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reader.go
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reader.go
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package reader
import (
"context"
"fmt"
"github.com/aaronland/go-roster"
"io"
"net/url"
"sort"
"strings"
)
var reader_roster roster.Roster
// ReaderInitializationFunc is a function defined by individual reader package and used to create
// an instance of that reader
type ReaderInitializationFunc func(ctx context.Context, uri string) (Reader, error)
// Reader is an interface for reading data from multiple sources or targets.
type Reader interface {
// Reader returns a `io.ReadSeekCloser` instance for a URI resolved by the instance implementing the `Reader` interface.
Read(context.Context, string) (io.ReadSeekCloser, error)
// The absolute path for the file is determined by the instance implementing the `Reader` interface.
ReaderURI(context.Context, string) string
}
// RegisterReader registers 'scheme' as a key pointing to 'init_func' in an internal lookup table
// used to create new `Reader` instances by the `NewReader` method.
func RegisterReader(ctx context.Context, scheme string, init_func ReaderInitializationFunc) error {
err := ensureReaderRoster()
if err != nil {
return err
}
return reader_roster.Register(ctx, scheme, init_func)
}
func ensureReaderRoster() error {
if reader_roster == nil {
r, err := roster.NewDefaultRoster()
if err != nil {
return err
}
reader_roster = r
}
return nil
}
// NewReader returns a new `Reader` instance configured by 'uri'. The value of 'uri' is parsed
// as a `url.URL` and its scheme is used as the key for a corresponding `ReaderInitializationFunc`
// function used to instantiate the new `Reader`. It is assumed that the scheme (and initialization
// function) have been registered by the `RegisterReader` method.
func NewReader(ctx context.Context, uri string) (Reader, error) {
u, err := url.Parse(uri)
if err != nil {
return nil, err
}
scheme := u.Scheme
i, err := reader_roster.Driver(ctx, scheme)
if err != nil {
return nil, err
}
init_func := i.(ReaderInitializationFunc)
return init_func(ctx, uri)
}
// Schemes returns the list of schemes that have been registered.
func Schemes() []string {
ctx := context.Background()
schemes := []string{}
err := ensureReaderRoster()
if err != nil {
return schemes
}
for _, dr := range reader_roster.Drivers(ctx) {
scheme := fmt.Sprintf("%s://", strings.ToLower(dr))
schemes = append(schemes, scheme)
}
sort.Strings(schemes)
return schemes
}