A valid JPEG must carry the quantization and Huffman tables the decoder needs. Today you serialize the standard tables into DQT and DHT segments.
Serialize a quantization table into a DQT segment and a Huffman table into a DHT segment with correct markers and lengths.
For a decoder to read your file it needs the same quantization and Huffman tables you encoded with, so the encoder must write them out. The DHT segment starts with marker FF C4, a two-byte length, and then each table’s class-and-id byte followed by its 16 count bytes and its symbol list. For the standard luminance DC table (16 counts + 12 symbols) that is a length of 2 + 1 + 16 + 12 = 31, or 00 1F, remembering that the length always counts its own two bytes. The DQT segment is analogous: FF DB, a length, then each table’s precision-and-id byte and its 64 values.
You use the same standard tables the spec’s Annex K defines and that the decoder chapters already understood - so the round trip is guaranteed to line up. Serializing tables is mechanical, but the length arithmetic is exactly the framing the decoder’s segment walk relies on, and an off-by-two here would derail the whole parse. With the tables writable, only the frame and scan headers and the final assembly remain.
// DHT: FF C4, 2-byte length, then per table: (Tc<<4|Th),// 16 BITS bytes, then HUFFVAL symbols.// DQT: FF DB, 2-byte length, then per table: (Pq<<4|Tq), 64 value bytes.// length always counts itself (the 2 length bytes).func writeDHT(tables []HuffSpec) []byte { }