Re: [FFmpeg-devel] [PATCH v5 1/1] avformat: Add IPFS protocol support.

[Mark Gaiser <markg85@gmail.com>]

On Sat, Feb 12, 2022 at 6:57 PM Mark Gaiser <markg85@gmail.com> wrote:

>
>
> On Sat, Feb 12, 2022 at 1:19 PM Tomas Härdin <tjoppen@acc.umu.se> wrote:
>
>> tor 2022-02-10 klockan 02:13 +0100 skrev Mark Gaiser:
>> > 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 | 326
>> > ++++++++++++++++++++++++++++++++++++++
>> >  libavformat/protocols.c   |   2 +
>> >  5 files changed, 362 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..9ebced10c7
>> > --- /dev/null
>> > +++ b/libavformat/ipfsgateway.c
>> > @@ -0,0 +1,326 @@
>> > +/*
>> > + * 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.
>> > +static int populate_ipfs_gateway(URLContext *h, char *gateway)
>> > +{
>> > +    char ipfs_full_data_folder[PATH_MAX];
>> > +    char ipfs_gateway_file[PATH_MAX];
>> > +    struct stat st;
>> > +    int stat_ret = 0;
>> > +    int ret = AVERROR(EINVAL);
>> > +    FILE *gateway_file = NULL;
>> > +    char gateway_file_data[PATH_MAX];
>> > +
>> > +    // We could already have a gateway (it would have been passed as
>> > -gateway).
>> > +    if (*gateway != '\0') {
>> > +        ret = 1;
>> > +        goto err;
>> > +    }
>>
>> Why even call this function if this is the case?
>>
>> > +
>> > +    // Test $IPFS_GATEWAY.
>> > +    if (getenv("IPFS_GATEWAY") != NULL) {
>> > +        snprintf(gateway, PATH_MAX, "%s", getenv("IPFS_GATEWAY"));
>>
>> Passing buffer length rather than assuming PATH_MAX would be better.
>> That way it can be changed without this breaking.
>>
>> Or stick the buffer in IPFSGatewayContext and use sizeof()
>>
>
> Awesome! Didn't even consider the option yet. Will do.
>
>>
>> > +        ret = 1;
>> > +        goto err;
>> > +    } else
>> > +        av_log(h, AV_LOG_DEBUG, "$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 = AVERROR(EINVAL);
>> > +            goto err;
>> > +        }
>> > +
>> > +        // Verify the composed path fits.
>> > +        if (snprintf(ipfs_full_data_folder, PATH_MAX, "%s/.ipfs/",
>>
>> sizeof(ipfs_full_data_folder)
>> This goes for most PATH_MAX in here
>>
>
> Yeah, i kinda thought using PATH_MAX everywhere would be consistent.
> Flipping all of those to sizeof(...)
>
>>
>> > +                     getenv("HOME")) > PATH_MAX) {
>> > +            av_log(h, AV_LOG_ERROR, "The IPFS data path exceeds the
>> > max path length (%i)\n", PATH_MAX);
>> > +            ret = AVERROR(EINVAL);
>> > +            goto err;
>> > +        }
>> > +
>> > +        // 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_INFO, "Unable to find IPFS folder. We
>> > tried:\n");
>> > +            av_log(h, AV_LOG_INFO, "- $IPFS_PATH, which was
>> > empty.\n");
>> > +            av_log(h, AV_LOG_INFO, "- $HOME/.ipfs (full uri: %s)
>> > which doesn't exist.\n", ipfs_full_data_folder);
>> > +            ret = AVERROR(ENOENT);
>> > +            goto err;
>> > +        }
>>
>> Right. This makes more sense
>>
>> > +    } else
>> > +        snprintf(ipfs_full_data_folder, PATH_MAX, "%s",
>> > getenv("IPFS_PATH"));
>> > +
>> > +    // Copy the fully composed gateway path into ipfs_gateway_file.
>> > +    if (snprintf(ipfs_gateway_file, PATH_MAX, "%sgateway",
>> > +                 ipfs_full_data_folder) > PATH_MAX) {
>> > +        av_log(h, AV_LOG_ERROR, "The IPFS gateway file path exceeds
>> > the max path length (%i)\n", PATH_MAX);
>> > +        ret = AVERROR(ENOENT);
>> > +        goto err;
>> > +    }
>> > +
>> > +    // 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 = AVERROR(ENOENT);
>> > +        goto err;
>> > +    }
>> > +
>> > +    // Read a single line (fgets stops at new line mark).
>> > +    fgets(gateway_file_data, PATH_MAX - 1, gateway_file);
>> > +
>> > +    // Replace the last char with \0
>> > +    gateway_file_data[PATH_MAX - 1] = 0;
>> > +
>> > +    // Replace first occurence of end of line with \0
>> > +    gateway_file_data[strcspn(gateway_file_data, "\r\n")] = 0;
>>
>> Won't this be just \n on Unix-like systems? Could be two lines, one
>> with strcspn(.., "\n") and the other with "\r".
>>
>
> The current logic works with linux.
> Splitting it up regardless, it can't hurt and might catch some nasty edge
> cases.
>
>>
>> > +
>> > +    // 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 = AVERROR(EILSEQ);
>> > +        goto err;
>> > +    }
>> > +
>> > +    // At this point gateway_file_data contains at least something.
>> > +    // Copy it into gateway.
>> > +    if (snprintf(gateway, PATH_MAX, "%s", gateway_file_data) > 0) {
>> > +        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);
>> > +
>> > +    return ret;
>> > +}
>> > +
>> > +// For now just makes sure that the gateway ends in url we expect.
>> > +// Like http://localhost:8080/.
>> > +// Explicitly with the traling slash.
>> > +static int sanitize_ipfs_gateway(URLContext *h, char *gateway)
>> > +{
>> > +    const char *url_without_protocol;
>> > +    int ret = 1;
>> > +
>> > +    // Test if the gateway starts with either http:// or https://
>> > +    // The remainder is stored in url_without_protocol
>> > +    if (av_stristart(gateway, "http://", &url_without_protocol) == 0
