From: =?utf-8?b?0L3QsNCx?= <nabijaczleweli@nabijaczleweli.xyz>
Date: Fri, 22 Aug 2025 00:55:56 +0200
Subject: Replace substdio and the resulting read(512)/write(512) loop with
 voreutils-derived splice/c_f_r/sendfile/[read(64k)/fwrite()] decay chain

---
 byte.h          |  9 --------
 meson.build     |  4 ----
 safecat.c       | 11 +++++++--
 stralloc_cat.c  |  1 -
 stralloc_catb.c |  4 ++--
 stralloc_copy.c |  1 -
 stralloc_opyb.c |  4 ++--
 substdi.c       | 30 ------------------------
 substdio.c      | 10 --------
 substdio.h      | 32 --------------------------
 substdio_copy.c | 16 -------------
 substdo.c       | 71 ---------------------------------------------------------
 writefile.c     | 59 +++++++++++++++++++++++++++++++----------------
 writefile.h     |  4 +++-
 14 files changed, 55 insertions(+), 201 deletions(-)
 delete mode 100644 byte.h
 delete mode 100644 substdi.c
 delete mode 100644 substdio.c
 delete mode 100644 substdio.h
 delete mode 100644 substdio_copy.c
 delete mode 100644 substdo.c

diff --git a/byte.h b/byte.h
deleted file mode 100644
index 8df08fa..0000000
--- a/byte.h
+++ /dev/null
@@ -1,9 +0,0 @@
-#ifndef BYTE_H
-#define BYTE_H
-
-#include <string.h>
-
-#define byte_copy(to, n, from) memcpy(to, from, n)
-#define byte_copyr(to, n, from) memmove(to, from, n)
-
-#endif
diff --git a/meson.build b/meson.build
index 91affc7..f5e9b04 100644
--- a/meson.build
+++ b/meson.build
@@ -14,10 +14,6 @@ executable('safecat',
 	'stralloc_pend.c',
 	'strerr_die.c',
 	'strerr_sys.c',
-	'substdi.c',
-	'substdio.c',
-	'substdo.c',
-	'substdio_copy.c',
 	'tempfile.c',
 	'writefile.c',
 	install: true)
diff --git a/safecat.c b/safecat.c
index 30e0a07..d0e15f9 100644
--- a/safecat.c
+++ b/safecat.c
@@ -39,6 +39,7 @@ int main(int argc, char *argv[]) {
   char *tempdir  = NULL;
   char *destdir  = NULL;
   int   outfd    = 0;
+  FILE *outfdf   = NULL;
   stralloc dstpath = {0};
   stralloc outfile = {0};
   stralloc outpath = {0};
@@ -98,11 +99,17 @@ int main(int argc, char *argv[]) {
     strerr_die_sys(111,"safecat: fatal: ","couldn't create output file: ");
   }
 
+  outfdf = fdopen(outfd, "w");
+  if (!outfdf) {
+    unlink(tmppath.s);
+    strerr_die_sys(111,"safecat: fatal: ","can't fdopen output file: ");
+  }
+
   /* Step 5:  Copy stdin to the temp file. */
-  writefile(outfd);
+  writefile(outfdf);
 
   /* Close the file, checking the return value. */
-  if(fsync(outfd) == -1 || close(outfd) == -1) {
+  if(fsync(outfd) == -1 || fclose(outfdf) == -1) {
     unlink(tmppath.s);
     strerr_die_sys(111,"safecat: fatal: ","can't fsync/close output file: ");
   }
diff --git a/stralloc_cat.c b/stralloc_cat.c
index ca95b9b..8891562 100644
--- a/stralloc_cat.c
+++ b/stralloc_cat.c
@@ -1,4 +1,3 @@
-#include "byte.h"
 #include "stralloc.h"
 
 int stralloc_cat(stralloc *sato, stralloc *safrom)
diff --git a/stralloc_catb.c b/stralloc_catb.c
index d9161d4..69b0839 100644
--- a/stralloc_catb.c
+++ b/stralloc_catb.c
@@ -1,11 +1,11 @@
 #include "stralloc.h"
-#include "byte.h"
+#include <string.h>
 
 int stralloc_catb(stralloc *sa, char *s, unsigned int n)
 {
   if (!sa->s) return stralloc_copyb(sa,s,n);
   if (!stralloc_readyplus(sa,n + 1)) return 0;
-  byte_copy(sa->s + sa->len,n,s);
+  memcpy(sa->s + sa->len,s,n);
   sa->len += n;
   sa->s[sa->len] = 'Z'; /* ``offensive programming'' */
   return 1;
diff --git a/stralloc_copy.c b/stralloc_copy.c
index f5d6200..dd3e16e 100644
--- a/stralloc_copy.c
+++ b/stralloc_copy.c
@@ -1,4 +1,3 @@
-#include "byte.h"
 #include "stralloc.h"
 
