Add slow logs for HTTP/2 Connection & Stream

[masaori335]

Similar to HTTP Slow Log, record and print HTTP/2 milestones to figure out bottleneck.

Prefix of logs are

• session : [CONNECTION ID]
• stream : [CONNECTION ID] [STREAM ID] [HTTP SM ID]

The first field (open) is absolute timestamp to compare with other logs. Other fields are relative time from the open field.

Example of milestones

[Jul 25 15:45:59.002] [ET_NET 0] NOTE: [0] [1] [0] H2 Stream Milestones: open: 1564037158335 dec_hdrs: 0.000 txn: 0.000 enc_hdrs: 0.228 tx_hdrs: 0.228 tx_data: 0.232 close: 0.666
[Jul 25 15:45:59.177] [ET_NET 0] NOTE: [0] [3] [1] H2 Stream Milestones: open: 1564037159014 dec_hdrs: 0.000 txn: 0.000 enc_hdrs: 0.063 tx_hdrs: 0.063 tx_data: 0.063 close: 0.161
[Jul 25 15:45:59.314] [ET_NET 0] NOTE: [0] [5] [2] H2 Stream Milestones: open: 1564037159190 dec_hdrs: 0.000 txn: 0.000 enc_hdrs: 0.061 tx_hdrs: 0.061 tx_data: 0.061 close: 0.123
[Jul 25 15:45:59.324] [ET_NET 0] NOTE: [0] H2 SSN Milestones: open: 1564037158333 close: 0.990

We might want to add more milestones. Let's do it on separate PR.

[bryancall]

We should follow the same design as slow log, naming the configuration option similar and having it a threshold vs on or off Alternatively this could be done with the normal logging.

[masaori335]

To follow HTTP/1.1 slow log design, add configs for threshold.

• proxy.config.http2.connection.slow.log.threshold
• proxy.config.http2.stream.slow.log.threshold