grokify/mogo

package ioutil

import (
    "bufio"
    "bytes"
    "fmt"
    "io"
    "reflect"
)

type AtReader interface {
    io.Reader
    io.ReaderAt
}

func IsReader(i any) bool {
    reader := reflect.TypeOf((*io.Reader)(nil)).Elem()
    return reflect.PointerTo(reflect.TypeOf(i).Elem()).Implements(reader)
}

func MustPrintReader(r io.Reader) {
    if b, err := io.ReadAll(r); err != nil {
        panic(err)
    } else {
        fmt.Println(string(b))
    }
}

/*
// ReaderToBytes reads from an io.Reader, e.g. io.ReadCloser
func ReaderToBytes(r io.Reader) ([]byte, error) {
    buf := new(bytes.Buffer)
    _, err := buf.ReadFrom(r)
    if err != nil {
        return []byte{}, err
    }
    return buf.Bytes(), nil
}
*/

// ReadAllOrError will successfully return the data
// or return the error in the value return value.
// This is useful to simply test scripts where the
// data is printed for debugging or testing.
func ReadAllOrError(r io.Reader) []byte {
    if b, err := io.ReadAll(r); err != nil {
        return []byte(err.Error())
    } else {
        return b
    }
}

// ReadLimit returns the first `limit` bytes from a reader.
func ReadLimit(r io.Reader, limit uint) ([]byte, error) {
    return io.ReadAll(io.LimitReader(r, int64(limit)))
}

// ReaderToReadSeeker converts an `io.Reader` to an `io.ReadSeeker`. It does this
// by reading all data in `io.Reader`.
func ReaderToReadSeeker(r io.Reader) (io.ReadSeeker, error) {
    if b, err := io.ReadAll(r); err != nil {
        return nil, err
    } else {
        return bytes.NewReader(b), nil
    }
}

// Write writes from `Writer` to a `Reader`. See `osutil.WriteFileReader()`.
func Write(w *bufio.Writer, r io.Reader) error {
    buf := make([]byte, 1024)
    for {
        // read a chunk
        n, err := r.Read(buf)
        if err != nil && err != io.EOF {
            return err
        }
        if n == 0 {
            break
        }
        // write a chunk
        if _, err := w.Write(buf[:n]); err != nil {
            return err
        }
    }
    return w.Flush()
}

// SkipWriter is an `io.Writer` that skips writing the first `n` bytes passed. This is
// useful when the `io.Writer` writes some undesirable data which will be omitted with
// this functionality.
type SkipWriter struct {
    // Rewritten from the following under MIT license: https://github.com/jdeng/goheif/blob/a0d6a8b3e68f9d613abd9ae1db63c72ba33abd14/heic2jpg/main.go
    w      io.Writer
    offset int
}

// NewSkipWriter returns an SkipWriter that writes to w skipping the first offset off bytes.
func NewSkipWriter(w io.Writer, off int) *SkipWriter {
    return &SkipWriter{w: w, offset: off}
}

// Write fulfills the `io.Writer` interface.
func (s *SkipWriter) Write(p []byte) (n int, err error) {
    if s.offset <= 0 {
        n, err = s.w.Write(p)
        return
    }

    if plen := len(p); plen < s.offset {
        s.offset -= plen
        n = plen
        return
    }

    n, err = s.w.Write(p[s.offset:])
    if err != nil {
        return
    }
    n += s.offset
    s.offset = 0
    return
}