108 lines
3.7 KiB
Go
108 lines
3.7 KiB
Go
// Package source provides the Source interface.
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// All source drivers must implement this interface, register themselves,
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// optionally provide a `WithInstance` function and pass the tests
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// in package source/testing.
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package source
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import (
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"fmt"
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"io"
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nurl "net/url"
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"sync"
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)
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var driversMu sync.RWMutex
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var drivers = make(map[string]Driver)
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// Driver is the interface every source driver must implement.
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//
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// How to implement a source driver?
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// 1. Implement this interface.
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// 2. Optionally, add a function named `WithInstance`.
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// This function should accept an existing source instance and a Config{} struct
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// and return a driver instance.
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// 3. Add a test that calls source/testing.go:Test()
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// 4. Add own tests for Open(), WithInstance() (when provided) and Close().
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// All other functions are tested by tests in source/testing.
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// Saves you some time and makes sure all source drivers behave the same way.
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// 5. Call Register in init().
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//
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// Guidelines:
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// * All configuration input must come from the URL string in func Open()
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// or the Config{} struct in WithInstance. Don't os.Getenv().
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// * Drivers are supposed to be read only.
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// * Ideally don't load any contents (into memory) in Open or WithInstance.
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type Driver interface {
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// Open returns a a new driver instance configured with parameters
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// coming from the URL string. Migrate will call this function
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// only once per instance.
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Open(url string) (Driver, error)
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// Close closes the underlying source instance managed by the driver.
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// Migrate will call this function only once per instance.
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Close() error
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// First returns the very first migration version available to the driver.
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// Migrate will call this function multiple times.
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// If there is no version available, it must return os.ErrNotExist.
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First() (version uint, err error)
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// Prev returns the previous version for a given version available to the driver.
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// Migrate will call this function multiple times.
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// If there is no previous version available, it must return os.ErrNotExist.
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Prev(version uint) (prevVersion uint, err error)
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// Next returns the next version for a given version available to the driver.
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// Migrate will call this function multiple times.
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// If there is no next version available, it must return os.ErrNotExist.
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Next(version uint) (nextVersion uint, err error)
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// ReadUp returns the UP migration body and an identifier that helps
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// finding this migration in the source for a given version.
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// If there is no up migration available for this version,
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// it must return os.ErrNotExist.
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// Do not start reading, just return the ReadCloser!
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ReadUp(version uint) (r io.ReadCloser, identifier string, err error)
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// ReadDown returns the DOWN migration body and an identifier that helps
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// finding this migration in the source for a given version.
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// If there is no down migration available for this version,
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// it must return os.ErrNotExist.
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// Do not start reading, just return the ReadCloser!
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ReadDown(version uint) (r io.ReadCloser, identifier string, err error)
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}
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// Open returns a new driver instance.
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func Open(url string) (Driver, error) {
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u, err := nurl.Parse(url)
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if err != nil {
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return nil, err
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}
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if u.Scheme == "" {
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return nil, fmt.Errorf("source driver: invalid URL scheme")
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}
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driversMu.RLock()
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d, ok := drivers[u.Scheme]
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driversMu.RUnlock()
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if !ok {
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return nil, fmt.Errorf("source driver: unknown driver %v (forgotton import?)", u.Scheme)
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}
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return d.Open(url)
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}
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// Register globally registers a driver.
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func Register(name string, driver Driver) {
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driversMu.Lock()
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defer driversMu.Unlock()
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if driver == nil {
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panic("Register driver is nil")
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}
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if _, dup := drivers[name]; dup {
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panic("Register called twice for driver " + name)
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}
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drivers[name] = driver
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}
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