FTP protocol support

Implementation of ftp protocol.

Fixes #1672

Signed-off-by: Lukasz Marek <lukasz.m.luki@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

7 files changed, 698 insertions, 0 deletions

diff --git a/Changelog b/Changelog
index 49291761e5..249e8c385a 100644
--- a/Changelog
+++ b/Changelog
@@ -50,6 +50,7 @@ version <next>:
 - Wavelet denoiser filter ported from libmpcodecs as owdenoise (formerly "ow")
 - Apple Intermediate Codec decoder
 - Escape 130 video decoder
+- FTP protocol support
 
 
 version 1.2:
diff --git a/MAINTAINERS b/MAINTAINERS
index cec22d8c56..9f4301d15b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -411,6 +411,7 @@ Muxers/Demuxers:
 
 Protocols:
   bluray.c                              Petri Hintukainen
+  ftp.c                                 Lukasz Marek
   http.c                                Ronald S. Bultje
   mms*.c                                Ronald S. Bultje
   udp.c                                 Luca Abeni
diff --git a/configure b/configure
index 1e444089a0..1b7a847fcb 100755
--- a/configure
+++ b/configure
@@ -2090,6 +2090,7 @@ ffrtmpcrypt_protocol_deps_any="gcrypt nettle openssl"
 ffrtmpcrypt_protocol_select="tcp_protocol"
 ffrtmphttp_protocol_deps="!librtmp_protocol"
 ffrtmphttp_protocol_select="http_protocol"
+ftp_protocol_select="tcp_protocol"
 gopher_protocol_select="network"
 httpproxy_protocol_select="tcp_protocol"
 http_protocol_select="tcp_protocol"
diff --git a/doc/protocols.texi b/doc/protocols.texi
index 0c56b8b510..a91103af66 100644
--- a/doc/protocols.texi
+++ b/doc/protocols.texi
@@ -100,6 +100,40 @@ The ff* tools default to the file protocol, that is a resource
 specified with the name "FILE.mpeg" is interpreted as the URL
 "file:FILE.mpeg".
 
+@section ftp
+
+FTP (File Transfer Protocol)
+
+Allow to read from or write to remote resources using FTP protocol.
+
+Following syntax is required.
+@example
+ftp://[user[:password]@@]server[:port]/path/to/remote/resource.mpeg
+@end example
+
+This protocol accepts the following options.
+
+@table @option
+@item timeout
+Set timeout of socket I/O operations used by the underlying low level
+operation. By default it is set to -1, which means that the timeout is
+not specified.
+
+@item ftp-anonymous-password
+Password used when login as anonymous user. Typically an e-mail address
+should be used.
+
+@item ftp-write-seekable
+Control seekability of connection during encoding. If set to 1 the
+resource is supposed to be seekable, if set to 0 it is assumed not
+to be seekable. Default value is 0.
+@end table
+
+NOTE: Protocol can be used as output, but it is recommended to not do
+it, unless special care is taken (tests, customized server configuration
+etc.). Different FTP servers behave in different way during seek
+operation. ff* tools may produce incomplete content due to server limitations.
+
 @section gopher
 
 Gopher protocol.
