Go Package io: Difference between revisions
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=<tt>Reader</tt>= | =<span id='Reader'></span><tt>io.Reader</tt>= | ||
{{External|https://golang.org/pkg/io/#Reader}} | {{External|https://golang.org/pkg/io/#Reader}} | ||
An interface that exposes <code>Read()</code>. | An interface that exposes <code>Read()</code>. | ||
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</syntaxhighlight> | </syntaxhighlight> | ||
=<tt>Writer</tt>= | =<span id='Writer'></span><tt>io.Writer</tt>= | ||
{{External|https://golang.org/pkg/io/#Writer}} | {{External|https://golang.org/pkg/io/#Writer}} | ||
<code>io.Writer</code> is the interface that wraps the basic Write method: | |||
<syntaxhighlight lang='go'> | |||
Write(p []byte) (n int, err error) | |||
</syntaxhighlight> | |||
<code>Write()</code> writes the given bytes to the underlying data stream. | |||
Files opened with <code>[[Go_Package_os#os.Create.28.29|os.Create()]]</code> implement <code>io.Writer</code>. | Files opened with <code>[[Go_Package_os#os.Create.28.29|os.Create()]]</code> implement <code>io.Writer</code>. | ||
==Capturing the Content Written into a Writer and Converting to String== | |||
<code>bytes.Buffer</code> implements <code>io.Writer</code> so a <code>bytes.Buffer</code> instance can be used to be written into and get the string representation. The following example dumps the content of a <code>net/http.Request</code> into a string, identically with how it will be sent over the wire: | <code>bytes.Buffer</code> implements <code>io.Writer</code> so a <code>bytes.Buffer</code> instance can be used to be written into and get the string representation. The following example dumps the content of a <code>net/http.Request</code> into a string, identically with how it will be sent over the wire: | ||
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var r = &http.Request{...} | var r = &http.Request{...} | ||
// Capturing the Content Written into a Writer and Converting to String. | |||
b := &bytes.Buffer{} | b := &bytes.Buffer{} | ||
if err := r.Write(b); err != nil { ... } | if err := r.Write(b); err != nil { ... } | ||
Latest revision as of 02:10, 21 July 2024
External
Internal
Overview
The io package consists of a few functions, but mostly interfaces used by other packages.
io.EOF
The error returned by I/O operations that encounter the end of file. It can be tested with:
_, err := ...
if errors.Is(err, io.EOF) {
// is EOF
...
}
io.Reader
An interface that exposes Read().
Readers can be used to unmarshall JSON into structs as shown here:
Files opened with os.Create() implement io.Reader.
Wrapping a []byte into a Reader
A []byte can be wrapped into a Reader with:
import "bytes"
bs := []byte("something")
r := bytes.NewReader(bs)
Getting a Reader from a string
s := "some string"
reader := strings.NewReader(s)
io.Writer
io.Writer is the interface that wraps the basic Write method:
Write(p []byte) (n int, err error)
Write() writes the given bytes to the underlying data stream.
Files opened with os.Create() implement io.Writer.
Capturing the Content Written into a Writer and Converting to String
bytes.Buffer implements io.Writer so a bytes.Buffer instance can be used to be written into and get the string representation. The following example dumps the content of a net/http.Request into a string, identically with how it will be sent over the wire:
var r = &http.Request{...}
// Capturing the Content Written into a Writer and Converting to String.
b := &bytes.Buffer{}
if err := r.Write(b); err != nil { ... }
s := b.String()
Closer
Files opened with os.Create() implement io.Closer.
ReadCloser
An interface that exposes basic Read() and Close() methods. The http.Request body is a ReadCloser. See Reader.