filter: Improve validation of expression

While making changes to filters you need to run `apply` to actually find
out whether the expression is valid. This is a slow feedback cycle for
developers and there is an API endpoint that allows you to validate
expressions before using them so it's a no brainer to improve the
validation in the schema.

This updates the `ValidateFunc` for `expression` to call out to the
validation API endpoint and raise those exceptions earlier in the
development cycle.

Fixes #846

cloudflare/resource_cloudflare_filter.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"html"
 	"log"
+	"os"
 	"strings"
 
 	cloudflare "github.com/cloudflare/cloudflare-go"
@@ -37,6 +38,22 @@ func resourceCloudflareFilter() *schema.Resource {
 				DiffSuppressFunc: func(k, old, new string, d *schema.ResourceData) bool {
 					return strings.TrimSpace(new) == old
 				},
+				ValidateFunc: func(val interface{}, key string) (warns []string, errs []error) {
+					// Validating the filter expression doesn't support API tokens (yet!)
+					// so use API key and email for now. Establishing a new client here
+					// isn't the best solution either however we don't have the `meta`
+					// interface available that holds the configured client.
+					api, err := cloudflare.New(os.Getenv("CLOUDFLARE_API_KEY"), os.Getenv("CLOUDFLARE_EMAIL"))
+					if err != nil {
+						log.Fatal(err)
+					}
+
+					expression := val.(string)
+					if err := api.ValidateFilterExpression(expression); err != nil {
+						errs = append(errs, fmt.Errorf("filter expression is invalid: %s", err))
+					}
+					return
+				},
 			},
 			"description": {
 				Type:         schema.TypeString,

cloudflare/resource_cloudflare_filter_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"regexp"
 	"testing"
 
 	"github.com/cloudflare/cloudflare-go"
@@ -66,6 +67,42 @@ func TestAccFilterSimple(t *testing.T) {
 	})
 }
 
+func TestAccFilterInvalid(t *testing.T) {
+	rnd := generateRandomResourceName()
+	zoneID := os.Getenv("CLOUDFLARE_ZONE_ID")
+
+	resource.Test(t, resource.TestCase{
+		PreCheck:  func() { testAccPreCheck(t) },
+		Providers: testAccProviders,
+		Steps: []resource.TestStep{
+			{
+				Config:      testFilterConfig(rnd, zoneID, "true", "this is notes", "invalid expression"),
+				ExpectError: regexp.MustCompile("config is invalid: filter expression is invalid"),
+			},
+		},
+	})
+}
+func TestAccFilterInvalidOver4kbString(t *testing.T) {
+	rnd := generateRandomResourceName()
+	zoneID := os.Getenv("CLOUDFLARE_ZONE_ID")
+
+	output := ""
+	for i := 1; i < 4100; i++ {
+		output += "x"
+	}
+
+	resource.Test(t, resource.TestCase{
+		PreCheck:  func() { testAccPreCheck(t) },
+		Providers: testAccProviders,
+		Steps: []resource.TestStep{
+			{
+				Config:      testFilterConfig(rnd, zoneID, "true", "this is notes", output),
+				ExpectError: regexp.MustCompile("config is invalid: filter expression is invalid"),
+			},
+		},
+	})
+}
+
 func testFilterConfig(resourceID, zoneID, paused, description, expression string) string {
 	return fmt.Sprintf(`
 		resource "cloudflare_filter" "%[1]s" {