64 lines
1.7 KiB
Go
64 lines
1.7 KiB
Go
package util
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import (
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"bytes"
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"errors"
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"io"
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"strings"
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)
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// PeekedReadCloser is a ReadCloser that allows peeking into a stream and buffering it in memory.
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// It can be instantiated using the Peek function. After a stream has been peeked, it can still be fully
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// read by reading the PeekedReadCloser. It first drained from the memory buffer, and then from the remaining
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// underlying reader.
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type PeekedReadCloser struct {
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PeekedBytes []byte
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LimitReached bool
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peeked io.Reader
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underlying io.ReadCloser
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closed bool
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}
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// Peek reads the underlying ReadCloser into memory up until the limit and returns a PeekedReadCloser.
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// It does not return an error if limit is reached. Instead, LimitReached will be set to true.
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func Peek(underlying io.ReadCloser, limit int) (*PeekedReadCloser, error) {
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if underlying == nil {
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underlying = io.NopCloser(strings.NewReader(""))
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}
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peeked := make([]byte, limit)
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read, err := io.ReadFull(underlying, peeked)
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if err != nil && !errors.Is(err, io.ErrUnexpectedEOF) && err != io.EOF {
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return nil, err
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}
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return &PeekedReadCloser{
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PeekedBytes: peeked[:read],
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LimitReached: read == limit,
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underlying: underlying,
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peeked: bytes.NewReader(peeked[:read]),
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closed: false,
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}, nil
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}
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// Read reads from the peeked bytes and then from the underlying stream
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func (r *PeekedReadCloser) Read(p []byte) (n int, err error) {
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if r.closed {
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return 0, io.EOF
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}
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n, err = r.peeked.Read(p)
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if errors.Is(err, io.EOF) {
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return r.underlying.Read(p)
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} else if err != nil {
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return 0, err
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}
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return
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}
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// Close closes the underlying stream
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func (r *PeekedReadCloser) Close() error {
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if r.closed {
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return io.EOF
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}
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r.closed = true
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return r.underlying.Close()
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}
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