[FFmpeg-devel] [PATCH v3 1/1] avformat: Add IPFS protocol support.

[Mark Gaiser <markg85@gmail.com>]

This patch adds support for:
- ffplay ipfs://<cid>
- ffplay ipns://<cid>

IPFS data can be played from so called "ipfs gateways".
A gateway is essentially a webserver that gives access to the
distributed IPFS network.

This protocol support (ipfs and ipns) therefore translates
ipfs:// and ipns:// to a http:// url. This resulting url is
then handled by the http protocol. It could also be https
depending on the gateway provided.

To use this protocol, a gateway must be provided.
If you do nothing it will try to find it in your
$HOME/.ipfs/gateway file. The ways to set it manually are:
1. Define a -gateway <url> to the gateway.
2. Define $IPFS_GATEWAY with the full http link to the gateway.
3. Define $IPFS_PATH and point it to the IPFS data path.
4. Have IPFS running in your local user folder (under $HOME/.ipfs).

Signed-off-by: Mark Gaiser <markg85@gmail.com>
---
 configure                 |   2 +
 doc/protocols.texi        |  30 ++++
 libavformat/Makefile      |   2 +
 libavformat/ipfsgateway.c | 329 ++++++++++++++++++++++++++++++++++++++
 libavformat/protocols.c   |   2 +
 5 files changed, 365 insertions(+)
 create mode 100644 libavformat/ipfsgateway.c

diff --git a/configure b/configure
index 5b19a35f59..6ff09e7974 100755
--- a/configure
+++ b/configure
@@ -3585,6 +3585,8 @@ udp_protocol_select="network"
 udplite_protocol_select="network"
 unix_protocol_deps="sys_un_h"
 unix_protocol_select="network"
+ipfs_protocol_select="https_protocol"
+ipns_protocol_select="https_protocol"
 
 # external library protocols
 libamqp_protocol_deps="librabbitmq"
diff --git a/doc/protocols.texi b/doc/protocols.texi
index d207df0b52..7c9c0a4808 100644
--- a/doc/protocols.texi
+++ b/doc/protocols.texi
@@ -2025,5 +2025,35 @@ decoding errors.
 
 @end table
 
+@section ipfs
+
+InterPlanetary File System (IPFS) protocol support. One can access files stored 
+on the IPFS network through so called gateways. Those are http(s) endpoints.
+This protocol wraps the IPFS native protocols (ipfs:// and ipns://) to be send 
+to such a gateway. Users can (and should) host their own node which means this 
+protocol will use your local machine gateway to access files on the IPFS network.
+
+If a user doesn't have a node of their own then the public gateway dweb.link is 
+used by default.
+
+You can use this protocol in 2 ways. Using IPFS:
+@example
+ffplay ipfs://QmbGtJg23skhvFmu9mJiePVByhfzu5rwo74MEkVDYAmF5T
+@end example
+
+Or the IPNS protocol (IPNS is mutable IPFS):
+@example
+ffplay ipns://QmbGtJg23skhvFmu9mJiePVByhfzu5rwo74MEkVDYAmF5T
+@end example
+
+You can also change the gateway to be used:
+
+@table @option
+
+@item gateway
+Defines the gateway to use. When nothing is provided the protocol will first try 
+your local gateway. If that fails dweb.link will be used.
+
+@end table
 
