Updated eula pdf upload size check to default max request body size (#43517)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** Resolves #40856

# Checklist for submitter

If some of the following don't apply, delete the relevant line.

- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.

## Testing

- [x] Added/updated automated tests
- [x] QA'd all new/changed functionality manually


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* EULA PDF upload size validation now reports the configured maximum
upload size (in MiB) instead of a fixed value, improving clarity of
rejection messages.

* **Tests**
* Added tests covering EULA upload size validation, ensuring oversized
uploads are rejected with the proper status and that configured
request-body limits are respected.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

changes/40856-eula-upload-updated-to-default-max-request-body-size-and-error

@@ -0,0 +1 @@
+- Updated to default max request body size for eula pdf upload size check

server/service/integration_mdm_test.go

@@ -39,6 +39,7 @@ import (
 
 	"github.com/MicahParks/jwkset"
 	"github.com/davecgh/go-spew/spew"
+	"github.com/docker/go-units"
 	"github.com/fleetdm/fleet/v4/server/dev_mode"
 	"github.com/fleetdm/fleet/v4/server/mdm/acme/testhelpers"
 	"github.com/fleetdm/fleet/v4/server/mdm/android"
@@ -48,6 +49,7 @@ import (
 	"github.com/fleetdm/fleet/v4/server/mdm/android/tests"
 	"github.com/fleetdm/fleet/v4/server/mdm/apple/apple_apps"
 	"github.com/fleetdm/fleet/v4/server/mdm/assets"
+	platform_http "github.com/fleetdm/fleet/v4/server/platform/http"
 	"github.com/fleetdm/fleet/v4/server/pubsub"
 	"github.com/golang-jwt/jwt/v4"
 	"google.golang.org/api/androidmanagement/v1"
@@ -4590,6 +4592,33 @@ func (s *integrationMDMTestSuite) TestEULA() {
 	// trying to upload an empty file fails
 	s.uploadEULA(&fleet.MDMEULA{Bytes: []byte{}, Name: "should-fail.pdf"}, http.StatusBadRequest, "invalid file type")
 
+	// file larger than the max EULA size should be rejected by the request size limit
+	largePDF := append(
+		[]byte("%PDF-1.7\n"),
+		bytes.Repeat([]byte("A"), int(fleet.MaxEULASize)+1-len("%PDF-1.7\n"))...,
+	)
+
+	s.uploadEULA(&fleet.MDMEULA{Bytes: largePDF, Name: "oversize.pdf"}, http.StatusRequestEntityTooLarge, "Request exceeds the max size limit")
+
+	// Test with MaxRequestBodySize set to unlimited (-1) - the endpoint still enforces the EULA request body limit
+	oldLimit := platform_http.MaxRequestBodySize
+	platform_http.MaxRequestBodySize = -1
+	largePDFUnlimited := append(
+		[]byte("%PDF-1.7\n"),
+		bytes.Repeat([]byte("A"), int(fleet.MaxEULASize)+1-len("%PDF-1.7\n"))...,
+	)
+	s.uploadEULA(&fleet.MDMEULA{Bytes: largePDFUnlimited, Name: "oversize_unlimited.pdf"}, http.StatusRequestEntityTooLarge, "Request exceeds the max size limit")
+	platform_http.MaxRequestBodySize = oldLimit
+
+	// Test with MaxRequestBodySize larger than MaxEULASize - should reject at MaxRequestBodySize
+	platform_http.MaxRequestBodySize = 50 * units.MiB
+	largePDFLarge := append(
+		[]byte("%PDF-1.7\n"),
+		bytes.Repeat([]byte("A"), int(50*units.MiB)+1-len("%PDF-1.7\n"))...,
+	)
+	s.uploadEULA(&fleet.MDMEULA{Bytes: largePDFLarge, Name: "oversize_large.pdf"}, http.StatusRequestEntityTooLarge, "Request exceeds the max size limit")
+	platform_http.MaxRequestBodySize = oldLimit
+
 	// admin is able to upload a new EULA
 	s.uploadEULA(&fleet.MDMEULA{Bytes: pdfBytes, Name: pdfName}, http.StatusOK, "")
 

server/service/mdm.go

@@ -269,7 +269,7 @@ func (createMDMEULARequest) DecodeRequest(ctx context.Context, r *http.Request)
 
 	if eula.Size > fleet.MaxEULASize {
 		return nil, &fleet.BadRequestError{
-			Message: "Uploaded EULA exceeds maximum allowed size of 500 MiB",
+			Message: fmt.Sprintf("Uploaded EULA exceeds maximum allowed size of %d MiB", fleet.MaxEULASize/1024/1024),
 		}
 	}