When using context.WithValue, immutable metadata within the request scope, such as user identity, request identity, etc.; it should not be used for parameter delivery or process control; 1. It is appropriate to pass meta information such as user ID, trace ID, etc.; 2. Avoid abuse of transferring too much content such as database connection; 3. Use custom key types to prevent conflicts; 4. Do not modify the existing context value, and create a new context when it needs to be updated.
When using context.WithValue
in Go, many people will use it, but not necessarily all of them are used correctly. The most core point is: it is only used to pass request scoped, immutable metadata, rather than to pass parameters or process control .

If you just want to pass some values ??into the context and keep them for later use, it is no problem, but you have to pay attention to the methods, otherwise it will be easy to bury the pit.
1. What is the right thing to pass with context.WithValue
?
The original intention of context.WithValue
is to carry some runtime meta information in the request processing chain, such as:

- User ID (such as user ID)
- Request a unique identifier (trace ID)
- Configuration items such as timeout or retry policy (although this type can also be handled through middleware or other methods)
These information are characterized by: they are valid throughout the request lifecycle and should not be changed frequently.
For example:

ctx := context.WithValue(parentCtx, "userID", "12345")
In this way, the downstream function can obtain the current user's ID through ctx.Value("userID")
for logging, permission judgment and other operations.
2. Don't abuse it! Don't spread too many things
Some people like to treat context as a "universal container" and stuff everything into it, such as database connections, configuration structures, and even function closures... This is a very unrecommended approach.
There are several reasons:
- Violating the principle of separation of duties : context should be lightweight and concise, not dependency injection containers.
- Type safety poor :
Value() interface{}
returns an empty interface, which is prone to errors. - Difficult to maintain and test : The caller does not know what values ??you need, and it is not convenient to mock it.
So the suggestion is: only put metadata that really belongs to the context , try to pass other things explicitly through parameters, or encapsulate them into middleware/service objects.
3. Use custom key types to avoid conflicts
Many people use strings directly as keys. For example, the previous example uses "userID"
, which is not a big problem in small projects, but there may be key conflicts in large systems.
The solution is simple: define your own key type
For example:
type contextKey string const ( userIDKey contextKey = "userID" traceIDKey contextKey = "traceID" )
Then use:
ctx := context.WithValue(ctx, userIDKey, "12345")
This prevents data overwriting caused by accidental use of the same string key between different packages.
4. Do not modify existing context values
Once the value of context is set, it should not be modified again. You can understand it as a read-only context snapshot .
If you really need to "update" a value, you should create a new context:
newCtx := context.WithValue(oldCtx, key, newValue)
Instead of trying to change the old context. Because context is chained, many goroutines may still use old ctx, and rash modification will affect concurrent behavior.
Basically that's it. The key to using context.WithValue
is to understand its positioning: it is additional information of the context, not a parameter transfer tool, nor is it a global variable substitute. If used correctly, it can help you sort out the request link; if used wrongly, it will make the code more difficult to understand and debug.
The above is the detailed content of Go context.WithValue best practices. For more information, please follow other related articles on the PHP Chinese website!

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