diff --git a/libavformat/Makefile b/libavformat/Makefile
index 24dd3cdc3f..abc2472875 100644
--- a/libavformat/Makefile
+++ b/libavformat/Makefile
@@ -424,6 +424,7 @@ OBJS-$(CONFIG_DATA_PROTOCOL)             += data_uri.o
 OBJS-$(CONFIG_FFRTMPCRYPT_PROTOCOL)      += rtmpcrypt.o rtmpdh.o
 OBJS-$(CONFIG_FFRTMPHTTP_PROTOCOL)       += rtmphttp.o
 OBJS-$(CONFIG_FILE_PROTOCOL)             += file.o
+OBJS-$(CONFIG_FTP_PROTOCOL)              += ftp.o
 OBJS-$(CONFIG_GOPHER_PROTOCOL)           += gopher.o
 OBJS-$(CONFIG_HLS_PROTOCOL)              += hlsproto.o
 OBJS-$(CONFIG_HTTP_PROTOCOL)             += http.o httpauth.o urldecode.o
diff --git a/libavformat/allformats.c b/libavformat/allformats.c
index 2b2d46dee1..ab6a548b82 100644
--- a/libavformat/allformats.c
+++ b/libavformat/allformats.c
@@ -313,6 +313,7 @@ void av_register_all(void)
     REGISTER_PROTOCOL(FFRTMPCRYPT,      ffrtmpcrypt);
     REGISTER_PROTOCOL(FFRTMPHTTP,       ffrtmphttp);
     REGISTER_PROTOCOL(FILE,             file);
+    REGISTER_PROTOCOL(FTP,              ftp);
     REGISTER_PROTOCOL(GOPHER,           gopher);
     REGISTER_PROTOCOL(HLS,              hls);
     REGISTER_PROTOCOL(HTTP,             http);
diff --git a/libavformat/ftp.c b/libavformat/ftp.c
new file mode 100644
index 0000000000..62b396c0f1
--- /dev/null
+++ b/libavformat/ftp.c
@@ -0,0 +1,659 @@
+/*
+ * Copyright (c) 2013 Lukasz Marek <lukasz.m.luki@gmail.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <stdlib.h>
+#include "libavutil/avstring.h"
+#include "libavutil/avassert.h"
+#include "avformat.h"
+#include "internal.h"
+#include "network.h"
+#include "os_support.h"
+#include "url.h"
+#include "libavutil/opt.h"
+
+#define CONTROL_BUFFER_SIZE 1024
+
+typedef enum {
+    UNKNOWN,
+    READY,
+    DOWNLOADING,
+    UPLOADING,
+    DISCONNECTED
+} FTPState;
+
+
+typedef struct {
+    const AVClass *class;
+    URLContext *conn_control;        /**< Control connection */
+    int conn_control_block_flag;     /**< Controls block/unblock mode of data connection */
+    AVIOInterruptCB conn_control_interrupt_cb; /**< Controls block/unblock mode of data connection */
+    URLContext *conn_data;           /**< Data connection, NULL when not connected */
+    uint8_t control_buffer[CONTROL_BUFFER_SIZE], *control_buf_ptr, *control_buf_end; /**< Control connection buffer */
+    int server_data_port;            /**< Data connection port opened by server, -1 on error. */
+    char hostname[512];              /**< Server address. */
+    char path[MAX_URL_SIZE];         /**< Path to resource on server. */
+    int64_t filesize;                /**< Size of file on server, -1 on error. */
+    int64_t position;                /**< Current position, calculated. */
+    int rw_timeout;                  /**< Network timeout. */
+    const char *anonymous_password;  /**< Password to be used for anonymous user. An email should be used. */
+    int write_seekable;              /**< Control seekability, 0 = disable, 1 = enable. */
+    FTPState state;                  /**< State of data connection */
+} FTPContext;
+
+#define OFFSET(x) offsetof(FTPContext, x)
+#define D AV_OPT_FLAG_DECODING_PARAM
+#define E AV_OPT_FLAG_ENCODING_PARAM
+static const AVOption options[] = {
+    {"timeout", "set timeout of socket I/O operations", OFFSET(rw_timeout), AV_OPT_TYPE_INT, {.i64 = -1}, -1, INT_MAX, D|E },
+    {"ftp-write-seekable", "control seekability of connection during encoding", OFFSET(write_seekable), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 1, E },
