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lib/curl/Request: move exception handling out of the WRITEFUNCTION

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libcurl's WRITEFUNCTION is pretty fragile; if we destroy the CURL*
instance or even unregister it using curl_multi_remove_handle(),
libcurl will crash instantly.  But still we need to be able to handle
exceptions from inside the WRITEFUNCTION, and call
CurlResponseHandler::OnError(), which may destroy the whole thing.  As
a workaround, I use DeferredMonitor to postpone the OnError() call
into a stack frame which is allowed to destroy the request.
This commit is contained in:
Max Kellermann 2017-01-08 14:28:58 +01:00
parent 1bab6d0dd7
commit 4297a7b0a4
2 changed files with 31 additions and 4 deletions
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18
src/lib/curl/Request.cxx
View File

@ -46,7 +46,8 @@
CurlRequest::CurlRequest(CurlGlobal &_global, const char *url,
CurlResponseHandler &_handler)
:global(_global), handler(_handler)
:DeferredMonitor(_global.GetEventLoop()),
global(_global), handler(_handler)
{
error_buffer[0] = 0;
@ -226,8 +227,11 @@ CurlRequest::DataReceived(const void *ptr, size_t received_size)
return CURL_WRITEFUNC_PAUSE;
} catch (...) {
state = State::CLOSED;
handler.OnError(std::current_exception());
return 0;
/* move the CurlResponseHandler::OnError() call into a
"safe" stack frame */
postponed_error = std::current_exception();
DeferredMonitor::Schedule();
return CURL_WRITEFUNC_PAUSE;
}
}
@ -243,3 +247,11 @@ CurlRequest::WriteFunction(void *ptr, size_t size, size_t nmemb, void *stream)
return c.DataReceived(ptr, size);
}
void
CurlRequest::RunDeferred()
{
assert(postponed_error);
handler.OnError(postponed_error);
}

17
src/lib/curl/Request.hxx
View File

@ -31,15 +31,17 @@
#define CURL_REQUEST_HXX
#include "Easy.hxx"
#include "event/DeferredMonitor.hxx"
#include <map>
#include <string>
#include <exception>
struct StringView;
class CurlGlobal;
class CurlResponseHandler;
class CurlRequest {
class CurlRequest final : DeferredMonitor {
CurlGlobal &global;
CurlResponseHandler &handler;
@ -55,6 +57,16 @@ class CurlRequest {
std::multimap<std::string, std::string> headers;
/**
* An exception caught by DataReceived(), which will be
* forwarded into a "safe" stack frame by
* DeferredMonitor::RunDeferred(). This works around the
* problem that libcurl crashes if you call
* curl_multi_remove_handle() from within the WRITEFUNCTION
* (i.e. DataReceived()).
*/
std::exception_ptr postponed_error;
/** error message provided by libcurl */
char error_buffer[CURL_ERROR_SIZE];
@ -129,6 +141,9 @@ private:
/** called by curl when new data is available */
static size_t WriteFunction(void *ptr, size_t size, size_t nmemb,
void *stream);
/* virtual methods from class DeferredMonitor */
void RunDeferred() override;
};
#endif