input/curl: use the I/O thread

src/input/curl_input_plugin.c

@@ -23,6 +23,7 @@
 #include "conf.h"
 #include "tag.h"
 #include "icy_metadata.h"
+#include "io_thread.h"
 #include "glib_compat.h"
 
 #include <assert.h>
@@ -73,14 +74,29 @@ struct input_curl {
 
 	/** the curl handles */
 	CURL *easy;
-	CURLM *multi;
+
+	/** the GMainLoop source used to poll all CURL file
+	    descriptors */
+	GSource *source;
+
+	/** the source id of #source */
+	guint source_id;
+
+	/** a linked list of all registered GPollFD objects */
+	GSList *fds;
 
 	/** list of buffers, where input_curl_writefunction() appends
 	    to, and input_curl_read() reads from them */
 	GQueue *buffers;
 
-	/** has something been added to the buffers list? */
-	bool buffered;
+#if LIBCURL_VERSION_NUM >= 0x071200
+	/**
+	 * Is the connection currently paused?  That happens when the
+	 * buffer was getting too large.  It will be unpaused when the
+	 * buffer is below the threshold again.
+	 */
+	bool paused;
+#endif
 
 	/** error message provided by libcurl */
 	char error[CURL_ERROR_SIZE];
@@ -94,6 +110,8 @@ struct input_curl {
 	/** the tag object ready to be requested via
 	    input_stream_tag() */
 	struct tag *tag;
+
+	GError *postponed_error;
 };
 
 /** libcurl should accept "ICY 200 OK" */
@@ -103,12 +121,525 @@ static struct curl_slist *http_200_aliases;
 static const char *proxy, *proxy_user, *proxy_password;
 static unsigned proxy_port;
 
+static struct {
+	GStaticMutex mutex;
+	GCond *cond;
+	CURLM *multi;
+
+	/**
+	 * A linked list of all active HTTP requests.  An active
+	 * request is one that doesn't have the "eof" flag set.
+	 */
+	GSList *requests;
+
+	/**
+	 * The GMainLoop source used to poll all CURL file
+	 * descriptors.
+	 */
+	GSource *source;
+
+	/**
+	 * The source id of #source.
+	 */
+	guint source_id;
+
+	GSList *fds;
+
+	/**
+	 * When this is non-zero, then an update of #fds is scheduled.
+	 */
+	guint dirty_source_id;
+
+#if LIBCURL_VERSION_NUM >= 0x070f04
+	/**
+	 * Did CURL give us a timeout?  If yes, then we need to call
+	 * curl_multi_perform(), even if there was no event on any
+	 * file descriptor.
+	 */
+	bool timeout;
+
+	/**
+	 * The absolute time stamp when the timeout expires.  This is
+	 * used in the GSource method check().
+	 */
+	GTimeVal absolute_timeout;
+#endif
+} curl = {
+	.mutex = G_STATIC_MUTEX_INIT,
+};
+
 static inline GQuark
 curl_quark(void)
 {
 	return g_quark_from_static_string("curl");
 }
 
