mime: latch last read callback status.

In case a read callback returns a status (pause, abort, eof,
error) instead of a byte count, drain the bytes read so far but
remember this status for further processing.
Takes care of not losing data when pausing, and properly resume a
paused mime structure when requested.
New tests 670-673 check unpausing cases, with easy or multi
interface and mime or form api.

Fixes #4813
Reported-by: MrdUkk on github

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/easy.c b/lib/easy.c
index d3a29f48b..b648e80c1 100644
--- a/lib/easy.c
+++ b/lib/easy.c
@@ -1003,6 +1003,14 @@ CURLcode curl_easy_pause(struct Curl_easy *data, int action)
     return CURLE_OK;
   }
 
+  /* Unpause parts in active mime tree. */
+  if((k->keepon & ~newstate & KEEP_SEND_PAUSE) &&
+     (data->mstate == CURLM_STATE_PERFORM ||
+      data->mstate == CURLM_STATE_TOOFAST) &&
+     data->state.fread_func == (curl_read_callback) Curl_mime_read) {
+    Curl_mime_unpause(data->state.in);
+  }
+
   /* put it back in the keepon */
   k->keepon = newstate;