doc: Improved the tutorial.

doc/sftp.dox

@@ -25,6 +25,9 @@ that you can do with local files:
   - create symbolic links
   - get information about mounted filesystems.
 
+The current implemented version of the SFTP protocol is version 3. All functions
+aren't implemented yet, but the most important are.
+
 
 @subsection sftp_section Opening and closing a SFTP session
 
@@ -35,8 +38,7 @@ The function sftp_new() creates a new SFTP session. The function sftp_init()
 initializes it. The function sftp_free() deletes it.
 
 As you see, all the SFTP-related functions start with the "sftp_" prefix
-instead of the usual "ssh_" prefix. In case of a problem, you use
-sftp_get_error() instead of ssh_get_error() to get the English error message.
+instead of the usual "ssh_" prefix.
 
 The example below shows how to use these functions:
 
@@ -71,18 +73,323 @@ int sftp_helloworld(ssh_session session)
 @endcode
 
 
+@subsection sftp_errors Analyzing SFTP errors
+
+In case of a problem, the function sftp_get_error() returns a SFTP-specific
+error number, in addition to the regular SSH error number returned by
+ssh_get_error_number().
+
+Possible errors are:
+  - SSH_FX_OK: no error
+  - SSH_FX_EOF: end-of-file encountered
+  - SSH_FX_NO_SUCH_FILE: file does not exist
+  - SSH_FX_PERMISSION_DENIED: permission denied
+  - SSH_FX_FAILURE: generic failure
+  - SSH_FX_BAD_MESSAGE: garbage received from server
+  - SSH_FX_NO_CONNECTION: no connection has been set up
+  - SSH_FX_CONNECTION_LOST: there was a connection, but we lost it
+  - SSH_FX_OP_UNSUPPORTED: operation not supported by libssh yet
+  - SSH_FX_INVALID_HANDLE: invalid file handle
+  - SSH_FX_NO_SUCH_PATH: no such file or directory path exists
+  - SSH_FX_FILE_ALREADY_EXISTS: an attempt to create an already existing file or directory has been made
+  - SSH_FX_WRITE_PROTECT: write-protected filesystem
+  - SSH_FX_NO_MEDIA: no media was in remote drive
+
+
 @subsection sftp_mkdir Creating a directory
 
-*** To be written ***
+The function sftp_mkdir() tahes the "SFTP session" we juste created as
+its first argument. It also needs the name of the file to create, and the
+desired permissions. The permissions are the same as for the usual mkdir()
+function. To get a comprehensive list of the available permissions, use the
+"man 2 stat" command. The desired permissions are combined with the remote
+user's mask to determine the effective permissions.
+
+The code below creates a directory named "helloworld" in the current directory that
+can be read and written only by its owner:
+
+@code
+#include <libssh/sftp.h>
+#include <sys/stat.h>
+
+int sftp_helloworld(ssh_session session, sftp_session sftp)
+{
+  int rc;
+
+  rc = sftp_mkdir(sftp, "helloworld", S_IRWXU);
+  if (rc != SSH_OK)
+  {
+    if (sftp_get_error(sftp) != SSH_FX_FILE_ALREADY_EXISTS)
+    {
+      fprintf(stderr, "Can't create directory: %s\n", ssh_get_error(session));
+        return rc;
+    }
+  }
+
+  ...
+
+  return SSH_OK;
+}
+@endcode
+
+Unlike its equivalent in the SCP subsystem, this function does NOT change the
+current directory to the newly created subdirectory.
 