+/**
+ * Find a request by its CURL "easy" handle.
+ *
+ * The caller must lock the mutex.
+ */
+static struct input_curl *
+input_curl_find_request(CURL *easy)
+{
+	for (GSList *i = curl.requests; i != NULL; i = g_slist_next(i)) {
+		struct input_curl *c = i->data;
+		if (c->easy == easy)
+			return c;
+	}
+
+	return NULL;
+}
+
+#if LIBCURL_VERSION_NUM >= 0x071200
+
+static gpointer
+input_curl_resume(gpointer data)
+{
+	struct input_curl *c = data;
+
+	if (c->paused) {
+		curl_easy_pause(c->easy, CURLPAUSE_CONT);
+		c->paused = false;
+	}
+
+	return NULL;
+}
+
+#endif
+
+/**
+ * Calculates the GLib event bit mask for one file descriptor,
+ * obtained from three #fd_set objects filled by curl_multi_fdset().
+ */
+static gushort
+input_curl_fd_events(int fd, fd_set *rfds, fd_set *wfds, fd_set *efds)
+{
+	gushort events = 0;
+
+	if (FD_ISSET(fd, rfds)) {
+		events |= G_IO_IN | G_IO_HUP | G_IO_ERR;
+		FD_CLR(fd, rfds);
+	}
+
+	if (FD_ISSET(fd, wfds)) {
+		events |= G_IO_OUT | G_IO_ERR;
+		FD_CLR(fd, wfds);
+	}
+
+	if (FD_ISSET(fd, efds)) {
+		events |= G_IO_HUP | G_IO_ERR;
+		FD_CLR(fd, efds);
+	}
+
+	return events;
+}
+
+/**
+ * Updates all registered GPollFD objects, unregisters old ones,
+ * registers new ones.
+ *
+ * The caller must lock the mutex.  Runs in the I/O thread.
+ */
+static void
+curl_update_fds(void)
+{
+	fd_set rfds, wfds, efds;
+
+	FD_ZERO(&rfds);
+	FD_ZERO(&wfds);
+	FD_ZERO(&efds);
+
+	int max_fd;
+	CURLMcode mcode = curl_multi_fdset(curl.multi, &rfds, &wfds,
+					   &efds, &max_fd);
+	if (mcode != CURLM_OK) {
+		g_warning("curl_multi_fdset() failed: %s\n",
+			  curl_multi_strerror(mcode));
+		return;
+	}
+
+	GSList *fds = curl.fds;
+	curl.fds = NULL;
+
+	while (fds != NULL) {
+		GPollFD *poll_fd = fds->data;
+		gushort events = input_curl_fd_events(poll_fd->fd, &rfds,
+						      &wfds, &efds);
+
+		assert(poll_fd->events != 0);
+
+		fds = g_slist_remove(fds, poll_fd);
+
+		if (events != poll_fd->events)
+			g_source_remove_poll(curl.source, poll_fd);
+
+		if (events != 0) {
+			if (events != poll_fd->events) {
+				poll_fd->events = events;
+				g_source_add_poll(curl.source, poll_fd);
+			}
+
+			curl.fds = g_slist_prepend(curl.fds, poll_fd);
+		} else {
+			g_free(poll_fd);
+		}
+	}
+
+	for (int fd = 0; fd <= max_fd; ++fd) {
+		gushort events = input_curl_fd_events(fd, &rfds, &wfds, &efds);
+		if (events != 0) {
+			GPollFD *poll_fd = g_new(GPollFD, 1);
+			poll_fd->fd = fd;
+			poll_fd->events = events;
+			g_source_add_poll(curl.source, poll_fd);
+			curl.fds = g_slist_prepend(curl.fds, poll_fd);
+		}
+	}
+}
+
+/**
+ * Callback for curl_schedule_update() that runs in the I/O thread.
+ */
+static gboolean
+input_curl_dirty_callback(G_GNUC_UNUSED gpointer data)
+{
+	g_static_mutex_lock(&curl.mutex);
+
+	assert(curl.dirty_source_id != 0 || curl.requests == NULL);
+	curl.dirty_source_id = 0;
+
+	curl_update_fds();
+
+	g_static_mutex_unlock(&curl.mutex);
+	return false;
+}
+
+/**
+ * Schedule a refresh of curl.fds.  Does nothing if that is already
+ * scheduled.
+ *
+ * The caller must lock the mutex.
+ */
+static void
+input_curl_schedule_update(void)
+{
+	if (curl.dirty_source_id != 0)
+		/* already scheduled */
+		return;
+
+	curl.dirty_source_id =
+		io_thread_idle_add(input_curl_dirty_callback, NULL);
+}
+
+static bool
+input_curl_easy_add(struct input_curl *c, GError **error_r)
+{
+	assert(c != NULL);
+	assert(c->easy != NULL);
+	assert(input_curl_find_request(c->easy) == NULL);
