curl:file2string: load large files much faster

... by using a more efficient realloc scheme.

Bug: https://curl.haxx.se/mail/lib-2019-09/0045.html

1 files changed, 22 insertions, 6 deletions

diff --git a/src/tool_paramhlp.c b/src/tool_paramhlp.c
index c9dac4f0f..9b6a0b1a9 100644
--- a/src/tool_paramhlp.c
+++ b/src/tool_paramhlp.c
@@ -59,7 +59,11 @@ struct getout *new_getout(struct OperationConfig *config)
 ParameterError file2string(char **bufp, FILE *file)
 {
   char *ptr;
-  char *string = NULL;
+  size_t alloc = 512;
+  size_t alloc_needed;
+  char *string = malloc(alloc);
+  if(!string)
+    return PARAM_NO_MEM;
 
   if(file) {
     char buffer[256];
@@ -73,12 +77,24 @@ ParameterError file2string(char **bufp, FILE *file)
       if(ptr)
         *ptr = '\0';
       buflen = strlen(buffer);
-      ptr = realloc(string, stringlen + buflen + 1);
-      if(!ptr) {
-        Curl_safefree(string);
-        return PARAM_NO_MEM;
+      alloc_needed = stringlen + buflen + 1;
+      if(alloc < alloc_needed) {
+#if SIZEOF_SIZE_T < 8
+        if(alloc >= (size_t)SIZE_T_MAX/2) {
+          Curl_safefree(string);
+          return PARAM_NO_MEM;
+        }
+#endif
+        /* doubling is enough since the string to add is always max 256 bytes
+           and the alloc size start at 512 */
+        alloc *= 2;
+        ptr = realloc(string, alloc);
+        if(!ptr) {
+          Curl_safefree(string);
+          return PARAM_NO_MEM;
+        }
+        string = ptr;
       }
-      string = ptr;
       strcpy(string + stringlen, buffer);
       stringlen += buflen;
     }