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package http
import (
"context"
"fmt"
"github.com/aws/smithy-go/middleware"
)
const contentMD5Header = "Content-Md5"
// contentMD5Checksum provides a middleware to compute and set
// content-md5 checksum for a http request
type contentMD5Checksum struct {
}
// AddContentChecksumMiddleware adds checksum middleware to middleware's
// build step.
func AddContentChecksumMiddleware(stack *middleware.Stack) error {
// This middleware must be executed before request body is set.
return stack.Build.Add(&contentMD5Checksum{}, middleware.Before)
}
// ID returns the identifier for the checksum middleware
func (m *contentMD5Checksum) ID() string { return "ContentChecksum" }
// HandleBuild adds behavior to compute md5 checksum and add content-md5 header
// on http request
func (m *contentMD5Checksum) HandleBuild(
ctx context.Context, in middleware.BuildInput, next middleware.BuildHandler,
) (
out middleware.BuildOutput, metadata middleware.Metadata, err error,
) {
req, ok := in.Request.(*Request)
if !ok {
return out, metadata, fmt.Errorf("unknown request type %T", req)
}
// if Content-MD5 header is already present, return
if v := req.Header.Get(contentMD5Header); len(v) != 0 {
return next.HandleBuild(ctx, in)
}
// fetch the request stream.
stream := req.GetStream()
// compute checksum if payload is explicit
if stream != nil {
if !req.IsStreamSeekable() {
return out, metadata, fmt.Errorf(
"unseekable stream is not supported for computing md5 checksum")
}
v, err := computeMD5Checksum(stream)
if err != nil {
return out, metadata, fmt.Errorf("error computing md5 checksum, %w", err)
}
// reset the request stream
if err := req.RewindStream(); err != nil {
return out, metadata, fmt.Errorf(
"error rewinding request stream after computing md5 checksum, %w", err)
}
// set the 'Content-MD5' header
req.Header.Set(contentMD5Header, string(v))
}
// set md5 header value
return next.HandleBuild(ctx, in)
}
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