+
+	curl.requests = g_slist_prepend(curl.requests, c);
+
+	CURLMcode mcode = curl_multi_add_handle(curl.multi, c->easy);
+	if (mcode != CURLM_OK) {
+		g_set_error(error_r, curl_quark(), mcode,
+			    "curl_multi_add_handle() failed: %s",
+			    curl_multi_strerror(mcode));
+		return false;
+	}
+
+	input_curl_schedule_update();
+
+	return true;
+}
+
+/**
+ * Frees the current "libcurl easy" handle, and everything associated
+ * with it.
+ *
+ * The caller must lock the mutex.
+ */
+static void
+input_curl_easy_free(struct input_curl *c)
+{
+	assert(c != NULL);
+
+	if (c->easy == NULL)
+		return;
+
+	curl.requests = g_slist_remove(curl.requests, c);
+
+	curl_multi_remove_handle(curl.multi, c->easy);
+	curl_easy_cleanup(c->easy);
+	c->easy = NULL;
+
+	curl_slist_free_all(c->request_headers);
+	c->request_headers = NULL;
+
+	g_free(c->range);
+	c->range = NULL;
+
+	c->base.ready = true;
+}
+
+static gpointer
+input_curl_easy_free_callback(gpointer data)
+{
+	struct input_curl *c = data;
+
+	g_static_mutex_lock(&curl.mutex);
+
+	input_curl_easy_free(c);
+	curl_update_fds();
+
+	g_static_mutex_unlock(&curl.mutex);
+
+	return NULL;
+}
+
+/**
+ * Frees the current "libcurl easy" handle, and everything associated
+ * with it.
+ *
+ * The mutex must not be locked.
+ */
+static void
+input_curl_easy_free_indirect(struct input_curl *c)
+{
+	io_thread_call(input_curl_easy_free_callback, c);
+	assert(c->easy == NULL);
+}
+
+/**
+ * Aborts and frees a running HTTP request.
+ *
+ * The caller must lock the mutex.  Runs in the I/O thread.
+ */
+static void
+input_curl_request_abort(struct input_curl *c, GError *error)
+{
+	assert(c != NULL);
+	assert(c->postponed_error == NULL);
+	assert(error != NULL);
+
+	input_curl_easy_free(c);
+
+	c->postponed_error = error;
+
+	g_cond_broadcast(curl.cond);
+}
+
+/**
+ * Abort and free all HTTP requests.
+ *
+ * The caller must lock the mutex.  Runs in the I/O thread.
+ */
+static void
+input_curl_abort_all_requests(GError *error)
+{
+	while (curl.requests != NULL) {
+		struct input_curl *is = curl.requests->data;
+		input_curl_request_abort(is, g_error_copy(error));
+	}
+
+	g_error_free(error);
+}
+
+/**
+ * A HTTP request is finished.
+ *
+ * The caller must lock the mutex.  Runs in the I/O thread.
+ */
+static void
+input_curl_request_done(struct input_curl *c, CURLcode result, long status)
+{
+	assert(c->easy == NULL);
+	assert(c->base.ready);
+
+	if (result != CURLE_OK) {
+		GError *error = g_error_new(curl_quark(), result,
+					    "curl failed: %s",
+					    c->error);
+		input_curl_request_abort(c, error);
+	} else if (status < 200 || status >= 300) {
+		GError *error = g_error_new(curl_quark(), 0,
+					    "got HTTP status %ld",
+					    status);
+		input_curl_request_abort(c, error);
+	} else {
+		g_cond_broadcast(curl.cond);
+	}
+}
+
+static void
+input_curl_handle_done(CURL *easy_handle, CURLcode result)
+{
+	struct input_curl *c = input_curl_find_request(easy_handle);
+	assert(c != NULL);
+
+	long status = 0;
+	curl_easy_getinfo(easy_handle, CURLINFO_RESPONSE_CODE, &status);
+
+	input_curl_easy_free(c);
+	input_curl_request_done(c, result, status);
+}
+
+/**
+ * Check for finished HTTP responses.
+ *
+ * The caller must lock the mutex.  Runs in the I/O thread.
+ */
+static void
+input_curl_info_read(void)
+{
+	CURLMsg *msg;
+	int msgs_in_queue;
+
+	while ((msg = curl_multi_info_read(curl.multi,
+					   &msgs_in_queue)) != NULL) {
+		if (msg->msg == CURLMSG_DONE)
