Only upload external file if it has been changed?

Terraform
1

I am using azurerm provider and more specifically the file share resource to upload a file.

resource "azurerm_storage_share_file" "file" {
  name                     = local.file_name
  storage_share_id         = azurerm_storage_share.storage_share.id
  path                     = "${local.root_path}/${local.file_name}"
  source                   = var.file_path
  content_type             = local.content_type_json
}

This is working fine. However, terraform does not really load the contents of my local file and thus, if I change the contents of it, terraform will not see any change in the plan stage. The resource also supports a checksum property. By using the md5 function, I can create a new checksum every time which results in a force replacement regardless if the file contents has changed or not.

content_md5 = md5(var.file_path)

It works but it is not ideal since I will always have the replacement, even if the contents have not changed:

-/+ resource "azurerm_storage_share_file" "file" {
      ~ content_length      = 100 -> (known after apply)
      - content_md5         = "g...." -> "123" # forces replacement

Is there a way to only replace/upload the file if the contents of the file has changed that is already uploaded to the file share? Perhaps there is a way to calculate a checksum in a different way that only changes when the file contents changes?

Update:
I have also now tried filemd5 function instead. It is strange however. On first creating, say I get checksum “123”. Then on the next plan I get checksum “789”. I hit apply which replaces the file. Then I plan again and I get “123” again! Strange.