在某些場景下，我們需要監(jiān)測系統(tǒng)中網(wǎng)絡(luò)接入情況的變化，據(jù)此作出相應(yīng)的處理。
例如，用戶成功接入了某一個網(wǎng)絡(luò)，移動場景下從一個WiFi網(wǎng)絡(luò)切換到另一個網(wǎng)絡(luò)，網(wǎng)絡(luò)斷開等。

下面基于Go語言，在Mac平臺實現(xiàn)了一個檢測網(wǎng)絡(luò)變化的例子。再這個示例中，使用到了cgo進行C和Go混合編程。Go語言負責處理業(yè)務(wù)邏輯，具體的操作系統(tǒng)事件的監(jiān)測由C語言的接口完成。

在循環(huán)中監(jiān)測到變化，調(diào)用C語言中定義的callback函數(shù)，具體的處理動作再調(diào)用Go中定義的networkchange()函數(shù)處理。

package main

/*
#cgo LDFLAGS: -framework SystemConfiguration -framework CoreFoundation
#include <SystemConfiguration/SystemConfiguration.h>
#include <stdlib.h>

void callback(SCDynamicStoreRef store, CFArrayRef changedKeys, void *info) {
    char **services = (char **)info;
    CFIndex count = CFArrayGetCount(changedKeys);
    for (CFIndex i = 0; i < count; i++) {
        CFStringRef key = CFArrayGetValueAtIndex(changedKeys, i);
        const char *cKey = CFStringGetCStringPtr(key, kCFStringEncodingUTF8);
        if (cKey) {
            services[i] = strdup(cKey);
        }
    }
}

    extern void networkchange();
    void callback(SCDynamicStoreRef store, CFArrayRef changedKeys, void *info) {
        printf("network event detected\n");
        networkchange();
    }
*/
import "C"
import (
    "fmt"
    "time"
    "unsafe"
)

func main() {
    storeName := C.CString("NetworkChangeDetector")
    defer C.free(unsafe.Pointer(storeName))

    cfString := C.CFStringCreateWithCString(C.kCFAllocatorDefault, storeName, C.kCFStringEncodingUTF8)
    defer C.CFRelease(C.CFTypeRef(cfString)) // 釋放 CFStringRef

    store := C.SCDynamicStoreCreate(nil, storeName, C.SCDynamicStoreCallBack(C.callback), nil)
    if *(*C.uintptr_t)(unsafe.Pointer(&store)) == 0 {
        fmt.Println("Failed to create SCDynamicStore")
        return
    }

    keys := C.CFArrayCreateMutable(nil, 0, &C.kCFTypeArrayCallBacks)
    defer C.CFRelease(C.CFTypeRef(keys))

    key1 := C.CFStringCreateWithCString(C.kCFAllocatorDefault, C.CString("State:/Network/Interface"), C.kCFStringEncodingUTF8)
    defer C.CFRelease(C.CFTypeRef(key1))
    C.CFArrayAppendValue(keys, unsafe.Pointer(key1))

    key2 := C.CFStringCreateWithCString(C.kCFAllocatorDefault, C.CString("State:/Network/Global/IPv4"), C.kCFStringEncodingUTF8)
    defer C.CFRelease(C.CFTypeRef(key2))
    C.CFArrayAppendValue(keys, unsafe.Pointer(key2))


    key3 := C.CFStringCreateWithCString(C.kCFAllocatorDefault, C.CString("State:/Network/Global/IPv6"), C.kCFStringEncodingUTF8)
    defer C.CFRelease(C.CFTypeRef(key1))
    C.CFArrayAppendValue(keys, unsafe.Pointer(key3))

    var context C.SCDynamicStoreContext
    context.version = 0
    context.info = nil
    context.retain = nil
    context.release = nil
    context.copyDescription = nil

    emptyArray := C.CreateEmptyCFArray()
    C.SCDynamicStoreSetNotificationKeys(store, keys, emptyArray)

    rl := C.CFRunLoopGetCurrent()
    src := C.SCDynamicStoreCreateRunLoopSource(nil, store, 0)
    C.CFRunLoopAddSource(rl, src, C.kCFRunLoopDefaultMode)
    C.CFRunLoopRun()
}


//export onNetworkChange
func onNetworkChange(count C.int, keys **C.char, info unsafe.Pointer) {
    ctx := (*Context)(info)
    fmt.Printf("Network services changed: %s\n", ctx.message)
    for i := 0; i < int(count); i++ {
        key := C.GoString(*(**C.char)(unsafe.Pointer(uintptr(unsafe.Pointer(keys)) + uintptr(i)*unsafe.Sizeof(uintptr(0)))))
        if key != "" {
            fmt.Println(key)
        }
    }