To expose memory usage statistics as expvar in Go, you can create a custom expvar.Var object that updates its value with the current memory usage. Here's an example of how you can do it:
package main
import (
"expvar"
"runtime"
"time"
)
type memoryStats struct {
startTime time.Time
}
func (m *memoryStats) String() string {
var memStats runtime.MemStats
runtime.ReadMemStats(&memStats)
return strconv.FormatUint(memStats.Alloc, 10)
}
func main() {
expvar.Publish("memoryAlloc", &memoryStats{startTime: time.Now()})
// Your application code here
}
In this example, we create a struct memoryStats that implements the String() method of the expvar.Var interface. This method is called by expvar package to retrieve the value of the variable.
Inside the String() method, we use runtime.ReadMemStats() to fetch the current memory statistics into a runtime.MemStats struct. We then extract the Alloc field, which represents the current memory allocation, and convert it to a string.
Finally, we publish the memoryStats object using expvar.Publish(), giving it a name (e.g. "memoryAlloc"). The expvar package then exposes this variable via the /debug/vars endpoint by default.
Remember to import the required packages (expvar and runtime) and modify the code according to your specific memory statistics needs.