+			input_curl_handle_done(msg->easy_handle, msg->data.result);
+	}
+}
+
+/**
+ * Give control to CURL.
+ *
+ * The caller must lock the mutex.  Runs in the I/O thread.
+ */
+static bool
+input_curl_perform(void)
+{
+	CURLMcode mcode;
+
+	do {
+		int running_handles;
+		mcode = curl_multi_perform(curl.multi, &running_handles);
+	} while (mcode == CURLM_CALL_MULTI_PERFORM);
+
+	if (mcode != CURLM_OK && mcode != CURLM_CALL_MULTI_PERFORM) {
+		GError *error = g_error_new(curl_quark(), mcode,
+					    "curl_multi_perform() failed: %s",
+					    curl_multi_strerror(mcode));
+		input_curl_abort_all_requests(error);
+		return false;
+	}
+
+	return true;
+}
+
+/*
+ * GSource methods
+ *
+ */
+
+/**
+ * The GSource prepare() method implementation.
+ */
+static gboolean
+input_curl_source_prepare(G_GNUC_UNUSED GSource *source, gint *timeout_r)
+{
+	curl_update_fds();
+
+#if LIBCURL_VERSION_NUM >= 0x070f04
+	curl.timeout = false;
+
+	long timeout2;
+	CURLMcode mcode = curl_multi_timeout(curl.multi, &timeout2);
+	if (mcode == CURLM_OK) {
+		if (timeout2 >= 0) {
+			g_source_get_current_time(source,
+						  &curl.absolute_timeout);
+			g_time_val_add(&curl.absolute_timeout,
+				       timeout2 * 1000);
+		}
+
+		if (timeout2 >= 0 && timeout2 < 10)
+			/* CURL 7.21.1 likes to report "timeout=0",
+			   which means we're running in a busy loop.
+			   Quite a bad idea to waste so much CPU.
+			   Let's use a lower limit of 10ms. */
+			timeout2 = 10;
+
+		*timeout_r = timeout2;
+
+		curl.timeout = timeout2 >= 0;
+	} else
+		g_warning("curl_multi_timeout() failed: %s\n",
+			  curl_multi_strerror(mcode));
+#else
+	(void)timeout_r;
+#endif
+
+	return false;
+}
+
+/**
+ * The GSource check() method implementation.
+ */
+static gboolean
+input_curl_source_check(G_GNUC_UNUSED GSource *source)
+{
+#if LIBCURL_VERSION_NUM >= 0x070f04
+	if (curl.timeout) {
+		/* when a timeout has expired, we need to call
+		   curl_multi_perform(), even if there was no file
+		   descriptor event */
+
+		GTimeVal now;
+		g_source_get_current_time(source, &now);
+		if (now.tv_sec > curl.absolute_timeout.tv_sec ||
+		    (now.tv_sec == curl.absolute_timeout.tv_sec &&
+		     now.tv_usec >= curl.absolute_timeout.tv_usec))
+			return true;
+	}
+#endif
+
+	for (GSList *i = curl.fds; i != NULL; i = i->next) {
+		GPollFD *poll_fd = i->data;
+		if (poll_fd->revents != 0)
+			return true;
+	}
+
+	return false;
+}
+
+/**
+ * The GSource dispatch() method implementation.  The callback isn't
+ * used, because we're handling all events directly.
+ */
+static gboolean
+input_curl_source_dispatch(G_GNUC_UNUSED GSource *source,
+			   G_GNUC_UNUSED GSourceFunc callback,
+			   G_GNUC_UNUSED gpointer user_data)
+{
+	g_static_mutex_lock(&curl.mutex);
+
+	if (input_curl_perform())
+		input_curl_info_read();
+
+	g_static_mutex_unlock(&curl.mutex);
+
+	return true;
+}
+
+/**
+ * The vtable for our GSource implementation.  Unfortunately, we
+ * cannot declare it "const", because g_source_new() takes a non-const
+ * pointer, for whatever reason.
+ */
+static GSourceFuncs curl_source_funcs = {
+	.prepare = input_curl_source_prepare,
+	.check = input_curl_source_check,
+	.dispatch = input_curl_source_dispatch,
+};
+
+/*
+ * input_plugin methods
+ *
+ */
+
 static bool
 input_curl_init(const struct config_param *param,
 		G_GNUC_UNUSED GError **error_r)
@@ -138,20 +669,61 @@ input_curl_init(const struct config_param *param,
 						   "");
 	}
 