>> > +        && av_stristart(gateway, "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 = AVERROR(EILSEQ);
>> > +        goto err;
>> > +    }
>> > +
>> > +    // We now know the remainder of the url without the protocol.
>> > Check it for
>> > +    // some length. At least 1 character.
>> > +    if (strlen(url_without_protocol) < 1) {
>> > +        av_log(h, AV_LOG_ERROR, "The gateway url (without the
>> > protocol part) is too short to be a valid URL.\n");
>> > +        ret = AVERROR(EILSEQ);
>> > +        goto err;
>> > +    }
>>
>> I think we can just rely on the http protocol stuff to deal with this
>>
>
> Do you mind if I keep it in? It doesn't seem to hurt and again does help
> in debugging scenarios.
>
>
>>
>> > +
>> > +
>> > +    if (gateway[strlen(gateway) - 1] != '/') {
>> > +        // Check if we have enough room to add a '/'
>> > +        // We already know that it's bigger then 0 because that's
>> > handled
>> > +        // in populate_ipfs_gateway
>> > +
>> > +        if (strlen(gateway) < (PATH_MAX - 2)) {
>> > +            // We have room. Get the length and add a '/' and a '\0'
>> > +            int gateway_length = strlen(gateway);
>> > +            gateway[gateway_length] = '/';
>> > +            gateway[gateway_length + 1] = '\0';
>> > +        } else
>> > +            av_log(h, AV_LOG_ERROR, "The gateway url is longer then
>> > the allowed max path length (%i).\n", PATH_MAX);
>> > +
>> > +        ret = 1;
>> > +        goto err;
>> > +    }
>>
>> Rolling this into the snprintf() would be prettier
>>
>
> Ugh :P
> Well, I did that before I changed it to this. It worked but it threw a
> compile warning about the resulting size truncating the gateway variable.
> This seemed simpler than checking for it. But then again, I am now
> checking for that length in other places too so I might as well do that
> here too.
>
>
>>
>> > +
>> > +err:
>> > +    return ret;
>> > +}
>> > +
>> > +static int translate_ipfs_to_http(URLContext *h, const char *uri,
>> > +                                  int flags, AVDictionary **options)
>> > +{
>> > +    const char *ipfs_cid;
>> > +    char *fulluri = NULL;
>> > +    char ipfs_gateway[PATH_MAX];
>> > +    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);
>> > +    int is_ipns = av_stristart(uri, "ipns://", &ipfs_cid);
>> > +
>> > +    // 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;
>> > +    }
>>
>> Shouldn't this check that the URL is precisely what the protocol
>> expects? ipfs for ff_ipfs_protocol and ipns for ff_ipns_protocol. Maybe
>> that's validated further up however..
>>
>
> Well, the protocol has 2 potential ways:
> <gateway>/<protocol>/<ipfs cid> (existed since the start of IPFS)
> and
> <ipfs cid>.<protocol>.<gateway> (called subdomain gateway)
>
> An example of both:
>
> http://localhost:8080/ipfs/bafybeigagd5nmnn2iys2f3doro7ydrevyr2mzarwidgadawmamiteydbzi
>
> http://bafybeigagd5nmnn2iys2f3doro7ydrevyr2mzarwidgadawmamiteydbzi.ipfs.localhost:8080
>
> Both are valid but the former is easier.
> The latter really mostly exists for website/browser purposes [1].
> Therefore I like to use the former because it's much easier. It only
> requires a geteway provided by the user.
> And after that it's only a matter of appending strings. The alternative
> option is more tricky to get right.
> Regardless, the way I concatenate the strings now is how I construct a
> valid url.
>
> If that URL isn't valid then there's likely a gateway permission issue.
> But that's outside the scope of this protocol and likely something the
> http(s) protocol informs you about anyhow.
>
> Anyhow, thank you again for the review!
> I'll send a V6 later this evening.
> Are we close to merging it? ;)
>
> [1]
> https://codeclimbing.com/why-i-am-excited-about-subdomain-ipfs-gateways/
>
>
Sorry for asking a perhaps stupid question but what is the normal sane way
in c to append to a stack array?
I now have this:
    if (c->gateway_buffer[strlen(c->gateway_buffer) - 1] != '/' &&
        strlen(c->gateway_buffer) < (sizeof(c->gateway_buffer) - 1)) {
        // Add a "/". strncat also takes care of adding a null terminating
character.
        strncat(c->gateway_buffer, "/",
                sizeof(c->gateway_buffer) - strlen(c->gateway_buffer) - 1);
        ret = 1;
        goto err;
    }

Using strncat. That works without errors or warnings.
But using snprintf to append keeps giving me these warnings that i don't
get:
libavformat/ipfsgateway.c:189:9: warning: ‘snprintf’ argument 4 overlaps
destination object ‘c’ [-Wrestrict]
  189 |     if (snprintf(c->gateway_buffer, sizeof(c->gateway_buffer) - 50,
"%s/",
      |
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  190 |                  c->gateway_buffer) > 0) {
      |                  ~~~~~~~~~~~~~~~~~~
libavformat/ipfsgateway.c:168:25: note: destination object referenced by
‘restrict’-qualified argument 1 was declared here
  168 |     IPFSGatewayContext *c = h->priv_data;
      |                         ^

It not an issue if the use of strncat is fine in the above example :)


>
>> /Tomas
>>
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>
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