+    {"ftp-anonymous-password", "password for anonynous login. E-mail address should be used.", OFFSET(anonymous_password), AV_OPT_TYPE_STRING, { 0 }, 0, 0, D|E },
+    {NULL}
+};
+
+static const AVClass ftp_context_class = {
+    .class_name     = "ftp",
+    .item_name      = av_default_item_name,
+    .option         = options,
+    .version        = LIBAVUTIL_VERSION_INT,
+};
+
+static int ftp_conn_control_block_control(void *data)
+{
+    FTPContext *s = data;
+    return s->conn_control_block_flag;
+}
+
+static int ftp_getc(FTPContext *s)
+{
+    int len;
+    if (s->control_buf_ptr >= s->control_buf_end) {
+        if (s->conn_control_block_flag)
+            return AVERROR_EXIT;
+        len = ffurl_read(s->conn_control, s->control_buffer, CONTROL_BUFFER_SIZE);
+        if (len < 0) {
+            return len;
+        } else if (!len) {
+            return -1;
+        } else {
+            s->control_buf_ptr = s->control_buffer;
+            s->control_buf_end = s->control_buffer + len;
+        }
+    }
+    return *s->control_buf_ptr++;
+}
+
+static int ftp_get_line(FTPContext *s, char *line, int line_size)
+{
+    int ch;
+    char *q = line;
+    int ori_block_flag = s->conn_control_block_flag;
+
+    for (;;) {
+        ch = ftp_getc(s);
+        if (ch < 0) {
+            s->conn_control_block_flag = ori_block_flag;
+            return ch;
+        }
+        if (ch == '\n') {
+            /* process line */
+            if (q > line && q[-1] == '\r')
+                q--;
+            *q = '\0';
+
+            s->conn_control_block_flag = ori_block_flag;
+            return 0;
+        } else {
+            s->conn_control_block_flag = 0; /* line need to be finished */
+            if ((q - line) < line_size - 1)
+                *q++ = ch;
+        }
+    }
+}
+
+/*
+ * This routine returns ftp server response code.
+ * Server may send more than one response for a certain command, following priorites are used:
+ *   - 5xx code is returned if occurred. (means error)
+ *   - When pref_code is set then pref_code is return if occurred. (expected result)
+ *   - The lowest code is returned. (means success)
+ */
+static int ftp_status(FTPContext *s, int *major, int *minor, int *extra, char **line, int pref_code)
+{
+    int err, result = -1, pref_code_found = 0;
+    char buf[CONTROL_BUFFER_SIZE];
+    unsigned char d_major, d_minor, d_extra;
+
+    /* Set blocking mode */
+    s->conn_control_block_flag = 0;
+    for (;;) {
+        if ((err = ftp_get_line(s, buf, CONTROL_BUFFER_SIZE)) < 0) {
+            if (err == AVERROR_EXIT)
+                return result;
+            return err;
+        }
+
+        if (strlen(buf) < 3)
+            continue;
+        d_major = buf[0];
+        if (d_major < '1' || d_major > '6' || d_major == '4')
+            continue;
+        d_minor = buf[1];
+        if (d_minor < '0' || d_minor > '9')
+            continue;
+        d_extra = buf[2];
+        if (d_extra < '0' || d_extra > '9')
+            continue;
+
+        av_log(s, AV_LOG_DEBUG, "%s\n", buf);
+
+        err = d_major * 100 + d_minor * 10 + d_extra - 111 * '0';
+
+        if ((result < 0 || err < result || pref_code == err) && !pref_code_found || d_major == '5') {
+            if (pref_code == err || d_major == '5')
+                pref_code_found = 1;
+            result = err;
+            if (major)
