(Unicode C) S3 Get Object Metadata, such as ETag

Demonstrates how to get an S3 object's metadata using a HEAD request.

Chilkat C/C++ Library Downloads
MS Visual C/C++ Linux/CentOS C/C++ Alpine Linux C/C++ MAC OS X C/C++	armhf/aarch64 C/C++ C++ Builder iOS C/C++ Android C/C++	Solaris C/C++ MinGW C/C++

#include <C_CkRestW.h>
#include <C_CkAuthAwsW.h>

void ChilkatSample(void)
    {
    HCkRestW rest;
    BOOL bTls;
    int port;
    BOOL bAutoReconnect;
    BOOL success;
    HCkAuthAwsW authAws;
    int statusCode;
    const wchar_t *etag;

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

    rest = CkRestW_Create();

    // Connect to the Amazon AWS REST server in the desired region.
    // In this case we connect to S3 in the "us-west-2" region.
    bTls = TRUE;
    port = 443;
    bAutoReconnect = TRUE;
    success = CkRestW_Connect(rest,L"s3-us-west-2.amazonaws.com",port,bTls,bAutoReconnect);

    // Provide AWS credentials.
    authAws = CkAuthAwsW_Create();
    CkAuthAwsW_putAccessKey(authAws,L"AWS_ACCESS_KEY");
    CkAuthAwsW_putSecretKey(authAws,L"AWS_SECRET_KEY");
    CkAuthAwsW_putServiceName(authAws,L"s3");

    // This particular bucket is in the Oregon region, as opposed to the US Standard,
    // therefore the Region must be set appropriately.
    // Also note that we connected to "s3-us-west-2.amazonaws.com".
    CkAuthAwsW_putRegion(authAws,L"us-west-2");

    success = CkRestW_SetAuthAws(rest,authAws);

    // Note: The above REST connection and setup of the AWS credentials
    // can be done once.  After connecting, any number of REST calls can be made.
    // The "auto reconnect" property passed to rest.Connect indicates that if
    // the connection is lost, a REST method call will automatically reconnect
    // if needed.
    // --------------------------------------------------------------------------

    // Set the bucket name via the HOST header.
    // In this case, the bucket name is "chilkat.ocean".
    // Note that the Host header should use "bucketName.s3.amazonaws.com", not "bucketName.s3-us-west-2.amazonaws.com"
    CkRestW_putHost(rest,L"chilkat.ocean.s3.amazonaws.com");

    // Our object is "starfish.jpg".
    // Get the metadata.
    // Since we are sending a HEAD request, we shouldn't use any of the Full* methods.
    // Instead, send the request, then just read the response header.
    success = CkRestW_SendReqNoBody(rest,L"HEAD",L"/starfish.jpg");
    if (success != TRUE) {
        wprintf(L"%s\n",CkRestW_lastErrorText(rest));
        CkRestW_Dispose(rest);
        CkAuthAwsW_Dispose(authAws);
        return;
    }

    // Now get the response header.
    statusCode = CkRestW_ReadResponseHeader(rest);
    if (statusCode < 0) {
        wprintf(L"%s\n",CkRestW_lastErrorText(rest));
        CkRestW_Dispose(rest);
        CkAuthAwsW_Dispose(authAws);
        return;
    }

    // When successful, the S3 Storage service will respond with a 200 response code,
    // with an XML body.  
    if (statusCode != 200) {
        // Examine the request/response to see what happened.
        wprintf(L"response status code = %d\n",statusCode);
        wprintf(L"response status text = %s\n",CkRestW_responseStatusText(rest));
        wprintf(L"response header: %s\n",CkRestW_responseHeader(rest));
        CkRestW_Dispose(rest);
        CkAuthAwsW_Dispose(authAws);
        return;
    }

    // The response header contains information about the S3 object.
    // For example:

    // 	HTTP/1.1 200 OK
    // 	x-amz-id-2: GrV/hrB2EUkBlWc0h3JDdmVIrYDXfPC7CGvo/qSVRmYRPwilAOry8+4r2YWl4xJfa1HRYXrP808=
    // 	x-amz-request-id: 4BDC6D6AEA0BDEF3
    // 	Date: Mon, 13 May 2019 22:03:13 GMT
    // 	Last-Modified: Mon, 10 Nov 2014 16:10:23 GMT
    // 	ETag: "2e9c59dbf2662367dc97dfdda85da048"
    // 	Accept-Ranges: bytes
    // 	Content-Type: image/jpg
    // 	Content-Length: 6229
    // 	Server: AmazonS3

    // Get the ETag response header value:
    etag = CkRestW_responseHdrByName(rest,L"ETag");
    wprintf(L"ETag: %s\n",etag);


    CkRestW_Dispose(rest);
    CkAuthAwsW_Dispose(authAws);

    }