feat: Migrate to encoding/json/v2

[mschfh]

No description provided.

[Copilot]

Pull request overview

This PR migrates the codebase from the standard encoding/json package to the experimental encoding/json/v2 package, which is enabled via the GOEXPERIMENT=jsonv2 flag in Go 1.25.

Changes:

• Updated all JSON import statements from encoding/json to encoding/json/v2 across 14 files
• Updated Go version from 1.24 to 1.25 in go.mod, README.md, and .golangci.yml
• Modified build and test commands to include GOEXPERIMENT=jsonv2 flag
• Updated test expectations to reflect json/v2 behavior differences (error messages, null vs empty array serialization)
• Refactored IsPingbackRequest to use streaming token parsing with encoding/json/jsontext
• Changed JSON struct tag from omitempty to omitzero for integer fields
• Updated test JSON data to include @os field (appears to be a protocol alignment fix)
• Added Docker build cache optimization

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
go.mod	Updated Go version to 1.25.0
README.md	Updated Go dependency documentation to 1.25
.golangci.yml	Updated linter Go version to 1.25
Makefile	Added GOEXPERIMENT=jsonv2 flag to build and test commands
Dockerfile	Added build cache mount and uses golang:1.25 base image
omaha/protocol/protocol.go	Refactored IsPingbackRequest with streaming parser, added jsontext import
omaha/protocol/protocol_test.go	Added comprehensive tests for IsPingbackRequest function
omaha/v3/protocol.go	Updated json import to v2
omaha/v3/protocol_test.go	Updated json import to v2
omaha/v3/request.go	Updated json import to v2
omaha/v3/request_test.go	Updated json import to v2, updated test data with @os field
omaha/v3/response.go	Updated json import to v2, changed SizeDiff tag to omitzero
omaha/v3/response_test.go	Updated json import to v2
omaha/v4/protocol.go	Updated json import to v2
omaha/v4/protocol_test.go	Updated json import to v2
omaha/v4/request.go	Updated json import to v2
omaha/v4/request_test.go	Updated json import to v2, updated test data with @os field
omaha/v4/response.go	Updated json import to v2
omaha/v4/response_test.go	Updated json import to v2
extension/extension.go	Updated json import to v2
extension/extensiontest/extensiontest.go	Updated test JSON strings with @os field
server/server_test.go	Updated json import, test expectations for error messages and empty arrays, changed assert.Nil to assert.Empty

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[Copilot]

The IsPingbackRequest function only checks the length of the value after finding an "events" key, but doesn't validate that the value is actually an array. If the JSON contains "events":"some-string" or "events":123, the function would incorrectly return true as long as the value's byte representation is longer than 2 characters.

Consider adding validation to ensure the value starts with '[' to confirm it's an array before checking the length, or using a more robust check that the value is a non-empty array.

Suggested change

	// Check if events array has content (length > 2 means more than just "[]")
	if len(val) > 2 {
	// Check that the "events" value is a non-empty JSON array.
	trimmed := bytes.TrimSpace(val)
	if len(trimmed) > 2 && trimmed[0] == '[' && trimmed[len(trimmed)-1] == ']' {