+                *major = d_major - '0';
+            if (minor)
+                *minor = d_minor - '0';
+            if (extra)
+                *extra = d_extra - '0';
+            if (line)
+                *line = av_strdup(buf);
+        }
+
+        /* first code received. Now get all lines in non blocking mode */
+        if (pref_code < 0 || pref_code_found)
+            s->conn_control_block_flag = 1;
+    }
+    return result;
+}
+
+static int ftp_auth(FTPContext *s, char *auth)
+{
+    const char *user = NULL, *pass = NULL;
+    char *end = NULL, buf[CONTROL_BUFFER_SIZE];
+    int err;
+    av_assert2(auth);
+
+    user = av_strtok(auth, ":", &end);
+    pass = av_strtok(end, ":", &end);
+
+    if (user) {
+        snprintf(buf, sizeof(buf), "USER %s\r\n", user);
+        if ((err = ffurl_write(s->conn_control, buf, strlen(buf))) < 0)
+            return err;
+        ftp_status(s, &err, NULL, NULL, NULL, -1);
+        if (err == 3) {
+            if (pass) {
+                snprintf(buf, sizeof(buf), "PASS %s\r\n", pass);
+                if ((err = ffurl_write(s->conn_control, buf, strlen(buf))) < 0)
+                    return err;
+                ftp_status(s, &err, NULL, NULL, NULL, -1);
+            } else
+                return AVERROR(EACCES);
+        }
+        if (err != 2) {
+            return AVERROR(EACCES);
+        }
+    } else {
+        const char* command = "USER anonymous\r\n";
+        if ((err = ffurl_write(s->conn_control, command, strlen(command))) < 0)
+            return err;
+        ftp_status(s, &err, NULL, NULL, NULL, -1);
+        if (err == 3) {
+            if (s->anonymous_password) {
+                snprintf(buf, sizeof(buf), "PASS %s\r\n", s->anonymous_password);
+            } else
+                snprintf(buf, sizeof(buf), "PASS nopassword\r\n");
+            if ((err = ffurl_write(s->conn_control, buf, strlen(buf))) < 0)
+                return err;
+            ftp_status(s, &err, NULL, NULL, NULL, -1);
+        }
+        if (err != 2) {
+            return AVERROR(EACCES);
+        }
+    }
+
+    return 0;
+}
+
+static int ftp_passive_mode(FTPContext *s)
+{
+    char *res = NULL, *start, *end;
+    int err, i;
+    const char *command = "PASV\r\n";
+
+    if ((err = ffurl_write(s->conn_control, command, strlen(command))) < 0)
+        return err;
+    if (ftp_status(s, NULL, NULL, NULL, &res, 227) != 227)
+        goto fail;
+
+    start = NULL;
+    for (i = 0; i < strlen(res); ++i) {
+        if (res[i] == '(') {
+            start = res + i + 1;
+        } else if (res[i] == ')') {
+            end = res + i;
+            break;
+        }
+    }
+    if (!start || !end)
+        goto fail;
+
+    *end  = '\0';
+    /* skip ip */
+    if (!av_strtok(start, ",", &end)) goto fail;
+    if (!av_strtok(end, ",", &end)) goto fail;
+    if (!av_strtok(end, ",", &end)) goto fail;
+    if (!av_strtok(end, ",", &end)) goto fail;
+
+    /* parse port number */
+    start = av_strtok(end, ",", &end);
+    if (!start) goto fail;
+    s->server_data_port = atoi(start) * 256;
+    start = av_strtok(end, ",", &end);
+    if (!start) goto fail;
+    s->server_data_port += atoi(start);
+    av_dlog(s, "Server data port: %d\n", s->server_data_port);
+
+    av_free(res);
+    return 0;
+
+  fail:
+    av_free(res);
+    s->server_data_port = -1;
+    return AVERROR(EIO);
+}
+
+static int ftp_current_dir(FTPContext *s)
+{
