Class, constructor and inherance.

[Rikki Cattermole via Digitalmars-d-learn]

On 13/10/15 5:56 AM, holo wrote:
> @Rikki:
>
>> If you didn't need to make it easily changeable I would say not even
>> bother with OOP at all.
>
> Basically that what i had was enough for me and on top of that i could
> build my app. It need to just periodically check for new instances and
> if they are started or stopped and count "up and running time" for
> billing purpose. But like i said i want to learn programming in D and
> basically OOP too so i want to make it "proper way".
>
> BTW: i think right now i understand what tuple is, but still don't know
> for what to duplicate struct functionalities :). Those Templates still
> don't understand but i hope that will came naturally with time and
> practice. eg.. they are very similar to normal functions but you can
> call it with types not only attributes.. strange ;)
>
> I red yours advises and try to create according to it my own first class.
>
> I moved time functions and variables to method "go" they need to be
> current as possible when im sending request, if wont authorization could
> not pass.. so i think they shouldn't be in constructor.
>
> I moved some other variables too, and created interface.
>
>  From all that things came out such monster which is working and doing
> its job :)
>
> module sigawsv4;
>
> import std.stdio, std.process;
> import std.digest.sha, std.digest.hmac;
> import std.string;
> import std.conv;
> import std.datetime;
> import std.net.curl;
>
> interface credential
> {
>      int go();
> }
>
> class sigv4 : credential
> {
>      //could be changed to take some structure as parameter instead of
> such ammount of attributes
>
>      this(string methodStr = "GET", string serviceStr = "ec2", string
> hostStr = "ec2.amazonaws.com", string regionStr = "us-east-1", string
> endpointStr = "https://ec2.amazonaws.com", string payloadStr = "",
> string parmStr = "Action=DescribeInstances&Version=2013-10-15")
>      {
>
>          this.method = methodStr;
>          this.service = serviceStr;
>          this.host = hostStr;
>          this.region = regionStr;
>          this.endpoint = endpointStr;
>          this.payload = payloadStr;
>          this.request_parameters = parmStr;
>
>          this.accessKey = environment.get("AWS_ACCESS_KEY");
>          this.secretKey = environment.get("AWS_SECRET_KEY");
>      }
>
>      public:
>          string method;
>          string service;
>          string host;
>          string region;
>          string endpoint;
>          string payload;
>          string request_parameters;
>
>
>          int go()
>          {
>              //time need to be set when we are sending request not before
>              auto currentClock = Clock.currTime(UTC());
>              auto currentDate = cast(Date)currentClock;
>              auto curDateStr = currentDate.toISOString;
>              auto currentTime = cast(TimeOfDay)currentClock;
>              auto curTimeStr = currentTime.toISOString;
>              auto xamztime = curDateStr ~ "T" ~ curTimeStr ~ "Z";
>
>              canonicalURI = "/";
>              canonicalQueryString = request_parameters;
>              canonicalHeadersString =  "host:" ~ this.host ~ "\n" ~
> "x-amz-date:" ~ xamztime ~ "\n";
>              signedHeaders = "host;x-amz-date";
>
>              auto canonicalRequest = getCanonicalRequest(canonicalURI,
> canonicalQueryString, canonicalHeadersString, signedHeaders);
>
>              string credentialScope = curDateStr ~ "/" ~ region ~ "/" ~
> service ~ "/" ~ "aws4_request";
>
>              string stringToSign = algorithm ~ "\n" ~ xamztime ~ "\n" ~
> credentialScope ~ "\n" ~ sha256Of(canonicalRequest).toHexString.toLower;
>
>              auto signingKey = getSignatureKey(secretKey, curDateStr,
> region, service);
>
>              string signature = hmac!SHA256(stringToSign.representation,
> signingKey).toHexString.toLower;
>
>              string authorizationHeader = algorithm ~ " " ~
> "Credential=" ~ accessKey ~ "/" ~ credentialScope ~ ", " ~
> "SignedHeaders=" ~ signedHeaders ~ ", " ~ "Signature=" ~ signature;
>
>
>              auto client = HTTP(endpoint ~ "?" ~ canonicalQueryString);
>              client.method = HTTP.Method.get;
>              client.addRequestHeader("x-amz-date", xamztime);
>              client.addRequestHeader("Authorization", authorizationHeader);
>              auto content = client.perform();
>
>              return content;
>          }
>
>      private:
>          const algorithm = "AWS4-HMAC-SHA256";
>
>          string accessKey;
>          string secretKey;
>
>          string currentClock;
>          string currentDate;
>          string curDateStr;
>          string currentTime;
>          string curTimeStr;
>          string xamztime;
>
>          string canonicalURI;
>          string canonicalQueryString;
>                 string canonicalHeadersString;
>                 string signedHeaders;
>
>
>
>          alias sign = hmac!SHA256;
>
>          auto getSignatureKey(string key, string dateStamp, string
> regionName, string serviceName)
>          {
>              auto kString = ("AWS4" ~ key).representation;
>              auto kDate = sign(dateStamp.representation, kString);
>              auto kRegion = sign(regionName.representation, kDate);
>              auto kService = sign(serviceName.representation, kRegion);
>              auto kSigning = sign("aws4_request".representation, kService);
>
>              return kSigning;
>          }
>
>
>          auto getCanonicalRequest(string canonicalURI, string
> canonicalQueryString, string canonicalHeadersString, string signedHeaders)
>          {
>              string payloadHash = sha256Of(payload).toHexString.toLower;
>              string canonicalRequest = method ~ "\n" ~ canonicalURI ~
> "\n" ~ canonicalQueryString ~ "\n" ~ canonicalHeadersString ~ "\n" ~
> signedHeaders ~ "\n" ~ payloadHash;
>              return canonicalRequest;
>          }
> }
>
> void main()
> {
>      sigv4 sig = new sigv4();
>      writeln(sig.go());
> }
>
> I want to ask you for  advises what i could do with that class to make
> it looks more "pro"/elegant/build in "proper way". Probably there are
> lot of mistakes which all beginners are doing.
>
> eg.: Did i use interface correctly?

You are reasonably close:
credential sig = new sigv4();

Although go is not really doing what I expect it to do.
To me go should be dedicated to performing a request given what ever you 
need for just that request. The class sigv4 is your global state aka 
what doesn't change per request.
To me what go returns is whatever is the common denominator for what you 
need from it is.

 From what I can see, you probably want go to take the payload as an 
argument.
That way you can reuse an instance of sigv4. Which is the ultimate goal.