How to propagate context values from Gin middleware to gqlgen resolvers?

Question

I am trying to extract user_id in token authentication middleware and pass it to gqlgen's graphql resolver function (to populate created_by and updated_by columns of GraphQL schema). Authentication part works without any problems.

The Gin middleware:

    var UID = "dummy"
    func TokenAuthMiddleware() gin.HandlerFunc {
        return func(c *gin.Context) {
            err := auth.TokenValid(c.Request)
            if err != nil {
                c.JSON(http.StatusUnauthorized, "You need to be authorized to access this route")
                c.Abort()
                return
            }
            //
            UID, _ = auth.ExtractTokenID(c.Request)
            //c.Set("user_id", UID)
            
            c.Next()
        }
    }

    func GetUID() string {
        return UID
    }

The graphql resolver:

    var ConstID = middleware.GetUID()
    
    func (r *mutationResolver) CreateFarmer(ctx context.Context, input model.NewFarmer) (*model.Farmer, error) {
        //Fetch Connection and close db
        db := model.FetchConnection()
        defer db.Close()
    
        //var ConstID, _ = uuid.NewRandom()
    
        log.Println(ctx)
    
        farmer := model.Farmer{Name: input.Name, Surname: input.Surname, Dob: input.Dob, Fin: input.Fin, PlotLocLat: input.PlotLocLat, PlotLocLong: input.PlotLocLong, CreatedAt: time.Now(), UpdatedAt: time.Now(), CreatedBy: ConstID, UpdatedBy: ConstID}
        db.Create(&farmer)
        return &farmer, nil
    }

Here, I tried to do it using global variable UID, but UID's value is not getting updated in the middleware, and as a result, I'm getting "dummy" values in CreatedBy and UpdatedBy columns. I understand that the use of global variables is discouraged and I am open to other ideas. Thanks

Answer 1

Propagate the value with context.Context.

If you are using gqlgen, you have to remember that the context.Context instance passed to resolver functions comes from the *http.Request (assuming that you set up the integration as recommended in gqlgen's documentation).

Therefore with Go-Gin you should be able to do this with some additional plumbing:

func TokenAuthMiddleware() gin.HandlerFunc {
    return func(c *gin.Context) {
        UID := // ... get the UID somehow
        
        ctx := context.WithValue(c.Request.Context(), "user_id", UID)
        c.Request = c.Request.WithContext(ctx)
        c.Next()
    }
}

And then you get the value in your resolver normally:

func (r *mutationResolver) CreateFarmer(ctx context.Context, input model.NewFarmer) (*model.Farmer, error) {
    UID, _ := ctx.Value("user_id").(string)
    // ...
}

An example (without Gin though) is also available here

Answer 2

The accepted answer didn't work for me. Digging through Gin source code told me I need to either use an engine where ContextWithFallback is true, or simply use c.Set(). If the key is a string, ctx.Value() will look it up in gin's context c.Keys and return it, even if accessing as context.Context and not *gin.Context.

So for me, this worked:

func TokenAuthMiddleware() gin.HandlerFunc {
    return func(c *gin.Context) {
        UID := // ... get the UID somehow
        
        c.Set("user_id", UID)
        c.Next()
    }
}

// ...
func (r *mutationResolver) CreateFarmer(ctx context.Context, input model.NewFarmer) (*model.Farmer, error) {
    UID, _ := ctx.Value("user_id").(string)
    // ...
}

I'm not sure why ContextWithFallback was false for me, but I like the result better anyway as it's simpler to read.

This applies to gin 1.8.1.