+    char *res = NULL, *start = NULL, *end = NULL;
+    int err, i;
+    const char *command = "PWD\r\n";
+
+    if ((err = ffurl_write(s->conn_control, command, strlen(command))) < 0)
+        return err;
+    if (ftp_status(s, NULL, NULL, NULL, &res, 257) != 257)
+        goto fail;
+
+    for (i = 0; res[i]; ++i) {
+        if (res[i] == '"') {
+            if (!start) {
+                start = res + i + 1;
+                continue;
+            }
+            end = res + i;
+            break;
+        }
+    }
+
+    if (!end)
+        goto fail;
+
+    if (end > res && end[-1] == '/') {
+        end[-1] = '\0';
+    } else
+        *end = '\0';
+    av_strlcpy(s->path, start, sizeof(s->path));
+
+    av_free(res);
+    return 0;
+
+  fail:
+    av_free(res);
+    return AVERROR(EIO);
+}
+
+static int ftp_file_size(FTPContext *s)
+{
+    char buf[CONTROL_BUFFER_SIZE];
+    int err;
+    char *res = NULL;
+
+    snprintf(buf, sizeof(buf), "SIZE %s\r\n", s->path);
+    if ((err = ffurl_write(s->conn_control, buf, strlen(buf))) < 0)
+        return err;
+    if (ftp_status(s, NULL, NULL, NULL, &res, 213) == 213) {
+        s->filesize = atoll(&res[4]);
+    } else {
+        s->filesize = -1;
+        av_free(res);
+        return AVERROR(EIO);
+    }
+
+    av_free(res);
+    return 0;
+}
+
+static int ftp_retrieve(FTPContext *s)
+{
+    char buf[CONTROL_BUFFER_SIZE];
+    int err;
+
+    snprintf(buf, sizeof(buf), "RETR %s\r\n", s->path);
+    if ((err = ffurl_write(s->conn_control, buf, strlen(buf))) < 0)
+        return err;
+    if (ftp_status(s, NULL, NULL, NULL, NULL, 150) != 150)
+        return AVERROR(EIO);
+
+    s->state = DOWNLOADING;
+
+    return 0;
+}
+
+static int ftp_store(FTPContext *s)
+{
+    char buf[CONTROL_BUFFER_SIZE];
+    int err;
+
+    snprintf(buf, sizeof(buf), "STOR %s\r\n", s->path);
+    if ((err = ffurl_write(s->conn_control, buf, strlen(buf))) < 0)
+        return err;
+    if (ftp_status(s, NULL, NULL, NULL, NULL, 150) != 150)
+        return AVERROR(EIO);
+
+    s->state = UPLOADING;
+
+    return 0;
+}
+
+static int ftp_send_command(FTPContext *s, const char* command)
+{
+    int err;
+
+    if ((err = ffurl_write(s->conn_control, command, strlen(command))) < 0)
+        return err;
+    ftp_status(s, &err, NULL, NULL, NULL, -1);
+    if (err != 2)
+        return AVERROR(EIO);
+
+    return 0;
+}
+
+static int ftp_reconnect_data_connection(URLContext *h)
+{
+    int err;
+    char buf[CONTROL_BUFFER_SIZE], opts_format[20];
+    AVDictionary *opts = NULL;
+    FTPContext *s = h->priv_data;
+
+    if (!s->conn_data) {
+        ff_url_join(buf, sizeof(buf), "tcp", NULL, s->hostname, s->server_data_port, NULL);
+        if (s->rw_timeout != -1) {
+            snprintf(opts_format, sizeof(opts_format), "%d", s->rw_timeout);
+            av_dict_set(&opts, "timeout", opts_format, 0);
+        } /* if option is not given, don't pass it and let tcp use its own default */
+        err = ffurl_open(&s->conn_data, buf, AVIO_FLAG_READ_WRITE,
+                         &h->interrupt_callback, &opts);
+        av_dict_free(&opts);
+        if (err < 0)
+            return err;
+    }
+    s->state = READY;
+    s->position = 0;
+    return 0;
+}
+
+static int ftp_open(URLContext *h, const char *url, int flags)
+{
+    char proto[10], auth[1024], path[MAX_URL_SIZE], buf[CONTROL_BUFFER_SIZE], opts_format[20];
+    AVDictionary *opts = NULL;
+    int port, err;
+    FTPContext *s = h->priv_data;
