Introduce time

[tatsuhiro-t]

This commit introduces time to count certain events in specific duration of time.

nghttp3_tstamp is the time instant, and nghttp3_duration is the duration of time. Both are nanosecond resolution. Some macros such as NGHTTP3_SECONDS have been introduced for convenience.

nghttp3_settings has been extended, and an application should set the initial timestamp to initial_ts field.

nghttp3_conn_read_stream has been deprecated in favor of nghttp3_conn_read_stream2 which takes nghttp3_tstamp as a final parameter.

[gemini-code-assist]

Summary of Changes

Hello @tatsuhiro-t, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request integrates a robust timekeeping mechanism into the library, enabling the tracking of events with nanosecond precision. It introduces new data types for timestamps and durations, along with utility macros for common time units. The nghttp3_settings structure has been enhanced to allow for an initial timestamp, and a new stream reading function, nghttp3_conn_read_stream2, has been added to leverage this new timing capability, replacing its predecessor.

Highlights

• New Time Types and Macros: Introduced nghttp3_tstamp and nghttp3_duration types for nanosecond resolution time, along with convenience macros like NGHTTP3_NANOSECONDS, NGHTTP3_MICROSECONDS, NGHTTP3_MILLISECONDS, and NGHTTP3_SECONDS.
• Extended nghttp3_settings: The nghttp3_settings structure has been extended with a new initial_ts field, allowing applications to provide an initial timestamp to the library.
• Deprecated nghttp3_conn_read_stream: The function nghttp3_conn_read_stream has been deprecated in favor of nghttp3_conn_read_stream2, which now accepts an nghttp3_tstamp parameter for more precise timing of stream data processing.
• Settings Version Update: The internal settings version has been updated to NGHTTP3_SETTINGS_V3 to reflect the new additions and changes.

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[gemini-code-assist]

Code Review

This pull request introduces time-related data types and functionality to the library, including nanosecond-resolution timestamps and durations. The changes are well-implemented across the API, documentation, and tests. A new function nghttp3_conn_read_stream2 is added to accept a timestamp, and the old function is deprecated. My review found one potential issue in the new timestamp handling logic that could lead to state corruption, for which I've provided a suggestion.

[tatsuhiro-t]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces time-related data types and functions to enable tracking of events over time. The changes include new typedefs for timestamp and duration, an initial_ts field in nghttp3_settings, and a new nghttp3_conn_read_stream2 function that accepts a timestamp. The existing nghttp3_conn_read_stream is deprecated. The implementation is consistent across the library, documentation, and tests. I have one suggestion to improve the robustness of the versioned settings struct size calculation.

[gemini-code-assist]

Using offsetof with the first field of the next version is a more robust way to determine the size of a versioned struct, as it correctly handles potential compiler padding between members. The current approach of offsetof(last_field) + sizeof(last_field) can be incorrect if there's padding after last_field.

    return offsetof(nghttp3_settings, initial_ts);