+	curl.multi = curl_multi_init();
+	if (curl.multi == NULL) {
+		g_set_error(error_r, curl_quark(), 0,
+			    "curl_multi_init() failed");
+		return false;
+	}
+
+	curl.cond = g_cond_new();
+
+	curl.source = g_source_new(&curl_source_funcs, sizeof(*curl.source));
+	curl.source_id = g_source_attach(curl.source, io_thread_context());
+
 	return true;
 }
 
+static gpointer
+curl_destroy_sources(G_GNUC_UNUSED gpointer data)
+{
+	g_source_destroy(curl.source);
+
+	if (curl.dirty_source_id != 0) {
+		GSource *source =
+			g_main_context_find_source_by_id(io_thread_context(),
+							 curl.dirty_source_id);
+		assert(source != NULL);
+		curl.dirty_source_id = 0;
+
+		g_source_destroy(source);
+	}
+
+	return NULL;
+}
+
 static void
 input_curl_finish(void)
 {
+	assert(curl.requests == NULL);
+
+	io_thread_call(curl_destroy_sources, NULL);
+
+	curl_multi_cleanup(curl.multi);
+	g_cond_free(curl.cond);
+
 	curl_slist_free_all(http_200_aliases);
 
 	curl_global_cleanup();
 }
 
+#if LIBCURL_VERSION_NUM >= 0x071200
+
 /**
  * Determine the total sizes of all buffers, including portions that
  * have already been consumed.
+ *
+ * The caller must lock the mutex.
  */
 G_GNUC_PURE
 static size_t
@@ -168,6 +740,8 @@ curl_total_buffer_size(const struct input_curl *c)
 	return total;
 }
 
+#endif
+
 static void
 buffer_free_callback(gpointer data, G_GNUC_UNUSED gpointer user_data)
 {
@@ -186,28 +760,6 @@ input_curl_flush_buffers(struct input_curl *c)
 }
 
 /**
- * Frees the current "libcurl easy" handle, and everything associated
- * with it.
- */
-static void
-input_curl_easy_free(struct input_curl *c)
-{
-	if (c->easy != NULL) {
-		curl_multi_remove_handle(c->multi, c->easy);
-		curl_easy_cleanup(c->easy);
-		c->easy = NULL;
-	}
-
-	curl_slist_free_all(c->request_headers);
-	c->request_headers = NULL;
-
-	g_free(c->range);
-	c->range = NULL;
-
-	c->base.ready = true;
-}
-
-/**
  * Frees this stream (but not the input_stream struct itself).
  */
 static void
@@ -217,12 +769,9 @@ input_curl_free(struct input_curl *c)
 		tag_free(c->tag);
 	g_free(c->meta_name);
 
-	input_curl_easy_free(c);
+	input_curl_easy_free_indirect(c);
 	input_curl_flush_buffers(c);
 
-	if (c->multi != NULL)
-		curl_multi_cleanup(c->multi);
-
 	g_queue_free(c->buffers);
 
 	g_free(c->url);
@@ -241,117 +790,15 @@ input_curl_tag(struct input_stream *is)
 }
 