 @c man end PROTOCOLS
diff --git a/libavformat/Makefile b/libavformat/Makefile
index 3dc6a479cc..4edce8420f 100644
--- a/libavformat/Makefile
+++ b/libavformat/Makefile
@@ -656,6 +656,8 @@ OBJS-$(CONFIG_SRTP_PROTOCOL)             += srtpproto.o srtp.o
 OBJS-$(CONFIG_SUBFILE_PROTOCOL)          += subfile.o
 OBJS-$(CONFIG_TEE_PROTOCOL)              += teeproto.o tee_common.o
 OBJS-$(CONFIG_TCP_PROTOCOL)              += tcp.o
+OBJS-$(CONFIG_IPFS_PROTOCOL)             += ipfsgateway.o
+OBJS-$(CONFIG_IPNS_PROTOCOL)             += ipfsgateway.o
 TLS-OBJS-$(CONFIG_GNUTLS)                += tls_gnutls.o
 TLS-OBJS-$(CONFIG_LIBTLS)                += tls_libtls.o
 TLS-OBJS-$(CONFIG_MBEDTLS)               += tls_mbedtls.o
diff --git a/libavformat/ipfsgateway.c b/libavformat/ipfsgateway.c
new file mode 100644
index 0000000000..72d431eac3
--- /dev/null
+++ b/libavformat/ipfsgateway.c
@@ -0,0 +1,329 @@
+/*
+ * IPFS and IPNS protocol support through IPFS Gateway.
+ * Copyright (c) 2022 Mark Gaiser
+ *
+ * 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 "avformat.h"
+#include "libavutil/avassert.h"
+#include "libavutil/avstring.h"
+#include "libavutil/internal.h"
+#include "libavutil/opt.h"
+#include "libavutil/tree.h"
+#include <fcntl.h>
+#if HAVE_IO_H
+#include <io.h>
+#endif
+#if HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+#include "os_support.h"
+#include "url.h"
+#include <stdlib.h>
+#include <sys/stat.h>
+
+typedef struct IPFSGatewayContext {
+    AVClass *class;
+    URLContext *inner;
+    char *gateway;
+} IPFSGatewayContext;
+
+// A best-effort way to find the IPFS gateway.
+// Only the most appropiate gateway is set. It's not actually requested
+// (http call) to prevent a potential slowdown in startup. A potential timeout
+// is handled by the HTTP protocol.
+//
+// Return codes can be:
+// 1 : A potential gateway is found and set in c->gateway
+// -1: The IPFS data folder could not be found
+// -2: The gateway file could not be found
+// -3: The gateway file is found but empty
+// -4: $HOME is empty
+// -9: Unhandled error
+static int populate_ipfs_gateway(URLContext *h)
+{
+    IPFSGatewayContext *c = h->priv_data;
+    char *ipfs_full_data_folder = NULL;
+    char *ipfs_gateway_file = NULL;
+    struct stat st;
+    int stat_ret = 0;
+    int ret = -9;
+    FILE *gateway_file = NULL;
+    char gateway_file_data[1000];
+
+    // First, test if there already is a path in c->gateway. If it is then it
+    // was provided as cli arument and should be used. It takes precdence.
+    if (c->gateway != NULL) {
+        ret = 1;
+        goto err;
+    }
+
+    // Test $IPFS_GATEWAY.
+    if (getenv("IPFS_GATEWAY") != NULL) {
+        av_free(c->gateway);
+        c->gateway = av_asprintf("%s", getenv("IPFS_GATEWAY"));
+        ret = 1;
+        goto err;
+    } else
+        av_log(h, AV_LOG_DEBUG, "$IPFS_GATEWAY is empty.\n");
+
+    // We need to know the IPFS folder to - eventually - read the contents of
+    // the "gateway" file which would tell us the gateway to use.
+    if (getenv("IPFS_PATH") == NULL) {
+        av_log(h, AV_LOG_DEBUG, "$IPFS_PATH is empty.\n");
+
+        // Try via the home folder.
+        if (getenv("HOME") == NULL) {
+            av_log(h, AV_LOG_ERROR, "$HOME appears to be empty.\n");
+            ret = -4;
+            goto err;
+        }
+
+        ipfs_full_data_folder = av_asprintf("%s/.ipfs/", getenv("HOME"));
+
+        // Stat the folder.
+        // It should exist in a default IPFS setup when run as local user.
+#ifndef _WIN32
+        stat_ret = stat(ipfs_full_data_folder, &st);
+#else
+        stat_ret = win32_stat(ipfs_full_data_folder, &st);
+#endif
+        if (stat_ret < 0) {
+            av_log(h, AV_LOG_DEBUG, "Unable to find IPFS folder. We tried:\n");
+            av_log(h, AV_LOG_DEBUG, "- $IPFS_PATH, which was empty.\n");
+            av_log(h, AV_LOG_DEBUG, "- $HOME/.ipfs (full uri: %s) which doesn't exist.\n", ipfs_full_data_folder);
+            ret = -1;
+            goto err;
+        }
+    } else
+        ipfs_full_data_folder = av_asprintf("%s", getenv("IPFS_PATH"));
+
+    ipfs_gateway_file = av_asprintf("%sgateway", ipfs_full_data_folder);
+
+    // Get the contents of the gateway file.
