io.PipeReader.Read() Function in Golang with Examples
Last Updated :
10 May, 2020
In Go language,
io packages supply fundamental interfaces to the I/O primitives. And its principal job is to enclose the ongoing implementations of such king of primitives. The
PipeReader.Read() function in Go language is used to implement the standard interface of the Read. It reads information from the pipe and blocks it until a writer appears or the write end of the pipe is closed. Moreover, this function is defined under the io package. Here, you need to import the "io" package in order to use these functions.
Syntax:
func (r *PipeReader) Read(data []byte) (n int, err error)
Here, "r" is a pointer to the PipeReader. Where, PipeReader is the read half of the pipe and "data" is a byte slice of specified length and the written data is read into it.
Return value: It returns the number of bytes read and an error if any. However, if the write end of the pipe is closed with an error then that error is returned as
err else the
err returned is an EOF error.
Example 1:
C
// Golang program to illustrate the usage of
// io.PipeReader.Read() function
// Including main package
package main
// Importing fmt and io
import (
"fmt"
"io"
)
// Calling main
func main() {
// Calling Pipe method
pipeReader, pipeWriter := io.Pipe()
// Writing data to the pipe
go func() {
pipeWriter.Write([]byte("GfG"))
pipeWriter.Write([]byte("GeeksforGeeks"))
pipeWriter.Write([]byte("GfG is a CS-Portal."))
// Closing write half of the pipe
pipeWriter.Close()
// Again calling Write method
pipeWriter.Write([]byte("Author!"))
}()
// Defining data parameter of Read method
data := make([]byte, 20)
// Using for loop
for i := 0; i < 3; i++ {
// Calling pipeReader.Read() method
n, err := pipeReader.Read(data)
// If error is not nil panic
if err != nil {
panic(err)
}
// Prints the content read in buffer
fmt.Printf("%s\n", data[:n])
// Prints number of bytes read
fmt.Printf("%v\n", n)
}
}
GfG
3
GeeksforGeeks
13
GfG is a CS-Portal.
19
Here, no error is returned as the write end of the pipe is not closed till the "for" loop runs.
Example 2:
C
// Golang program to illustrate the usage of
// io.PipeReader.Read() function
// Including main package
package main
// Importing fmt and io
import (
"fmt"
"io"
)
// Calling main
func main() {
// Calling Pipe method
pipeReader, pipeWriter := io.Pipe()
// Writing data to the pipe
go func() {
pipeWriter.Write([]byte("GfG"))
pipeWriter.Write([]byte("GeeksforGeeks"))
pipeWriter.Write([]byte("GfG is a CS-Portal."))
// Closing write half of the pipe
pipeWriter.Close()
// Again calling Write method
pipeWriter.Write([]byte("Author!"))
}()
// Defining data parameter of Read method
data := make([]byte, 20)
// Using for loop
for i := 0; i < 4; i++ {
// Calling pipeReader.Read() method
n, err := pipeReader.Read(data)
// If error is not nil panic
if err != nil {
panic(err)
}
// Prints the content read in buffer
fmt.Printf("%s\n", data[:n])
// Prints number of bytes read
fmt.Printf("%v\n", n)
}
}
GfG
3
GeeksforGeeks
13
GfG is a CS-Portal.
19
panic: EOF
goroutine 1 [running]:
main.main()
/tmp/sandbox634835876/prog.go:43 +0x364
Here, an EOF error is returned as the write end of the pipe is closed after the third iteration of the for loop.