lofty-rs Corrupting flac files

Reproducer

Summary

I've been running into issues with lofty corrupting flac files in the following situations:

It's a "bare" flac file (eg STREAMINFO is the final block, no tag metadata, no SEEKTABLE),
There's no padding or metadata, just a STREAMINFO and SEEKTABLE.

I'm not entirely sure of my understanding of the bug. I've laid out below what I think is the problem, but I dont have enough confidence in my understanding to offer a PR:

Right here (https://github.com/Serial-ATA/lofty-rs/blob/2727c5ce65501dc57075e3995958ecdea1ea4569/lofty/src/flac/write.rs#L83). last_block_info is later used as (header_first_byte, header_offset, payload_end). You’re overwriting the header offset with (end - start) (the length), and the “header first byte” with block.byte (which is just the value of the first header byte, not an offset). This causes file_bytes[last_block_info.1] = first_byte; (https://github.com/Serial-ATA/lofty-rs/blob/2727c5ce65501dc57075e3995958ecdea1ea4569/lofty/src/flac/write.rs#L127) to write the “is_last” flag into a length-sized index. The causes file corruption when we need to adding a padding block.
If there are no blocks to remove, we corrupt the file right here (https://github.com/Serial-ATA/lofty-rs/blob/2727c5ce65501dc57075e3995958ecdea1ea4569/lofty/src/flac/write.rs#L152) file_bytes.splice(0..0, comment_blocks); overwrites the first 4 fLaC bytes in the file.

Expected behavior

No response

Assets

No response

Sep 28 '25 18:09 phayes

I've opened a PR for this here: #550 - I would appreciate a careful review since I'm not 100% confident I'm following all the various accouting being done to keep track of things.

Sep 28 '25 19:09 phayes

@Serial-ATA facing the same issue in Spotube (v5.1.0 latest) which uses lofty-rs for tagging. You can actually check the downloaded FLAC files with ffprobe and it shows:

Btw, use the DAB Music plugin from the plugins page which provides FLAC streaming support`

