[FFmpeg-devel] [PATCH] avformat/file: add fd protocol

[Zhao Zhili]

From: Zhao Zhili <zhilizhao at tencent.com>

Unlike the pipe protocol, fd protocol has seek support if it
corresponding to a regular file.
---
Sometimes it's the only way to access files via file descriptor, e.g.,
requesting a shared file on Android:
https://developer.android.com/training/secure-file-sharing/request-file

 doc/protocols.texi      | 24 +++++++++++++++++++
 libavformat/Makefile    |  1 +
 libavformat/file.c      | 51 +++++++++++++++++++++++++++++++++++++++++
 libavformat/protocols.c |  1 +
 libavformat/version.h   |  4 ++--
 5 files changed, 79 insertions(+), 2 deletions(-)

diff --git a/doc/protocols.texi b/doc/protocols.texi
index 5e9198e67c..d9f2d2dec3 100644
--- a/doc/protocols.texi
+++ b/doc/protocols.texi
@@ -275,6 +275,30 @@ For example, to convert a GIF file given inline with @command{ffmpeg}:
 ffmpeg -i "data:image/gif;base64,R0lGODdhCAAIAMIEAAAAAAAA//8AAP//AP///////////////ywAAAAACAAIAAADF0gEDLojDgdGiJdJqUX02iB4E8Q9jUMkADs=" smiley.png
 @end example
 
+ at section fd
+
+File descriptor access protocol.
+
+The accepted syntax is:
+ at example
+fd:[@var{number}]
+ at end example
+
+ at var{number} is the number corresponding to a file descriptor. Unlike the pipe
+protocol, fd protocol has seek support if it corresponding to a regular file.
+If @var{number} is not specified, by default the stdout file descriptor will
+be used for writing, stdin for reading.
+
+This protocol accepts the following options:
+
+ at table @option
+ at item blocksize
+Set I/O operation maximum block size, in bytes. Default value is
+ at code{INT_MAX}, which results in not limiting the requested block size.
+Setting this value reasonably low improves user termination request reaction
+time, which is valuable if data transmission is slow.
+ at end table
+
 @section file
 
 File access protocol.
diff --git a/libavformat/Makefile b/libavformat/Makefile
index d7f198bf39..1452216e29 100644
--- a/libavformat/Makefile
+++ b/libavformat/Makefile
@@ -647,6 +647,7 @@ OBJS-$(CONFIG_DATA_PROTOCOL)             += data_uri.o
 OBJS-$(CONFIG_FFRTMPCRYPT_PROTOCOL)      += rtmpcrypt.o rtmpdigest.o rtmpdh.o
 OBJS-$(CONFIG_FFRTMPHTTP_PROTOCOL)       += rtmphttp.o
 OBJS-$(CONFIG_FILE_PROTOCOL)             += file.o
+OBJS-$(CONFIG_FD_PROTOCOL)               += file.o
 OBJS-$(CONFIG_FTP_PROTOCOL)              += ftp.o urldecode.o
 OBJS-$(CONFIG_GOPHER_PROTOCOL)           += gopher.o
 OBJS-$(CONFIG_GOPHERS_PROTOCOL)          += gopher.o
diff --git a/libavformat/file.c b/libavformat/file.c
index 6103c37b34..765ad21d67 100644
--- a/libavformat/file.c
+++ b/libavformat/file.c
@@ -109,6 +109,13 @@ static const AVClass pipe_class = {
     .version    = LIBAVUTIL_VERSION_INT,
 };
 
+static const AVClass fd_class = {
+    .class_name = "fd",
+    .item_name  = av_default_item_name,
+    .option     = pipe_options,
+    .version    = LIBAVUTIL_VERSION_INT,
+};
+
 static int file_read(URLContext *h, unsigned char *buf, int size)
 {
     FileContext *c = h->priv_data;
@@ -412,3 +419,47 @@ const URLProtocol ff_pipe_protocol = {
 };
 
 #endif /* CONFIG_PIPE_PROTOCOL */
+
+#if CONFIG_FD_PROTOCOL
+
+static int fd_open(URLContext *h, const char *filename, int flags)
+{
+    FileContext *c = h->priv_data;
+    int fd;
+    char *final;
+    struct stat st;
+
+    av_strstart(filename, "fd:", &filename);
+
+    fd = strtol(filename, &final, 10);
+    if((filename == final) || *final ) {/* No digits found, or something like 10ab */
+        if (flags & AVIO_FLAG_WRITE) {
+            fd = 1;
+        } else {
+            fd = 0;
+        }
+    }
+#if HAVE_SETMODE
+    setmode(fd, O_BINARY);
+#endif
+    if (fstat(fd, &st) < 0)
+        return AVERROR(errno);
+    h->is_streamed = !(S_ISREG(st.st_mode) || S_ISBLK(st.st_mode));
+    c->fd = fd;
+    return 0;
+}
+
+const URLProtocol ff_fd_protocol = {
+    .name                = "fd",
+    .url_open            = fd_open,
+    .url_read            = file_read,
+    .url_write           = file_write,
+    .url_seek            = file_seek,
+    .url_get_file_handle = file_get_handle,
+    .url_check           = file_check,
+    .priv_data_size      = sizeof(FileContext),
+    .priv_data_class     = &fd_class,
+    .default_whitelist   = "crypto,data"
+};
+
+#endif /* CONFIG_FD_PROTOCOL */
diff --git a/libavformat/protocols.c b/libavformat/protocols.c
index 8b7d1b940f..82cb1033e4 100644
--- a/libavformat/protocols.c
+++ b/libavformat/protocols.c
@@ -29,6 +29,7 @@ extern const URLProtocol ff_concat_protocol;
 extern const URLProtocol ff_concatf_protocol;
 extern const URLProtocol ff_crypto_protocol;
 extern const URLProtocol ff_data_protocol;
+extern const URLProtocol ff_fd_protocol;
 extern const URLProtocol ff_ffrtmpcrypt_protocol;
 extern const URLProtocol ff_ffrtmphttp_protocol;
 extern const URLProtocol ff_file_protocol;
diff --git a/libavformat/version.h b/libavformat/version.h
index 7c9d50b7b3..f5a7f579b3 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -31,8 +31,8 @@
 
 #include "version_major.h"
 
-#define LIBAVFORMAT_VERSION_MINOR  34
-#define LIBAVFORMAT_VERSION_MICRO 101
+#define LIBAVFORMAT_VERSION_MINOR  35
+#define LIBAVFORMAT_VERSION_MICRO 100
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \
-- 
2.25.1