Add backtraces to errors (#1498)

Error handling has been reworked to always go through the new `error_template`,
`error_json` and `error_atom` macros.
They all accept a status code followed by a string message or an exception
object. `error_json` accepts a hash with additional fields as third argument.

If the second argument is an exception a backtrace will be printed, if it is a
string only the string is printed. Since up till now only the exception message
was printed a new `InfoException` class was added for situations where no
backtrace is intended but a string cannot be used.

`error_template` with a string message automatically localizes the message.
Missing error translations have been collected in https://github.com/iv-org/invidious/issues/1497
`error_json` with a string message does not localize the message. This is the
same as previous behavior. If translations are desired for `error_json` they
can be added easily but those error messages have not been collected yet.

Uncaught exceptions previously only printed a generic message ("Looks like
you've found a bug in Invidious. [...]"). They still print that message
but now also include a backtrace.

src/invidious/helpers/errors.cr

@@ -0,0 +1,90 @@
+# InfoExceptions are for displaying information to the user.
+#
+# An InfoException might or might not indicate that something went wrong.
+# Historically Invidious didn't differentiate between these two options, so to
+# maintain previous functionality InfoExceptions do not print backtraces.
+class InfoException < Exception
+end
+
+macro error_template(*args)
+  error_template_helper(env, config, locale, {{*args}})
+end
+
+def error_template_helper(env : HTTP::Server::Context, config : Config, locale : Hash(String, JSON::Any) | Nil, status_code : Int32, exception : Exception)
+  if exception.is_a?(InfoException)
+    return error_template_helper(env, config, locale, status_code, exception.message || "")
+  end
+  env.response.status_code = status_code
+  error_message = <<-END_HTML
+    Looks like you've found a bug in Invidious. Feel free to open a new issue
+    <a href="https://github.com/iv-org/invidious/issues">here</a>
+    or send an email to
+    <a href="mailto:#{CONFIG.admin_email}">#{CONFIG.admin_email}</a>.
+    <br>
+    <br>
+    <br>
+    Please include the following text in your message:
+    <pre style="padding: 20px; background: rgba(0, 0, 0, 0.12345);">#{exception.inspect_with_backtrace}</pre>
+  END_HTML
+  return templated "error"
+end
+
+def error_template_helper(env : HTTP::Server::Context, config : Config, locale : Hash(String, JSON::Any) | Nil, status_code : Int32, message : String)
+  env.response.status_code = status_code
+  error_message = translate(locale, message)
+  return templated "error"
+end
+
+macro error_atom(*args)
+  error_atom_helper(env, config, locale, {{*args}})
+end
+
+def error_atom_helper(env : HTTP::Server::Context, config : Config, locale : Hash(String, JSON::Any) | Nil, status_code : Int32, exception : Exception)
+  if exception.is_a?(InfoException)
+    return error_atom_helper(env, config, locale, status_code, exception.message || "")
+  end
+  env.response.content_type = "application/atom+xml"
+  env.response.status_code = status_code
+  return "<error>#{exception.inspect_with_backtrace}</error>"
+end
+
+def error_atom_helper(env : HTTP::Server::Context, config : Config, locale : Hash(String, JSON::Any) | Nil, status_code : Int32, message : String)
+  env.response.content_type = "application/atom+xml"
+  env.response.status_code = status_code
+  return "<error>#{message}</error>"
+end
+
+macro error_json(*args)
+  error_json_helper(env, config, locale, {{*args}})
+end
+
+def error_json_helper(env : HTTP::Server::Context, config : Config, locale : Hash(String, JSON::Any) | Nil, status_code : Int32, exception : Exception, additional_fields : Hash(String, Object) | Nil)
+  if exception.is_a?(InfoException)
+    return error_json_helper(env, config, locale, status_code, exception.message || "", additional_fields)
+  end
+  env.response.content_type = "application/json"
+  env.response.status_code = status_code
+  error_message = {"error" => exception.message, "errorBacktrace" => exception.inspect_with_backtrace}
+  if additional_fields
+    error_message = error_message.merge(additional_fields)
+  end
+  return error_message.to_json
+end
+
+def error_json_helper(env : HTTP::Server::Context, config : Config, locale : Hash(String, JSON::Any) | Nil, status_code : Int32, exception : Exception)
+  return error_json_helper(env, config, locale, status_code, exception, nil)
+end
+
+def error_json_helper(env : HTTP::Server::Context, config : Config, locale : Hash(String, JSON::Any) | Nil, status_code : Int32, message : String, additional_fields : Hash(String, Object) | Nil)
+  env.response.content_type = "application/json"
+  env.response.status_code = status_code
+  error_message = {"error" => message}
+  if additional_fields
+    error_message = error_message.merge(additional_fields)
+  end
+  return error_message.to_json
+end
+
+def error_json_helper(env : HTTP::Server::Context, config : Config, locale : Hash(String, JSON::Any) | Nil, status_code : Int32, message : String)
+  error_json_helper(env, config, locale, status_code, message, nil)
+end