Configuration

The service reads its configuration from environment variables in loadConfig (src/server.mjs). There is no configuration file. Every numeric setting has its default in DEFAULTS in src/app.mjs, and its variable name is the setting’s name in upper snake case (linkAttemptWindowMs is LINK_ATTEMPT_WINDOW_MS).

An unset or empty variable takes the default. A malformed value throws at start, so the service does not run with a bad configuration. src/admin.mjs reads the same variables.

Origin, paths and payload

Variable	Type	Default	Meaning
PUBLIC_ORIGIN	Origin: http:// or https://, host, optional port, no path	http://localhost:8080	The only Origin accepted on POST and DELETE, and the base of every returned URL and redirect.
LINK_TARGET_PATH	Path: / then A-Z a-z 0-9 . _ ~ / -	/	Where /s/<id> sends the browser. The payload is appended to it.
LINK_MISSING_PATH	Path, same rule	/link-not-found	Where an unknown or expired id goes. The app serves this page.
PAYLOAD_PREFIX	# then up to 32 of A-Z a-z 0-9 . _ ~ = -	#state=v1.	The fragment prefix every payload must start with. The maximum body length is this prefix’s length plus 65,536.

Network and client identity

Variable	Type	Default	Meaning
HOST	String	All interfaces	Listen address.
PORT	Non-negative integer	8080	Listen port.
TRUSTED_PROXIES	Comma-separated IPv4 or IPv6 CIDR ranges	Empty	Peers whose forwarded header is read to find the client. Empty means the TCP peer is the client.
FORWARDED_HEADER	Header name: A-Z a-z 0-9 -	x-forwarded-for	The header those proxies set, for example x-real-ip. Lower-cased.

Storage and maintenance

Variable	Type	Default	Meaning
DATA_DIR	Path	./data (/data in the image)	Holds links.sqlite, images.sqlite and backups/. Created if missing.
MAX_LINKS	Non-negative integer	20000	Link store count cap.
MAX_LINK_BYTES	Non-negative integer	268435456 (256 MiB)	Link store byte cap, summed over payloads.
UNOPENED_TTL_MS	Non-negative integer	2592000000 (30 days)	Time a new link has to be opened once before it expires.
MAX_IMAGES	Non-negative integer	2000	Image store count cap.
MAX_IMAGE_BYTES	Non-negative integer	209715200 (200 MiB)	Image store byte cap. This is not the per-file limit, which is a fixed 1.5 MiB.
BACKUP_KEEP	Non-negative integer	7	Daily link backups kept.
IMAGE_BACKUP_KEEP	Non-negative integer	2	Daily image backups kept.
BACKUP_INTERVAL_MS	Non-negative integer	3600000 (1 hour)	How often backups and the expiry sweep run. 0 turns off the periodic run. One run still happens at start.
MAX_IN_FLIGHT_BYTES	Non-negative integer	16777216 (16 MiB)	Request bodies held in memory at once, across both POST routes.

Link rate limits

All values are non-negative integers. Windows are in milliseconds.

Variables	Defaults	Counts
LINK_ATTEMPT_LIMIT, LINK_ATTEMPT_WINDOW_MS	60, 600000 (10 min)	Every POST to /api/links of a client, before the body is read.
LINK_CREATE_LIMIT, LINK_CREATE_WINDOW_MS	30, 600000 (10 min)	New links stored by a client.
LINK_DAILY_LIMIT, LINK_DAILY_WINDOW_MS	200, 86400000 (1 day)	New links stored by a client per day.
LINK_BYTES_LIMIT, LINK_BYTES_WINDOW_MS	2097152 (2 MiB), 86400000	Bytes of new links stored by a client per day.
LINK_GLOBAL_LIMIT, LINK_GLOBAL_WINDOW_MS	600, 3600000 (1 hour)	New links stored by all clients.
READ_LIMIT, READ_WINDOW_MS	240, 60000 (1 min)	Reads of a client: /s/, /api/links/<id> and /api/images/<id> together.

Image rate limits

Variables	Defaults	Counts
IMAGE_ATTEMPT_LIMIT, IMAGE_ATTEMPT_WINDOW_MS	30, 600000 (10 min)	Every POST to /api/images and every DELETE of an image by a client.
IMAGE_CREATE_LIMIT, IMAGE_CREATE_WINDOW_MS	10, 3600000 (1 hour)	New images stored by a client.
IMAGE_DAILY_LIMIT, IMAGE_DAILY_WINDOW_MS	20, 86400000 (1 day)	New images stored by a client per day.
IMAGE_BYTES_LIMIT, IMAGE_BYTES_WINDOW_MS	6291456 (6 MiB), 86400000	Bytes of new images stored by a client per day.
IMAGE_GLOBAL_LIMIT, IMAGE_GLOBAL_WINDOW_MS	100, 3600000 (1 hour)	New images stored by all clients.

How these limits are checked and charged is described in rate limits, memory budget and storage caps.

Fixed values

These are constants in the code, not settings:

Value	Where
Image body at most 1.5 MiB (1,572,864 bytes)	MAX_IMAGE_BYTES in src/image.mjs
Image sides 16 to 2048 pixels	MIN_IMAGE_SIDE, MAX_IMAGE_SIDE in src/image.mjs
Payload: 48 KiB compressed, 256 KiB of JSON after inflating	MAX_COMPRESSED_BYTES, MAX_JSON_BYTES in src/payload.mjs
Ids of ten base62 characters	ID_LENGTH in src/link-store.mjs
Retry-After: 5 on 503 busy	src/app.mjs
At most 10,000 keys per rate limiter	createRateLimiter in src/rate-limit.mjs
headersTimeout 10 s, requestTimeout 15 s, keepAliveTimeout 5 s, 16 KiB of headers, 64 headers	start in src/server.mjs

Example

PUBLIC_ORIGIN=https://app.example.com \
LINK_TARGET_PATH=/editor \
LINK_MISSING_PATH=/link-not-found \
TRUSTED_PROXIES=10.0.0.2/32 \
DATA_DIR=/var/lib/share-links \
LINK_CREATE_LIMIT=10 \
npm start