+    gateway_file = av_fopen_utf8(ipfs_gateway_file, "r");
+    if (!gateway_file) {
+        av_log(h, AV_LOG_ERROR, "The IPFS gateway file (full uri: %s) doesn't exist. Is the gateway enabled?\n", ipfs_gateway_file);
+        ret = -2;
+        goto err;
+    }
+
+    // Read a single line (fgets stops at new line mark).
+    fgets(gateway_file_data, sizeof(gateway_file_data) - 1, gateway_file);
+
+    // Replace first occurence of end of line to \0
+    gateway_file_data[strcspn(gateway_file_data, "\r\n")] = 0;
+
+    // If strlen finds anything longer then 0 characters then we have a
+    // potential gateway url.
+    if (strlen(gateway_file_data) < 1) {
+        av_log(h, AV_LOG_ERROR, "The IPFS gateway file (full uri: %s) appears to be empty. Is the gateway started?\n", ipfs_gateway_file);
+        ret = -3;
+        goto err;
+    }
+
+    // At this point gateway_file_data contains at least something.
+    // Copy it into c->gateway.
+    c->gateway = av_asprintf("%s", gateway_file_data);
+    if (c->gateway) {
+        ret = 1;
+        goto err;
+    } else
+        av_log(h, AV_LOG_DEBUG, "Unknown error in the IPFS gateway file.\n");
+
+err:
+    if (gateway_file)
+        fclose(gateway_file);
+
+    av_free(ipfs_full_data_folder);
+    av_free(ipfs_gateway_file);
+    return ret;
+}
+
+// For now just makes sure that the gateway ends in url we expect.
+// Like http://localhost:8080/.
+// Explicitly with the traling slash.
+//
+// Return codes can be: (any code above 0 is OK)
+// 2 : c->gateway modified to add a trailing "/"
+// 1 : c->gateway is set with a string that looks to be a valid URL
+// -1: The gateway is too short to be any kind of URL.
+// -2: The gateway didn't start with http:// or https://
+// -3: The gateway url part (without the protocol) is too short. We expect 3
+//     characters minimal. So http://aaa would be the bare minimal.
+// -9: Unhandled error
+static int sanitize_ipfs_gateway(URLContext *h)
+{
+    IPFSGatewayContext *c = h->priv_data;
+    char last_gateway_char;
+    const char *url_without_protocol;
+    const char *uri = c->gateway;
+    int ret = -9;
+
+    // "http://" is already 7 characters. Lets be really conservative and say a
+    // url must be 10 chatacters at the very least.
+    if (strlen(c->gateway) < 10) {
+        av_log(h, AV_LOG_ERROR, "The gateway URL must be at least 10 characters long.\n");
+        ret = -1;
+        goto err;
+    }
+
+    // Test if the gateway starts with either http:// or https://
+    // The remainder is stored in url_without_protocol
+    if (av_stristart(uri, "http://", &url_without_protocol) == 0
+        && av_stristart(uri, "https://", &url_without_protocol) == 0) {
+        av_log(h, AV_LOG_ERROR, "The gateway URL didn't start with http:// or https:// and is therefore invalid.\n");
+        ret = -2;
+        goto err;
+    }
+
+    // We now know the remainder of the url without the protocol. Check it for
+    // some length. At least 3 characters.
+    if (strlen(url_without_protocol) < 3) {
+        av_log(h, AV_LOG_ERROR, "The gateway url (without the protocol part) is too short to be a valid URL.\n");
+        ret = -3;
+        goto err;
+    }
+
+    last_gateway_char = c->gateway[strlen(c->gateway) - 1];
+
+    if (last_gateway_char != '/') {
+        c->gateway = av_asprintf("%s/", c->gateway);
+        ret = 2;
+        goto err;
+    }
+
+err:
+    return ret;
+}
+
+static int translate_ipfs_to_http(URLContext *h, const char *uri,
+                                  int flags, AVDictionary **options)
+{
+    const char *ipfs_cid;
+    const char *protocol_path_suffix = "ipfs/";
+    char *fulluri = NULL;
+    int ret;
+    IPFSGatewayContext *c = h->priv_data;
+
+    // Test for ipfs://, ipfs:, ipns:// and ipns:. This prefix is stripped from
+    // the string leaving just the CID in ipfs_cid.
+    int is_ipfs = (av_stristart(uri, "ipfs://", &ipfs_cid)
+                   || av_stristart(uri, "ipfs:", &ipfs_cid));
+    int is_ipns = (av_stristart(uri, "ipns://", &ipfs_cid)
+                   || av_stristart(uri, "ipns:", &ipfs_cid));
+
+    // Populate the IPFS gateway if we have any.
+    // If not, inform the user how to properly set one.
