Add data_base64 support and simplify CE JSON marshaling

[zer0stars]

Summary

• Add data_base64 support to RawEvent: RawEvent is now a standalone struct (no longer a type alias) with custom MarshalJSON/UnmarshalJSON that handles both "data" and "data_base64" per the CloudEvents JSON spec, including round-trip preservation and MIME-based wire form selection.
• Simplify JSON marshaling: Replace headerToMap helper with sjson for consistent header serialization across CloudEventHeader, CloudEvent[A], and RawEvent. Simplify unmarshalCloudEventWithPayload by using the cloudEventHeader type alias instead of per-field deserialization.
• CloudEvent[A] stores data_base64 opaquely without decoding; consumers decide how to handle it.
• Add helpers: BytesForSignature() for signature verification and IsJSONDataContentType() for MIME detection.
• Reject mutually exclusive fields: Returns error if both "data" and "data_base64" are present.
• Comprehensive tests: Positive tests for RawEvent marshal/unmarshal, round-trip, wire format selection, BytesForSignature, IsJSONDataContentType; negative tests for invalid base64, both fields present, invalid time, missing data.

Breaking changes

RawEvent changed from type RawEvent = CloudEvent[json.RawMessage] to a standalone struct. Callers constructing RawEvent via CloudEvent[json.RawMessage]{...} will need to update.

Test plan

• All existing tests pass
• New positive and negative test cases pass
• Round-trip marshal/unmarshal preserves data_base64

Made with Cursor

[Copilot]

Pull request overview

This PR adds support for the CloudEvents data_base64 field per the CloudEvents JSON Event Format specification, enabling proper handling of binary or non-JSON payloads. The implementation redesigns RawEvent from a type alias to a standalone struct with custom JSON marshaling/unmarshaling, and adds DataBase64 field support to CloudEvent[A] with different semantics suited to each type's use case.

Changes:

• Add data_base64 support with automatic encoding/decoding based on content type and round-trip preservation
• Convert RawEvent from type alias to struct with full data_base64 handling (decodes into Data field)
• Add DataBase64 field to CloudEvent[A] (stored opaquely without decoding)
• Simplify JSON marshaling by using sjson library and type aliases instead of custom helper functions
• Add BytesForSignature() and IsJSONDataContentType() helper methods
• Comprehensive test coverage for positive and negative cases including round-trip preservation

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
cloudevent.go	Converted RawEvent to standalone struct, added DataBase64 field to CloudEvent[A], implemented custom marshal/unmarshal for RawEvent with data_base64 support, added BytesForSignature and IsJSONDataContentType helpers
cloudevent_json.go	Refactored CloudEvent[A] marshal/unmarshal to support data_base64, simplified implementation using sjson and type aliases, added unmarshalCloudEventWithPayload for shared logic
cloudevent_test.go	Added comprehensive tests for data_base64 support in both CloudEvent[A] and RawEvent, including round-trip, error cases, wire format selection, and helper functions

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[Copilot]

The json tag on the DataBase64 field includes omitempty, but this tag has no effect because CloudEvent[A] has a custom MarshalJSON method that explicitly controls which field to emit (data vs data_base64). Consider removing the json tag entirely or changing it to json:"-" to make it clear that this field is not directly marshaled by the standard JSON encoder, preventing potential confusion for future maintainers.

Suggested change

	DataBase64 string `json:"data_base64,omitempty"`
	DataBase64 string `json:"-"`

[Copilot]

The comment on line 117 mentions "data_base64 (CloudEvents spec)" but should clarify that this refers to the CloudEvents JSON format specification. Consider being more specific, e.g., "data_base64 field per CloudEvents JSON Event Format" with a reference to the spec version if appropriate.

Suggested change

	// data_base64 (CloudEvents spec). When set, MarshalJSON emits data_base64 for
	// round-trip; otherwise wire form is chosen from DataContentType and Data.
	// the data_base64 field per the CloudEvents JSON Event Format (for example,
	// CloudEvents v1.0.2). When set, MarshalJSON emits data_base64 for round-trip;
	// otherwise wire form is chosen from DataContentType and Data.

[Copilot]

The json tags on the Data and DataBase64 fields include omitempty, but these tags have no effect because RawEvent has a custom MarshalJSON method that explicitly controls which field to emit. Consider removing the json tags entirely or changing them to json:"-" to make it clear that these fields are not directly marshaled by the standard JSON encoder.

Suggested change

	Data json.RawMessage `json:"data,omitempty"`
	// DataBase64 is the raw "data_base64" string when the event was received with
	// data_base64 (CloudEvents spec). When set, MarshalJSON emits data_base64 for
	// round-trip; otherwise wire form is chosen from DataContentType and Data.
	DataBase64 string `json:"data_base64,omitempty"`
	Data json.RawMessage `json:"-"`
	// DataBase64 is the raw "data_base64" string when the event was received with
	// data_base64 (CloudEvents spec). When set, MarshalJSON emits data_base64 for
	// round-trip; otherwise wire form is chosen from DataContentType and Data.
	DataBase64 string `json:"-"`