blob: 988f34a6313a50dd44c9e9ce54a652889666a958 [file] [log] [blame]
// Copyright 2021 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
syntax = "proto3";
package pw.log;
import "pw_tokenizer/proto/options.proto";
option java_outer_classname = "Log";
// A log message and metadata. Logs come in a few different forms:
//
// 1. A tokenized log message (recommended for production)
// 2. A non-tokenized log message (good for development)
// 3. A "log missed" tombstone, indicating that some logs were dropped
//
// Size analysis for tokenized log messages, including each field's proto tag:
//
// - message - 6-12 bytes, depending on number and value of arguments
// - line_level - 3 bytes; 4 bytes if line > 2048 (uncommon)
// - timestamp - 3 bytes; assuming delta encoding
// - thread_name - 6 bytes
//
// Adding the fields gives the total proto message size:
//
// 6-12 bytes - log
// 9-15 bytes - log + level + line
// 12-18 bytes - log + level + line + timestamp
//
// An analysis of a project's log token database revealed the following
// distribution of the number of arguments to log messages:
//
// # args # messages
// 0 2,700
// 1 2,400
// 2 1,200
// 3+ 1,000
//
// Note: The below proto makes some compromises compared to what one might
// expect for a "clean" proto design, in order to shave bytes off of the
// messages. It is critical that the log messages are as small as possible to
// enable storing more logs in limited memory. This is why, for example, there
// is no separate "DroppedLog" type, or a "TokenizedLog" and "StringLog", which
// would add at least 2 extra bytes per message
message LogEntry {
// The log message, which may be tokenized.
//
// If tokenized logging is used, implementations may encode metadata in the
// log message rather than as separate proto fields. This reduces the size of
// the protobuf with no overhead.
//
// The standard format for encoding metadata in the log message is defined by
// the pw_log_tokenized module. The message and metadata are encoded as
// key-value pairs using ■ and ♦ as delimiters. For example:
//
// ■msg♦This is the log message: %d■module♦wifi■file♦../path/to/file.cc
//
// See http://pigweed.dev/pw_log_tokenized for full details. When
// pw_log_tokenized is used, this metadata is automatically included as
// described.
//
// The level and flags are not included since they may be runtime values and
// thus cannot always be tokenized. The line number is not included because
// line numbers change frequently and a new token is created for each line.
//
// Size analysis when tokenized:
//
// tag+wire = 1 byte
// size = 1 byte; payload will almost always be < 127 bytes
// payload = N bytes; typically 4-10 in practice
//
// Total: 2 + N ~= 6-12 bytes
optional bytes message = 1 [(tokenizer.format) = TOKENIZATION_OPTIONAL];
// Packed log level and line number. Structure:
//
// Level: Bottom 3 bits; level = line_level & 0x7
// Line: Remaining bits; line = (line_level >> 3)
//
// Note: This packing saves two bytes per log message in most cases compared
// to having line and level separately; and is zero-cost if the log backend
// omits the line number.
optional uint32 line_level = 2;
// Some log messages have flags to indicate attributes such as whether they
// are from an assert or if they contain PII. The particular flags are
// product- and implementation-dependent.
optional uint32 flags = 3;
// Timestamps are either specified with an absolute timestamp or relative to
// the previous log entry.
oneof time {
// The absolute timestamp in implementation-defined ticks. Applications
// determine how to interpret this on the receiving end. In the simplest
// case, these ticks might be milliseconds or microseconds since boot.
// Applications could also access clock information out-of-band with a
// ClockParameters protobuf.
int64 timestamp = 4;
// Time since the last entry in implementation-defined ticks, as for the
// timestamp field. This enables delta encoding when batching entries
// together.
//
// Size analysis for this field including tag and varint, assuming 1 kHz
// ticks:
//
// < 127 ms gap == 127 ms == 7 bits == 2 bytes
// < 16,000 ms gap == 16 seconds == 14 bits == 3 bytes
// < 2,000,000 ms gap == 35 minutes == 21 bits == 4 bytes
// < 300,000,000 ms gap == 74 hours == 28 bits == 5 bytes
//
// Log bursts will thus consume just 2 bytes (tag + up to 127ms delta) for
// the timestamp, which is a good improvement over an absolute timestamp.
int64 time_since_last_entry = 5;
}
// The following fields are planned but will not be added until they are
// needed. Protobuf field numbers over 15 use an extra byte, so these fields
// are left out for now to avoid reserving field numbers unnecessarily.
// When the log buffers are full but more logs come in, the logs are counted
// and a special log message is omitted with only counts for the number of
// messages dropped. The timestamp indicates the time that the "missed logs"
// message was inserted into the queue.
//
// As an alternative to these fields, implementations may simply send a
// message stating the drop count.
// optional uint32 dropped = ?;
// optional uint32 dropped_warning_or_above = ?;
// Represents the device from which the log originated. The meaning of this
// field is implementation defined
// optional uint32 source_id = ?;
// The task or thread name that created the log message. If the log was not
// created on a thread, it should use a name appropriate to that context.
// optional bytes thread_name = ?
// [(tokenizer.format) = TOKENIZATION_OPTIONAL];
// The file path where this log was created, if not encoded in the message.
// optional bytes file = ? [(tokenizer.format) = TOKENIZATION_OPTIONAL];
// The PW_LOG_MODULE_NAME for this log message, if it is not encoded in the
// message.
// optional bytes module_name = ?
// [(tokenizer.format) = TOKENIZATION_OPTIONAL];
// Some messages are associated with trace events, which may carry additional
// contextual data. This is a tuple of a data format string which could be
// used by the decoder to identify the data (e.g. printf-style tokens) and the
// data itself in bytes.
// optional bytes data_format = ?
// [(tokenizer.format) = TOKENIZATION_OPTIONAL];
// optional bytes data = ?;
}
message LogRequest {
// This will include fields for configuring log filtering.
}
message LogEntries {
repeated LogEntry entries = 1;
}
// RPC service for accessing logs.
service Logs {
rpc Listen(LogRequest) returns (stream LogEntries);
}