examples/sftpuploadresume: resume upload via CURLOPT_APPEND

URL: https://curl.haxx.se/mail/lib-2018-02/0072.html

docs/examples/Makefile.inc

@@ -5,7 +5,7 @@
 #                            | (__| |_| |  _ <| |___
 #                             \___|\___/|_| \_\_____|
 #
-# Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
+# Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
 #
 # This software is licensed as described in the file COPYING, which
 # you should have received as part of this distribution. The terms
@@ -34,7 +34,7 @@ check_PROGRAMS = 10-at-a-time anyauthput cookie_interface debug fileupload \
   imap-tls imap-multi url2file sftpget ftpsget postinmemory http2-download \
   http2-upload http2-serverpush getredirect ftpuploadfrommem               \
   ftpuploadresume sslbackend postit2-formadd multi-formadd                 \
-  shared-connection-cache
+  shared-connection-cache sftpuploadresume
 
 # These examples require external dependencies that may not be commonly
 # available on POSIX systems, so don't bother attempting to compile them here.

docs/examples/sftpuploadresume.c

@@ -0,0 +1,130 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+/* <DESC>
+ * Upload to SFTP, resuming a previously aborted transfer.
+ * </DESC>
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <curl/curl.h>
+
+/* read data to upload */
+static size_t readfunc(void *ptr, size_t size, size_t nmemb, void *stream)
+{
+  FILE *f = (FILE *)stream;
+  size_t n;
+
+  if(ferror(f))
+    return CURL_READFUNC_ABORT;
+
+  n = fread(ptr, size, nmemb, f) * size;
+
+  return n;
+}
+
+/*
+ * sftpGetRemoteFileSize returns the remote file size in byte; -1 on error
+ */
+static curl_off_t sftpGetRemoteFileSize(const char *i_remoteFile)
+{
+  CURLcode result = CURLE_GOT_NOTHING;
+  curl_off_t remoteFileSizeByte = -1;
+  CURL *curlHandlePtr = NULL;
+
+  curlHandlePtr = curl_easy_init();
+  curl_easy_setopt(curlHandlePtr, CURLOPT_VERBOSE, 1L);
+
+  curl_easy_setopt(curlHandlePtr, CURLOPT_URL, i_remoteFile);
+  curl_easy_setopt(curlHandlePtr, CURLOPT_NOPROGRESS, 1);
+  curl_easy_setopt(curlHandlePtr, CURLOPT_NOBODY, 1);
+  curl_easy_setopt(curlHandlePtr, CURLOPT_HEADER, 1);
+  curl_easy_setopt(curlHandlePtr, CURLOPT_FILETIME, 1);
+
+  result = curl_easy_perform(curlHandlePtr);
+  if(CURLE_OK == result) {
+    result = curl_easy_getinfo(curlHandlePtr,
+                               CURLINFO_CONTENT_LENGTH_DOWNLOAD_T,
+                               &remoteFileSizeByte);
+    printf("filesize: %ld \n", remoteFileSizeByte);
+  }
+  curl_easy_cleanup(curlHandlePtr);
+
+  return remoteFileSizeByte;
+}
+
+
+static int sftpResumeUpload(CURL *curlhandle, const char *remotepath,
+                            const char *localpath)
+{
+  FILE *f = NULL;
+  CURLcode result = CURLE_GOT_NOTHING;
+
+  curl_off_t remoteFileSizeByte = sftpGetRemoteFileSize(remotepath);
+  if(-1 == remoteFileSizeByte) {
+    printf("Error reading the remote file size: unable to resume upload\n");
+    return -1;
+  }
+
+  f = fopen(localpath, "rb");
+  if(!f) {
+    perror(NULL);
+    return 0;
+  }
+
+  curl_easy_setopt(curlhandle, CURLOPT_UPLOAD, 1L);
+  curl_easy_setopt(curlhandle, CURLOPT_URL, remotepath);
+  curl_easy_setopt(curlhandle, CURLOPT_READFUNCTION, readfunc);
+  curl_easy_setopt(curlhandle, CURLOPT_READDATA, f);
+
+  fseek(f, remoteFileSizeByte, SEEK_SET);
+  curl_easy_setopt(curlhandle, CURLOPT_APPEND, 1L);
+  result = curl_easy_perform(curlhandle);
+
+  fclose(f);
+
+  if(result == CURLE_OK)
+    return 1;
+  else {
+    fprintf(stderr, "%s\n", curl_easy_strerror(result));
+    return 0;
+  }
+}
+
+int main(void)
+{
+  const char *remote = "sftp://user:pass@example.com/path/filename";
+  const char *filename = "filename";
+  CURL *curlhandle = NULL;
+
+  curl_global_init(CURL_GLOBAL_ALL);
+  curlhandle = curl_easy_init();
+
+  if(!sftpResumeUpload(curlhandle, remote, filename)) {
+    printf("resumed upload using curl %s failed\n", curl_version());
+  }
+
+  curl_easy_cleanup(curlhandle);
+  curl_global_cleanup();
+
+  return 0;
+}