 static bool
-input_curl_multi_info_read(struct input_curl *c, GError **error_r)
-{
-	CURLMsg *msg;
-	int msgs_in_queue;
-
-	while ((msg = curl_multi_info_read(c->multi,
-					   &msgs_in_queue)) != NULL) {
-		if (msg->msg == CURLMSG_DONE) {
-			CURLcode result = msg->data.result;
-
-			input_curl_easy_free(c);
-
-			if (result != CURLE_OK) {
-				g_set_error(error_r, curl_quark(), result,
-					    "curl failed: %s", c->error);
-				return false;
-			}
-		}
-	}
-
-	return true;
-}
-
-/**
- * Wait for the libcurl socket.
- *
- * @return -1 on error, 0 if no data is available yet, 1 if data is
- * available
- */
-static int
-input_curl_select(struct input_curl *c, GError **error_r)
-{
-	fd_set rfds, wfds, efds;
-	int max_fd, ret;
-	CURLMcode mcode;
-	struct timeval timeout = {
-		.tv_sec = 1,
-		.tv_usec = 0,
-	};
-
-	assert(c->easy != NULL);
-
-	FD_ZERO(&rfds);
-	FD_ZERO(&wfds);
-	FD_ZERO(&efds);
-
-	mcode = curl_multi_fdset(c->multi, &rfds, &wfds, &efds, &max_fd);
-	if (mcode != CURLM_OK) {
-		g_set_error(error_r, curl_quark(), mcode,
-			    "curl_multi_fdset() failed: %s",
-			    curl_multi_strerror(mcode));
-		return -1;
-	}
-
-#if LIBCURL_VERSION_NUM >= 0x070f04
-	long timeout2;
-	mcode = curl_multi_timeout(c->multi, &timeout2);
-	if (mcode != CURLM_OK) {
-		g_warning("curl_multi_timeout() failed: %s\n",
-			  curl_multi_strerror(mcode));
-		return -1;
-	}
-
-	if (timeout2 >= 0) {
-		if (timeout2 > 10000)
-			timeout2 = 10000;
-
-		timeout.tv_sec = timeout2 / 1000;
-		timeout.tv_usec = (timeout2 % 1000) * 1000;
-	}
-#endif
-
-	ret = select(max_fd + 1, &rfds, &wfds, &efds, &timeout);
-	if (ret < 0)
-		g_set_error(error_r, g_quark_from_static_string("errno"),
-			    errno,
-			    "select() failed: %s\n", g_strerror(errno));
-
-	return ret;
-}
-
-static bool
 fill_buffer(struct input_curl *c, GError **error_r)
 {
-	CURLMcode mcode = CURLM_CALL_MULTI_PERFORM;
-
-	while (c->easy != NULL && g_queue_is_empty(c->buffers)) {
-		int running_handles;
-		bool bret;
-
-		if (mcode != CURLM_CALL_MULTI_PERFORM) {
-			/* if we're still here, there is no input yet
-			   - wait for input */
-			int ret = input_curl_select(c, error_r);
-			if (ret <= 0)
-				/* no data yet or error */
-				return false;
-		}
-
-		mcode = curl_multi_perform(c->multi, &running_handles);
-		if (mcode != CURLM_OK && mcode != CURLM_CALL_MULTI_PERFORM) {
-			g_set_error(error_r, curl_quark(), mcode,
-				    "curl_multi_perform() failed: %s",
-				    curl_multi_strerror(mcode));
-			input_curl_easy_free(c);
-			return false;
-		}
+	while (c->easy != NULL && g_queue_is_empty(c->buffers))
+		g_cond_wait(curl.cond, g_static_mutex_get_mutex(&curl.mutex));
 
-		bret = input_curl_multi_info_read(c, error_r);
-		if (!bret)
-			return false;
+	if (c->postponed_error != NULL) {
+		g_propagate_error(error_r, c->postponed_error);
+		c->postponed_error = NULL;
+		return false;
 	}
 
 	return !g_queue_is_empty(c->buffers);
@@ -456,12 +903,16 @@ input_curl_read(struct input_stream *is, void *ptr, size_t size,
 	size_t nbytes = 0;
 	char *dest = ptr;
 
+	g_static_mutex_lock(&curl.mutex);
+
 	do {
 		/* fill the buffer */
 
 		success = fill_buffer(c, error_r);
-		if (!success)
+		if (!success) {
+			g_static_mutex_unlock(&curl.mutex);
 			return 0;
+		}
 
 		/* send buffer contents */
 
@@ -479,6 +930,13 @@ input_curl_read(struct input_stream *is, void *ptr, size_t size,
 
 	is->offset += (goffset)nbytes;
 
