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File metadata and controls

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The hash() function and the splitPieceHashes() function serve different purposes in the context of handling torrent files, particularly in relation to SHA-1 hashing. Here’s a breakdown of each function’s purpose:

Purpose of hash() Function

  1. Creating an Info Hash:

    • The hash() function generates a SHA-1 hash for the entire bencodeInfo struct, which contains metadata about the torrent, such as the name, piece length, total length, and the concatenated SHA-1 hashes of the pieces.
    • This generated hash is known as the info hash and uniquely identifies the torrent itself across the network.

  2. Data Integrity:

    • The info hash is used to verify that the torrent metadata is valid and has not been tampered with. When a torrent client connects to a tracker or other peers, it uses this info hash to identify the specific torrent being downloaded.

  3. Single Hash Output:

    • The hash() function returns a single [20]byte array that represents the SHA-1 hash of the serialized bencodeInfo data. This is a unique identifier for the entire torrent's metadata, not just individual pieces.

Purpose of splitPieceHashes() Function

  1. Extracting Individual Piece Hashes:

    • In contrast, the splitPieceHashes() function takes the concatenated string of SHA-1 hashes from the pieces field in the bencodeInfo struct and splits it into individual [20]byte arrays.
    • Each array represents the SHA-1 hash for a specific piece of the file being shared.

  2. Integrity Verification for Pieces:

    • These individual piece hashes are crucial for verifying the integrity of each piece during the downloading process. After downloading a piece, the client computes the SHA-1 hash of the downloaded data and compares it to the expected hash from the torrent metadata to ensure that the piece is correct.

  3. Multiple Hash Outputs:

    • The splitPieceHashes() function returns a slice of [20]byte arrays, each containing a SHA-1 hash for an individual piece, allowing for piece-wise integrity checks.

Summary

  • hash(): Generates a single info hash for the entire torrent's metadata, used to identify the torrent in the network.
  • splitPieceHashes(): Extracts and splits the concatenated piece hashes from the torrent metadata, allowing for individual verification of each piece as it is downloaded.

Both functions are essential but focus on different aspects of torrent handling: one on the overall torrent identity and the other on the integrity of its individual pieces. If you have more questions or need clarification on anything specific, feel free to ask!