124 lines
3.5 KiB
Go
124 lines
3.5 KiB
Go
package odb
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import (
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"compress/zlib"
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"crypto/sha1"
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"fmt"
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"hash"
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"io"
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"sync/atomic"
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)
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// ObjectWriter provides an implementation of io.Writer that compresses and
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// writes data given to it, and keeps track of the SHA1 hash of the data as it
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// is written.
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type ObjectWriter struct {
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// w is the underling writer that this ObjectWriter is writing to.
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w io.Writer
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// sum is the in-progress hash calculation.
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sum hash.Hash
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// wroteHeader is a uint32 managed by the sync/atomic package. It is 1
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// if the header was written, and 0 otherwise.
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wroteHeader uint32
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// closeFn supplies an optional function that, when called, frees an
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// resources (open files, memory, etc) held by this instance of the
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// *ObjectWriter.
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//
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// closeFn returns any error encountered when closing/freeing resources
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// held.
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//
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// It is allowed to be nil.
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closeFn func() error
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}
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var _ io.WriteCloser = (*ObjectWriter)(nil)
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// nopCloser provides a no-op implementation of the io.WriteCloser interface by
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// taking an io.Writer and wrapping it with a Close() method that returns nil.
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type nopCloser struct {
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// Writer is an embedded io.Writer that receives the Write() method
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// call.
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io.Writer
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}
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var _ io.WriteCloser = (*nopCloser)(nil)
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// Close implements the io.Closer interface by returning nil.
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func (n *nopCloser) Close() error {
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return nil
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}
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// NewObjectWriter returns a new *ObjectWriter instance that drains incoming
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// writes into the io.Writer given, "w".
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func NewObjectWriter(w io.Writer) *ObjectWriter {
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return NewObjectWriteCloser(&nopCloser{w})
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}
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// NewObjectWriter returns a new *ObjectWriter instance that drains incoming
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// writes into the io.Writer given, "w".
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//
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// Upon closing, it calls the given Close() function of the io.WriteCloser.
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func NewObjectWriteCloser(w io.WriteCloser) *ObjectWriter {
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zw := zlib.NewWriter(w)
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sum := sha1.New()
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return &ObjectWriter{
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w: io.MultiWriter(zw, sum),
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sum: sum,
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closeFn: func() error {
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if err := zw.Close(); err != nil {
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return err
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}
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if err := w.Close(); err != nil {
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return err
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}
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return nil
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},
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}
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}
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// WriteHeader writes object header information and returns the number of
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// uncompressed bytes written, or any error that was encountered along the way.
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//
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// WriteHeader MUST be called only once, or a panic() will occur.
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func (w *ObjectWriter) WriteHeader(typ ObjectType, len int64) (n int, err error) {
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if !atomic.CompareAndSwapUint32(&w.wroteHeader, 0, 1) {
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panic("git/odb: cannot write headers more than once")
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}
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return fmt.Fprintf(w, "%s %d\x00", typ, len)
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}
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// Write writes the given buffer "p" of uncompressed bytes into the underlying
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// data-stream, returning the number of uncompressed bytes written, along with
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// any error encountered along the way.
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//
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// A call to WriteHeaders MUST occur before calling Write, or a panic() will
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// occur.
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func (w *ObjectWriter) Write(p []byte) (n int, err error) {
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if atomic.LoadUint32(&w.wroteHeader) != 1 {
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panic("git/odb: cannot write data without header")
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}
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return w.w.Write(p)
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}
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// Sha returns the in-progress SHA1 of the compressed object contents.
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func (w *ObjectWriter) Sha() []byte {
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return w.sum.Sum(nil)
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}
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// Close closes the ObjectWriter and frees any resources held by it, including
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// flushing the zlib-compressed content to the underling writer. It must be
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// called before discarding of the Writer instance.
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//
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// If any error occurred while calling close, it will be returned immediately,
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// otherwise nil.
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func (w *ObjectWriter) Close() error {
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if w.closeFn == nil {
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return nil
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}
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return w.closeFn()
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}
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