Mayfly.ErrorPayload (Mayfly v1.0.0-rc.1)

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Builds the error document Lambda expects on /runtime/invocation/<id>/error and /runtime/init/error:

%{errorType: "KeyError", errorMessage: "key :a not found", stackTrace: [...]}

Error types

  • Exceptions raised by a handler use their module name ("KeyError", "MyApp.ValidationError").
  • {:error, reason} returned by a handler is "HandlerError", unless reason is already a map with errorType/errorMessage (atom or string keys), which is passed through so handlers can emit structured errors.
  • exit/1 and throw/1 become "Exit" and "Throw".
  • Runtime-detected problems use Runtime.* types (Runtime.InvalidResponse, Runtime.NoSuchHandler, ...).

Header type

Lambda classifies errors by the Lambda-Runtime-Function-Error-Type header and normalises anything not shaped like <Category.Reason> (Category being Runtime or Function) to Runtime.Unknown/Function.Unknown. header_type/1 derives a conforming value: Runtime.* is kept as is, every other type is prefixed with Function. and stripped of dots.

Whatever a handler returns in {:error, reason} ends up in the payload, which API Gateway may forward to clients. Terms are rendered with a bounded inspect/2.

Summary

Types

t()

Functions

format_stacktrace(stacktrace)

Formats a stacktrace as a list of lines, dropping frames that belong to Mayfly itself so the handler's frames come first.

from_caught(atom, reason, stacktrace)

Builds a payload from a value caught with catch kind, reason.

from_term(term, stacktrace \\ nil)

Builds a payload from an exception, a handler {:error, reason} value or any term.

header_type(type)

Value for the Lambda-Runtime-Function-Error-Type header.

runtime(reason, message)

Builds a runtime error payload with an explicit Runtime.* type.

xray_cause(map)

X-Ray cause document (Lambda-Runtime-Function-Xray-Error-Cause).

Types

t()

@type t() :: %{
  errorType: String.t(),
  errorMessage: String.t(),
  stackTrace: [String.t()]
}

Functions

format_stacktrace(stacktrace)

@spec format_stacktrace(Exception.stacktrace() | nil) :: [String.t()]

Formats a stacktrace as a list of lines, dropping frames that belong to Mayfly itself so the handler's frames come first.

from_caught(atom, reason, stacktrace)

@spec from_caught(:exit | :throw | :error, term(), Exception.stacktrace() | nil) ::
  t()

Builds a payload from a value caught with catch kind, reason.

from_term(term, stacktrace \\ nil)

@spec from_term(term(), Exception.stacktrace() | nil) :: t()

Builds a payload from an exception, a handler {:error, reason} value or any term.

header_type(type)

@spec header_type(String.t()) :: String.t()

Value for the Lambda-Runtime-Function-Error-Type header.

iex> Mayfly.ErrorPayload.header_type("Runtime.InvalidResponse")
"Runtime.InvalidResponse"
iex> Mayfly.ErrorPayload.header_type("MyApp.Validation.Error")
"Function.MyAppValidationError"
iex> Mayfly.ErrorPayload.header_type("HandlerError")
"Function.HandlerError"

runtime(reason, message)

@spec runtime(String.t(), String.t()) :: t()

Builds a runtime error payload with an explicit Runtime.* type.

xray_cause(map)

@spec xray_cause(t()) :: map()

X-Ray cause document (Lambda-Runtime-Function-Xray-Error-Cause).