77 lines
2.2 KiB
Go
77 lines
2.2 KiB
Go
package multihash
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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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mhreg "github.com/multiformats/go-multihash/core"
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)
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// ErrSumNotSupported is returned when the Sum function code is not implemented
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var ErrSumNotSupported = mhreg.ErrSumNotSupported
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var ErrLenTooLarge = errors.New("requested length was too large for digest")
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// Sum obtains the cryptographic sum of a given buffer. The length parameter
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// indicates the length of the resulting digest. Passing a negative value uses
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// default length values for the selected hash function.
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func Sum(data []byte, code uint64, length int) (Multihash, error) {
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// Get the algorithm.
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hasher, err := GetHasher(code)
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if err != nil {
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return nil, err
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}
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// Feed data in.
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hasher.Write(data)
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return encodeHash(hasher, code, length)
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}
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// SumStream obtains the cryptographic sum of a given stream. The length
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// parameter indicates the length of the resulting digest. Passing a negative
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// value uses default length values for the selected hash function.
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func SumStream(r io.Reader, code uint64, length int) (Multihash, error) {
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// Get the algorithm.
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hasher, err := GetHasher(code)
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if err != nil {
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return nil, err
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}
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// Feed data in.
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if _, err = io.Copy(hasher, r); err != nil {
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return nil, err
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}
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return encodeHash(hasher, code, length)
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}
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func encodeHash(hasher hash.Hash, code uint64, length int) (Multihash, error) {
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// Compute final hash.
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// A new slice is allocated. FUTURE: see other comment below about allocation, and review together with this line to try to improve.
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sum := hasher.Sum(nil)
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// Deal with any truncation.
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// Unless it's an identity multihash. Those have different rules.
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if length < 0 {
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length = hasher.Size()
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}
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if len(sum) < length {
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return nil, ErrLenTooLarge
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}
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if length >= 0 {
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if code == IDENTITY {
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if length != len(sum) {
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return nil, fmt.Errorf("the length of the identity hash (%d) must be equal to the length of the data (%d)", length, len(sum))
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}
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}
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sum = sum[:length]
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}
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// Put the multihash metainfo bytes at the front of the buffer.
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// FUTURE: try to improve allocations here. Encode does several which are probably avoidable, but it's the shape of the Encode method arguments that forces this.
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return Encode(sum, code)
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}
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