libvo_amrwbenc,libvorbis,libvpx_vp8,libvpx_vp9,libwebp,libwebp_anim,libxvid,mjpeg,mjpeg_qsv,mjpeg_vaapi,mlp,mp2,mp2fixed,mpeg1video,mpeg2_qsv,mpeg2_vaapi,mpeg2video,mpeg4,mpeg4_v4l2m2m,msmpeg4v2,msmpeg4v3,msvideo1,nellymoser,opus,pam,pbm,pcm_alaw,pcm_f32be,pcm_f32le,pcm_f64be,pcm_f64le,pcm_mulaw,pcm_s16be,pcm_s16be_planar,pcm_s16le,pcm_s16le_planar,pcm_s24be,pcm_s24le,pcm_s24le_planar,pcm_s32be,pcm_s32le,pcm_s32le_planar,pcm_s8,pcm_s8_planar,pcm_u16be,pcm_u16le,pcm_u24be,pcm_u24le,pcm_u32be,pcm_u32le,pcm_u8,pcx,pgm,pgmyuv,phm,png,ppm,prores,prores_aw,prores_ks,qoi,qtrle,r10k,r210,ra_144,rawvideo,roq,roq_dpcm,rpza,rv10,rv20,s302m,sbc,sgi,smc,snow,sonic,sonic_ls,speedhq,srt,ssa,subrip,sunrast,svq1,targa,text,tiff,truehd,tta,ttml,utvideo,v210,v308,v408,v410,vc1_qsv,vc1_v4l2m2m,vc2,vnull,vorbis,vp8_qsv,vp8_v4l2m2m,vp8_vaapi,vp9_qsv,vp9_vaapi,wavpack,wbmp,webvtt,wmav1,wmav2,wmv1,wmv2,wrapped_avframe,xbm,xface,xsub,xwd,y41p,yuv4,zlib,zmbv,' --enable-decoder=',aac,aasc,libfdk_aac,ac3,acelp_kelvin,adpcm_4xm,adpcm_adx,adpcm_afc,adpcm_agm,adpcm_aica,adpcm_argo,adpcm_ct,adpcm_dtk,adpcm_ea,adpcm_ea_maxis_xa,adpcm_ea_r1,adpcm_ea_r2,adpcm_ea_r3,adpcm_ea_xas,adpcm_g722,adpcm_g726,adpcm_g726le,adpcm_ima_acorn,adpcm_ima_alp,adpcm_ima_amv,adpcm_ima_apc,adpcm_ima_apm,adpcm_ima_cunning,adpcm_ima_dat4,adpcm_ima_dk3,adpcm_ima_dk4,adpcm_ima_ea_eacs,adpcm_ima_ea_sead,adpcm_ima_iss,adpcm_ima_moflex,adpcm_ima_mtf,adpcm_ima_oki,adpcm_ima_qt,adpcm_ima_qt_at,adpcm_ima_rad,adpcm_ima_smjpeg,adpcm_ima_ssi,adpcm_ima_wav,adpcm_ima_ws,adpcm_ms,adpcm_mtaf,adpcm_psx,adpcm_sbpro_2,adpcm_sbpro_3,adpcm_sbpro_4,adpcm_swf,adpcm_thp,adpcm_thp_le,adpcm_vima,adpcm_xa,adpcm_xmd,adpcm_yamaha,adpcm_zork,aic,alac,alias_pix,amrnb,amrwb,amv,anm,ansi,anull,apac,ape,apng,arbc,argo,ass,asv1,asv2,atrac1,atrac3,atrac3al,atrac3p,atrac3pal,aura,aura2,av1,av1_qsv,bethsoftvid,bfi,bink,binkaudio_dct,binkaudio_rdft,bintext,bitpacked,bmp,bmv_audio,bmv_video,bonk,brender_pix,c93,cbd2_dpcm,ccaption,cdgraphics,cdtoons,cdxl,cinepak,clearvideo,cljr,cook,cpia,cscd,cyuv,dca,dds,derf_dpcm,dfa,dfpwm,dirac,dnxhd,dnxhr,dolby_e,dpx,dsd_lsbf,dsd_msbf,dsicinaudio,dsicinvideo,dss_sp,dvaudio,dvbsub,dvdsub,dvvideo,dxa,dxtory,eacmv,eamad,eatgq,eatgv,eatqi,eightbps,eightsvx_exp,eightsvx_fib,escape124,escape130,evrc,exr,ffv1,ffvhuff,ffwavesynth,fits,flac,flashsv,flashsv2,flic,flv,fmvc,fourxm,ftr,g723_1,g729,gdv,gem,gif,gremlin_dpcm,gsm,gsm_ms,gsm_ms_at,h261,h263,h263_v4l2m2m,h263i,h263p,hap,hca,hcom,hdr,hnm4_video,hq_hqa,hqx,huffyuv,hymt,iac,idcin,idf,iff_ilbm,ilbc,imc,indeo2,indeo3,indeo4,indeo5,interplay_acm,interplay_dpcm,interplay_video,ipu,jacosub,jpeg2000,jpegls,jv,kgv1,kmvc,lagarith,libaribb24,libaribcaption,libaom,libaom_av1,libcodec2,libdav1d,libgsm,libgsm_ms,libilbc,libjxl,liblc3,libopencore_amrnb,libopencore_amrwb,libopenh264,libopenjpeg,libopus,librsvg,libschroedinger,libspeex,libvorbis,libvpx_vp8,libvpx_vp9,libzvbi_teletext,loco,lscr,m101,mace3,mace6,mdec,media100,metasound,microdvd,mimic,misc4,mjpeg,mjpeg_qsv,mjpegb,mlp,mmvideo,motionpixels,mp1,mp1float,mp2,mp2float,mp3,mp3adu,mp3adufloat,mp3float,mp3on4,mp3on4float,mpc7,mpc8,mpeg1_v4l2m2m,mpeg1video,mpeg2_qsv,mpeg2_v4l2m2m,mpeg2video,mpeg4,mpeg4_v4l2m2m,mpegvideo,mpl2,msa1,mscc,msmpeg4v1,msmpeg4v2,msmpeg4v3,msnsiren,msp2,msrle,mss1,mss2,msvideo1,mszh,mts2,mv30,mvc1,mvc2,mvdv,mvha,mwsc,mxpeg,nellymoser,nuv,on2avc,opus,paf_audio,paf_video,pam,pbm,pcm_alaw,pcm_bluray,pcm_dvd,pcm_f16le,pcm_f24le,pcm_f32be,pcm_f32le,pcm_f64be,pcm_f64le,pcm_lxf,pcm_mulaw,pcm_s16be,pcm_s16be_planar,pcm_s16le,pcm_s16le_planar,pcm_s24be,pcm_s24daud,pcm_s24le,pcm_s24le_planar,pcm_s32be,pcm_s32le,pcm_s32le_planar,pcm_s64be,pcm_s64le,pcm_s8,pcm_s8_planar,pcm_sga,pcm_u16be,pcm_u16le,pcm_u24be,pcm_u24le,pcm_u32be,pcm_u32le,pcm_u8,pcm_vidc,pcx,pfm,pgm,pgmyuv,pgssub,pgx,phm,photocd,pictor,pjs,png,ppm,prores,prosumer,psd,ptx,qcelp,qdm2,qdmc,qdraw,qoa,qoi,qpeg,qtrle,r10k,r210,ra_144,ra_288,rasc,rawvideo,realtext,rka,rl2,roq,roq_dpcm,rpza,rscc,rv10,rv20,s302m,sami,sanm,sbc,screenpresso,sdx2_dpcm,sgi,sgirle,shorten,simbiosis_imx,sipr,siren,smackaud,smacker,smc,smvjpeg,snow,sol_dpcm,sonic,sp5x,speedhq,speex,srgc,srt,ssa,stl,subrip,subviewer,subviewer1,sunrast,svq1,svq3,tak,targa,targa_y216,tdsc,text,theora,thp,tiertexseqvideo,tiff,tmv,truehd,truemotion1,truemotion2,truemotion2rt,truespeech,tscc,tscc2,tta,twinvq,txd,ulti,utvideo,v210,v210x,v308,v408,v410,vb,vble,vcr1,vmdaudio,vmdvideo,vmnc,vnull,vorbis,vp3,vp4,vp5,vp6,vp6a,vp6f,vp7,vp8,vp8_qsv,vp8_v4l2m2m,vp9,vp9_qsv,vp9_v4l2m2m,vplayer,vqa,vqc,wady_dpcm,wavarc,wavpack,wbmp,wcmv,webp,webvtt,wmav1,wmav2,wmavoice,wmv1,wmv2,wnv1,wrapped_avframe,ws_snd1,xan_dpcm,xan_wc3,xan_wc4,xbin,xbm,xface,xl,xpm,xsub,xwd,y41p,ylc,yop,yuv4,zero12v,zerocodec,zlib,zmbv,'
  libavutil      59. 39.100 / 59. 39.100
  libavcodec     61. 19.101 / 61. 19.101
  libavformat    61.  7.100 / 61.  7.100
  libavdevice    61.  3.100 / 61.  3.100
  libavfilter    10.  4.100 / 10.  4.100
  libswscale      8.  3.100 /  8.  3.100
  libswresample   5.  3.100 /  5.  3.100
  libpostproc    58.  3.100 / 58.  3.100
[flac @ 0x5558c8d17e80] invalid sync code
[flac @ 0x5558c8d17e80] invalid frame header
[flac @ 0x5558c8d17e80] decode_frame() failed
Input #0, flac, from '~/Downloads/Spotube/R U Mine - Arctic Monkeys.flac':
  Metadata:
    TITLE           : R U Mine?
    ALBUM           : AM
    album_artist    : Arctic Monkeys
    ARTIST          : Arctic Monkeys
    YEAR            : 2013
  Duration: 00:03:21.73, start: 0.000000, bitrate: 1673 kb/s
  Stream #0:0: Audio: flac, 44100 Hz, stereo, s32 (24 bit)
  Stream #0:1: Video: mjpeg (Baseline), yuvj444p(pc, bt470bg/unknown/unknown), 300x300 [SAR 118:118 DAR 1:1], 90k tbr, 90k tbn (attached pic)
      Metadata:
        comment         : Cover (front)

Nov 17 '25 04:11 KRTirtho

I did some work on #550 a bit ago, but got caught up working on other issues. I'll see if I can finish it up soon.

Nov 17 '25 05:11 Serial-ATA