 int stralloc_copy(stralloc *sato, stralloc *safrom)
diff --git a/stralloc_opyb.c b/stralloc_opyb.c
index 04bf72e..6f9d687 100644
--- a/stralloc_opyb.c
+++ b/stralloc_opyb.c
@@ -1,10 +1,10 @@
 #include "stralloc.h"
-#include "byte.h"
+#include <string.h>
 
 int stralloc_copyb(stralloc *sa, char *s, unsigned int n)
 {
   if (!stralloc_ready(sa,n + 1)) return 0;
-  byte_copy(sa->s,n,s);
+  memcpy(sa->s,s,n);
   sa->len = n;
   sa->s[n] = 'Z'; /* ``offensive programming'' */
   return 1;
diff --git a/substdi.c b/substdi.c
deleted file mode 100644
index 23892af..0000000
--- a/substdi.c
+++ /dev/null
@@ -1,30 +0,0 @@
-#include "substdio.h"
-#include "byte.h"
-#include <errno.h>
-
-static int oneread(int (*op)(int fd, char *buf, int len), int fd, char *buf, int len)
-{
-  register int r;
-
-  for (;;) {
-    r = op(fd,buf,len);
-    if (r == -1) if (errno == EINTR) continue;
-    return r;
-  }
-}
-
-int substdio_feed(substdio *s)
-{
-  register int r;
-  register int q;
-
-  if (s->p) return s->p;
-  q = s->n;
-  r = oneread(s->op,s->fd,s->x,q);
-  if (r <= 0) return r;
-  s->p = r;
-  q -= r;
-  s->n = q;
-  if (q > 0) /* damn, gotta shift */ byte_copyr(s->x + q,r,s->x);
-  return r;
-}
diff --git a/substdio.c b/substdio.c
deleted file mode 100644
index a6160f3..0000000
--- a/substdio.c
+++ /dev/null
@@ -1,10 +0,0 @@
-#include "substdio.h"
-
-void substdio_fdbuf(substdio *s, int (*op)(), int fd, char *buf, int len)
-{
-  s->x = buf;
-  s->fd = fd;
-  s->op = op;
-  s->p = 0;
-  s->n = len;
-}
diff --git a/substdio.h b/substdio.h
deleted file mode 100644
index 0fdf4db..0000000
--- a/substdio.h
+++ /dev/null
@@ -1,32 +0,0 @@
-#ifndef SUBSTDIO_H
-#define SUBSTDIO_H
-
-typedef struct substdio {
-  char *x;
-  int p;
-  int n;
-  int fd;
-  int (*op)(int fd, char *buf, int len);
-} substdio;
-
-#define SUBSTDIO_FDBUF(op,fd,buf,len) { (buf), 0, (len), (fd), (op) }
-
-extern void substdio_fdbuf(substdio *s, int (*op)(int fd, char *buf, int len), int fd, char *buf, int len);
-
-extern int substdio_flush(substdio *s);
-extern int substdio_put(substdio *s, char *buf, int len);
-extern int substdio_bput(substdio *s, char *buf, int len);
-extern int substdio_puts(substdio *s, char *buf);
-
-extern int substdio_feed(substdio *s);
-
-#define substdio_fileno(s) ((s)->fd)
-
-#define SUBSTDIO_OUTSIZE 8192
-
-#define substdio_PEEK(s) ( (s)->x + (s)->n )
-#define substdio_SEEK(s,len) ( ( (s)->p -= (len) ) , ( (s)->n += (len) ) )
-
-extern int substdio_copy(substdio *ssout, substdio *ssin);
-
-#endif
diff --git a/substdio_copy.c b/substdio_copy.c
deleted file mode 100644
index 5bbfd3f..0000000
--- a/substdio_copy.c
+++ /dev/null
@@ -1,16 +0,0 @@
-#include "substdio.h"
-
-int substdio_copy(substdio *ssout, substdio *ssin)
-{
-  register int n;
-  register char *x;
-
-  for (;;) {
-    n = substdio_feed(ssin);
-    if (n < 0) return -2;
-    if (!n) return 0;
-    x = substdio_PEEK(ssin);
-    if (substdio_put(ssout,x,n) == -1) return -3;
-    substdio_SEEK(ssin,n);
-  }
-}
diff --git a/substdo.c b/substdo.c
deleted file mode 100644
index cd75e28..0000000
--- a/substdo.c
+++ /dev/null
@@ -1,71 +0,0 @@
-#include "substdio.h"
-#include "byte.h"
-#include <string.h>
-#include <errno.h>
-
-static int allwrite(int (*op)(int fd, char *buf, int len), int fd, char *buf, int len)
-{
-  register int w;
-
-  while (len) {
-    w = op(fd,buf,len);
-    if (w == -1) {
-      if (errno == EINTR) continue;
-      return -1; /* note that some data may have been written */
-    }
-    buf += w;
-    len -= w;
-  }
-  return 0;
-}
-
-int substdio_flush(substdio *s)
-{
-  register int p;
-
-  p = s->p;
-  if (!p) return 0;
-  s->p = 0;
-  return allwrite(s->op,s->fd,s->x,p);
-}
-
-int substdio_bput(substdio *s, char *buf, int len)
-{
-  register int n;
-
-  while (len > (n = s->n - s->p)) {
-    byte_copy(s->x + s->p,n,buf); s->p += n; buf += n; len -= n;
-    if (substdio_flush(s) == -1) return -1;
-  }
-  /* now len <= s->n - s->p */
-  byte_copy(s->x + s->p,len,buf);
-  s->p += len;
-  return 0;
-}
-
-int substdio_put(substdio *s, char *buf, int len)
-{
-  register int n;
-
-  n = s->n;
-  if (len > n - s->p) {
-    if (substdio_flush(s) == -1) return -1;
-    /* now s->p == 0 */
-    if (n < SUBSTDIO_OUTSIZE) n = SUBSTDIO_OUTSIZE;
-    while (len > s->n) {
-      if (n > len) n = len;
-      if (allwrite(s->op,s->fd,buf,n) == -1) return -1;
-      buf += n;
-      len -= n;
-    }
-  }
-  /* now len <= s->n - s->p */
-  byte_copy(s->x + s->p,len,buf);
-  s->p += len;
-  return 0;
-}
-
-int substdio_puts(substdio *s, char *buf)
-{
-  return substdio_put(s,buf,strlen(buf));
-}
diff --git a/writefile.c b/writefile.c
index 5ca8a37..02414b9 100644
--- a/writefile.c
+++ b/writefile.c
@@ -1,36 +1,55 @@
+/* Copyright (c) 2025, наб <nabijaczlweli@nabijaczlweli.xyz> */
 /* Copyright (c) 2017, Adrian Perez de Castro <aperez@igalia.com> */
 /* Copyright (c) 2000, Len Budney. See COPYING for details. */
+#if __linux__
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <sys/sendfile.h>
+#endif
 #include "stralloc.h"
 #include "strerr.h"
-#include "substdio.h"
 #include "writefile.h"
 #include <errno.h>
 #include <unistd.h>
 
