ledger: wrap response errors with HTTP metadata

[adamdecaf]

I found enhancing the error helps to debug problems. I don't consider the URL (i.e. account ID) sensitive since it would end up in load balancer logs.

[sudhirj]

Looks fine to me, @ilayaraja89 ?

[ilayaraja89-zz]

@sudhirj @adamdecaf Client applications might want to differentiate between 4xx and 5xx responses from Ledger. But now both are generalised as error, skipping the switch case of http status codes.

https://github.com/RealImage/qledger-sdk-go/blob/master/transactions.go#L39
https://github.com/RealImage/qledger-sdk-go/blob/master/transactions.go#L48

[adamdecaf]

With Go's current error handling the best people can do is match on == or strings.Contains(err.Error(), ...) to determine which error was returned. This change only breaks strict equality, ==.

[ilayaraja89-zz]

I think, in client applications, comparing against variables like ErrTransactionDuplicate, ErrAccountConflict will be more handy compared to inspecting error texts.

Eg. https://github.com/RealImage/qledger-sdk-go/blob/master/transactions_test.go#L108

@adamdecaf Can you also check whether tests pass after this change ?

[adamdecaf]

They don't pass. This change would break the comparison you're talking about. I'm ok closing this change if it won't work.