[FFmpeg-devel] [PATCH v7 0/1] Add IPFS protocol support.

[FFmpeg-devel] [PATCH v7 0/1] Add IPFS protocol support.

[Mark Gaiser]

Hi,

This patch series adds support for IPFS.
V7:
- Removed sanitize_ipfs_gateway. Only the http/https check stayed and that's
  now in translate_ipfs_to_http.
- Added a check for ipfs_cid. It's only to show an error is someone happens to
  profide `ffplay ipfs://` without a cid.
- All snprintf usages are now checked.
- Adding a / to a gateway if it didn't end with it is now done in the same line
  that composes the full resulting url.
- And a couple more minor things.
V6:
- Moved the gateway buffer (now called gateway_buffer) to IPFSGatewayContext
- Changed nearly all PATH_MAX uses to sizeof(...) uses for future flexibility
- The rest is relatively minor feedback changes
V5:
- "c->gateway" is now not modified anymore
- Moved most variables to the stack
- Even more strict checks with the auto detection logic
- Errors are now AVERROR :)
- Added more logging and changed some debug ones to info ones as they are 
  valuable to aid debugging as a user when something goes wrong.
V3 (V4):
- V4: title issue from V3..
- A lot of style changes
- Made url checks a lot more strict
- av_asprintf leak fixes
- So many changes that a diff to v2 is again not sensible.
V2:
- Squashed and changed so much that a diff to v1 was not sensible.

The following is a short summary. In the IPFS ecosystem you access it's content
by a "Content IDentifier" (CID). This CID is, in simplified terms, a hash of 
the content. IPFS itself is a distributed network where any user can run a node
to be part of the network and access files by their CID. If any reachable node 
within that network has the CID, you can get it.

IPFS (as a technology) has two protocols, ipfs and ipns.
The ipfs protocol is the immutable way to access content.
The ipns protocol is a mutable layer on top of it. It's essentially a new CID 
that points to a ipfs CID. This "pointer" if you will can be changed to point 
to something else.
Much more information on how this technology works can be found here [1].

This patch series allows to interact natively with IPFS. That means being able
to access files like:
- ffplay ipfs://<cid>
- ffplay ipns://<cid>

There are multiple ways to access files on the IPFS network. This patch series
uses the gateway driven way. An IPFS node - by default - exposes a local 
gateway (say http://localhost:8080) which is then used to get content from IPFS.
The gateway functionality on the IPFS side contains optimizations to
be as ideal to streaming data as it can be. Optimizations that the http protocol
in ffmpeg also has and are thus reused for free in this approach.

A note on other "more appropiate" ways, as I received some feedback on that.
For ffmpeg purposes the gateway approach is ideal! There is a "libipfs" but
that would spin up an ipfs node with the overhead of:
- bootstrapping
- connecting to nodes
- finding other nodes to connect too
- finally finding your file

This alternative approach could take minutes before a file is played. The
gateway approach immediately connects to an already running node thus gives
the file the fastest.

Much of the logic in this patch series is to find that gateway and essentially 
rewrite:

"ipfs://<cid>"

to:

"http://localhost:8080/ipfs/<cid>"

Once that's found it's forwared to the protocol handler where eventually the
http protocol is going to handle it. Note that it could also be https. There's 
enough flexibility in the implementation to allow the user to provide a 
gateway. There are also public https gateways which can be used just as well.

After this patch is accepted, I'll work on getting IPFS supported in:
- mpv (requires this ffmpeg patch)
- vlc (prefers this patch but can be made to work without this patch)
- kodi (requires this ffmpeg patch)

Best regards,
Mark Gaiser

[1] https://docs.ipfs.io/concepts/

Mark Gaiser (1):
  avformat: Add IPFS protocol support.

 configure                 |   2 +
 doc/protocols.texi        |  30 ++++
 libavformat/Makefile      |   2 +
 libavformat/ipfsgateway.c | 312 ++++++++++++++++++++++++++++++++++++++
 libavformat/protocols.c   |   2 +
 5 files changed, 348 insertions(+)
 create mode 100644 libavformat/ipfsgateway.c

-- 
2.35.1

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[FFmpeg-devel] [PATCH v7 1/1] avformat: Add IPFS protocol support.

