Error Handler

User-defined error pages

When web application encounters some unexpected situations, it may send 404 response to the client. You may want to use user-defined 404 pages, then you can use resp to return 404 response.

proc hello(ctx: Context) {.async.} =
  resp "Something is wrong, please retry.", Http404

Prologue also provides an error404 helper function to create a 404 response.

proc hello(ctx: Context) {.async.} =
  resp error404(headers = ctx.response.headers)

Or use errorPage to create a more descriptive error page.

proc hello(ctx: Context) {.async.} =
  resp errorPage("Something is wrong"), Http404

Default error handler

Users can also set the default error handler. When ctx.response.body is empty, web application will use the default error handler.

The basic example with respDefault which is equal to resp errorPage("Something is wrong"), Http404.

proc hello(ctx: Context) {.async.} =
  respDefault Http404

Prologue has registered two error handlers before application starts, namely default404Handler for Http404 and default500Handler for Http500. You can change them using registerErrorHandler.

proc go404*(ctx: Context) {.async.} =
  resp "Something wrong!", Http404

proc go20x*(ctx: Context) {.async.} =
  resp "Ok!", Http200

proc go30x*(ctx: Context) {.async.} =
  resp "EveryThing else?", Http301

app.registerErrorHandler(Http404, go404)
app.registerErrorHandler({Http200 .. Http204}, go20x)
app.registerErrorHandler(@[Http301, Http304, Http307], go30x)

If you don't want to use the default Error handler, you could clear the whole error handler table.

var app = newApp(errorHandlerTable = newErrorHandlerTable())

HTTP 500 handler

Http 500 indicates the internal error of the framework. In debug mode(settings.debug = true), the framework will send the exception msgs to the web browser if the length of error msgs is greater than zero. Otherwise, the framework will use the default error handled which has been registered before the application starts. Users could cover this handler by using their own error handler.