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media.go
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media.go
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// Copyright 2022, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
package gax
import (
"io"
"net/http"
"google.golang.org/api/googleapi"
)
const sniffBuffSize = 512
func newContentSniffer(r io.Reader) *contentSniffer {
return &contentSniffer{r: r}
}
// contentSniffer wraps a Reader, and reports the content type determined by sniffing up to 512 bytes from the Reader.
type contentSniffer struct {
r io.Reader
start []byte // buffer for the sniffed bytes.
err error // set to any error encountered while reading bytes to be sniffed.
ctype string // set on first sniff.
sniffed bool // set to true on first sniff.
}
func (cs *contentSniffer) Read(p []byte) (n int, err error) {
// Ensure that the content type is sniffed before any data is consumed from Reader.
_, _ = cs.ContentType()
if len(cs.start) > 0 {
n := copy(p, cs.start)
cs.start = cs.start[n:]
return n, nil
}
// We may have read some bytes into start while sniffing, even if the read ended in an error.
// We should first return those bytes, then the error.
if cs.err != nil {
return 0, cs.err
}
// Now we have handled all bytes that were buffered while sniffing. Now just delegate to the underlying reader.
return cs.r.Read(p)
}
// ContentType returns the sniffed content type, and whether the content type was successfully sniffed.
func (cs *contentSniffer) ContentType() (string, bool) {
if cs.sniffed {
return cs.ctype, cs.ctype != ""
}
cs.sniffed = true
// If ReadAll hits EOF, it returns err==nil.
cs.start, cs.err = io.ReadAll(io.LimitReader(cs.r, sniffBuffSize))
// Don't try to detect the content type based on possibly incomplete data.
if cs.err != nil {
return "", false
}
cs.ctype = http.DetectContentType(cs.start)
return cs.ctype, true
}
// DetermineContentType determines the content type of the supplied reader.
// If the content type is already known, it can be specified via ctype.
// Otherwise, the content of media will be sniffed to determine the content type.
// If media implements googleapi.ContentTyper (deprecated), this will be used
// instead of sniffing the content.
// After calling DetectContentType the caller must not perform further reads on
// media, but rather read from the Reader that is returned.
func DetermineContentType(media io.Reader, ctype string) (io.Reader, string) {
// Note: callers could avoid calling DetectContentType if ctype != "",
// but doing the check inside this function reduces the amount of
// generated code.
if ctype != "" {
return media, ctype
}
// For backwards compatibility, allow clients to set content
// type by providing a ContentTyper for media.
if typer, ok := media.(googleapi.ContentTyper); ok {
return media, typer.ContentType()
}
sniffer := newContentSniffer(media)
if ctype, ok := sniffer.ContentType(); ok {
return sniffer, ctype
}
// If content type could not be sniffed, reads from sniffer will eventually fail with an error.
return sniffer, ""
}