+    if (populate_ipfs_gateway(h) < 0) {
+        av_log(h, AV_LOG_ERROR, "No IPFS gateway was set. Make sure a local IPFS instance is running.\n");
+        av_log(h, AV_LOG_INFO, "There are multiple options to define this gateway. The below options are in order of precedence:\n");
+        av_log(h, AV_LOG_INFO, "1. Define a -gateway <url> to the gateway without trailing forward slash.\n");
+        av_log(h, AV_LOG_INFO, "2. Define $IPFS_GATEWAY with the full http link to the gateway without trailing forward slash.\n");
+        av_log(h, AV_LOG_INFO, "3. Define $IPFS_PATH and point it to the IPFS data path.\n");
+        av_log(h, AV_LOG_INFO, "4. Have IPFS running in your local user folder (under $HOME/.ipfs).\n");
+        av_log(h, AV_LOG_INFO, "In all path cases, a file named gateway is expected. See https://github.com/ipfs/specs/issues/261 for more information.\n");
+        ret = AVERROR(EINVAL);
+        goto err;
+    }
+
+    // Sanitize the gateway to a format we expect.
+    if (sanitize_ipfs_gateway(h) < 1)
+        goto err;
+
+    // We must have either ipns or ipfs.
+    if (!is_ipfs && !is_ipns) {
+        ret = AVERROR(EINVAL);
+        av_log(h, AV_LOG_ERROR, "Unsupported url %s\n", uri);
+        goto err;
+    }
+
+    // If we have IPNS, update the protocol.
+    if (is_ipns)
+        protocol_path_suffix = "ipns/";
+
+    // Concatenate the url.
+    // This ends up with something like: http://localhost:8080/ipfs/Qm.....
+    fulluri = av_asprintf("%s%s%s", c->gateway, protocol_path_suffix, ipfs_cid);
+
+    // Pass the URL back to FFMpeg's protocol handler.
+    if ((ret = ffurl_open_whitelist(&c->inner, fulluri, flags,
+                                    &h->interrupt_callback, options,
+                                    h->protocol_whitelist,
+                                    h->protocol_blacklist, h))
+        < 0) {
+        av_log(h, AV_LOG_ERROR, "Unable to open resource: %s\n", fulluri);
+        goto err;
+    }
+
+err:
+    av_free(fulluri);
+    return ret;
+}
+
+static int ipfs_read(URLContext *h, unsigned char *buf, int size)
+{
+    IPFSGatewayContext *c = h->priv_data;
+    return ffurl_read(c->inner, buf, size);
+}
+
+static int64_t ipfs_seek(URLContext *h, int64_t pos, int whence)
+{
+    IPFSGatewayContext *c = h->priv_data;
+    return ffurl_seek(c->inner, pos, whence);
+}
+
+static int ipfs_close(URLContext *h)
+{
+    IPFSGatewayContext *c = h->priv_data;
+    return ffurl_closep(&c->inner);
+}
+
+#define OFFSET(x) offsetof(IPFSGatewayContext, x)
+
+static const AVOption options[] = {
+    {"gateway", "The gateway to ask for IPFS data.", OFFSET(gateway), AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0, AV_OPT_FLAG_DECODING_PARAM},
+    {NULL},
+};
+
+static const AVClass ipfs_context_class = {
+    .class_name   = "IPFS",
+    .item_name    = av_default_item_name,
+    .option       = options,
+    .version      = LIBAVUTIL_VERSION_INT,
+};
+
+const URLProtocol ff_ipfs_protocol = {
+    .name             = "ipfs",
+    .url_open2        = translate_ipfs_to_http,
+    .url_read         = ipfs_read,
+    .url_seek         = ipfs_seek,
+    .url_close        = ipfs_close,
+    .priv_data_size   = sizeof(IPFSGatewayContext),
+    .priv_data_class  = &ipfs_context_class,
+};
+
+const URLProtocol ff_ipns_protocol = {
+    .name             = "ipns",
+    .url_open2        = translate_ipfs_to_http,
+    .url_read         = ipfs_read,
+    .url_seek         = ipfs_seek,
+    .url_close        = ipfs_close,
+    .priv_data_size   = sizeof(IPFSGatewayContext),
+    .priv_data_class  = &ipfs_context_class,
+};
diff --git a/libavformat/protocols.c b/libavformat/protocols.c
index 948fae411f..675b684bd3 100644
--- a/libavformat/protocols.c
+++ b/libavformat/protocols.c
@@ -73,6 +73,8 @@ extern const URLProtocol ff_libsrt_protocol;
 extern const URLProtocol ff_libssh_protocol;
 extern const URLProtocol ff_libsmbclient_protocol;
 extern const URLProtocol ff_libzmq_protocol;
+extern const URLProtocol ff_ipfs_protocol;
+extern const URLProtocol ff_ipns_protocol;
 
 #include "libavformat/protocol_list.c"
 
-- 
2.35.1

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