+#if LIBCURL_VERSION_NUM >= 0x071200
+	if (c->paused && curl_total_buffer_size(c) < CURL_MAX_BUFFERED)
+		io_thread_call(input_curl_resume, c);
+#endif
+
+	g_static_mutex_unlock(&curl.mutex);
+
 	return nbytes;
 }
 
@@ -495,7 +953,11 @@ input_curl_eof(G_GNUC_UNUSED struct input_stream *is)
 {
 	struct input_curl *c = (struct input_curl *)is;
 
-	return c->easy == NULL && g_queue_is_empty(c->buffers);
+	g_static_mutex_lock(&curl.mutex);
+	bool eof = c->easy == NULL && g_queue_is_empty(c->buffers);
+	g_static_mutex_unlock(&curl.mutex);
+
+	return eof;
 }
 
 static int
@@ -503,40 +965,21 @@ input_curl_buffer(struct input_stream *is, GError **error_r)
 {
 	struct input_curl *c = (struct input_curl *)is;
 
-	if (curl_total_buffer_size(c) >= CURL_MAX_BUFFERED)
-		return 0;
+	g_static_mutex_lock(&curl.mutex);
 
-	CURLMcode mcode;
-	int running_handles;
-	bool ret;
+	int result;
+	if (c->postponed_error != NULL) {
+		g_propagate_error(error_r, c->postponed_error);
+		c->postponed_error = NULL;
+		result = -1;
+	} else if (g_queue_is_empty(c->buffers))
+		result = 0;
+	else
+		result = 1;
 
-	c->buffered = false;
-
-	if (!is->ready && c->easy != NULL)
-		/* not ready yet means the caller is waiting in a busy
-		   loop; relax that by calling select() on the
-		   socket */
-		if (input_curl_select(c, error_r) < 0)
-			return -1;
-
-	do {
-		mcode = curl_multi_perform(c->multi, &running_handles);
-	} while (mcode == CURLM_CALL_MULTI_PERFORM &&
-		 g_queue_is_empty(c->buffers));
+	g_static_mutex_unlock(&curl.mutex);
 
-	if (mcode != CURLM_OK && mcode != CURLM_CALL_MULTI_PERFORM) {
-		g_set_error(error_r, curl_quark(), mcode,
-			    "curl_multi_perform() failed: %s",
-			    curl_multi_strerror(mcode));
-		input_curl_easy_free(c);
-		return -1;
-	}
-
-	ret = input_curl_multi_info_read(c, error_r);
-	if (!ret)
-		return -1;
-
-	return c->buffered;
+	return result;
 }
 
 /** called by curl when new data is available */
@@ -634,15 +1077,24 @@ input_curl_writefunction(void *ptr, size_t size, size_t nmemb, void *stream)
 	if (size == 0)
 		return 0;
 
+#if LIBCURL_VERSION_NUM >= 0x071200
+	if (curl_total_buffer_size(c) + size >= CURL_MAX_BUFFERED) {
+		c->paused = true;
+		return CURL_WRITEFUNC_PAUSE;
+	}
+#endif
+
 	buffer = g_malloc(sizeof(*buffer) - sizeof(buffer->data) + size);
 	buffer->size = size;
 	buffer->consumed = 0;
 	memcpy(buffer->data, ptr, size);
+
 	g_queue_push_tail(c->buffers, buffer);
 
-	c->buffered = true;
 	c->base.ready = true;
 
+	g_cond_broadcast(curl.cond);
+
 	return size;
 }
 
@@ -650,7 +1102,6 @@ static bool
 input_curl_easy_init(struct input_curl *c, GError **error_r)
 {
 	CURLcode code;
-	CURLMcode mcode;
 
 	c->easy = curl_easy_init();
 	if (c->easy == NULL) {
@@ -659,14 +1110,6 @@ input_curl_easy_init(struct input_curl *c, GError **error_r)
 		return false;
 	}
 
