Add function to detect whether Packer is running on Azure

builder/azure/common/detect_azure.go

@@ -0,0 +1,8 @@
+// +build !linux
+
+package common
+
+// IsAzure returns true if Packer is running on Azure (currently only works on Linux)
+func IsAzure() bool {
+	return false
+}

builder/azure/common/detect_azure_linux.go

@@ -0,0 +1,23 @@
+package common
+
+import (
+	"bytes"
+	"io/ioutil"
+)
+
+var (
+	smbiosAssetTagFile = "/sys/class/dmi/id/chassis_asset_tag"
+	azureAssetTag      = []byte("7783-7084-3265-9085-8269-3286-77\n")
+)
+
+// IsAzure returns true if Packer is running on Azure
+func IsAzure() bool {
+	return isAzureAssetTag(smbiosAssetTagFile)
+}
+
+func isAzureAssetTag(filename string) bool {
+	if d, err := ioutil.ReadFile(filename); err == nil {
+		return bytes.Compare(d, azureAssetTag) == 0
+	}
+	return false
+}

builder/azure/common/detect_azure_linux_test.go

@@ -0,0 +1,29 @@
+package common
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIsAzure(t *testing.T) {
+	f, err := ioutil.TempFile("", "TestIsAzure*")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(f.Name())
+
+	f.Seek(0, 0)
+	f.Truncate(0)
+	f.Write([]byte("not the azure assettag"))
+
+	assert.False(t, isAzureAssetTag(f.Name()), "asset tag is not Azure's")
+
+	f.Seek(0, 0)
+	f.Truncate(0)
+	f.Write(azureAssetTag)
+
+	assert.True(t, isAzureAssetTag(f.Name()), "asset tag is Azure's")
+}