Surveillance

Representation-agnostic filewatching with streams in Scala

Surveillance watches directories for changes, and provides a LazyList of streaming WatchEvents. While it works well with Galilei, it can work with any representation of paths.

Features

simple API for most common filesystem operations
read from and write to files on disk with a variety of different types
simple streaming to and from disk with LazyLists
employs IArray[Byte] for fast, random-access, immutable chunking of byte data
encoding-aware operations involving Strings

Availability Plan

Surveillance has not yet been published. The medium-term plan is to build Surveillance with Fury and to publish it as a source build on Vent. This will enable ordinary users to write and build software which depends on Surveillance.

Subsequently, Surveillance will also be made available as a binary in the Maven Central repository. This will enable users of other build tools to use it.

For the overeager, curious and impatient, see building.

Getting Started

Surveillance watches directories for changes to their contents, through an extension method, watch(), on a type representing a directory or a Seq of such types. For Galilei's Directory type, this works straight away. Other libraries which provide directory-like types can integrate with Surveillance just by defining two simple typeclass instances.

Watching

A simple setup for watching a directory looks like this:

import galilei.*
import serpentine.*
import surveillance.*

val dir = (Unix / p"home" / p"work" / p"updates").directory()
val watcher = dir.watch()

Constructing a new Watcher on a directory will register that directory with the filesystem's filewatching service and start a new thread to respond to updates.

The most important method of a Watcher is its stream method, which will return a LazyList[WatchEvent]

Status

Surveillance is classified as fledgling. For reference, Scala One projects are categorized into one of the following five stability levels:

embryonic: for experimental or demonstrative purposes only, without any guarantees of longevity
fledgling: of proven utility, seeking contributions, but liable to significant redesigns
maturescent: major design decisions broady settled, seeking probatory adoption and refinement
dependable: production-ready, subject to controlled ongoing maintenance and enhancement; tagged as version 1.0.0 or later
adamantine: proven, reliable and production-ready, with no further breaking changes ever anticipated

Projects at any stability level, even embryonic projects, can still be used, as long as caution is taken to avoid a mismatch between the project's stability level and the required stability and maintainability of your own project.

Surveillance is designed to be small. Its entire source code currently consists of 122 lines of code.

Building

Surveillance will ultimately be built by Fury, when it is published. In the meantime, two possibilities are offered, however they are acknowledged to be fragile, inadequately tested, and unsuitable for anything more than experimentation. They are provided only for the necessity of providing some answer to the question, "how can I try Surveillance?".

Copy the sources into your own project

Read the fury file in the repository root to understand Surveillance's build structure, dependencies and source location; the file format should be short and quite intuitive. Copy the sources into a source directory in your own project, then repeat (recursively) for each of the dependencies.

The sources are compiled against the latest nightly release of Scala 3. There should be no problem to compile the project together with all of its dependencies in a single compilation.
Build with Wrath

Wrath is a bootstrapping script for building Surveillance and other projects in the absence of a fully-featured build tool. It is designed to read the fury file in the project directory, and produce a collection of JAR files which can be added to a classpath, by compiling the project and all of its dependencies, including the Scala compiler itself.

Download the latest version of wrath, make it executable, and add it to your path, for example by copying it to /usr/local/bin/.

Clone this repository inside an empty directory, so that the build can safely make clones of repositories it depends on as peers of surveillance. Run wrath -F in the repository root. This will download and compile the latest version of Scala, as well as all of Surveillance's dependencies.

If the build was successful, the compiled JAR files can be found in the .wrath/dist directory.

Contributing

Contributors to Surveillance are welcome and encouraged. New contributors may like to look for issues marked beginner.

We suggest that all contributors read the Contributing Guide to make the process of contributing to Surveillance easier.

Please do not contact project maintainers privately with questions unless there is a good reason to keep them private. While it can be tempting to repsond to such questions, private answers cannot be shared with a wider audience, and it can result in duplication of effort.

Author

Surveillance was designed and developed by Jon Pretty, and commercial support and training on all aspects of Scala 3 is available from Propensive OÜ.

Name

This library watches directories for changes, which is to say it keeps them under surveillance.

In general, Scala One project names are always chosen with some rationale, however it is usually frivolous. Each name is chosen for more for its uniqueness and intrigue than its concision or catchiness, and there is no bias towards names with positive or "nice" meanings—since many of the libraries perform some quite unpleasant tasks.

Names should be English words, though many are obscure or archaic, and it should be noted how willingly English adopts foreign words. Names are generally of Greek or Latin origin, and have often arrived in English via a romance language.

Logo

The logo shows a glistening eye, watching or surveilling.

propensive / surveillance