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README
¶
go-reader
There are many interfaces for reading files. This one is ours. It returns io.ReadSeekCloser instances.
This package supersedes the go-whosonfirst-readwrite package.
Documentation
Example
Readers are instantiated with the reader.NewReader method which takes as its arguments a context.Context instance and a URI string. The URI's scheme represents the type of reader it implements and the remaining (URI) properties are used by that reader type to instantiate itself.
For example to read files from a directory on the local filesystem you would write:
package main
import (
"context"
"github.com/whosonfirst/go-reader"
"io"
"os"
)
func main() {
ctx := context.Background()
r, _ := reader.NewReader(ctx, "file:///usr/local/data")
fh, _ := r.Read(ctx, "example.txt")
defer fh.Close()
io.Copy(os.Stdout, fh)
}
There is also a handy "null" reader in case you need a "pretend" reader that doesn't actually do anything:
package main
import (
"context"
"github.com/whosonfirst/go-reader"
"io"
"os"
)
func main() {
ctx := context.Background()
r, _ := reader.NewReader(ctx, "null://")
fh, _ := r.Read(ctx, "example.txt")
defer fh.Close()
io.Copy(os.Stdout, fh)
}
Interfaces
reader.Reader
type Reader interface {
Read(context.Context, string) (io.ReadSeekCloser, error)
ReaderURI(context.Context, string) string
}
Custom readers
Custom readers need to:
- Implement the interface above.
- Announce their availability using the
go-reader.RegisterReadermethod on initialization, passing in an initialization function implementing thego-reader.ReaderInitializationFuncinterface.
For example, this is how the go-reader-http reader is implemented:
package reader
import (
"context"
"errors"
wof_reader "github.com/whosonfirst/go-reader"
"github.com/whosonfirst/go-ioutil"
"io"
_ "log"
"net/http"
"net/url"
"path/filepath"
"time"
)
type HTTPReader struct {
wof_reader.Reader
url *url.URL
throttle <-chan time.Time
}
func init() {
ctx := context.Background()
schemes := []string{
"http",
"https",
}
for _, s := range schemes {
err := wof_reader.RegisterReader(ctx, s, NewHTTPReader)
if err != nil {
panic(err)
}
}
}
func NewHTTPReader(ctx context.Context, uri string) (wof_reader.Reader, error) {
u, err := url.Parse(uri)
if err != nil {
return nil, err
}
rate := time.Second / 3
throttle := time.Tick(rate)
r := HTTPReader{
throttle: throttle,
url: u,
}
return &r, nil
}
func (r *HTTPReader) Read(ctx context.Context, uri string) (io.ReadSeekCloser, error) {
<-r.throttle
u, _ := url.Parse(r.url.String())
u.Path = filepath.Join(u.Path, uri)
url := u.String()
rsp, err := http.Get(url)
if err != nil {
return nil, err
}
if rsp.StatusCode != 200 {
return nil, errors.New(rsp.Status)
}
fh, err := ioutil.NewReadSeekCloser(rsp.Body)
if err != nil {
return nil, err
}
return fh, nil
}
func (r *HTTPReader) ReaderURI(ctx context.Context, uri string) string {
return uri
}
And then to use it you would do this:
package main
import (
"context"
"github.com/whosonfirst/go-reader"
_ "github.com/whosonfirst/go-reader-http"
"io"
"os"
)
func main() {
ctx := context.Background()
r, _ := reader.NewReader(ctx, "https://data.whosonfirst.org")
fh, _ := r.Read(ctx, "101/736/545/101736545.geojson")
defer fh.Close()
io.Copy(os.Stdout, fh)
}
Available readers
"blob"
Read files from any registered Go Cloud Blob source. For example:
import (
"context"
"github.com/whosonfirst/go-reader"
_ "github.com/whosonfirst/go-reader-blob"
_ "gocloud.dev/blob/s3blob"
)
func main() {
ctx := context.Background()
r, _ := reader.NewReader(ctx, "s3://whosonfirst-data?region=us-west-1")
}
github://
Read files from a GitHub repository.
import (
"context"
"github.com/whosonfirst/go-reader"
_ "github.com/whosonfirst/go-reader-github"
)
func main() {
ctx := context.Background()
r, _ := reader.NewReader(ctx, "github://{GITHUB_OWNER}/{GITHUB_REPO}")
// to specify a specific branch you would do this:
// r, _ := reader.NewReader(ctx, "github://{GITHUB_OWNER}/{GITHUB_REPO}?branch={GITHUB_BRANCH}")
}
githubapi://
Read files from a GitHub repository using the GitHub API.
import (
"context"
"github.com/whosonfirst/go-reader"
_ "github.com/whosonfirst/go-reader-github"
)
func main() {
ctx := context.Background()
r, _ := reader.NewReader(ctx, "githubapi://{GITHUB_OWNER}/{GITHUB_REPO}?access_token={GITHUBAPI_ACCESS_TOKEN}")
// to specify a specific branch you would do this:
// r, _ := reader.NewReader(ctx, "githubapi://{GITHUB_OWNER}/{GITHUB_REPO}/{GITHUB_BRANCH}?access_token={GITHUBAPI_ACCESS_TOKEN}")
}
http:// and https://
Read files from an HTTP(S) endpoint.
