EC
io.ErrNoProgress
GoERRORCriticalIO

multiple Read calls return no data or error

Quick Answer

Fix the underlying Reader so that Read returns either data or a non-nil error on every call.

What this means

Returned by io.Reader wrappers when multiple successive Read calls return 0 bytes and no error, indicating a broken Reader implementation.

Why it happens
  1. 1Custom io.Reader implementation returns (0, nil) repeatedly instead of io.EOF
  2. 2Middleware wrapper fails to propagate underlying reader progress

Fix

Fix Reader to return EOF

Fix Reader to return EOF
func (r *MyReader) Read(p []byte) (int, error) {
    if r.done { return 0, io.EOF }
    return copy(p, r.data), nil
}

Why this works

Returning io.EOF when exhausted satisfies the io.Reader contract and stops ErrNoProgress.

Code examples
Detectgo
_, err := io.ReadAll(r)
if errors.Is(err, io.ErrNoProgress) {
    fmt.Println("reader stuck")
}
Correct EOF returngo
if len(r.data) == 0 {
    return 0, io.EOF
}
Test with LimitedReadergo
lr := &io.LimitedReader{R: src, N: 100}
io.ReadAll(lr)
Same error in other languages
io.EOFin Go→io.ErrUnexpectedEOFin Go→
Sources
Official documentation ↗

Go standard library

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