Adding upstream version 0.28.1.

Signed-off-by: Daniel Baumann <daniel@debian.org>

tools/filesystem/blob/writer.go

@@ -0,0 +1,184 @@
+package blob
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"hash"
+	"io"
+	"net/http"
+)
+
+// Largely copied from gocloud.dev/blob.Writer to minimize breaking changes.
+//
+// -------------------------------------------------------------------
+// Copyright 2019 The Go Cloud Development Kit Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// -------------------------------------------------------------------
+
+var _ io.WriteCloser = (*Writer)(nil)
+
+// Writer writes bytes to a blob.
+//
+// It implements io.WriteCloser (https://golang.org/pkg/io/#Closer), and must be
+// closed after all writes are done.
+type Writer struct {
+	drv          Driver
+	w            DriverWriter
+	key          string
+	cancel       func() // cancels the ctx provided to NewTypedWriter if contentMD5 verification fails
+	contentMD5   []byte
+	md5hash      hash.Hash
+	bytesWritten int
+	closed       bool
+
+	// These fields are non-zero values only when w is nil (not yet created).
+	//
+	// A ctx is stored in the Writer since we need to pass it into NewTypedWriter
+	// when we finish detecting the content type of the blob and create the
+	// underlying driver.Writer. This step happens inside Write or Close and
+	// neither of them take a context.Context as an argument.
+	//
+	// All 3 fields are only initialized when we create the Writer without
+	// setting the w field, and are reset to zero values after w is created.
+	ctx  context.Context
+	opts *WriterOptions
+	buf  *bytes.Buffer
+}
+
+// sniffLen is the byte size of Writer.buf used to detect content-type.
+const sniffLen = 512
+
+// Write implements the io.Writer interface (https://golang.org/pkg/io/#Writer).
+//
+// Writes may happen asynchronously, so the returned error can be nil
+// even if the actual write eventually fails. The write is only guaranteed to
+// have succeeded if Close returns no error.
+func (w *Writer) Write(p []byte) (int, error) {
+	if len(w.contentMD5) > 0 {
+		if _, err := w.md5hash.Write(p); err != nil {
+			return 0, err
+		}
+	}
+
+	if w.w != nil {
+		return w.write(p)
+	}
+
+	// If w is not yet created due to no content-type being passed in, try to sniff
+	// the MIME type based on at most 512 bytes of the blob content of p.
+
+	// Detect the content-type directly if the first chunk is at least 512 bytes.
+	if w.buf.Len() == 0 && len(p) >= sniffLen {
+		return w.open(p)
+	}
+
+	// Store p in w.buf and detect the content-type when the size of content in
+	// w.buf is at least 512 bytes.
+	n, err := w.buf.Write(p)
+	if err != nil {
+		return 0, err
+	}
+
+	if w.buf.Len() >= sniffLen {
+		// Note that w.open will return the full length of the buffer; we don't want
+		// to return that as the length of this write since some of them were written in
+		// previous writes. Instead, we return the n from this write, above.
+		_, err := w.open(w.buf.Bytes())
+		return n, err
+	}
+
+	return n, nil
+}
+
+// Close closes the blob writer. The write operation is not guaranteed
+// to have succeeded until Close returns with no error.
+//
+// Close may return an error if the context provided to create the
+// Writer is canceled or reaches its deadline.
+func (w *Writer) Close() (err error) {
+	w.closed = true
+
+	// Verify the MD5 hash of what was written matches the ContentMD5 provided by the user.
+	if len(w.contentMD5) > 0 {
+		md5sum := w.md5hash.Sum(nil)
+		if !bytes.Equal(md5sum, w.contentMD5) {
+			// No match! Return an error, but first cancel the context and call the
+			// driver's Close function to ensure the write is aborted.
+			w.cancel()
+			if w.w != nil {
+				_ = w.w.Close()
+			}
+			return fmt.Errorf("the WriterOptions.ContentMD5 you specified (%X) did not match what was written (%X)", w.contentMD5, md5sum)
+		}
+	}
+
+	defer w.cancel()
+
+	if w.w != nil {
+		return wrapError(w.drv, w.w.Close(), w.key)
+	}
+
+	if _, err := w.open(w.buf.Bytes()); err != nil {
+		return err
+	}
+
+	return wrapError(w.drv, w.w.Close(), w.key)
+}
+
+// open tries to detect the MIME type of p and write it to the blob.
+// The error it returns is wrapped.
+func (w *Writer) open(p []byte) (int, error) {
+	ct := http.DetectContentType(p)
+
+	var err error
+	w.w, err = w.drv.NewTypedWriter(w.ctx, w.key, ct, w.opts)
+	if err != nil {
+		return 0, wrapError(w.drv, err, w.key)
+	}
+
+	// Set the 3 fields needed for lazy NewTypedWriter back to zero values
+	// (see the comment on Writer).
+	w.buf = nil
+	w.ctx = nil
+	w.opts = nil
+
+	return w.write(p)
+}
+
+func (w *Writer) write(p []byte) (int, error) {
+	n, err := w.w.Write(p)
+	w.bytesWritten += n
+	return n, wrapError(w.drv, err, w.key)
+}
+
+// ReadFrom reads from r and writes to w until EOF or error.
+// The return value is the number of bytes read from r.
+//
+// It implements the io.ReaderFrom interface.
+func (w *Writer) ReadFrom(r io.Reader) (int64, error) {
+	// If the reader has a WriteTo method, use it to do the copy.
+	// Don't do this for our own *Reader to avoid infinite recursion.
+	// Avoids an allocation and a copy.
+	switch r.(type) {
+	case *Reader:
+	default:
+		if wt, ok := r.(io.WriterTo); ok {
+			return wt.WriteTo(w)
+		}
+	}
+
+	nr, _, err := readFromWriteTo(r, w)
+	return nr, err
+}