import (
"context"
"github.com/whosonfirst/go-reader"
_ "github.com/whosonfirst/go-reader-http"
)
func main() {
ctx := context.Background()
r, _ := reader.NewReader(ctx, "https://{HTTP_HOST_AND_PATH}")
}
file://
Read files from a local filesystem.
import (
"context"
"github.com/whosonfirst/go-reader"
)
func main() {
ctx := context.Background()
r, _ := reader.NewReader(ctx, "file://{PATH_TO_DIRECTORY}")
}
If you are importing the go-reader-blob package and using the GoCloud's fileblob driver then instantiating the file:// scheme will fail since it will have already been registered. You can work around this by using the fs:// scheme. For example:
r, _ := reader.NewReader(ctx, "fs://{PATH_TO_DIRECTORY}")
null://
Pretend to read files.
import (
"context"
"github.com/whosonfirst/go-reader"
)
func main() {
ctx := context.Background()
r, _ := reader.NewReader(ctx, "null://")
}
See also
stdin://
Read "files" from STDIN
import (
"context"
"github.com/whosonfirst/go-reader"
)
func main() {
ctx := context.Background()
r, _ := reader.NewReader(ctx, "stdin://")
}
And then to use, something like:
> cat README.md | ./bin/read -reader-uri stdin:// - | wc -l
339
Note the use of - for a URI. This is the convention (when reading from STDIN) but it can be whatever you want it to be.
See also
Documentation
¶
Overview ¶
Example:
package main
import (
"context"
"github.com/whosonfirst/go-reader"
"io"
"os"
)
func main() {
ctx := context.Background()
r, _ := reader.NewReader(ctx, "fs:///usr/local/data")
fh, _ := r.Read(ctx, "example.txt")
defer fh.Close()
io.Copy(os.Stdout, fh)
}
Package reader provides a common interface for reading from a variety of sources. It has the following interface:
type Reader interface {
Read(context.Context, string) (io.ReadSeekCloser, error)
ReaderURI(string) string
}
Reader intstances are created either by calling a package-specific New{SOME_READER}Reader method or by invoking the reader.NewReader method passing in a context.Context instance and a URI specific to the reader class. For example:
r, _ := reader.NewReader(ctx, "fs:///usr/local/data")
Custom reader packages implement the reader.Reader interface and register their availability by calling the reader.RegisterRegister method on initialization. For example:
func init() {
ctx := context.Background()
err = RegisterReader(ctx, "file", NewFileReader)
if err != nil {
panic(err)
}
}
Index ¶
- func Readers() []string
- func RegisterReader(ctx context.Context, scheme string, init_func ReaderInitializationFunc) error
- func Schemes() []string
- type FileReader
- type MultiReader
- type NullReader
- type Reader
- func NewFileReader(ctx context.Context, uri string) (Reader, error)
- func NewMultiReader(ctx context.Context, readers ...Reader) (Reader, error)
- func NewMultiReaderFromURIs(ctx context.Context, uris ...string) (Reader, error)
- func NewNullReader(ctx context.Context, uri string) (Reader, error)
- func NewReader(ctx context.Context, uri string) (Reader, error)
- func NewStdinReader(ctx context.Context, uri string) (Reader, error)
- type ReaderInitializationFunc
- type StdinReader
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func RegisterReader ¶ added in v0.1.1
func RegisterReader(ctx context.Context, scheme string, init_func ReaderInitializationFunc) error
Types ¶
type FileReader ¶
type FileReader struct {
Reader
// contains filtered or unexported fields
}
func (*FileReader) Read ¶
func (r *FileReader) Read(ctx context.Context, path string) (io.ReadSeekCloser, error)
type MultiReader ¶ added in v0.2.1
type MultiReader struct {
Reader
// contains filtered or unexported fields
}
func (*MultiReader) Read ¶ added in v0.2.1
func (mr *MultiReader) Read(ctx context.Context, uri string) (io.ReadSeekCloser, error)
type NullReader ¶
type NullReader struct {
Reader
}
func (*NullReader) Read ¶
func (r *NullReader) Read(ctx context.Context, uri string) (io.ReadSeekCloser, error)
type Reader ¶
type Reader interface {
Read(context.Context, string) (io.ReadSeekCloser, error)
ReaderURI(context.Context, string) string
}
func NewMultiReader ¶ added in v0.2.1
func NewMultiReaderFromURIs ¶ added in v0.2.1
type ReaderInitializationFunc ¶ added in v0.1.1
type StdinReader ¶ added in v0.8.0
type StdinReader struct {
Reader
}
func (*StdinReader) Read ¶ added in v0.8.0
func (r *StdinReader) Read(ctx context.Context, uri string) (io.ReadSeekCloser, error)
Source Files
Directories