+
+    av_dlog(h, "ftp protocol open\n");
+
+    s->state = DISCONNECTED;
+    s->filesize = -1;
+    s->conn_control_interrupt_cb.opaque = s;
+    s->conn_control_interrupt_cb.callback = ftp_conn_control_block_control;
+
+    av_url_split(proto, sizeof(proto),
+                 auth, sizeof(auth),
+                 s->hostname, sizeof(s->hostname),
+                 &port,
+                 path, sizeof(path),
+                 url);
+
+    if (port < 0)
+        port = 21;
+
+    if (!s->conn_control) {
+        ff_url_join(buf, sizeof(buf), "tcp", NULL, s->hostname, port, NULL);
+        if (s->rw_timeout != -1) {
+            snprintf(opts_format, sizeof(opts_format), "%d", s->rw_timeout);
+            av_dict_set(&opts, "timeout", opts_format, 0);
+        } /* if option is not given, don't pass it and let tcp use its own default */
+        err = ffurl_open(&s->conn_control, buf, AVIO_FLAG_READ_WRITE,
+                         &s->conn_control_interrupt_cb, &opts);
+        av_dict_free(&opts);
+        if (err < 0)
+            goto fail;
+
+        /* consume all messages from server */
+        if (ftp_status(s, NULL, NULL, NULL, NULL, 220) != 220) {
+            av_log(h, AV_LOG_ERROR, "Server not ready for new users\n");
+            err = AVERROR(EACCES);
+            goto fail;
+        }
+
+        if ((err = ftp_auth(s, auth)) < 0)
+            goto fail;
+
+        if ((err = ftp_send_command(s, "TYPE I\r\n")) < 0)
+            goto fail;
+
+        if ((err = ftp_current_dir(s)) < 0)
+            goto fail;
+        av_strlcat(s->path, path, sizeof(s->path));
+
+        if ((err = ftp_passive_mode(s)) < 0)
+            goto fail;
+
+        if (ftp_file_size(s) < 0 && flags & AVIO_FLAG_READ)
+            h->is_streamed = 1;
+        if (s->write_seekable != 1 && flags & AVIO_FLAG_WRITE)
+            h->is_streamed = 1;
+    }
+
+    if ((err = ftp_reconnect_data_connection(h)) < 0)
+        goto fail;
+
+    return 0;
+  fail:
+    av_log(h, AV_LOG_ERROR, "FTP open failed\n");
+    ffurl_closep(&s->conn_control);
+    ffurl_closep(&s->conn_data);
+    return err;
+}
+
+static int ftp_read(URLContext *h, unsigned char *buf, int size)
+{
+    FTPContext *s = h->priv_data;
+    int read;
+
+    av_dlog(h, "ftp protocol read %d bytes\n", size);
+
+    if (s->state == READY) {
+        ftp_retrieve(s);
+    }
+    if (s->conn_data && s->state == DOWNLOADING) {
+        read = ffurl_read(s->conn_data, buf, size);
+        if (read >= 0) {
+            s->position += read;
+            if (s->position >= s->filesize) {
+                ffurl_closep(&s->conn_data);
+                s->state = DISCONNECTED;
+                if (ftp_status(s, NULL, NULL, NULL,NULL, 226) != 226)
+                    return AVERROR(EIO);
+            }
+        }
+        return read;
+    }
+
+    av_log(h, AV_LOG_DEBUG, "FTP read failed\n");
+    return AVERROR(EIO);
+}
+
+static int ftp_write(URLContext *h, const unsigned char *buf, int size)
+{
+    FTPContext *s = h->priv_data;
+    int written;
+
+    av_dlog(h, "ftp protocol write %d bytes\n", size);
+
+    if (s->state == READY) {
+        ftp_store(s);
+    }
+    if (s->conn_data && s->state == UPLOADING) {
+        written = ffurl_write(s->conn_data, buf, size);
+        if (written > 0) {
+            s->position += written;
+            s->filesize = FFMAX(s->filesize, s->position);
+        }
+        return written;
+    }
+
