mirror of
https://github.com/bower/bower.git
synced 2026-02-11 14:34:58 -05:00
256 lines
13 KiB
Markdown
256 lines
13 KiB
Markdown
# Bower rewrite
|
|
|
|
## Why?
|
|
|
|
Bower codebase is becoming unmanageable, especially at its core.
|
|
Main issues are:
|
|
|
|
- __No separation of concerns. The overall codebase has grown in a patch fashion, which has lead to a bloated and tight coupled solution.__
|
|
- __Monolithic Package.js that handles all package types (both local and remote `Git`, URL, local files, etc).__
|
|
- __Package.js has a big nesting level of callbacks, causing confusion and making the code hard to read.__
|
|
- Some commands, such as install and update, have incorrect behaviour ([#200](https://github.com/twitter/bower/issues/200), [#256](https://github.com/twitter/bower/issues/256))
|
|
- This is directly related with the current implementation of bower core: Package.js and Manager.js
|
|
- Programmatic usage needs improvement
|
|
- Unable to spawn multiple commands in parallel in different folders
|
|
- Some commands simply do not fire the `end` event
|
|
- Others fire the `error` event many times
|
|
- Some commands should fire more meaningful events (e.g.: install should fire each installed package)
|
|
|
|
|
|
## Main goals
|
|
|
|
- Ease the process of gathering more contributors.
|
|
- Clear architecture and separation of concerns.
|
|
- Installation/update speedup.
|
|
- Named endpoints on the CLI install.
|
|
- Offline installation of packages, thanks to the cache.
|
|
- Ability to easily add package types (`SVN`, etc).
|
|
- Support for commit hashes and branches in targets for `Git` endpoints.
|
|
- Improved output after installation/update.
|
|
- Integrate with update-notifier and yeomen insight.
|
|
|
|
|
|
## Implementation details
|
|
|
|
### Term dictionary
|
|
|
|
- **Canonical package:** A folder containing all the files that belong to a package. May include a `bower.json` file inside. (typically what gets installed)
|
|
- **Source:** URL, git endpoint, etc.
|
|
- **Target:** `semver` range, commit hash, branch (indicates a version).
|
|
- **Endpoint:** source#target
|
|
- **Named endpoint:** name@endpoint#target
|
|
- **UoW:** Unit of Work
|
|
- **Components folder:** The folder in which components are installed (`bower_components` by default).
|
|
|
|
### Overall strategy
|
|
|
|
|
|
|
|
Bower is composed of the following components:
|
|
|
|
- `CLI`: Command line interface for Bower.
|
|
- `.bowerrc`: Allows for customisations of Bower behaviour at the project/user level.
|
|
- `bower.json`: Main purpose is to declare the component dependencies and other component related information.
|
|
- `Manager`: Main coordinator, responsible for:
|
|
- Checking which packages are already installed in the current `bower folder`.
|
|
- Deciding which version of the dependencies should be fetched from the `PackageRepository`, while keeping every dependant compatible (note that the `Manager` is `server` aware).
|
|
- Tracking which dependencies have been fetched, which ones failed to fetch, and which ones are being fetched.
|
|
- Requesting the `PackageRepository` to fail-fast, in case it realises there is no resolution for the current dependency tree.
|
|
- `PackageRepository`: Abstraction to the underlying complexity of heterogeneous source types. Responsible for:
|
|
- Storing new entries in `ResolveCache`.
|
|
- Queueing resolvers into the `UoW`, if no suitable entry is found in the `ResolveCache`.
|
|
- `ResolveCache`: Keeps a cache of previously resolved endpoints. Lookup can be done using an endpoint.
|
|
- `UnitOfWork`: Work coordinator, responsible for:
|
|
- Keeping track of which resolvers are being resolved.
|
|
- Limiting amount of parallel resolutions.
|
|
- `ResolverFactory`: Parses an endpoint and returns a `Resolver` capable of resolving the source type.
|
|
- `Resolver`: Base resolver, which can be extended by concrete resolvers, like `UrlResolver`, `GitRemoteResolver`, etc.
|
|
|
|
You can find additional details about each of these components below, in [Architecture components details](#architecture-components-details).
|
|
|
|
|
|
#### Resolve process
|
|
|
|
Here's an overview of the dependency resolve process:
|
|
|
|
1. **INSTALL/UPDATE** - A set of named endpoints and/or endpoints is requested to be installed/updated, and these are passed to the `Manager`.
|
|
|
|
2. **ANALIZE COMPONENTS FOLDER** - `Manager` starts by reading the *components folder* and understanding which packages are already installed.
