feat(lib): read audio attributes from shared files at scan time

Every search reply we sent carried no bitrate or duration, so our files
failed every bitrate filter in other clients and sorted last in
SoulseekQt, whatever their quality. The share scan now reads each MP3's
first frame header (and Xing block for variable bitrate) and each FLAC's
STREAMINFO, advertising bitrate, duration, VBR, sample rate and bit
depth as far as the format gives them; other files stay bare. Only the
file's head is read, no crate is needed, and a file that does not parse
is shared without attributes rather than skipped.

soulseek-rs/tests/cli_e2e.rs

@@ -1084,8 +1084,11 @@ impl FilterFixture {
 
     fn new(server: &TestServer, sharer: &str) -> (Self, Client) {
         let share = Scratch::new("filter-share");
+        // The mp3 is a real 128 kbps stream so the bitrate filter has
+        // something to read; the others are padding of a known size.
+        std::fs::write(share.path().join("flt_alpha_keepme.mp3"), cbr_mp3(10))
+            .expect("share file");
         for (name, size) in [
-            ("flt_alpha_keepme.mp3", Self::MEDIUM),
             ("flt_beta_skipme.flac", Self::SMALL),
             ("flt_gamma_keepme.ogg", Self::LARGE),
         ] {
@@ -1098,6 +1101,18 @@ impl FilterFixture {
     }
 }
 
+/// A constant-bitrate MP3: `frames` MPEG-1 Layer III frames at 128 kbps and
+/// 44.1 kHz, 417 bytes each; ten of them land between the fixture's SMALL
+/// and LARGE sizes.
+fn cbr_mp3(frames: usize) -> Vec<u8> {
+    let mut out = Vec::new();
+    for _ in 0..frames {
+        out.extend_from_slice(&[0xFF, 0xFB, 0x90, 0x00]);
+        out.resize(out.len() + 413, 0);
+    }
+    out
+}
+
 /// Search for the fixture as a fresh user and return the matching file names,
 /// sorted so the assertion does not depend on result order.
 ///
@@ -1155,6 +1170,30 @@ fn extension_keeps_one_type_and_repeats_into_a_union() {
     assert_eq!(several, ["flt_beta_skipme.flac", "flt_gamma_keepme.ogg"]);
 }
 
+#[test]
+fn a_bitrate_floor_keeps_only_files_that_advertise_at_least_that_much() {
+    let server = server_or_skip!();
+    let (_fixture, _sharer) = FilterFixture::new(&server, "cli_e2e_flt_kbps");
+
+    // Only the mp3 carries a bitrate; the padding files have none and an
+    // unknown bitrate cannot satisfy a floor.
+    let (exit, enough) = filtered_names(
+        &server,
+        "cli_e2e_seek_kbps_128",
+        &["--min-bitrate", "128"],
+    );
+    assert_eq!(exit, EXIT_OK);
+    assert_eq!(enough, ["flt_alpha_keepme.mp3"]);
+
+    let (exit, none) = filtered_names(
+        &server,
+        "cli_e2e_seek_kbps_320",
+        &["--min-bitrate", "320"],
+    );
+    assert_eq!(exit, EXIT_NO_RESULTS);
+    assert!(none.is_empty());
+}
+
 #[test]
 fn size_bounds_narrow_the_result_set_from_either_end() {
     let server = server_or_skip!();