Notifications to show on the next request, after redirection

# In a login action
response = found()
|> Location.set("/my-account")
|> Flash.write(success: "Welcome back.")

# After being redirected to `/my-account`
[success: "Welcome back."] = Flash.read(request)

Multiple flash messages can be written, read will always return a list of messages.

Flash messages are the combination of tag and content. Default tags are:

• danger - e.g. Account has expired
• warning - e.g. Username required for signup
• success - e.g. Email was updated
• info - e.g. Anything else

The Flash module defines working with flash messages. A specific transfer mechanism must be selected for flash messages.

Tokumei.Flash.Query is the default flash transfer mechanism.

Examples

# Flash messages will be added to response headers
iex> Response.see_other()
...> |> Flash.write(danger: "Bad times :-0")
...> |> Map.get(:headers)
[{"tokumei-flash", {:danger, "Bad times :-0"}}]

# Multiple flash messages can be added
iex> Response.see_other()
...> |> Flash.write(success: "Good news first.")
...> |> Flash.write(warning: "But also...")
...> |> Map.get(:headers)
[
  {"tokumei-flash", {:success, "Good news first."}},
  {"tokumei-flash", {:warning, "But also..."}}]

# Flash messages can be read off a request
iex> Request.get("/", [{"tokumei-flash", {:danger, "Bad times :-0"}}])
...> |> Flash.read()
[danger: "Bad times :-0"]

Extensions

• Configurable list of known tags.
• Log warnings when writing to a message that is not a redirect.
• Configurable header name.