[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 | 312 ++++++++++++++++++++++++++++++++++++++
 libavformat/protocols.c   |   2 +
 5 files changed, 348 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..35456c00c4
--- /dev/null
+++ b/libavformat/ipfsgateway.c
@@ -0,0 +1,312 @@
+/*
+ * 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;
+    // Is filled by the -gateway argument and not changed after.
+    char *gateway;
+    // If the above gateway is non null, it will be copied into this buffer.
+    // Else this buffer will contain the auto detected gateway.
+    // In either case, the gateway to use will be in this buffer.
+    char gateway_buffer[PATH_MAX];
+} 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)
+{
+    IPFSGatewayContext *c = h->priv_data;
+    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;
+
+    // Set the first character of c->gateway_buffer to 0.
+    c->gateway_buffer[0] = '\0';
+
+    // Test $IPFS_GATEWAY.
+    if (getenv("IPFS_GATEWAY") != NULL) {
+        if (snprintf(c->gateway_buffer, sizeof(c->gateway_buffer), "%s",
+                     getenv("IPFS_GATEWAY")) >= sizeof(c->gateway_buffer)) {
+            av_log(h, AV_LOG_ERROR, "The IPFS_GATEWAY environment variable exceeds the maximum length. We allow a max of %li characters\n", sizeof(c->gateway_buffer));
+            ret = AVERROR(EINVAL);
+            goto err;
+        }
+
+        ret = 1;
+        goto err;
+    } else
+        av_log(h, AV_LOG_DEBUG, "$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, sizeof(ipfs_full_data_folder),
+                     "%s/.ipfs/", getenv("HOME")) >= sizeof(ipfs_full_data_folder)) {
+            av_log(h, AV_LOG_ERROR, "The IPFS data path exceeds the max path length (%li)\n", sizeof(ipfs_full_data_folder));
+            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;
+        }
+    } else {
+        if (snprintf(ipfs_full_data_folder, sizeof(ipfs_full_data_folder), "%s",
+                 getenv("IPFS_PATH")) >= sizeof(ipfs_full_data_folder)) {
+            av_log(h, AV_LOG_ERROR, "The IPFS_PATH environment variable exceeds the maximum length. We allow a max of %li characters\n", sizeof(c->gateway_buffer));
+            ret = AVERROR(EINVAL);
+            goto err;
+        }
+
+    }
+
+    // Copy the fully composed gateway path into ipfs_gateway_file.
+    if (snprintf(ipfs_gateway_file, sizeof(ipfs_gateway_file), "%sgateway",
+                 ipfs_full_data_folder) >= sizeof(ipfs_gateway_file)) {
+        av_log(h, AV_LOG_ERROR, "The IPFS gateway file path exceeds the max path length (%li)\n", sizeof(ipfs_gateway_file));
+        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(c->gateway_buffer, sizeof(c->gateway_buffer) - 1, gateway_file);
+
+    // Replace the last char with \0
+    c->gateway_buffer[sizeof(c->gateway_buffer) - 1] = 0;
+
+    // Replace first occurence of end of line with \0
+    c->gateway_buffer[strcspn(c->gateway_buffer, "\r")] = 0;
+    c->gateway_buffer[strcspn(c->gateway_buffer, "\n")] = 0;
+
+    // If strlen finds anything longer then 0 characters then we have a
+    // potential gateway url.
+    if (strlen(c->gateway_buffer) < 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;
+    } else {
+        // We're done, the c->gateway_buffer has something that looks valid.
+        ret = 1;
+        goto err;
+    }
+
+err:
+    if (gateway_file)
+        fclose(gateway_file);
+
+    return ret;
+}
+
+static int translate_ipfs_to_http(URLContext *h, const char *uri,
+                                  int flags, AVDictionary **options)
+{
+    const char *ipfs_cid;
+    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);
+    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;
+    }
+
+    // If the CID has a length greater then 0 then we assume we have a proper working one.
+    // It could still be wrong but in that case the gateway should save us and
+    // ruturn a 403 error. The http protocol handles this.
+    if (strlen(ipfs_cid) < 1) {
+        av_log(h, AV_LOG_ERROR, "A CID must be provided.\n");
+        ret = AVERROR(EILSEQ);
+        goto err;
+    }
+
+    // Populate c->gateway_buffer with whatever is in c->gateway
+    if (c->gateway != NULL) {
+        if (snprintf(c->gateway_buffer, sizeof(c->gateway_buffer), "%s",
+                     c->gateway) >= sizeof(c->gateway_buffer)) {
+            av_log(h, AV_LOG_ERROR, "The -gateway parameter is too long. We allow a max of %li characters\n", sizeof(c->gateway_buffer));
+            ret = AVERROR(EINVAL);
+            goto err;
+        }
+    } else {
+        // Populate the IPFS gateway if we have any.
+        // If not, inform the user how to properly set one.
+        ret = populate_ipfs_gateway(h);
+
+        if (ret < 1) {
+            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");
+            goto err;
+        }
+    }
+
+    // Test if the gateway starts with either http:// or https://
+    if (av_stristart(c->gateway_buffer, "http://", NULL) == 0
+        && av_stristart(c->gateway_buffer, "https://", NULL) == 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;
+    }
+
+    // Concatenate the url.
+    // This ends up with something like: http://localhost:8080/ipfs/Qm.....
+    // The format of "%s%s%s%s" is the following:
+    // 1st %s = The gateway.
+    // 2nd %s = If the gateway didn't end in a slash, add a "/". Otherwise it's an empty string
+    // 3rd %s = Either ipns/ or ipfs/.
+    // 4th %s = The IPFS CID (Qm..., bafy..., ...).
+    fulluri = av_asprintf("%s%s%s%s",
+                          c->gateway_buffer,
+                          (c->gateway_buffer[strlen(c->gateway_buffer) - 1] == '/') ? "" : "/",
+                          (is_ipns) ? "ipns/" : "ipfs/",
+                          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;
+    av_free(c->gateway);
+    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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Re: [FFmpeg-devel] [PATCH v7 1/1] avformat: Add IPFS protocol support.

