Rust

Dropbox Content Hash

See more Dropbox Examples

Demonstrates how to compute the Dropbox content_hash of a file. (This is the "content_hash" found in the Dropbox FileMetadata object.

Note: This example requires Chilkat v9.5.0.79 or greater because it uses the fac.ReadBlockBd method.

Rust

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

let crypt = chilkat::Crypt2::new();

// To calculate the content_hash of a file:
// Split the file into blocks of 4 MB (4,194,304 or 4 * 1024 * 1024 bytes). The last block (if any) may be smaller than 4 MB.
// Compute the hash of each block using SHA-256.
// Concatenate the hash of all blocks in the binary format to form a single binary string.
// Compute the hash of the concatenated string using SHA-256. Output the resulting hash in hexadecimal format.

crypt.set_hash_algorithm("sha256");
crypt.set_encoding_mode("hex_lower");

// We're going to calculate the content_hash for the Milky Way JPG image linked here:  https://www.dropbox.com/developers/reference/content-hash

let fac = chilkat::FileAccess::new();
let bd = chilkat::BinData::new();
let bd_hashes = chilkat::BinData::new();

if fac.open_for_read("qa_data/jpg/milky-way-nasa.jpg").is_err() {
    println!("{}", fac.last_error_text());
    return;
}

let block_size = 4194304;
let num_blocks = fac.get_num_blocks(block_size);

let mut i = 0;
while i < num_blocks {
    // Read the next 4MB block into bd.
    let _ = bd.clear();
    let _ = fac.read_block_bd(i, block_size, &bd).is_ok();

    let hash_hex = crypt.hash_bd_enc(&bd).unwrap_or_default();
    println!("{}: {}", i, hash_hex);
    let _ = bd_hashes.append_encoded(&hash_hex, "hex_lower");

    i = i + 1;
}

fac.file_close();

// Hash the concatenated SHA-256 hashes.
let content_hash = crypt.hash_bd_enc(&bd_hashes).unwrap_or_default();
println!("content_hash = {}", content_hash);