 
 @subsection sftp_write Copying a file to the remote computer
 
-*** To be written ***
+You handle the contents of a remote file just like you would do with a
+local file: you open the file in a given mode, move the file pointer in it,
+read or write data, and close the file.
+
+The sftp_open() function is very similar to the regular open() function,
+excepted that it returns a file handle of type sftp_file. This file handle
+is then used by the other file manipulation functions and remains valid
+until you close the remote file with sftp_close().
+
+The example below creates a new file named "helloworld.txt" in the
+newly created "helloworld" directory. If the file already exists, it will
+be truncated. It then writes the famous "Hello, World!" sentence to the
+file, followed by a new line character. Finally, the file is closed:
+
+@code
+#include <libssh/sftp.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+int sftp_helloworld(ssh_session session, sftp_session sftp)
+{
+  int access_type = O_WRONLY | O_CREAT | O_TRUNC;
+  sftp_file file;
+  const char *helloworld = "Hello, World!\n";
+  int length = strlen(helloworld);
+  int rc, nwritten;
+
+  ...
+
+  file = sftp_open(sftp, "helloworld/helloworld.txt", access_type, S_IRWXU);
+  if (file == NULL)
+  {
+    fprintf(stderr, "Can't open file for writing: %s\n", ssh_get_error(session));
+    return SSH_ERROR;
+  }
+
+  nwritten = sftp_write(file, helloworld, length);
+  if (nwritten != length)
+  {
+    fprintf(stderr, "Can't write data to file: %s\n", ssh_get_error(session));
+    sftp_close(file);
+    return SSH_ERROR;
+  }
+
+  rc = sftp_close(file);
+  if (rc != SSH_OK)
+  {
+    fprintf(stderr, "Can't close the written file: %s\n", ssh_get_error(session));
+    return rc;
+  }
+
+  return SSH_OK;
+}
+@endcode
 