+    av_log(h, AV_LOG_ERROR, "FTP write failed\n");
+    return AVERROR(EIO);
+}
+
+static int64_t ftp_seek(URLContext *h, int64_t pos, int whence)
+{
+    FTPContext *s = h->priv_data;
+    char buf[CONTROL_BUFFER_SIZE];
+    int err;
+    int64_t new_pos;
+
+    av_dlog(h, "ftp protocol seek %"PRId64" %d\n", pos, whence);
+
+    switch(whence) {
+    case AVSEEK_SIZE:
+        return s->filesize;
+    case SEEK_SET:
+        new_pos = pos;
+        break;
+    case SEEK_CUR:
+        new_pos = s->position + pos;
+        break;
+    case SEEK_END:
+        if (s->filesize < 0)
+            return AVERROR(EIO);
+        new_pos = s->filesize + pos;
+        break;
+    default:
+        return AVERROR(EINVAL);
+    }
+
+    if  (h->is_streamed)
+        return AVERROR(EIO);
+
+    if (new_pos < 0 || (s->filesize >= 0 && new_pos > s->filesize))
+        return AVERROR(EINVAL);
+
+    if (new_pos != s->position) {
+        /* close existing data connection */
+        if (s->state != READY) {
+            if (s->conn_data) {
+                /* abort existing transfer */
+                if (s->state == DOWNLOADING) {
+                    snprintf(buf, sizeof(buf), "ABOR\r\n");
+                    if ((err = ffurl_write(s->conn_control, buf, strlen(buf))) < 0)
+                        return err;
+                }
+                ffurl_closep(&s->conn_data);
+                s->state = DISCONNECTED;
+                /* Servers return 225 or 226 */
+                ftp_status(s, &err, NULL, NULL, NULL, -1);
+                if (err != 2)
+                    return AVERROR(EIO);
+            }
+
+            /* set passive */
+            if ((err = ftp_passive_mode(s)) < 0)
+                return err;
+
+            /* open new data connection */
+            if ((err = ftp_reconnect_data_connection(h)) < 0)
+                return err;
+        }
+
+        /* resume from pos position */
+        snprintf(buf, sizeof(buf), "REST %"PRId64"\r\n", pos);
+        if ((err = ffurl_write(s->conn_control, buf, strlen(buf))) < 0)
+            return err;
+        if (ftp_status(s, NULL, NULL, NULL, NULL, 350) != 350)
+            return AVERROR(EIO);
+
+        s->position = pos;
+    }
+    return new_pos;
+}
+
+static int ftp_close(URLContext *h)
+{
+    FTPContext *s = h->priv_data;
+
+    av_dlog(h, "ftp protocol close\n");
+
+    ffurl_closep(&s->conn_control);
+    ffurl_closep(&s->conn_data);
+
+    return 0;
+}
+
+static int ftp_get_file_handle(URLContext *h)
+{
+    FTPContext *s = h->priv_data;
+
+    av_dlog(h, "ftp protocol get_file_handle\n");
+
+    if (s->conn_data)
+        return ffurl_get_file_handle(s->conn_data);
+
+    return AVERROR(EIO);
+}
+
+static int ftp_shutdown(URLContext *h, int flags)
+{
+    FTPContext *s = h->priv_data;
+
+    av_dlog(h, "ftp protocol shutdown\n");
+
+    if (s->conn_data)
+        return ffurl_shutdown(s->conn_data, flags);
+
+    return AVERROR(EIO);
+}
+
+URLProtocol ff_ftp_protocol = {
+    .name                = "ftp",
+    .url_open            = ftp_open,
+    .url_read            = ftp_read,
+    .url_write           = ftp_write,
+    .url_seek            = ftp_seek,
+    .url_close           = ftp_close,
+    .url_get_file_handle = ftp_get_file_handle,
+    .url_shutdown        = ftp_shutdown,
+    .priv_data_size      = sizeof(FTPContext),
+    .priv_data_class     = &ftp_context_class,
+    .flags               = URL_PROTOCOL_FLAG_NETWORK,
+};