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Document the streaming serializer
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LPardue committed Mar 24, 2020
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275 changes: 220 additions & 55 deletions tools/qlog/README.md
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Expand Up @@ -9,86 +9,118 @@ The crate uses Serde for conversion between Rust and JSON.
[qlog QUIC and HTTP/3 events]: https://quiclog.github.io/internet-drafts/draft-marx-qlog-event-definitions-quic-h3
[TypeScript schema]: https://github.com/quiclog/qlog/blob/master/TypeScript/draft-01/QLog.ts

Getting Started
---------------
Overview
--------
qlog is a hierarchical logging format, with a rough structure of:

* Log
* Trace(s)
* Event(s)

In practice, a single QUIC connection maps to a single Trace file with one
or more Events. Applications can decide whether to combine Traces from
different connections into the same Log.

## Traces

A [`Trace`] contains metadata such as the [`VantagePoint`] of capture and
the [`Configuration`] of the `Trace`.

### Creating a trace
A very important part of the `Trace` is the definition of `event_fields`. A
qlog Event is a vector of [`EventField`]; this provides great flexibility to
log events with any number of `EventFields` in any order. The `event_fields`
property describes the format of event logging and it is important that
events comply with that format. Failing to do so it going to cause problems
for qlog analysis tools. For information is available at
https://tools.ietf.org/html/draft-marx-qlog-main-schema-01#section-3.3.4

A typical application needs a single qlog trace that it appends QUIC and/or
HTTP/3 events to:
In order to make using qlog a bit easier, this crate expects a qlog Event to
consist of the following EventFields in the following order:
[`EventField::RelativeTime`], [`EventField::Category`],
[`EventField::Event`] and [`EventField::Data`]. A set of methods are
provided to assist in creating a Trace and appending events to it in this
format.

## Writing out logs
As events occur during the connection, the application appends them to the
trace. The qlog crate supports two modes of writing logs: the buffered mode
stores everything in memory and requires the application to serialize and write
the output, the streaming mode progressively writes serialized JSON output to a
writer designated by the application.

Buffered Mode
---------------

Create the trace:

```rust
let trace = Trace {
vantage_point: VantagePoint {
name: "Example client",
ty: VantagePointType::Client,
let mut trace = qlog::Trace::new(
qlog::VantagePoint {
name: Some("Example client".to_string()),
ty: qlog::VantagePointType::Client,
flow: None,
},
title: Some("Example qlog trace".to_string()),
description: Some("Example qlog trace description".to_string()),
configuration: Some(Configuration {
Some("Example qlog trace".to_string()),
Some("Example qlog trace description".to_string()),
Some(qlog::Configuration {
time_offset: Some("0".to_string()),
time_units: Some(TimeUnits::Ms),
time_units: Some(qlog::TimeUnits::Ms),
original_uris: None,
}),
common_fields: None,
event_fields: vec![
"relative_time".to_string(),
"category".to_string(),
"event".to_string(),
"data".to_string(),
],
events: Vec::new(),
};

None,
);
```

### Adding events

Qlog Events are added to `qlog::Trace.events`. Utility method are provided for
the various types of QUIC and HTTP/3 events. The following example demonstrates
how to log a QUIC packet containing a single Crypto frame, it uses the
`push_transport_event()` and `QuicFrame::crypto()` methods to capture a
Qlog Events are added to `qlog::Trace.events`.

It is recommended to use the provided utility methods to append semantically
valid events to a trace. However, there is nothing preventing you from
creating the events manually.

The following example demonstrates how to log a QUIC packet
containing a single Crypto frame. It uses the [`QuicFrame::crypto()`],
[`packet_sent_min()`] and [`push_event()`] methods to create and log a
PacketSent event and its EventData.

```rust
trace.push_transport_event(
"0".to_string(),
TransportEventType::PacketSent,
EventData::PacketSent {
raw_encrypted: None,
raw_decrypted: None,
packet_type: PacketType::Initial,
header: PacketHeader {
packet_number: "0".to_string(),
packet_size: Some(1251),
payload_length: Some(1224),
version: Some("0xff000018".to_string()),
scil: Some("8".to_string()),
dcil: Some("8".to_string()),
scid: Some("7e37e4dcc6682da8".to_string()),
dcid: Some("36ce104eee50101c".to_string()),
},
frames: Some(vec![
QuicFrame::crypto(
"0".to_string(),
"1000".to_string(),
)
]),
is_coalesced: None,
},
let scid = [0x7e, 0x37, 0xe4, 0xdc, 0xc6, 0x68, 0x2d, 0xa8];
let dcid = [0x36, 0xce, 0x10, 0x4e, 0xee, 0x50, 0x10, 0x1c];

let pkt_hdr = qlog::PacketHeader::new(
0,
Some(1251),
Some(1224),
Some(0xff00001b),
Some(b"7e37e4dcc6682da8"),
Some(&dcid),
);

let frames =
vec![qlog::QuicFrame::crypto("0".to_string(), "1000".to_string())];

let event = qlog::event::Event::packet_sent_min(
qlog::PacketType::Initial,
pkt_hdr,
Some(frames),
);

trace.push_event(std::time::Duration::new(0, 0), event);
```

### Serializing

Simply:
The qlog crate has only been tested with `serde_json`, however other serializer
targets might work.

