Implement metadata stripping for uploaded videos

- Extend `strip_media` to support video files using `ffmpeg`.
- Use `ffmpeg -map_metadata -1 -c copy` to strip global metadata.
- Support formats: mp4, m4v, mov, webm, mkv, avi.
- Add `ffmpeg_path` configuration option.
- Implement robust relative path handling (`user/` heuristic) to support jailed environments.
- Enforce strict checks on startup: fail if tools (mogrify/ffmpeg) are missing when enabled.

1 files changed, 99 insertions, 13 deletions

diff --git a/snac.c b/snac.c
index f4528cd..a3ba6b7 100644
--- a/snac.c
+++ b/snac.c
@@ -33,6 +33,8 @@
 #include <sys/time.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
+#include <limits.h>
+#include <stdlib.h>
 
 xs_str *srv_basedir = NULL;
 xs_dict *srv_config = NULL;
@@ -177,12 +179,25 @@ int strip_media(const char *fn)
 /* strips EXIF data from a file */
 {
     int ret = 0;
+
     const xs_val *v = xs_dict_get(srv_config, "strip_exif");
 
     if (xs_type(v) == XSTYPE_TRUE) {
-        xs *l_fn = xs_tolower_i(xs_dup(fn));
+        /* Heuristic: find 'user/' in the path to make it relative */
+        /* This works for ~/user/..., /var/snac/user/..., etc. */
+        const char *r_fn = strstr(fn, "user/");
+        
+        if (r_fn == NULL) {
+            /* Fallback: try to strip ~/ if present */
+            if (strncmp(fn, "~/", 2) == 0)
+                r_fn = fn + 2;
+            else
+                r_fn = fn;
+        }
 
-        /* check extensions */
+        xs *l_fn = xs_tolower_i(xs_dup(r_fn));
+
+        /* check image extensions */
         if (xs_endswith(l_fn, ".jpg") || xs_endswith(l_fn, ".jpeg") ||
             xs_endswith(l_fn, ".png") || xs_endswith(l_fn, ".webp") ||
             xs_endswith(l_fn, ".heic") || xs_endswith(l_fn, ".heif") ||
@@ -193,7 +208,7 @@ int strip_media(const char *fn)
             if (mp == NULL)
                 mp = "mogrify";
 
-            xs *cmd = xs_fmt("%s -strip \"%s\" 2>/dev/null", mp, fn);
+            xs *cmd = xs_fmt("cd \"%s\" && %s -auto-orient -strip \"%s\" 2>/dev/null", srv_basedir, mp, r_fn);
 
             ret = system(cmd);
 
@@ -203,12 +218,64 @@ int strip_media(const char *fn)
                     code = WEXITSTATUS(ret);
                 
                 if (code == 127)
-                    srv_log(xs_fmt("strip_media: error stripping %s. '%s' not found (exit 127). Set 'mogrify_path' in server.json.", fn, mp));
+                    srv_log(xs_fmt("strip_media: error stripping %s. '%s' not found (exit 127). Set 'mogrify_path' in server.json.", r_fn, mp));
                 else
-                    srv_log(xs_fmt("strip_media: error stripping %s %d", fn, ret));
+                    srv_log(xs_fmt("strip_media: error stripping %s %d", r_fn, ret));
             }
             else
-                srv_debug(1, xs_fmt("strip_media: stripped %s", fn));
+                srv_debug(1, xs_fmt("strip_media: stripped %s", r_fn));
+        }
+        else
+        /* check video extensions */
+        if (xs_endswith(l_fn, ".mp4") || xs_endswith(l_fn, ".m4v") ||
+            xs_endswith(l_fn, ".mov") || xs_endswith(l_fn, ".webm") ||
+            xs_endswith(l_fn, ".mkv") || xs_endswith(l_fn, ".avi")) {
+
+            const char *fp = xs_dict_get(srv_config, "ffmpeg_path");
+            if (fp == NULL)
+                fp = "ffmpeg";
+
+            /* ffmpeg cannot modify in-place, so we need a temp file */
+            /* we must preserve valid extension for ffmpeg to guess the format */
+            const char *ext = strrchr(r_fn, '.');
+            if (ext == NULL) ext = "";
+            xs *tmp_fn = xs_fmt("%s.tmp%s", r_fn, ext);
+            
+            /* -map_metadata -1 strips all global metadata */
+            /* -c copy copies input streams without re-encoding */
+            /* we don't silence stderr so we can debug issues */
+            /* we explicitly cd to srv_basedir to ensure relative paths work */
+            xs *cmd = xs_fmt("cd \"%s\" && %s -y -i \"%s\" -map_metadata -1 -c copy \"%s\"", srv_basedir, fp, r_fn, tmp_fn);
+
+            ret = system(cmd);
+
+            if (ret != 0) {
+                int code = 0;
+                if (WIFEXITED(ret))
+                    code = WEXITSTATUS(ret);
+                
+                if (code == 127)
+                    srv_log(xs_fmt("strip_media: error stripping %s. '%s' not found (exit 127). Set 'ffmpeg_path' in server.json.", r_fn, fp));
+                else {
+                    srv_log(xs_fmt("strip_media: error stripping %s %d", r_fn, ret));
+                    srv_log(xs_fmt("strip_media: command was: %s", cmd));
+                }
+                
+                /* try to cleanup, just in case */
+                /* unlink needs full path too if we are not in basedir */
+                xs *full_tmp_fn = xs_fmt("%s/%s", srv_basedir, tmp_fn);
+                unlink(full_tmp_fn);
+            }
+            else {
+                /* rename tmp file to original */
+                /* use full path for source because it was created relative to basedir */
+                xs *full_tmp_fn = xs_fmt("%s/%s", srv_basedir, tmp_fn);
+                
+                if (rename(full_tmp_fn, fn) == 0)
+                    srv_debug(1, xs_fmt("strip_media: stripped %s", fn));
+                else
+                    srv_log(xs_fmt("strip_media: error renaming %s to %s", full_tmp_fn, fn));
+            }
         }
     }
 
@@ -222,14 +289,33 @@ int check_strip_tool(void)
     int ret = 1;
 
     if (xs_type(v) == XSTYPE_TRUE) {
-        const char *mp = xs_dict_get(srv_config, "mogrify_path");
-        if (mp == NULL)
-            mp = "mogrify";
+        /* check mogrify */
+        {
+            const char *mp = xs_dict_get(srv_config, "mogrify_path");
+            if (mp == NULL)
+                mp = "mogrify";
 
-        xs *cmd = xs_fmt("%s -version 2>/dev/null >/dev/null", mp);
-        
-        if (system(cmd) != 0)
-            ret = 0;
+            xs *cmd = xs_fmt("%s -version 2>/dev/null >/dev/null", mp);
+            
+            if (system(cmd) != 0) {
+                srv_log(xs_fmt("check_strip_tool: '%s' not working", mp));
+                ret = 0;
+            }
+        }
+
+        /* check ffmpeg */
+        if (ret) {
+            const char *fp = xs_dict_get(srv_config, "ffmpeg_path");
+            if (fp == NULL)
+                fp = "ffmpeg";
+
+            xs *cmd = xs_fmt("%s -version 2>/dev/null >/dev/null", fp);
+            
+            if (system(cmd) != 0) {
+                srv_log(xs_fmt("check_strip_tool: '%s' not working", fp));
+                ret = 0;
+            }
+        }
     }
 
     return ret;