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(C# UWP/WinRT) Dropbox Content HashDemonstrates 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. For more information, see https://www.dropbox.com/developers/reference/content-hash
// This example requires the Chilkat API to have been previously unlocked. // See Global Unlock Sample for sample code. Chilkat.Crypt2 crypt = new Chilkat.Crypt2(); // 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.HashAlgorithm = "sha256"; crypt.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 Chilkat.FileAccess fac = new Chilkat.FileAccess(); Chilkat.BinData bd = new Chilkat.BinData(); Chilkat.BinData bdHashes = new Chilkat.BinData(); bool success = fac.OpenForRead("qa_data/jpg/milky-way-nasa.jpg"); if (success == false) { Debug.WriteLine(fac.LastErrorText); return; } int blockSize = 4194304; int numBlocks = fac.GetNumBlocks(blockSize); int i = 0; while ((i < numBlocks)) { // Read the next 4MB block into bd. bd.Clear(); success = fac.ReadBlockBd(i,blockSize,bd); string hashHex = crypt.HashBdENC(bd); Debug.WriteLine(Convert.ToString(i) + ": " + hashHex); bdHashes.AppendEncoded(hashHex,"hex_lower"); i = i + 1; } fac.FileClose(); // Hash the concatenated SHA-256 hashes. string content_hash = crypt.HashBdENC(bdHashes); Debug.WriteLine("content_hash = " + content_hash); |
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