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, 4 insertions, 8 deletions

diff --git a/lib/formdata.c b/lib/formdata.c
index 50a37e0e7..57ec6ad25 100644
--- a/lib/formdata.c
+++ b/lib/formdata.c
@@ -728,14 +728,10 @@ int curl_formget(struct curl_httppost *form, void *arg,
     if(!nread)
       break;
 
-    switch(nread) {
-    default:
-      if(append(arg, buffer, nread) != nread)
-        result = CURLE_READ_ERROR;
-      break;
-    case CURL_READFUNC_ABORT:
-    case CURL_READFUNC_PAUSE:
-      break;
+    if(nread > sizeof(buffer) || append(arg, buffer, nread) != nread) {
+      result = CURLE_READ_ERROR;
+      if(nread == CURL_READFUNC_ABORT)
+        result = CURLE_ABORTED_BY_CALLBACK;
     }
   }