Improved error messages for file validtors

[phlogisticfugu]

Is there an existing issue that is already proposing this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe it

Not related to an explicit bug in Nest.js - this is an enhancement request

Describe the solution you'd like

Within the FileTypeValidator

nest/packages/common/pipes/file/file-type.validator.ts

Lines 23 to 25 in 198eaf7

	buildErrorMessage(): string {
	return `Validation failed (expected type is ${this.validationOptions.fileType})`;
	}

to change the buildErrorMessage() method to:

• take in the file: any input supported by the FileValidator
• use that to also log the actual file?.type which was observed - to make troubleshooting easier

While we are at it, the MaxFileSizeValidator

nest/packages/common/pipes/file/max-file-size.validator.ts

Lines 20 to 27 in 198eaf7

	buildErrorMessage(): string {
	if ('message' in this.validationOptions) {
	if (typeof this.validationOptions.message === 'function') {
	return this.validationOptions.message(this.validationOptions.maxSize);
	}
	return this.validationOptions.message;
	}

could also be modified to improve its error message to show the actual file size, in addition to the expected file size

Teachability, documentation, adoption, migration strategy

for the changelog:
Improved error messages for MaxSizeValidator and FileTypeValidator to include the observed actual size or filetype.

What is the motivation / use case for changing the behavior?

We are using the FileTypeValidator() within a @uploadedfile - and are getting errors in production where the user is uploading the wrong file type, and triggering this validator. However, the error message we see in our logs is: BadRequestException: Validation failed (expected type is .(png|jpeg|jpg|pdf)) - which does not describe the actual file type that the user actually used.

[VeerChaurasia]

hey @phlogisticfugu can I Take this one?

[kamilmysliwiec]

PRs are more than welcome