diff --git a/contrib/lnav/README.md b/contrib/lnav/README.md
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+# `lnav` config for Synapse logs
+
+[lnav](https://lnav.org/) is a log-viewing tool. It is particularly useful when
+you need to interleave multiple log files, or for exploring a large log file
+with regex filters. The downside is that it is not as ubiquitous as tools like
+`less`, `grep`, etc.
+
+This directory contains an `lnav` [log format definition](
+ https://docs.lnav.org/en/v0.10.1/formats.html#defining-a-new-format
+) for Synapse logs as
+emitted by Synapse with the default [logging configuration](
+ https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#log_config
+). It supports lnav 0.10.1 because that's what's packaged by my distribution.
+
+This should allow lnav:
+
+- to interpret timestamps, allowing log interleaving;
+- to interpret log severity levels, allowing colouring by log level(!!!);
+- to interpret request IDs, allowing you to skip through a specific request; and
+- to highlight room, event and user IDs in logs.
+
+See also https://gist.github.com/benje/e2ab750b0a81d11920d83af637d289f7 for a
+ similar example.
+
+## Example
+
+[](https://asciinema.org/a/556133)
+
+## Tips
+
+- `lnav -i /path/to/synapse/checkout/contrib/lnav/synapse-log-format.json`
+- `lnav my_synapse_log_file` or `lnav synapse_log_files.*`, etc.
+- `lnav --help` for CLI help.
+
+Within lnav itself:
+
+- `?` for help within lnav itself.
+- `q` to quit.
+- `/` to search a-la `less` and `vim`, then `n` and `N` to continue searching
+ down and up.
+- Use `o` and `O` to skip through logs based on the request ID (`POST-1234`, or
+ else the value of the [`request_id_header`](
+ https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html?highlight=request_id_header#listeners
+ ) header). This may get confused if the same request ID is repeated among
+ multiple files or process restarts.
+- ???
+- Profit
diff --git a/contrib/lnav/synapse-log-format.json b/contrib/lnav/synapse-log-format.json
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+{
+ "$schema": "https://lnav.org/schemas/format-v1.schema.json",
+ "synapse": {
+ "title": "Synapse logs",
+ "description": "Logs output by Synapse, a Matrix homesever, under its default logging config.",
+ "regex": {
+ "log": {
+ "pattern": ".*(?<timestamp>\\d{4}-\\d{2}-\\d{2} \\d{2}:\\d{2}:\\d{2},\\d{3}) - (?<logger>.+) - (?<lineno>\\d+) - (?<level>\\w+) - (?<context>.+) - (?<body>.*)"
+ }
+ },
+ "json": false,
+ "timestamp-field": "timestamp",
+ "timestamp-format": [
+ "%Y-%m-%d %H:%M:%S,%L"
+ ],
+ "level-field": "level",
+ "body-field": "body",
+ "opid-field": "context",
+ "level": {
+ "critical": "CRITICAL",
+ "error": "ERROR",
+ "warning": "WARNING",
+ "info": "INFO",
+ "debug": "DEBUG"
+ },
+ "sample": [
+ {
+ "line": "my-matrix-server-generic-worker-4 | 2023-01-27 09:47:09,818 - synapse.replication.tcp.client - 381 - ERROR - PUT-32992 - Timed out waiting for stream receipts",
+ "level": "error"
+ },
+ {
+ "line": "my-matrix-server-federation-sender-1 | 2023-01-25 20:56:20,995 - synapse.http.matrixfederationclient - 709 - WARNING - federation_transaction_transmission_loop-3 - {PUT-O-3} [example.com] Request failed: PUT matrix://example.com/_matrix/federation/v1/send/1674680155797: HttpResponseException('403: Forbidden')",
+ "level": "warning"
+ },
+ {
+ "line": "my-matrix-server | 2023-01-25 20:55:54,433 - synapse.storage.databases - 66 - INFO - main - [database config 'master']: Checking database server",
+ "level": "info"
+ },
+ {
+ "line": "my-matrix-server | 2023-01-26 15:08:40,447 - synapse.access.http.8008 - 460 - INFO - PUT-74929 - 0.0.0.0 - 8008 - {@alice:example.com} Processed request: 0.011sec/0.000sec (0.000sec, 0.000sec) (0.001sec/0.008sec/3) 2B 200 \"PUT /_matrix/client/r0/user/%40alice%3Atexample.com/account_data/im.vector.setting.breadcrumbs HTTP/1.0\" \"Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Element/1.11.20 Chrome/108.0.5359.179 Electron/22.0.3 Safari/537.36\" [0 dbevts]",
+ "level": "info"
+ }
+ ],
+ "highlights": {
+ "user_id": {
+ "pattern": "(@|%40)[^:% ]+(:|%3A)[\\[\\]0-9a-zA-Z.\\-:]+(:\\d{1,5})?(?<!:)",
+ "underline": true
+ },
+ "room_id": {
+ "pattern": "(!|%21)[^:% ]+(:|%3A)[\\[\\]0-9a-zA-Z.\\-:]+(:\\d{1,5})?(?<!:)",
+ "underline": true
+ },
+ "room_alias": {
+ "pattern": "(#|%23)[^:% ]+(:|%3A)[\\[\\]0-9a-zA-Z.\\-:]+(:\\d{1,5})?(?<!:)",
+ "underline": true
+ },
+ "event_id_v1_v2": {
+ "pattern": "(\\$|%25)[^:% ]+(:|%3A)[\\[\\]0-9a-zA-Z.\\-:]+(:\\d{1,5})?(?<!:)",
+ "underline": true
+ },
+ "event_id_v3_plus": {
+ "pattern": "(\\$|%25)([A-Za-z0-9+/_]|-){43}",
+ "underline": true
+ }
+ }
+ }
+}
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