RETR: use sendfile() to transmit files for improved performance and reduced memory footprint

Makefile.posix

@@ -21,6 +21,7 @@ VERSION_TAG := $(shell git describe --abbrev=6 --dirty --always --tags)
 CFLAGS := -Wall -Werror -DVERSION_TAG=\"$(VERSION_TAG)\" -I.
 SOURCE := srv.c cmd.c notify.c io.c self.c sha256.c
 SOURCE += posix/main.c posix/cmd.c posix/self.c
+SOURCE += io-linux.c
 
 all: $(ELF)
 

Makefile.ps4

@@ -30,6 +30,7 @@ VERSION_TAG := $(shell git describe --abbrev=6 --dirty --always --tags)
 CFLAGS := -Wall -Werror -DVERSION_TAG=\"$(VERSION_TAG)\" -I.
 SOURCE := srv.c cmd.c notify.c io.c self.c sha256.c
 SOURCE += orbis/main.c orbis/cmd.c orbis/self.c
+SOURCE += io-freebsd.c
 
 all: $(ELF)
 

Makefile.ps5

@@ -30,6 +30,7 @@ VERSION_TAG := $(shell git describe --abbrev=6 --dirty --always --tags)
 CFLAGS := -Wall -Werror -DVERSION_TAG=\"$(VERSION_TAG)\" -I.
 SOURCE := srv.c cmd.c notify.c io.c self.c sha256.c
 SOURCE += prospero/main.c prospero/cmd.c prospero/self.c
+SOURCE += io-freebsd.c
 
 all: $(ELF)
 

cmd.c

@@ -19,6 +19,7 @@ along with this program; see the file COPYING. If not, see
 #include <fcntl.h>
 #include <inttypes.h>
 #include <netinet/in.h>
+#include <netinet/tcp.h>
 #include <stdarg.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -518,9 +519,6 @@ ftp_cmd_RETR_fd(ftp_env_t *env, int fd) {
   if(fstat(fd, &st)) {
     return ftp_perror(env);
   }
-  if(lseek(fd, off, SEEK_SET) < 0) {
-    return ftp_perror(env);
-  }
 
   if(ftp_active_printf(env, "150 Starting data transfer\r\n")) {
     return -1;
@@ -530,16 +528,18 @@ ftp_cmd_RETR_fd(ftp_env_t *env, int fd) {
     return ftp_perror(env);
   }
 
-  if(io_ncopy(fd, env->data_fd, st.st_size - off)) {
-    err = ftp_perror(env);
-    ftp_data_close(env);
-    return err;
-  }
+  err = io_sendfile(fd, env->data_fd, off, st.st_size - off);
 
   if(ftp_data_close(env)) {
     return ftp_perror(env);
   }
 
+  if(err) {
+    return ftp_perror(env);
+  }
+
+  env->data_offset = 0;
+
   return ftp_active_printf(env, "226 Transfer completed\r\n");
 }
 

io-freebsd.c

@@ -0,0 +1,55 @@
+/* Copyright (C) 2026 John Törnblom
+
+This program is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation; either version 3, or (at your option) any
+later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; see the file COPYING. If not, see
+<http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+
+#include <sys/socket.h>
+#include <sys/errno.h>
+
+#include "io.h"
+
+
+int
+io_sendfile(int fd, int s, off_t offset, size_t n) {
+  off_t copied = 0;
+  off_t sbytes = 0;
+  size_t nbytes;
+
+  while (copied < n) {
+    nbytes = n - copied;
+    if(nbytes > IO_COPY_BUFSIZE) {
+      nbytes = IO_COPY_BUFSIZE;
+    }
+
+    if(sendfile(fd, s, offset, nbytes, 0, &sbytes, 0) < 0) {
+      if(errno == EINTR) {
+	continue;
+      }
+      return -1;
+    }
+
+    if(sbytes == 0) {
+      errno = EPIPE;
+      return -1;
+    }
+
+    copied += sbytes;
+    offset += sbytes;
+  }
+
+  return 0;
+}
+

io-linux.c

@@ -0,0 +1,53 @@
+/* Copyright (C) 2026 John Törnblom
+
+This program is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation; either version 3, or (at your option) any
+later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; see the file COPYING. If not, see
+<http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+
+#include <sys/sendfile.h>
+#include <sys/errno.h>
+
+#include "io.h"
+
+
+int
+io_sendfile(int in_fd, int out_fd, off_t offset, size_t n) {
+  off_t copied = 0;
+  size_t count;
+  ssize_t r;
+
+  while (copied < n) {
+    count = n - copied;
+    if(count > IO_COPY_BUFSIZE) {
+      count = IO_COPY_BUFSIZE;
+    }
+
+    if((r=sendfile(out_fd, in_fd, &offset, count)) < 0) {
+      if(errno == EINTR) {
+	continue;
+      }
+      return -1;
+    }
+    if(r == 0) {
+      errno = EPIPE;
+      return -1;
+    }
+
+    copied += r;
+  }
+
+  return 0;
+}
+

io.h

@@ -43,6 +43,12 @@ int io_nwrite(int fd, const void* buf, size_t n);
 int io_ncopy(int fd_in, int fd_out, size_t n);
 
 
+/**
+ * Copy exactly N bytes from a file descriptor to a socket.
+ **/
+int io_sendfile(int fd, int sock, off_t off, size_t n);
+
+
 /**
  * Read exactly N bytes from the given file descriptor without affecting its
  * position.