-	mcode = curl_multi_add_handle(c->multi, c->easy);
-	if (mcode != CURLM_OK) {
-		g_set_error(error_r, curl_quark(), mcode,
-			    "curl_multi_add_handle() failed: %s",
-			    curl_multi_strerror(mcode));
-		return false;
-	}
-
 	curl_easy_setopt(c->easy, CURLOPT_USERAGENT,
 			 "Music Player Daemon " VERSION);
 	curl_easy_setopt(c->easy, CURLOPT_HEADERFUNCTION,
@@ -712,26 +1155,6 @@ input_curl_easy_init(struct input_curl *c, GError **error_r)
 }
 
 static bool
-input_curl_send_request(struct input_curl *c, GError **error_r)
-{
-	CURLMcode mcode;
-	int running_handles;
-
-	do {
-		mcode = curl_multi_perform(c->multi, &running_handles);
-	} while (mcode == CURLM_CALL_MULTI_PERFORM);
-
-	if (mcode != CURLM_OK) {
-		g_set_error(error_r, curl_quark(), mcode,
-			    "curl_multi_perform() failed: %s",
-			    curl_multi_strerror(mcode));
-		return false;
-	}
-
-	return true;
-}
-
-static bool
 input_curl_seek(struct input_stream *is, goffset offset, int whence,
 		GError **error_r)
 {
@@ -796,7 +1219,7 @@ input_curl_seek(struct input_stream *is, goffset offset, int whence,
 
 	/* close the old connection and open a new one */
 
-	input_curl_easy_free(c);
+	input_curl_easy_free_indirect(c);
 	input_curl_flush_buffers(c);
 
 	is->offset = offset;
@@ -818,18 +1241,34 @@ input_curl_seek(struct input_stream *is, goffset offset, int whence,
 		curl_easy_setopt(c->easy, CURLOPT_RANGE, c->range);
 	}
 
-	ret = input_curl_send_request(c, error_r);
-	if (!ret)
+	g_static_mutex_lock(&curl.mutex);
+
+	c->base.ready = false;
+
+	if (!input_curl_easy_add(c, error_r)) {
+		g_static_mutex_unlock(&curl.mutex);
 		return false;
+	}
+
+	while (!c->base.ready)
+		g_cond_wait(curl.cond, g_static_mutex_get_mutex(&curl.mutex));
 
-	return input_curl_multi_info_read(c, error_r);
+	if (c->postponed_error != NULL) {
+		g_propagate_error(error_r, c->postponed_error);
+		c->postponed_error = NULL;
+		g_static_mutex_unlock(&curl.mutex);
+		return false;
+	}
+
+	g_static_mutex_unlock(&curl.mutex);
+
+	return true;
 }
 
 static struct input_stream *
 input_curl_open(const char *url, GError **error_r)
 {
 	struct input_curl *c;
-	bool ret;
 
 	if (strncmp(url, "http://", 7) != 0)
 		return NULL;
@@ -840,35 +1279,27 @@ input_curl_open(const char *url, GError **error_r)
 	c->url = g_strdup(url);
 	c->buffers = g_queue_new();
 
-	c->multi = curl_multi_init();
-	if (c->multi == NULL) {
-		g_set_error(error_r, curl_quark(), 0,
-			    "curl_multi_init() failed");
-		input_curl_free(c);
-		return NULL;
-	}
-
 	icy_clear(&c->icy_metadata);
 	c->tag = NULL;
 
-	ret = input_curl_easy_init(c, error_r);
-	if (!ret) {
-		input_curl_free(c);
-		return NULL;
-	}
+#if LIBCURL_VERSION_NUM >= 0x071200
+	c->paused = false;
+#endif
 
-	ret = input_curl_send_request(c, error_r);
-	if (!ret) {
+	if (!input_curl_easy_init(c, error_r)) {
 		input_curl_free(c);
 		return NULL;
 	}
 
-	ret = input_curl_multi_info_read(c, error_r);
-	if (!ret) {
+	g_static_mutex_lock(&curl.mutex);
+	if (!input_curl_easy_add(c, error_r)) {
+		g_static_mutex_unlock(&curl.mutex);
 		input_curl_free(c);
 		return NULL;
 	}
 
+	g_static_mutex_unlock(&curl.mutex);
+
 	return &c->base;
 }