67 lines
1.4 KiB
Go
67 lines
1.4 KiB
Go
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package reader
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import (
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"errors"
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"fmt"
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"hash"
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"io"
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)
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var _ io.Reader = &Hasher{}
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// Hasher wraps io.Reader.
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// You can ask it for the digest of the hash function used internally, and the
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// number of bytes written.
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type Hasher struct {
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r io.Reader
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h hash.Hash
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bytesRead uint32
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}
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func NewHasher(r io.Reader, h hash.Hash) *Hasher {
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return &Hasher{
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r: r,
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h: h,
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bytesRead: 0,
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}
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}
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func (h *Hasher) Read(p []byte) (int, error) {
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nRead, rdErr := h.r.Read(p)
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// write the number of bytes read from the reader to the hash.
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// We need to do this independently on whether there's been error.
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// n always describes the number of successfully written bytes.
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nHash, hashErr := h.h.Write(p[0:nRead])
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if hashErr != nil {
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return nRead, fmt.Errorf("unable to write to hash: %w", hashErr)
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}
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// We assume here the hash function accepts the whole p in one Go,
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// and doesn't early-return on the Write.
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// We compare it with nRead and bail out if that was not the case.
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if nHash != nRead {
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return nRead, fmt.Errorf("hash didn't accept the full write")
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}
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// update bytesWritten
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h.bytesRead += uint32(nRead)
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if rdErr != nil {
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if errors.Is(rdErr, io.EOF) {
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return nRead, rdErr
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}
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return nRead, fmt.Errorf("error from underlying reader: %w", rdErr)
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}
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return nRead, hashErr
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}
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func (h *Hasher) BytesWritten() uint32 {
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return h.bytesRead
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}
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func (h *Hasher) Sum(b []byte) []byte {
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return h.h.Sum(b)
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}
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