Ruby

Dropbox Content Hash

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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.

Ruby

require 'chilkat'

success = false

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

crypt = Chilkat::CkCrypt2.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.put_HashAlgorithm("sha256")
crypt.put_EncodingMode("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

fac = Chilkat::CkFileAccess.new()
bd = Chilkat::CkBinData.new()
bdHashes = Chilkat::CkBinData.new()

success = fac.OpenForRead("qa_data/jpg/milky-way-nasa.jpg")
if (success == false)
    print fac.lastErrorText() + "\n";
    exit
end

blockSize = 4194304
numBlocks = fac.GetNumBlocks(blockSize)

i = 0
while (i < numBlocks)
    # Read the next 4MB block into bd.
    bd.Clear()
    success = fac.ReadBlockBd(i,blockSize,bd)

    hashHex = crypt.hashBdENC(bd)
    print i.to_s() + ": " + hashHex + "\n";
    bdHashes.AppendEncoded(hashHex,"hex_lower")

    i = i + 1
end

fac.FileClose()

# Hash the concatenated SHA-256 hashes.
content_hash = crypt.hashBdENC(bdHashes)
print "content_hash = " + content_hash + "\n";