resource/aws_storagegateway_upload_buffer: Replace Provider produced inconsistent result after apply with actual error message (#17880)

Reference: #16796
Reference: #17809

Output from acceptance testing:

```
--- PASS: TestAccAWSStorageGatewayUploadBuffer_basic (455.25s)
```

Author: bflad

.changelog/17880.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+resource/aws_storagegateway_upload_buffer: Replace `Provider produced inconsistent result after apply` with actual error message
+```

aws/internal/service/storagegateway/finder/finder.go

@@ -0,0 +1,33 @@
+package finder
+
+import (
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/service/storagegateway"
+)
+
+func UploadBufferDisk(conn *storagegateway.StorageGateway, gatewayARN string, diskID string) (*string, error) {
+	input := &storagegateway.DescribeUploadBufferInput{
+		GatewayARN: aws.String(gatewayARN),
+	}
+
+	var result *string
+
+	output, err := conn.DescribeUploadBuffer(input)
+
+	if err != nil {
+		return nil, err
+	}
+
+	if output == nil {
+		return nil, nil
+	}
+
+	for _, diskId := range output.DiskIds {
+		if aws.StringValue(diskId) == diskID {
+			result = diskId
+			break
+		}
+	}
+
+	return result, err
+}

aws/resource_aws_storagegateway_upload_buffer.go

@@ -9,6 +9,7 @@ import (
 	"github.com/aws/aws-sdk-go/aws/arn"
 	"github.com/aws/aws-sdk-go/service/storagegateway"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
+	"github.com/terraform-providers/terraform-provider-aws/aws/internal/service/storagegateway/finder"
 )
 
 func resourceAwsStorageGatewayUploadBuffer() *schema.Resource {
@@ -66,42 +67,29 @@ func resourceAwsStorageGatewayUploadBufferRead(d *schema.ResourceData, meta inte
 		return err
 	}
 
-	input := &storagegateway.DescribeUploadBufferInput{
-		GatewayARN: aws.String(gatewayARN),
-	}
-
-	log.Printf("[DEBUG] Reading Storage Gateway upload buffer: %s", input)
-	output, err := conn.DescribeUploadBuffer(input)
-	if err != nil {
-		if isAWSErrStorageGatewayGatewayNotFound(err) {
-			log.Printf("[WARN] Storage Gateway upload buffer %q not found - removing from state", d.Id())
-			d.SetId("")
-			return nil
-		}
-		return fmt.Errorf("error reading Storage Gateway upload buffer: %s", err)
-	}
+	foundDiskID, err := finder.UploadBufferDisk(conn, gatewayARN, diskID)
 
-	if output == nil || len(output.DiskIds) == 0 {
-		log.Printf("[WARN] Storage Gateway upload buffer %q not found - removing from state", d.Id())
+	if !d.IsNewResource() && isAWSErrStorageGatewayGatewayNotFound(err) {
+		log.Printf("[WARN] Storage Gateway Upload Buffer (%s) not found, removing from state", d.Id())
 		d.SetId("")
 		return nil
 	}
 
-	found := false
-	for _, existingDiskID := range output.DiskIds {
-		if aws.StringValue(existingDiskID) == diskID {
-			found = true
-			break
-		}
+	if err != nil {
+		return fmt.Errorf("error reading Storage Gateway Upload Buffer (%s): %w", d.Id(), err)
 	}
 
-	if !found {
-		log.Printf("[WARN] Storage Gateway upload buffer %q not found - removing from state", d.Id())
+	if foundDiskID == nil {
+		if d.IsNewResource() {
+			return fmt.Errorf("error reading Storage Gateway Upload Buffer (%s): not found", d.Id())
+		}
+
+		log.Printf("[WARN] Storage Gateway Upload Buffer (%s) not found, removing from state", d.Id())
 		d.SetId("")
 		return nil
 	}
 
-	d.Set("disk_id", diskID)
+	d.Set("disk_id", foundDiskID)
 	d.Set("gateway_arn", gatewayARN)
 
 	return nil

aws/resource_aws_storagegateway_upload_buffer_test.go

@@ -4,11 +4,10 @@ import (
 	"fmt"
 	"testing"
 
-	"github.com/aws/aws-sdk-go/aws"
-	"github.com/aws/aws-sdk-go/service/storagegateway"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/acctest"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/resource"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/terraform"
+	"github.com/terraform-providers/terraform-provider-aws/aws/internal/service/storagegateway/finder"
 )
 
 func TestDecodeStorageGatewayUploadBufferID(t *testing.T) {
@@ -111,27 +110,17 @@ func testAccCheckAWSStorageGatewayUploadBufferExists(resourceName string) resour
 			return err
 		}
 
-		input := &storagegateway.DescribeUploadBufferInput{
-			GatewayARN: aws.String(gatewayARN),
-		}
-
-		output, err := conn.DescribeUploadBuffer(input)
+		foundDiskID, err := finder.UploadBufferDisk(conn, gatewayARN, diskID)
 
 		if err != nil {
-			return fmt.Errorf("error reading Storage Gateway upload buffer: %s", err)
-		}
-
-		if output == nil || len(output.DiskIds) == 0 {
-			return fmt.Errorf("Storage Gateway upload buffer %q not found", rs.Primary.ID)
+			return fmt.Errorf("error reading Storage Gateway Upload Buffer (%s): %w", rs.Primary.ID, err)
 		}
 
-		for _, existingDiskID := range output.DiskIds {
-			if aws.StringValue(existingDiskID) == diskID {
-				return nil
-			}
+		if foundDiskID == nil {
+			return fmt.Errorf("Storage Gateway Upload Buffer (%s) not found", rs.Primary.ID)
 		}
 
-		return fmt.Errorf("Storage Gateway upload buffer %q not found", rs.Primary.ID)
+		return nil
 	}
 }