For example, serializing the trace created above:

```rust
serde_json::to_string_pretty(&trace).unwrap();
```

which would generate the following:
would generate the following:

```
{
Expand Down Expand Up @@ -119,7 +151,7 @@ which would generate the following:
"packet_number": "0",
"packet_size": 1251,
"payload_length": 1224,
"version": "0xff000018",
"version": "0xff00001b",
"scil": "8",
"dcil": "8",
"scid": "7e37e4dcc6682da8",
Expand All @@ -137,3 +169,136 @@ which would generate the following:
]
}
```

Streaming Mode
---------------

Create the trace:

```rust
let mut trace = qlog::Trace::new(
qlog::VantagePoint {
name: Some("Example client".to_string()),
ty: qlog::VantagePointType::Client,
flow: None,
},
Some("Example qlog trace".to_string()),
Some("Example qlog trace description".to_string()),
Some(qlog::Configuration {
time_offset: Some("0".to_string()),
time_units: Some(qlog::TimeUnits::Ms),
original_uris: None,
}),
None,
);
```

Create an object with the [`Write`] trait:

```rust
let mut file = std::fs::File::create("foo.qlog").unwrap();
```

Create a [`QlogStreamer`] and start serialization to foo.qlog
using [`start_log()`]:

```rust
let mut streamer = qlog::QlogStreamer::new(
qlog::QLOG_VERSION.to_string(),
Some("Example qlog".to_string()),
Some("Example qlog description".to_string()),
None,
std::time::Instant::now(),
trace,
Box::new(file),
);

streamer.start_log().ok();

```

### Adding simple events

Once logging has started you can stream events. Simple events can be written in
one step using [`add_event()`]:

```rust
let event = qlog::event::Event::metrics_updated_min();
streamer.add_event(event).ok();
```

### Adding events with frames
Some events contain optional arrays of QUIC frames. If the event has
`Some(Vec<QuicFrame>)`, even if it is empty, the streamer enters a frame
serializing mode that must be finalized before other events can be logged.

In this example, a PacketSent event is created with an empty frame array and
frames are written out later:

```rust
let qlog_pkt_hdr = qlog::PacketHeader::with_type(
qlog::PacketType::OneRtt,
0,
Some(1251),
Some(1224),
Some(0xff00001b),
Some(b"7e37e4dcc6682da8"),
Some(b"36ce104eee50101c"),
);

let event = qlog::event::Event::packet_sent_min(
qlog::PacketType::OneRtt,
qlog_pkt_hdr,
Some(Vec::new()),
);

streamer.add_event(event).ok();

```

In this example, the frames contained in the QUIC packet
are PING and PADDING. Each frame is written using the
[`add_frame()`] method. Frame writing is concluded with
[`finish_frames()`].

```rust
let ping = qlog::QuicFrame::ping();
let padding = qlog::QuicFrame::padding();

streamer.add_frame(ping, false).ok();
streamer.add_frame(padding, false).ok();

streamer.finish_frames().ok();
```

Once all events have have been written, the log
can be finalized with [`finish_log()`]:

```rust
streamer.finish_log().ok();
```

### Serializing

Serialization to JSON occurs as methods on the [`QlogStreamer`]
are called. No additional steps are required.

[`Trace`]: struct.Trace.html
[`VantagePoint`]: struct.VantagePoint.html
[`Configuration`]: struct.Configuration.html
[`EventField`]: enum.EventField.html
[`EventField::RelativeTime`]: enum.EventField.html#variant.RelativeTime
[`EventField::Category`]: enum.EventField.html#variant.Category
[`EventField::Type`]: enum.EventField.html#variant.Type
[`EventField::Data`]: enum.EventField.html#variant.Data
[`qlog::Trace.events`]: struct.Trace.html#structfield.events
[`push_event()`]: struct.Trace.html#method.push_event
[`packet_sent_min()`]: event/struct.Event.html#method.packet_sent_min
[`QuicFrame::crypto()`]: enum.QuicFrame.html#variant.Crypto
[`QlogStreamer`]: struct.QlogStreamer.html
[`Write`]: https://doc.rust-lang.org/std/io/trait.Write.html
[`start_log()`]: struct.QlogStreamer.html#method.start_log
[`add_event()`]: struct.QlogStreamer.html#method.add_event
[`add_frame()`]: struct.QlogStreamer.html#method.add_frame
[`finish_frames()`]: struct.QlogStreamer.html#method.finish_frames
[`finish_log()`]: struct.QlogStreamer.html#method.finish_log
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