feat: add per route busboy configuration

[grigoran]

There was a need to restrict the file size in each route when used alongside attachFieldsToBody. These changes will enable route-specific busboy configuration.
Example

fastify.post('/', {
    schema: {
        consumes: ['multipart/form-data'],
        body: Type.Object({
            // file: {isFile: true} as unknown as TSchema
            file: Type.Unsafe<{ toBuffer: () => Promise<Buffer> }>({ isFile: true })
        }),
        response: {
            200: Type.Object({
                ok: Type.Boolean()
            })
        }
    },
    config: {
        multipart_options: {
            limits: {
                fileSize: 1024*1024*2 // 2MB
            }
        }
    }
}, async (req, rep) => {
    const buf = req.body.file.toBuffer();
    return { ok: true }
})

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[Eomm]

Could you add some unit test?

[grigoran]

Thank you! Done

[mcollina]

docs are missing

[mcollina]

Please add a test for this type

[grigoran]

Done

[is2ei]

@grigoran

The file size limitation error isn’t caused by this configuration.
In this test, it should occur only when the request configuration is set, as described in the title.

[grigoran]

@is2ei
Hello! The error is caused by this exact configuration; I've verified it locally. This configuration is also specified in the title, except for the multipart_options(multipartOptions) field name. If I've misunderstood something, please correct me

[is2ei]

@grigoran

Could you share how you verified it locally?
I commented out the config, but the test still passed.
It seems the error may not be caused by the config.

diff --git a/test/multipart-fileLimit.test.js b/test/multipart-fileLimit.test.js
index 6aed6a5..d6d4462 100644
--- a/test/multipart-fileLimit.test.js
+++ b/test/multipart-fileLimit.test.js
@@ -331,13 +331,13 @@ test('should throw fileSize limitation error when used alongside attachFieldsToB
   crypto.randomFillSync(randomFileBuffer)
 
   fastify.post('/', {
-    config: {
-      multipartOptions: {
-        limits: {
-          fileSize: 1_000_000
-        }
-      }
-    }
+    // config: {
+    //   multipartOptions: {
+    //     limits: {
+    //       fileSize: 1_000_000
+    //     }
+    //   }
+    // }
   }, async function (req, reply) {
     t.assert.fail('it should throw')

[grigoran]

@is2ei
Got it. I tested it by changing the fileSize value to 2_500_000. Commenting out the configuration results in an error due to the default fileSize value, which is fastify.initialConfig.bodyLimit = 1_000_000.

[grigoran]

If necessary, I can change the values ​​to make it clearer what is causing the error.

[is2ei]

@grigoran

The test should be updated so that the error is caused by the config, as the message states:

should throw fileSize limitation error when used alongside attachFieldsToBody and set request config