checksum_middleware.go

Documentation: github.com/aws/smithy-go/transport/http

     1  package http
     2  
     3  import (
     4  	"context"
     5  	"fmt"
     6  
     7  	"github.com/aws/smithy-go/middleware"
     8  )
     9  
    10  const contentMD5Header = "Content-Md5"
    11  
    12  // contentMD5Checksum provides a middleware to compute and set
    13  // content-md5 checksum for a http request
    14  type contentMD5Checksum struct {
    15  }
    16  
    17  // AddContentChecksumMiddleware adds checksum middleware to middleware's
    18  // build step.
    19  func AddContentChecksumMiddleware(stack *middleware.Stack) error {
    20  	// This middleware must be executed before request body is set.
    21  	return stack.Build.Add(&contentMD5Checksum{}, middleware.Before)
    22  }
    23  
    24  // ID returns the identifier for the checksum middleware
    25  func (m *contentMD5Checksum) ID() string { return "ContentChecksum" }
    26  
    27  // HandleBuild adds behavior to compute md5 checksum and add content-md5 header
    28  // on http request
    29  func (m *contentMD5Checksum) HandleBuild(
    30  	ctx context.Context, in middleware.BuildInput, next middleware.BuildHandler,
    31  ) (
    32  	out middleware.BuildOutput, metadata middleware.Metadata, err error,
    33  ) {
    34  	req, ok := in.Request.(*Request)
    35  	if !ok {
    36  		return out, metadata, fmt.Errorf("unknown request type %T", req)
    37  	}
    38  
    39  	// if Content-MD5 header is already present, return
    40  	if v := req.Header.Get(contentMD5Header); len(v) != 0 {
    41  		return next.HandleBuild(ctx, in)
    42  	}
    43  
    44  	// fetch the request stream.
    45  	stream := req.GetStream()
    46  	// compute checksum if payload is explicit
    47  	if stream != nil {
    48  		if !req.IsStreamSeekable() {
    49  			return out, metadata, fmt.Errorf(
    50  				"unseekable stream is not supported for computing md5 checksum")
    51  		}
    52  
    53  		v, err := computeMD5Checksum(stream)
    54  		if err != nil {
    55  			return out, metadata, fmt.Errorf("error computing md5 checksum, %w", err)
    56  		}
    57  
    58  		// reset the request stream
    59  		if err := req.RewindStream(); err != nil {
    60  			return out, metadata, fmt.Errorf(
    61  				"error rewinding request stream after computing md5 checksum, %w", err)
    62  		}
    63  
    64  		// set the 'Content-MD5' header
    65  		req.Header.Set(contentMD5Header, string(v))
    66  	}
    67  
    68  	// set md5 header value
    69  	return next.HandleBuild(ctx, in)
    70  }
    71
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