From 0a23d1655f2bf14f55b8e7bc785e7fb2e0d5d5a4 Mon Sep 17 00:00:00 2001
From: Leon Timmermans <fawaka@gmail.com>
Date: Thu, 28 Dec 2017 15:09:11 +0100
Subject: [PATCH] WIP

---
 sv.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/sv.c b/sv.c
index 1fc1dda96d5a..b45421c73646 100644
--- a/sv.c
+++ b/sv.c
@@ -8432,6 +8432,8 @@ in the SV (typically, C<SvCUR(sv)> is a suitable choice).
 =cut
 */
 
+#define DEFAULT_BUFFER_SIZE 8192
+
 char *
 Perl_sv_gets(pTHX_ SV *const sv, PerlIO *const fp, I32 append)
 {
@@ -8444,8 +8446,10 @@ Perl_sv_gets(pTHX_ SV *const sv, PerlIO *const fp, I32 append)
 #ifdef USE_HEAP_INSTEAD_OF_STACK	/* Slower way. */
     STDCHAR *buf = NULL;
 #else
-    STDCHAR buf[8192];
+    STDCHAR buf[DEFAULT_BUFFER_SIZE];
 #endif
+    char *bufptr = NULL;
+    size_t bufsize = 0;
 
 
     PERL_ARGS_ASSERT_SV_GETS;
@@ -8499,10 +8503,13 @@ Perl_sv_gets(pTHX_ SV *const sv, PerlIO *const fp, I32 append)
 #ifdef PERL_COPY_ON_WRITE
                 /* Add an extra byte for the sake of copy-on-write's
                  * buffer reference count. */
-		(void) SvGROW(sv, (STRLEN)((st.st_size - offset) + append + 2));
+		STRLEN length = (st.st_size - offset) + append + 2;
 #else
-		(void) SvGROW(sv, (STRLEN)((st.st_size - offset) + append + 1));
+		STRLEN length = (st.st_size - offset) + append + 1;
 #endif
+		(void) SvGROW(sv, length);
+                bufptr = SvPVX(sv);
+                bufsize = length;
 	    }
 	}
 	rsptr = NULL;
@@ -8553,30 +8560,34 @@ Perl_sv_gets(pTHX_ SV *const sv, PerlIO *const fp, I32 append)
     }
 
 #ifdef USE_HEAP_INSTEAD_OF_STACK	/* Slower way. */
-    Newx(buf, 8192, STDCHAR);
+    Newx(buf, DEFAULT_BUFFER_SIZE, STDCHAR);
     assert(buf);
 #endif
+    if (bufptr == NULL) {
+        bufptr = (char*)buf;
+        bufsize = DEFAULT_BUFFER_SIZE;
+    }
 
   screamer:
     if (rslen)
-        cnt = PerlIO_readdelim(fp, buf, sizeof(buf), rslast);
+        cnt = PerlIO_readdelim(fp, bufptr, bufsize, rslast);
     else
-	    cnt = PerlIO_read(fp,(char*)buf, sizeof(buf));
+        cnt = PerlIO_read(fp, bufptr, bufsize);
 
 	    /* Accommodate broken VAXC compiler, which applies U8 cast to
 	     * both args of ?: operator, causing EOF to change into 255
 	     */
 	    if (cnt > 0)
-		 i = (U8)buf[cnt - 1];
+         i = (U8)bufptr[cnt - 1];
 	    else
 		 i = EOF;
 
 	if (cnt < 0)
 	    cnt = 0;  /* we do need to re-set the sv even when cnt <= 0 */
 	if (append)
-            sv_catpvn_nomg(sv, (char *) buf, cnt);
+        sv_catpvn_nomg(sv, (char *) bufptr, cnt);
 	else
-            sv_setpvn(sv, (char *) buf, cnt);   /* "nomg" is implied */
+        sv_setpvn(sv, (char *) bufptr, cnt);   /* "nomg" is implied */
 
     if (cnt > 0 &&			/* joy */
 	    (!rslen ||
@@ -8595,7 +8606,7 @@ Perl_sv_gets(pTHX_ SV *const sv, PerlIO *const fp, I32 append)
 	     *
 	     * - jik 9/25/96
 	     */
-	    if (!(cnt < (I32)sizeof(buf) && PerlIO_eof(fp)))
+        if (!(cnt < (I32)bufsize && PerlIO_eof(fp)))
             goto screamer;
 	}