CURLOPT_BUFFERSIZE: 1024 bytes is now the minimum size

The buffer is needed to receive FTP, HTTP CONNECT responses etc so
already at this size things risk breaking and smaller is certainly not
wise.

lib/url.c

@@ -2284,15 +2284,17 @@ CURLcode Curl_setopt(struct Curl_easy *data, CURLoption option,
      * The application kindly asks for a differently sized receive buffer.
      * If it seems reasonable, we'll use it.
      */
-    data->set.buffer_size = va_arg(param, long);
+    arg = va_arg(param, long);
 
-    if(data->set.buffer_size > MAX_BUFSIZE)
-      data->set.buffer_size = MAX_BUFSIZE; /* huge internal default */
-    else if(data->set.buffer_size < 1)
-      data->set.buffer_size = BUFSIZE;
+    if(arg > MAX_BUFSIZE)
+      arg = MAX_BUFSIZE; /* huge internal default */
+    else if(arg < 1)
+      arg = BUFSIZE;
+    else if(arg < MIN_BUFSIZE)
+      arg = BUFSIZE;
 
     /* Resize only if larger than default buffer size. */
-    if(data->set.buffer_size > BUFSIZE) {
+    if(arg > BUFSIZE) {
       char *newbuff = realloc(data->state.buffer, data->set.buffer_size + 1);
       if(!newbuff) {
         DEBUGF(fprintf(stderr, "Error: realloc of buffer failed\n"));
@@ -2301,6 +2303,7 @@ CURLcode Curl_setopt(struct Curl_easy *data, CURLoption option,
       else
         data->state.buffer = newbuff;
     }
+    data->set.buffer_size = arg;
 
     break;
 

lib/urldata.h

@@ -205,6 +205,7 @@
 #define BUFSIZE CURL_MAX_WRITE_SIZE
 #undef MAX_BUFSIZE
 #define MAX_BUFSIZE CURL_MAX_READ_SIZE
+#define MIN_BUFSIZE 1024
 #define CURL_BUFSIZE(x) ((x)?(x):(BUFSIZE))
 
 /* Initial size of the buffer to store headers in, it'll be enlarged in case