a4fadc596b
Now that we have most of the services required for use with containerd, it was found that common patterns were used throughout services. By defining a central `errdefs` package, we ensure that services will map errors to and from grpc consistently and cleanly. One can decorate an error with as much context as necessary, using `pkg/errors` and still have the error mapped correctly via grpc. We make a few sacrifices. At this point, the common errors we use across the repository all map directly to grpc error codes. While this seems positively crazy, it actually works out quite well. The error conditions that were specific weren't super necessary and the ones that were necessary now simply have better context information. We lose the ability to add new codes, but this constraint may not be a bad thing. Effectively, as long as one uses the errors defined in `errdefs`, the error class will be mapped correctly across the grpc boundary and everything will be good. If you don't use those definitions, the error maps to "unknown" and the error message is preserved. Signed-off-by: Stephen J Day <stephen.day@docker.com>
129 lines
3.2 KiB
Go
129 lines
3.2 KiB
Go
package content
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import (
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"context"
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"fmt"
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"io"
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"io/ioutil"
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"github.com/containerd/containerd/errdefs"
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"github.com/opencontainers/go-digest"
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"github.com/pkg/errors"
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)
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// ReadBlob retrieves the entire contents of the blob from the provider.
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//
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// Avoid using this for large blobs, such as layers.
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func ReadBlob(ctx context.Context, provider Provider, dgst digest.Digest) ([]byte, error) {
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rc, err := provider.Reader(ctx, dgst)
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if err != nil {
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return nil, err
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}
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defer rc.Close()
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return ioutil.ReadAll(rc)
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}
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// WriteBlob writes data with the expected digest into the content store. If
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// expected already exists, the method returns immediately and the reader will
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// not be consumed.
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//
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// This is useful when the digest and size are known beforehand.
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//
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// Copy is buffered, so no need to wrap reader in buffered io.
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func WriteBlob(ctx context.Context, cs Ingester, ref string, r io.Reader, size int64, expected digest.Digest) error {
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cw, err := cs.Writer(ctx, ref, size, expected)
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if err != nil {
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if !errdefs.IsAlreadyExists(err) {
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return err
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}
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return nil // all ready present
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}
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defer cw.Close()
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return Copy(cw, r, size, expected)
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}
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// Copy copies data with the expected digest from the reader into the
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// provided content store writer.
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//
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// This is useful when the digest and size are known beforehand. When
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// the size or digest is unknown, these values may be empty.
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//
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// Copy is buffered, so no need to wrap reader in buffered io.
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func Copy(cw Writer, r io.Reader, size int64, expected digest.Digest) error {
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ws, err := cw.Status()
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if err != nil {
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return err
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}
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if ws.Offset > 0 {
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r, err = seekReader(r, ws.Offset, size)
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if err != nil {
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if !isUnseekable(err) {
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return errors.Wrapf(err, "unabled to resume write to %v", ws.Ref)
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}
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// reader is unseekable, try to move the writer back to the start.
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if err := cw.Truncate(0); err != nil {
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return errors.Wrapf(err, "content writer truncate failed")
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}
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}
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}
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buf := bufPool.Get().([]byte)
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defer bufPool.Put(buf)
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if _, err := io.CopyBuffer(cw, r, buf); err != nil {
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return err
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}
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if err := cw.Commit(size, expected); err != nil {
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if !errdefs.IsAlreadyExists(err) {
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return errors.Wrapf(err, "failed commit on ref %q", ws.Ref)
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}
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}
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return nil
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}
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var errUnseekable = errors.New("seek not supported")
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func isUnseekable(err error) bool {
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return errors.Cause(err) == errUnseekable
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}
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// seekReader attempts to seek the reader to the given offset, either by
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// resolving `io.Seeker` or by detecting `io.ReaderAt`.
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func seekReader(r io.Reader, offset, size int64) (io.Reader, error) {
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// attempt to resolve r as a seeker and setup the offset.
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seeker, ok := r.(io.Seeker)
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if ok {
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nn, err := seeker.Seek(offset, io.SeekStart)
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if nn != offset {
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return nil, fmt.Errorf("failed to seek to offset %v", offset)
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}
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if err != nil {
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return nil, err
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}
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return r, nil
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}
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// ok, let's try io.ReaderAt!
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readerAt, ok := r.(io.ReaderAt)
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if ok && size > offset {
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sr := io.NewSectionReader(readerAt, offset, size)
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return sr, nil
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}
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return r, errors.Wrapf(errUnseekable, "seek to offset %v failed", offset)
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}
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func readFileString(path string) (string, error) {
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p, err := ioutil.ReadFile(path)
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return string(p), err
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}
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