|
|
|
|
3. **ENQUEUE ENDPOINTS** - For each endpoint that should be fetched, the `Manager` enqueues the *named endpoints*/endpoints in the `PackageRepository`. Some considerations:
|
|
- If a package should be fetched or not depends on the following conditions:
|
|
- What operation is being done (install/update).
|
|
- If package is already installed.
|
|
- If `Manager` has already enqueued that *named endpoint*/endpoint in the current runtime (regardless of the fetch being currently in progress, already complete, or failed).
|
|
- Additional flags (force, etc).
|
|
|
|
4. **FABRICATE RESOLVERS** - For each of the endpoints, the `PackageRepository` requests the `ResolverFactory` for suitable resolvers, capable of handling the source type. Some considerations:
|
|
- The factory method takes the source string as its main argument, and is also provided with target, and package name if possible (all this information is extracted from the *named endpoint*/endpoint).
|
|
- This method is asynchronous, in order to allow for I/O operations to happen, without blocking the whole process (e.g., querying registry, etc).
|
|
- There is a runtime internal cache of sources that have already been analysed, and what type of `Resolver` resulted from that analysis. This speeds up the decision process, particularly for aliases (registered packages), and published packages, which would required HTTP requests.
|
|
|
|
5. **LOOKUP CACHE** - `PackageRepository` looks up the `ResolveCache` using the endpoint, for a cached *canonical package* that complies to the endpoint target. Some considerations:
|
|
- The lookup is performed using an endpoint that is fetched from the `Resolver`. This allows the resolver to guarantee that the endpoint has been normalised (twitter/bootstrap -> git://github.com/twitter/bootstrap.git, etc).
|
|
- The `ResolveCache` is `semver` aware. What this means, is that if you try to lookup `~1.2.1`, and the cache has a entries for versions `1.2.3` and `1.2.4`, it will give a hit with `1.2.4`.
|
|
|
|
6. **CACHE HIT VALIDATION** - At this stage, and only for the cache hits, the `PackageRepository` will question the `Resolver` if there is any version higher than the one fetched from cache that also complies with the endpoint target. Some considerations:
|
|
- This step is ignored in case a flag like `offline` is passed.
|
|
- How the `Resolver` checks this, depends on the `Resolver` type. (e.g. `GitRemoteResolver` would fetch the git refs with `git ls-remote --tags --heads`, and check if there is a higher version that complies with the target).
|
|
- This check should be as quick as possible. If the process of checking a new version is too slow, it's preferable to just assume there is a new version.
|
|
- If there is no way to check if there is a higher version, assume that there is.
|
|
- If the `Resolver` indicates that the cached version is outdated, then it is treated as a cache miss.
|
|
|
|
7. **RESOLVE CACHE MISSES** - Any cache miss needs to be resolved, so the `PackageRepository` requests each of the remaining resolvers to resolve, and waits.
|
|
|
|
8. **CACHE RESOLVED PACKAGES** - As the resolvers complete the resolution, the `PackageRepository` stores the canonic packages in the `ResolveCache`, along with the source, version, and any additional information that the `Resolver` provides. This allows resolvers to store additional details about the fetched package to be used for future *cache hit validations* (e.g. store HTTP expiration headers in the case of the `UrlPackage`).
|
|
|
|
9. **RETURN PACKAGE TO MANAGER** - The `PackageRepository` returns the canonical package to the `Manager`.
|
|
|
|
10. **EVALUATE RESOLVED PACKAGE DEPENDENCIES** - The `Manager` checks if the returned canonical packages have a `bower.json` file describing additional dependencies and, if so, continue in point #3. If there are no more unresolved dependencies, finish up the installation procedure.
|
|
|
|
-----
|
|
|
|
### Architecture components details
|
|
|
|
|
|
#### Manager
|
|
|
|
TODO
|
|
|
|
|
|
#### PackageRepository
|
|
|
|
TODO
|
|
|
|
|
|
#### ResolverFactory
|
|
|
|
Simple function that takes a *named endpoint*/endpoint with options and creates an instance of a concrete `Resolver` that obeys the base `Resolver` interface.
|
|
|
|
```js
|
|
function createResolver(endpoint, options) -> Promise
|
|
```
|
|
|
|
This function will perform transformations/normalisations to the endpoint, like expanding shorthand andendpoints.
|
|
The function is async to allow querying the Bower registry, etc.
|
|
|
|
|
|
#### ResolveCache
|
|
|
|
TODO
|
|
|
|
|
|
#### Resolver
|
|
|
|
The `Resolver` class extends `EventEmitter`.
|
|
Think of it as an abstract class that implements the resolver interface as well as serving as a base for other resolver types.