[Tomas Härdin]

> +    IPFSGatewayContext *c = h->priv_data;
> +    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;
> +
> +    // Set the first character of c->gateway_buffer to 0.
> +    c->gateway_buffer[0] = '\0';

unnecessary

> +
> +    // Test $IPFS_GATEWAY.
> +    if (getenv("IPFS_GATEWAY") != NULL) {
> +        if (snprintf(c->gateway_buffer, sizeof(c->gateway_buffer),
> "%s",
> +                     getenv("IPFS_GATEWAY")) >= sizeof(c-
> >gateway_buffer)) {
> +            av_log(h, AV_LOG_ERROR, "The IPFS_GATEWAY environment
> variable exceeds the maximum length. We allow a max of %li
> characters\n", sizeof(c->gateway_buffer));

nit: seems a bit weird to break the if but not the av_log()
Also this should be %zu not %li

/Tomas

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Re: [FFmpeg-devel] [PATCH v7 1/1] avformat: Add IPFS protocol support.

[Mark Gaiser]

On Thu, Feb 17, 2022 at 2:57 PM Tomas Härdin <tjoppen@acc.umu.se> wrote:

> > +    IPFSGatewayContext *c = h->priv_data;
> > +    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;
> > +
> > +    // Set the first character of c->gateway_buffer to 0.
> > +    c->gateway_buffer[0] = '\0';
>
> unnecessary
>

Hmm, interesting. I tried to be secure and not let any potential strlen
trip when there is garbage data in c->gateway_buffer.
Just to set it in a function that always overwrites it anyhow ;)
Aka, useless.

>
> > +
> > +    // Test $IPFS_GATEWAY.
> > +    if (getenv("IPFS_GATEWAY") != NULL) {
> > +        if (snprintf(c->gateway_buffer, sizeof(c->gateway_buffer),
> > "%s",
> > +                     getenv("IPFS_GATEWAY")) >= sizeof(c-
> > >gateway_buffer)) {
> > +            av_log(h, AV_LOG_ERROR, "The IPFS_GATEWAY environment
> > variable exceeds the maximum length. We allow a max of %li
> > characters\n", sizeof(c->gateway_buffer));
>
> nit: seems a bit weird to break the if but not the av_log()
> Also this should be %zu not %li
>

The compiler doesn't complain about this one.
How do you know %zu is right? I used this table and it knows nothing about
%z...
https://www.cplusplus.com/reference/cstdio/printf/

Anyhow, I'm certainly not doubting you so changing it (and all other %li
occurrences). Other sites seem to indicate it's for printing size_t .

So.. erm... the next version can finally be merged?


> /Tomas
>
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Re: [FFmpeg-devel] [PATCH v7 1/1] avformat: Add IPFS protocol support.

[Tomas Härdin]

tor 2022-02-17 klockan 15:26 +0100 skrev Mark Gaiser:
> > 
> > > +
> > > +    // Test $IPFS_GATEWAY.
> > > +    if (getenv("IPFS_GATEWAY") != NULL) {
> > > +        if (snprintf(c->gateway_buffer, sizeof(c-
> > > >gateway_buffer),
> > > "%s",
> > > +                     getenv("IPFS_GATEWAY")) >= sizeof(c-
> > > > gateway_buffer)) {
> > > +            av_log(h, AV_LOG_ERROR, "The IPFS_GATEWAY
> > > environment
> > > variable exceeds the maximum length. We allow a max of %li
> > > characters\n", sizeof(c->gateway_buffer));
> > 
> > nit: seems a bit weird to break the if but not the av_log()
> > Also this should be %zu not %li
> > 
> 
> The compiler doesn't complain about this one.
> How do you know %zu is right? I used this table and it knows nothing
> about
> %z...
> https://www.cplusplus.com/reference/cstdio/printf/

sizeof() returns size_t

/Tomas

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