| 1 | package testutils |
| 2 | |
| 3 | import "math/bits" |
| 4 | |
| 5 | // VarintLen returns the number of bytes needed to encode v as a protobuf varint. |
| 6 | func VarintLen(v uint64) int { |
| 7 | return int(9*uint32(bits.Len64(v))+64) / 64 |
| 8 | } |
| 9 | |
| 10 | // LinkSerializedSize calculates the serialized size of a single PBLink in a dag-pb block. |
| 11 | // This matches the calculation in boxo/ipld/unixfs/io/directory.go estimatedBlockSize(). |
| 12 | // |
| 13 | // The protobuf wire format for a PBLink is: |
| 14 | // |
| 15 | // PBNode.Links wrapper tag (1 byte) |
| 16 | // + varint length of inner message |
| 17 | // + Hash field: tag (1) + varint(cidLen) + cidLen |
| 18 | // + Name field: tag (1) + varint(nameLen) + nameLen |
| 19 | // + Tsize field: tag (1) + varint(tsize) |
| 20 | func LinkSerializedSize(nameLen, cidLen int, tsize uint64) int { |
| 21 | // Inner link message size |
| 22 | linkLen := 1 + VarintLen(uint64(cidLen)) + cidLen + // Hash field |
| 23 | 1 + VarintLen(uint64(nameLen)) + nameLen + // Name field |
| 24 | 1 + VarintLen(tsize) // Tsize field |
| 25 | |
| 26 | // Outer wrapper: tag (1 byte) + varint(linkLen) + linkLen |
| 27 | return 1 + VarintLen(uint64(linkLen)) + linkLen |
| 28 | } |
| 29 | |
| 30 | // EstimateFilesForBlockThreshold estimates how many files with given name/cid lengths |
| 31 | // will fit under the block size threshold. |
| 32 | // Returns the number of files that keeps the block size just under the threshold. |
| 33 | func EstimateFilesForBlockThreshold(threshold, nameLen, cidLen int, tsize uint64) int { |
| 34 | linkSize := LinkSerializedSize(nameLen, cidLen, tsize) |
| 35 | // Base overhead for empty directory node (Data field + minimal structure) |
| 36 | // Empirically determined to be 4 bytes for dag-pb directories |
| 37 | baseOverhead := 4 |
| 38 | return (threshold - baseOverhead) / linkSize |
| 39 | } |