 
 @subsection sftp_read Reading a file from the remote computer
 
-*** To be written ***
+The nice thing with reading a file over the network through SFTP is that it
+can be done both in a synchronous way or an asynchronous way. If you read the file
+asynchronously, your program can do something else while it waits for the
+results to come.
+
+Synchronous read is done with sftp_read().
+
+The following example prints the contents of remote file "/etc/profile". For
+each 1024 bytes of information read, it waits until the end of the read operation:
+
+@code
+int sftp_read_sync(ssh_session session, sftp_session sftp)
+{
+  int access_type;
+  sftp_file file;
+  char buffer[1024];
+  int nbytes, rc;
+
+  access_type = O_RDONLY;
+  file = sftp_open(sftp, "/etc/profile", access_type, 0);
+  if (file == NULL)
+  {
+    fprintf(stderr, "Can't open file for reading: %s\n", ssh_get_error(session));
+    return SSH_ERROR;
+  }
+
+  nbytes = sftp_read(file, buffer, sizeof(buffer));
+  while (nbytes > 0)
+  {
+    if (write(1, buffer, nbytes) != nbytes)
+    {
+      sftp_close(file);
+      return SSH_ERROR;
+    }
+    nbytes = sftp_read(file, buffer, sizeof(buffer));
+  }
+
+  if (nbytes < 0)
+  {
+    fprintf(stderr, "Error while reading file: %s\n", ssh_get_error(session));
+    sftp_close(file);
+    return SSH_ERROR;
+  }
+
+  rc = sftp_close(file);
+  if (rc != SSH_OK)
+  {
+    fprintf(stderr, "Can't close the read file: %s\n", ssh_get_error(session));
+    return rc;
+  }
+
+  return SSH_OK;
+}
+@endcode
+
+Asynchronous read is done in two steps, first sftp_async_read_begin(), which
+returns a "request handle", and then sftp_async_read(), which uses that request handle.
+If the file has been opened in nonblocking mode, then sftp_async_read()
+might return SSH_AGAIN, which means that the request hasn't completed yet
+and that the function should be called again later on. Otherwise,
+sftp_async_read() waits for the data to come. To open a file in nonblocking mode,
+call sftp_file_set_nonblocking() right after you opened it. Default is blocking mode.
+
+The example below reads a very big file in asynchronous, nonblocking, mode. Each
+time the data are not ready yet, a counter is incrementer.
+
+@code
+int sftp_read_async(ssh_session session, sftp_session sftp)
+{
+  int access_type;
+  sftp_file file;
+  char buffer[1024];
+  int async_request;
+  int nbytes;
+  long counter;
+  int rc;
+
+  access_type = O_RDONLY;
+  file = sftp_open(sftp, "some_very_big_file", access_type, 0);
+  if (file == NULL)
+  {
+    fprintf(stderr, "Can't open file for reading: %s\n", ssh_get_error(session));
+    return SSH_ERROR;
+  }
+  sftp_file_set_nonblocking(file);
+
+  async_request = sftp_async_read_begin(file, sizeof(buffer));
+  counter = 0L;
+  usleep(10000);
+  if (async_request >= 0)
+    nbytes = sftp_async_read(file, buffer, sizeof(buffer), async_request);
+  else nbytes = -1;
+  while (nbytes > 0 || nbytes == SSH_AGAIN)
+  {
+    if (nbytes > 0)
+    {
+      write(1, buffer, nbytes);
+      async_request = sftp_async_read_begin(file, sizeof(buffer));
+    }
+    else counter++;
+    usleep(10000);
+    if (async_request >= 0)
+      nbytes = sftp_async_read(file, buffer, sizeof(buffer), async_request);
+    else nbytes = -1;
+  }
+
+  if (nbytes < 0)
+  {
+    fprintf(stderr, "Error while reading file: %s\n", ssh_get_error(session));
+    sftp_close(file);
+    return SSH_ERROR;
+  }
+
+  printf("The counter has reached value: %ld\n", counter);
+
+  rc = sftp_close(file);
+  if (rc != SSH_OK)
+  {
+    fprintf(stderr, "Can't close the read file: %s\n", ssh_get_error(session));
+    return rc;
+  }
+
+  return SSH_OK;
+}
+@endcode
+
+@subsection sftp_ls Listing the contents of a directory
+
+The functions sftp_opendir(), sftp_readdir(), sftp_dir_eof(),
+and sftp_closedir() enable to list the contents of a directory. 
+They use a new handle_type, "sftp_dir", which gives access to the
+directory being read.
+
+In addition, sftp_readdir() returns a "sftp_attributes" which is a pointer
+to a structure with informations about a directory entry:
+  - name: the name of the file or directory
+  - size: its size in bytes
+  - etc.
+
+sftp_readdir() might return NULL under two conditions:
+  - when the end of the directory has been met
+  - when an error occured
+
+To tell the difference, call sftp_dir_eof().
+
+The attributes must be freed with sftp_attributes_free() when no longer
+needed.
+
+The following example reads the contents of some remote directory:
+
+@code
+int sftp_list_dir(ssh_session session, sftp_session sftp)
+{
+  sftp_dir dir;
+  sftp_attributes attributes;
+  int rc;
+
+  dir = sftp_opendir(sftp, "/var/log");
+  if (!dir)
+  {
+    fprintf(stderr, "Directory not opened: %s\n", ssh_get_error(session));
+    return SSH_ERROR;
+  }
+
+  printf("Name                         Size Perms    Owner\tGroup\n");
+
+  while ((attributes = sftp_readdir(sftp, dir)) != NULL)
+  {
+    printf("%-22s %10llu %.8o %s(%d)\t%s(%d)\n",
+     attributes->name,
+     (long long unsigned int) attributes->size,
+     attributes->permissions,
+     attributes->owner,
+     attributes->uid,
+     attributes->group,
+     attributes->gid);
+
+     sftp_attributes_free(attributes);
+  }
+
+  if (!sftp_dir_eof(dir))
+  {
+    fprintf(stderr, "Can't list directory: %s\n", ssh_get_error(session));
+    sftp_closedir(dir);
+    return SSH_ERROR;
+  }
+
+  rc = sftp_closedir(dir);
+  if (rc != SSH_OK)
+  {
+    fprintf(stderr, "Can't close directory: %s\n", ssh_get_error(session));
+    return rc;
+  }
+}
+@endcode
 
 */