412 Precondition Failed

The client set special conditions in its headers (like ‘only update if the file hasn’t changed’), and the condition wasn’t met.

When and Why to Use It

Use this when a client sends an ‘If-Match’ header (saying ‘Only update this file if it hasn’t been edited since yesterday’), but someone else already edited it today.

Usage Examples

Shokupan (Functional)

import { HttpException, get } from 'shokupan';

export const getResource = get('/resource', () => {
    throw new HttpException('Precondition Failed', 412);
});

Shokupan (Controller)

import { Controller, Get, HttpException } from 'shokupan';

@Controller('/api')
export class ExampleController {
    @Get('/resource')
    getResource() {
        throw new HttpException('Precondition Failed', 412);
    }
}

Express

import express from 'express';
const app = express();

app.get('/resource', (req, res) => {
    res.status(412).json({ error: 'Precondition Failed' });
});

Nest

import { Controller, Get, HttpException } from '@nestjs/common';

@Controller('api')
export class ExampleController {
  @Get('resource')
  getResource() {
    throw new HttpException('Precondition Failed', 412);
  }
}

Koa

import Koa from 'koa';
const app = new Koa();

app.use(async ctx => {
  if (ctx.path === '/resource' && ctx.method === 'GET') {
    ctx.status = 412;
    ctx.body = { error: 'Precondition Failed' };
  }
});