http: limit the initial send amount to used upload buffer size

Previously this logic would cap the send to CURL_MAX_WRITE_SIZE bytes,
but for the situations where a larger upload buffer has been set, this
function can benefit from sending more bytes. With default size used,
this does the same as before.

Also changed the storage of the size to an 'unsigned int' as it is not
allowed to be set larger than 2M.

Also added cautions to the man pages about changing buffer sizes in
run-time.

Closes #7022

docs/libcurl/opts/CURLOPT_BUFFERSIZE.3

@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 1998 - 2017, 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
 .\" *
 .\" * This software is licensed as described in the file COPYING, which
 .\" * you should have received as part of this distribution. The terms
@@ -39,6 +39,9 @@ actually get the given size.
 This buffer size is by default \fICURL_MAX_WRITE_SIZE\fP (16kB). The maximum
 buffer size allowed to be set is \fICURL_MAX_READ_SIZE\fP (512kB). The minimum
 buffer size allowed to be set is 1024.
+
+DO NOT set this option on a handle that is currently used for an active
+transfer as that may lead to unintended consequences.
 .SH DEFAULT
 CURL_MAX_WRITE_SIZE (16kB)
 .SH PROTOCOLS

docs/libcurl/opts/CURLOPT_UPLOAD_BUFFERSIZE.3

@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 1998 - 2018, 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
 .\" *
 .\" * This software is licensed as described in the file COPYING, which
 .\" * you should have received as part of this distribution. The terms
@@ -43,6 +43,9 @@ allowed to be set is 2 megabytes. The minimum buffer size allowed to be set is
 
 Since curl 7.61.1 the upload buffer is allocated on-demand - so if the handle
 isn't used for upload, this buffer will not be allocated at all.
+
+DO NOT set this option on a handle that is currently used for an active
+transfer as that may lead to unintended consequences.
 .SH DEFAULT
 64 kB
 .SH PROTOCOLS

lib/http.c

@@ -1273,14 +1273,6 @@ CURLcode Curl_buffer_send(struct dynbuf *in,
     else
       sendsize = size;
 
-    /* We never send more than CURL_MAX_WRITE_SIZE bytes in one single chunk
-       when we speak HTTPS, as if only a fraction of it is sent now, this data
-       needs to fit into the normal read-callback buffer later on and that
-       buffer is using this size.
-    */
-    if(sendsize > CURL_MAX_WRITE_SIZE)
-      sendsize = CURL_MAX_WRITE_SIZE;
-
     /* OpenSSL is very picky and we must send the SAME buffer pointer to the
        library when we attempt to re-send this buffer. Sending the same data
        is not enough, we must use the exact same address. For this reason, we
@@ -1293,6 +1285,14 @@ CURLcode Curl_buffer_send(struct dynbuf *in,
       Curl_dyn_free(in);
       return result;
     }
+    /* We never send more than upload_buffer_size bytes in one single chunk
+       when we speak HTTPS, as if only a fraction of it is sent now, this data
+       needs to fit into the normal read-callback buffer later on and that
+       buffer is using this size.
+    */
+    if(sendsize > (size_t)data->set.upload_buffer_size)
+      sendsize = (size_t)data->set.upload_buffer_size;
+
     memcpy(data->state.ulbuf, ptr, sendsize);
     ptr = data->state.ulbuf;
   }

lib/setopt.c

@@ -2198,7 +2198,7 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option, va_list param)
     else if(arg < UPLOADBUFFER_MIN)
       arg = UPLOADBUFFER_MIN;
 
-    data->set.upload_buffer_size = arg;
+    data->set.upload_buffer_size = (unsigned int)arg;
     Curl_safefree(data->state.ulbuf); /* force a realloc next opportunity */
     break;
 

lib/smb.c

@@ -627,9 +627,8 @@ static CURLcode smb_send_and_recv(struct Curl_easy *data, void **msg)
 
   /* Check if there is data in the transfer buffer */
   if(!smbc->send_size && smbc->upload_size) {
-    size_t nread = smbc->upload_size > data->set.upload_buffer_size ?
-      data->set.upload_buffer_size :
-      smbc->upload_size;
+    size_t nread = smbc->upload_size > (size_t)data->set.upload_buffer_size ?
+      (size_t)data->set.upload_buffer_size : smbc->upload_size;
     data->req.upload_fromhere = data->state.ulbuf;
     result = Curl_fillreadbuffer(data, nread, &nread);
     if(result && result != CURLE_AGAIN)

lib/smtp.c

@@ -1821,7 +1821,7 @@ CURLcode Curl_smtp_escape_eob(struct Curl_easy *data, const ssize_t nread)
       return CURLE_OUT_OF_MEMORY;
     }
   }
-  DEBUGASSERT(data->set.upload_buffer_size >= (size_t)nread);
+  DEBUGASSERT((size_t)data->set.upload_buffer_size >= (size_t)nread);
 
   /* Have we already sent part of the EOB? */
   eob_sent = smtp->eob;

lib/urldata.h

@@ -1722,8 +1722,8 @@ struct UserDefined {
   struct ssl_general_config general_ssl; /* general user defined SSL stuff */
   long dns_cache_timeout; /* DNS cache timeout */
   long buffer_size;      /* size of receive buffer to use */
-  size_t upload_buffer_size; /* size of upload buffer to use,
-                                keep it >= CURL_MAX_WRITE_SIZE */
+  unsigned int upload_buffer_size; /* size of upload buffer to use,
+                                      keep it >= CURL_MAX_WRITE_SIZE */
   void *private_data; /* application-private data */
   struct curl_slist *http200aliases; /* linked list of aliases for http200 */
   unsigned char ipver; /* the CURL_IPRESOLVE_* defines in the public header