client API: allow using msg-level option for log messages

Client API users can enable log output with mpv_request_log_messages().
But you can enable only a single log level. This is normally enough, but
the --msg-level option (which controls the terminal log level) provides
more flexibility. Due to internal complexity, it would be hard to
provide the same flexibility for each client API handle. But there's a
simple way to achieve basically the same thing: add an option that sends
log messages to the API handle, which would also be printed to the
terminal as by --msg-level.

The only change is that we don't disable this logic if the terminal is
disabled. Instead we check for this before the message is output, which
in theory can lower performance if messages are being spammed. It could
be handled with some more effort, but the gain would be negligible.

DOCS/client-api-changes.rst

@@ -32,6 +32,7 @@ API changes
 
 ::
 
+ 1.19   - mpv_request_log_messages() now accepts "terminal-default" as parameter
  1.18   - add MPV_END_FILE_REASON_REDIRECT, and change behavior of
           MPV_EVENT_END_FILE accordingly
         - a bunch of interface-changes.rst changes

common/msg.c

@@ -106,16 +106,12 @@ static void update_loglevel(struct mp_log *log)
 {
     struct mp_log_root *root = log->root;
     pthread_mutex_lock(&mp_msg_lock);
-    log->level = -1;
-    log->terminal_level = -1;
-    if (log->root->use_terminal) {
-        log->level = MSGL_STATUS + log->root->verbose; // default log level
-        for (int n = 0; root->msg_levels && root->msg_levels[n * 2 + 0]; n++) {
-            if (match_mod(log->verbose_prefix, root->msg_levels[n * 2 + 0]))
-                log->level = mp_msg_find_level(root->msg_levels[n * 2 + 1]);
-        }
-        log->terminal_level = log->root->use_terminal ? log->level : -1;
+    log->level = MSGL_STATUS + log->root->verbose; // default log level
+    for (int n = 0; root->msg_levels && root->msg_levels[n * 2 + 0]; n++) {
+        if (match_mod(log->verbose_prefix, root->msg_levels[n * 2 + 0]))
+            log->level = mp_msg_find_level(root->msg_levels[n * 2 + 1]);
     }
+    log->terminal_level = log->level;
     for (int n = 0; n < log->root->num_buffers; n++)
         log->level = MPMAX(log->level, log->root->buffers[n]->level);
     if (log->root->log_file)
@@ -239,7 +235,7 @@ static void pretty_print_module(FILE* stream, const char *prefix, bool use_color
 
 static bool test_terminal_level(struct mp_log *log, int lev)
 {
-    return lev <= log->terminal_level &&
+    return lev <= log->terminal_level && log->root->use_terminal &&
            !(lev == MSGL_STATUS && terminal_in_background());
 }
 
@@ -297,7 +293,10 @@ static void write_msg_to_buffers(struct mp_log *log, int lev, char *text)
     struct mp_log_root *root = log->root;
     for (int n = 0; n < root->num_buffers; n++) {
         struct mp_log_buffer *buffer = root->buffers[n];
-        if (lev <= buffer->level && lev != MSGL_STATUS) {
+        int buffer_level = buffer->level;
+        if (buffer_level == MP_LOG_BUFFER_MSGL_TERM)
+            buffer_level = log->terminal_level;
+        if (lev <= buffer_level && lev != MSGL_STATUS) {
             // Assuming a single writer (serialized by msg lock)
             int avail = mp_ring_available(buffer->ring) / sizeof(void *);
             if (avail < 1)

common/msg_control.h

@@ -18,6 +18,9 @@ struct mp_log_buffer_entry {
     char *text;
 };
 
+// Use --msg-level option for log level of this log buffer
+#define MP_LOG_BUFFER_MSGL_TERM (MSGL_MAX + 1)
+
 struct mp_log_buffer;
 struct mp_log_buffer *mp_msg_log_buffer_new(struct mpv_global *global,
                                             int size, int level,

libmpv/client.h

@@ -198,7 +198,7 @@ extern "C" {
  * relational operators (<, >, <=, >=).
  */
 #define MPV_MAKE_VERSION(major, minor) (((major) << 16) | (minor) | 0UL)
-#define MPV_CLIENT_API_VERSION MPV_MAKE_VERSION(1, 18)
+#define MPV_CLIENT_API_VERSION MPV_MAKE_VERSION(1, 19)
 
 /**
  * Return the MPV_CLIENT_API_VERSION the mpv source has been compiled with.
@@ -1418,6 +1418,9 @@ int mpv_request_event(mpv_handle *ctx, mpv_event_id event, int enable);
  * @param min_level Minimal log level as string. Valid log levels:
  *                      no fatal error warn info status v debug trace
  *                  The value "no" disables all messages. This is the default.
+ *                  An exception is the value "terminal-default", which uses the
+ *                  log level as set by the "--msg-level" option. This works
+ *                  even if the terminal is disabled. (Since API version 1.19.)
  *                  Also see mpv_log_level.
  */
 int mpv_request_log_messages(mpv_handle *ctx, const char *min_level);

player/client.c

@@ -1523,6 +1523,9 @@ int mpv_request_log_messages(mpv_handle *ctx, const char *min_level)
             break;
         }
     }
+    if (strcmp(min_level, "terminal-default") == 0)
+        level = MP_LOG_BUFFER_MSGL_TERM;
+
     if (level < 0 && strcmp(min_level, "no") != 0)
         return MPV_ERROR_INVALID_PARAMETER;