|
|
|
|
Resolvers are responsible for the following:
|
|
|
|
- Based on an endpoint, fetch the contents of the package into a temporary folder (step is implemented by the `_resolveSelf()` method).
|
|
- After the package is fetched, the `bower.json`/`component.json` (deprecated) file is read, validated and normalised (fill in properties). If this file does not exist, one is created, with the information that was inferred. Note that validation should be done using a node module that is common for both the Bower client and the server.
|
|
- Update any relevant information based on the `json` (e.g. this step may emit a `name_change`).
|
|
- Attach any additional meta data to the `json` file. (e.g. the `UrlResolver` might store some `HTTP` response headers, to aid the `hasNew()` decision later on).
|
|
- Applying the `ignore` constraint based on the `json` file. Files are effectively removed in this step.
|
|
|
|
|
|
##### Events
|
|
|
|
- `name_change`: fired when the name of the package has changed
|
|
- `action`: fired to inform the current action being performed by the resolver
|
|
- `warn`: fired to inform a warning, e.g.: deprecation
|
|
|
|
##### Constructor
|
|
|
|
`Resolver(source, options)`
|
|
|
|
Options:
|
|
|
|
- `name` - the name (if none is passed, one will be guessed from the source)
|
|
- `target` - the target (defaults to *)
|
|
- `config` - the config to use (defaults to the global config)
|
|
|
|
------------
|
|
|
|
##### Public functions
|
|
|
|
`Resolver#getName()`: String
|
|
|
|
Returns the name.
|
|
|
|
`Resolver#getSource()`: String
|
|
|
|
Returns the source.
|
|
|
|
`Resolver#getTarget()`: String
|
|
|
|
Returns the target.
|
|
|
|
`Resolver#getTempDir()`: String
|
|
|
|
Returns the local temporary folder into which the package is being fetched. The files will remain here until the folder is moved when installing.
|
|
|
|
`Resolver#hasNew(oldVersion, oldResolution)`: Promise
|
|
|
|
Checks if there is a new version. Takes the old version and resolution to be used when comparing.
|
|
Resolves to a boolean when done.
|
|
|
|
`Resolver#resolve()`: Promise
|
|
|
|
Resolves the resolver.
|
|
The resolve process obeys a very explicit flow:
|
|
|
|
- calls `_createTempDir()` and waits
|
|
- When done, calls #_resolveSelf and waits
|
|
- When done, calls #_readJson and waits
|
|
- When done, calls #_parseJson and waits
|
|
- When done, resolves the promise with the resolution.
|
|
|
|
`Resolver#getJson()`: Object
|
|
|
|
Get the `bower.json` of the resolved package.
|
|
Throws an error if the resolver is not yet resolved.
|
|
|
|
-----------
|
|
|
|
Protected functions
|
|
|
|
##### Resolver#_createTempDir() -> Promise
|
|
Creates a temporary dir.
|
|
|
|
##### Resolver#_readJson() -> Promise
|
|
Reads `bower.json`, possibly by using a dedicated `read-json` package that will be available in the Bower organization. It will ensure everything is valid.
|
|
|
|
##### Resolver#_parseJson(json) -> Promise
|
|
Parses the json:
|
|
|
|
- Checks if the resolver name is different from the json one. If so and if the name was "guessed", the name of the package will be updated and a `name_change` event will be emitted.
|
|
- Deletes files that are specified in the `ignore` property of the json from the temporary directory.
|
|
|
|
--------
|
|
|
|
Abstract functions that must be implemented by concrete resolvers.
|
|
|
|
##### Resolver#_resolveSelf() -> Promise
|
|
Resolves self. This method should be implemented by the concrete resolvers. For instance, the UrlResolver would download the contents of a URL into the temporary directory.
|
|
|
|
#### Types of Resolvers
|
|
|
|
The following resolvers will extend from `Resolver.js` and will obey its interface.
|
|
|
|
- `LocalResolver` extends `Resolver` (dependencies pointing to files of folders in the own system)
|
|
- `UrlResolver` extends `Resolver` (dependencies pointing to downloadable resources)
|
|
- `GitFsResolver` extends `Resolver` (git dependencies available in the local file system)
|
|
- `GitRemoteResolver` extends `Resolver` or `GitFsResolver` (remote git dependencies)
|
|
- `PublishedResolver` extends `Resolver` (? makes sense if bower supports a publish model, just like `npm`).
|
|
|
|
These type of resolvers will be known and created (instantiated) by the `ResolverFactory`.
|
|
|
|
This architecture will make it very easy for the community to create others package types, for instance, a `MercurialLocalPackage`, `MercurialRemotePackage`, `SvnResolver`, etc.
|
|
|
|
|
|
#### Unit of work
|
|
|
|
TODO
|
|
|