 extern stralloc tmppath;
 
-static int false_read(int fd, char *buf, int len) {
-  return read(fd, buf, len);
-}
-
-static int false_write(int fd, char *buf, int len) {
-  return write(fd, buf, len);
-}
-
 /* ****************************************************************** */
-void writefile(int fd) {
-  char inbuf[512];
-  char outbuf[512];
-  substdio ssin;
-  substdio ssout;
-
-  /* Prepare substdio buffers for reading and writing. */
-  substdio_fdbuf(&ssin,false_read,0,inbuf,sizeof(inbuf));
-  substdio_fdbuf(&ssout,false_write,fd,outbuf,sizeof(outbuf));
+void writefile(FILE * fd) {
+  ssize_t rd;
+#if __linux__ // derived from voreutils cat
+  // We use the special state of knowing that fd was /just/ fdopen()ed and isn't dirty.
+  // All errors are better-served when detected by the read()/fwrite() loop below
+  while((rd = splice(0, NULL, fileno(fd), NULL, 128 * 1024 * 1024, SPLICE_F_MOVE | SPLICE_F_MORE)) > 0)
+    ;
+  if(rd != -1)
+    return;
+
+  while((rd = copy_file_range(0, NULL, fileno(fd), NULL, 128 * 1024 * 1024, 0)) > 0)
+    ;
+  if(rd != -1)
+    return;
+
+  while((rd = sendfile(fileno(fd), 0, NULL, 128 * 1024 * 1024)) > 0)
+    ;
+  if(rd != -1)
+    return;
+#endif
 
   /* Copy stdin to the output file, watching the return values each time. */
-  if (substdio_copy(&ssout,&ssin) < 0) goto fail;
-  if (substdio_flush(&ssout) == -1) goto fail;
+  for(char buf[64 * 1024];;) {
+    while((rd = read(0, buf, sizeof(buf))) == -1 && errno == EINTR)
+      ;
+    if(rd == -1)
+      goto fail;
+    if(!rd)
+      break;
+
+    if(fwrite(buf, 1, rd, fd) != rd)
+      goto fail;
+  }
+  if(fflush(fd))
+    goto fail;
 
   /* The file is copied. */
   return;
diff --git a/writefile.h b/writefile.h
index 2dd5218..4c471c2 100644
--- a/writefile.h
+++ b/writefile.h
@@ -1,4 +1,6 @@
 /* Copyright (c) 2000, Len Budney. See COPYING for details. */
 
+#include <stdio.h>
+
 /* Copy stdin to the given file descriptor, treating all failures as fatal. */
-void writefile(int fd);
+void writefile(FILE * fd);