding, downloadData);
}
if (writeException)
failEx(writeException);
if (callbackException)
failEx(callbackException);
else if (code == CURLE_OK && successfulStatuses.count(httpStatus))
{