Tokens | Ethereum Token Contracts | Cryptocurrency library

Unsure if this fully addresses your issue, but one way that I've fetched metadata for all tokens in a wallet is by using the metaplex library:

This is a bug in GCC. C 2018 6.10.3.2 specifies behavior of the # operator. Paragraph 1 says “Each # preprocessing token in the replacement list for a function-like macro shall be followed by a parameter as the next preprocessing token in the replacement list.” We see this in the #x of #define STR_(x) #x.

Paragraph 2 says:

If, in the replacement list, a parameter is immediately preceded by a # preprocessing token, both are replaced by a single character string literal preprocessing token that contains the spelling of the preprocessing token sequence for the corresponding argument. Each occurrence of white space between the argument’s preprocessing tokens becomes a single space character in the character string literal. White space before the first preprocessing token and after the last preprocessing token composing the argument is deleted…

The X(Y,Y) macro invocation must have resulted in the tokens Y and Y, and we see in #define X(x,y) x y that they would have white space between them.

White-space in a macro replacement list is significant, per 6.10.3 1, which says:

Two replacement lists are identical if and only if the preprocessing tokens in both have the same number, ordering, spelling, and white-space separation, where all white-space separations are considered identical.

Thus, in #define X(x,y) x y, the replacement list should not be considered to be just the two tokens x and y, with white space disregarded. The replacement list is x, white space, and y.

Further, when the macro is replaced, it is replaced by the replacement list (and hence includes white space), not merely by the tokens in the replacement list, per 6.10.3 10:

… Each subsequent instance of the function-like macro name followed by a ( as the next preprocessing token introduces the sequence of preprocessing tokens that is replaced by the replacement list in the definition (an invocation of the macro)… Within the sequence of preprocessing tokens making up an invocation of a function-like macro, new-line is considered a normal white-space character.

Having the same issue while working on the same course as you, maybe try using node 10 and redeploy everything.

Let me know if that works.

In the OP's example with std::max, an ODR violation does indeed occur, and the program is ill-formed NDR. To avoid this issue, you might consider one of the following fixes:

• give the doMath function internal linkage, or
• move the declaration of kTwo inside doMath

A variable that is used by an expression is considered to be odr-used unless there is a certain kind of simple proof that the reference to the variable can be replaced by the compile-time constant value of the variable without changing the result of the expression. If such a simple proof exists, then the standard requires the compiler perform such a replacement; consequently the variable is not odr-used (in particular, it does not require a definition, and the issue described by the OP would be avoided because none of the translation units in which doMath is defined would actually reference a definition of kTwo). If the expression is too complicated, however, then all bets are off. The compiler might still replace the variable with its value, in which case the program may work as you expect; or the program may exhibit bugs or crash. That's the reality with IFNDR programs.

The case where the variable is immediately passed by reference to a function, with the reference binding directly, is one common case where the variable is used in a way that is too complicated and the compiler is not required to determine whether or not it may be replaced by its compile-time constant value. This is because doing so would necessarily require inspecting the definition of the function (such as std::max in this example).

You can "help" the compiler by writing int(kTwo) and using that as the argument to std::max as opposed to kTwo itself; this prevents an odr-use since the lvalue-to-rvalue conversion is now immediately applied prior to calling the function. I don't think this is a great solution (I recommend one of the two solutions that I previously mentioned) but it has its uses (GoogleTest uses this in order to avoid introducing odr-uses in statements like EXPECT_EQ(2, kTwo)).

If you want to know more about how to understand the precise definition of odr-use, involving "potential results of an expression e...", that would be best addressed with a separate question.

It appears that you are using text fields so it hides data or sometimes it may overflow borders by black and yellow stripes

better to use SingleChildScrollView and for scrolling direction use scrollDirection with parameters Axis.vertical or Axis.horizontal

The issue you're going to have to confront is how to deal with function calls. I can't really give you any concrete advice based on your question, because the grammar you provide lacks any indication of the intended syntax of functions calls, but the hint that print(5) is a valid statement makes it clear that there are two distinct situations, which need to be handled separately.

Consider:

There's compiler warning C4067. It looks like you need to set the flag /Za for it to apply to #endif directives.

In the Visual Studio properties page, this flag is controlled by the setting "Disable Language Extensions" in the Language subsection of the C/C++ section.

There are quite a few gaps in the code posted, but I attempted to replicate and in doing so ended up refactoring a bit.

This version seems pretty robust, with the actual call to SendAsync wrapped in an adapter class.

I accept this doesn't necessarily answer the question directly, but in the absence of being able to replicate your problem exactly, offers an alternative way of structuring the code that may eliminate the problem.

There is this general confusion around token-based auth, so let's try to clear some of it up.

First, JWTs are not just "encoded" by the server, they are "signed" (which more precisely is message authentication usually). The purpose is that such a token can not be altered or changed by the client, any field (claim) in the token can be trusted to be as the issuer created it, otherwise validation will fail.

This yields two important takeaways:

• validating tokens is important (obviously) in any implementation
• the contents (claims) of a JWT are not encrypted, ie. it's not a secret and can be viewed by the client

Such a token can be used to maintain a session without server-side state, if it contains some kind of an identity for the subject (user, like a user id or email address), and an expiry.

Another important takeaway though:

• Logout (immediate session invalidation) is not possible in a stateless way, which is a drawback. To be able to log out as in invalidate an existing session, the server must store and check revoked tokens, which is necessarily a stateful operation.

Also a JWT token is typically stored in a way that it's accessible for client-side code (javascript), so things like who the user is and when the token will expire can be read by the client app. It need not be so, yet most implementations do this, eg. store it in localstorage. This makes these tokens susceptible to XSS attacks, meaning that any successful XSS will be able to get the token.

For the reasons discussed so far, JWT authentication is inherently less secure than a plain old session, and should only be used if there is a need. Many times when token auth is used, it is not actually necessary, just fancy.

Sometimes such a token is stored in a httpOnly cookie, but in that case the token cannot be sent to multiple origins (one benefit of localStorage) and a plain old session id could also have been used, and would actually be more secure.

Ok, so what are refresh tokens. As you correctly stated, limiting the lifetime of an access token is useful to limit the validity of a compromised token. So a refresh token can be used to get a new access token when the old one expired. The key is where these are stored.

A key takeaway:

• If a refresh token is stored the same way as the access token, it usually doesn't make any sense. This is a common mistake in implementations.

In a better architecture, the following can happen:

• There are (both logically and "physically" as much as it makes sense in today's cloud world) at least two separate components: the identity provider (IdP, or "login service"), and the resource server (eg. an API).
• When a user logs in, they actually create a session with the IdP. In this case either a plain old session id (acting as refresh token) or an actual JWT refresh token is set up for the IdP origin (domain name).
• An access token is then created when needed for the resource server origin, using the existing session with the identity provider.
• Now even if there is a total compromise of the resource server, like in case of successful XSS, the refresh token belongs to a completely separate origin, so cannot be accessed by the attacker. Even if it's the same origin, but the refresh token is in a httpOnly cookie, that helps, because the attacker then needs to be able to perform repeated XSS against a victim user to receive new access tokens.

There can be implementation variants of this, but the point is the above, separation of access to the two tokens.

A one-to-one mapping of refresh tokens to access tokens as you described would I think be unusual and also unnecessary, but one session per user is in fact sometimes a requirement (especially in financial applications where you want to have a very clear audit trail of what a user did). But this is not much related to the things discussed above.

Also as stated above, proper logout (session invalidation) is not possible in a stateless way. Fortunately, very few applications actually need to be truly stateless on the server-side.