Golang input/output

Documentation

fmt	https://pkg.go.dev/fmt@go1.18.2
io/ioutil (read/write)	https://pkg.go.dev/io/ioutil@go1.18.3
textproto (sockets)	https://pkg.go.dev/net/textproto@go1.18.3

Stdin, Stdout, Stderr

fmt.Fprintln(os.Stdout, "writes stdout")
fmt.Fprintln(os.Stderr, "writes stderr")

Reader, Writer

// read a file into `[]bytes` until EOF
conts, err := os.ReadAll(reader)

buf := make([]byte, 64)
_, err := os.ReadFull(reader, buf) // fill buffer to capacity, reading from reader
switch {
    case errors.Is(err, os.EOF):
        // nothing to read (0 bytes)
    case errors.Is(err, os.ErrUnexpectedEOF):
        // end of file, before filling buffer
}

filepath := "/var/tmp/foo.txt"

_, err := os.WriteString(writer, "abcd")

Files

If the files are small, you can work with them using os

require "os"

// write
err := os.WriteFile("/var/tmp/foo.txt", []byte("abc"), 0644)

// read
conts, err := os.ReadFile("/var/tmp/foo.txt")

If the files are larger, read in in chunks.

func check(e error) {
    if e != nil {
        panic(e)
    }
}

// create or open file for reading
filepath = "/var/tmp/foo.txt"
fd, err := os.Open(filepath)   // open for reading
fd, err := os.Create(filepath) // create, or truncate file (0666 perms)
check(err)

// read up to 5 bytes
buf := make([]byte, 5)
bytes_r, err := fd.Read(buf)
check(err)

fd, err := os.Create(filepath) // create, or truncate file (0666 perms)
check(err)

bytes_w, err := fd.Write([]byte("abc"))
check(err)

bytes_w, err := fd.WriteString("abc")
check(err)

fd.Sync()

Networking

Sockets

net.Dial() creates sockets of various types.

import "net"

// unix socketfile
conn, err = net.Dial("unix", "/var/tmp/foo.sock")

// inet socket
conn, err = net.Dial("tcp", "10.10.10.10:6600")
defer conn.Close()

// sending message to socket
_, err = conn.Write([]byte("search title 'it ceases to be'"))
reply := make([]byte, 1024)
_, err = conn.Read(reply)
fmt.Println(string(reply))

HTTP