最近在做大檔案分割，分片上傳，達到充分利用網路頻寬

> 檔案的上傳與下載極易出錯，尤其涉及使用斷點續傳方式上傳或下載的檔案。
> 目的：校驗MD5值是為了防止在傳輸的過程當中丟包或者資料包被篡改

MD5值得作用：任何一個字串或檔案，無論是可執行程式、影象檔案、臨時檔案或者其他任何型別的檔案，也不管它體積多大，都有且只有一個獨一無二的MD5資訊碼，並且如果這個檔案被修改過，它的MD5碼也將隨之改變。

Mac，如何通過終端驗證檔案的MD5

在終端執行命令： md5 檔案的路徑
例如：

OC 根據視訊檔案路徑獲取檔案MD5

程式碼如下：
需要匯入標頭檔案和定義巨集

#import <CommonCrypto/CommonDigest.h>

#define FileHashDefaultChunkSizeForReadingData 1024*8


- (NSString*)getFileMD5WithPath:(NSString*)path
{
    return (__bridge_transfer NSString *)FileMD5HashCreateWithPath((__bridge CFStringRef)path, FileHashDefaultChunkSizeForReadingData);
}

CFStringRef FileMD5HashCreateWithPath(CFStringRef filePath,size_t chunkSizeForReadingData) {
    // Declare needed variables
 

    CFStringRef result = NULL;
    CFReadStreamRef readStream = NULL;
    // Get the file URL
    CFURLRef fileURL =
    CFURLCreateWithFileSystemPath(kCFAllocatorDefault,
                                  (CFStringRef)filePath,
                                  kCFURLPOSIXPathStyle,
                                  (Boolean)false
 
);
    if (!fileURL) goto done;
    // Create and open the read stream
    readStream = CFReadStreamCreateWithFile(kCFAllocatorDefault,
                                            (CFURLRef)fileURL);
    if (!readStream) goto done;
    bool didSucceed = (bool)CFReadStreamOpen(readStream);
    if (!didSucceed) goto done;
    // Initialize the hash object
    CC_MD5_CTX hashObject;
    CC_MD5_Init(&hashObject);
    // Make sure chunkSizeForReadingData is valid
    if (!chunkSizeForReadingData) {
        chunkSizeForReadingData = FileHashDefaultChunkSizeForReadingData;
    }
    // Feed the data to the hash object
    bool hasMoreData = true;
    while (hasMoreData) {
        uint8_t buffer[chunkSizeForReadingData];
        CFIndex readBytesCount = CFReadStreamRead(readStream,(UInt8 *)buffer,(CFIndex)sizeof(buffer));
        if (readBytesCount == -1) break;
        if (readBytesCount == 0) {
            hasMoreData = false;
            continue;
        }
        CC_MD5_Update(&hashObject,(const void *)buffer,(CC_LONG)readBytesCount);
    }
    // Check if the read operation succeeded
    didSucceed = !hasMoreData;
    // Compute the hash digest
    unsigned char digest[CC_MD5_DIGEST_LENGTH];
    CC_MD5_Final(digest, &hashObject);
    // Abort if the read operation failed
    if (!didSucceed) goto done;
    // Compute the string result
    char hash[2 * sizeof(digest) + 1];
    for (size_t i = 0; i < sizeof(digest); ++i) {
        snprintf(hash + (2 * i), 3, "%02x", (int)(digest[i]));
    }
    result = CFStringCreateWithCString(kCFAllocatorDefault,(const char *)hash,kCFStringEncodingUTF8);

done:
    if (readStream) {
        CFReadStreamClose(readStream);
        CFRelease(readStream);
    }
    if (fileURL) {
        CFRelease(fileURL);
    }
    return result;
}

親身實踐驗證，獲取的檔案MD5值和MAC終端生產的MD5值一致，可放心使用 ~
共同學習，共同進步，共勉 ~