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(PHP Extension) 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
<?php // The version number (9_5_0) should match version of the Chilkat extension used, omitting the micro-version number. // For example, if using Chilkat v9.5.0.48, then include as shown here: include("chilkat_9_5_0.php"); // This example requires the Chilkat API to have been previously unlocked. // See Global Unlock Sample for sample code. $crypt = new CkCrypt2(); // 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 = new CkFileAccess(); $bd = new CkBinData(); $bdHashes = new CkBinData(); $success = $fac->OpenForRead('qa_data/jpg/milky-way-nasa.jpg'); if ($success == false) { print $fac->lastErrorText() . "\n"; exit; } $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 . ': ' . $hashHex . "\n"; $bdHashes->AppendEncoded($hashHex,'hex_lower'); $i = $i + 1; } $fac->FileClose(); // Hash the concatenated SHA-256 hashes. $content_hash = $crypt->hashBdENC($bdHashes); print 'content_hash = ' . $content_hash . "\n"; ?> |
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