fix: handle "x-amz-copy-source" header starting with '/' in s3api

The "x-amz-copy-source" header may start with '/' as observed with
WinSCP. However, '/' is also the separator between the bucket and the
object path in "x-amz-copy-source".

Consider the following code in VerifyObjectCopyAccess():

    srcBucket, srcObject, found := strings.Cut(copySource, "/")

If `copySource` starts with '/', then `srcBucket` is set to an empty
string. Later, an error is returned because bucket "" does not exist.

This issue was fixed in the Posix and Azure backends by the following
commit:

 * 5e484f2 fix: Fixed CopySource parsing to handle the values starting with '/' in CopyObject action in posix and azure backends.

But the issue was not fixed in `VerifyObjectCopyAccess`.

This commit sanitizes "x-amz-copy-source" right after the header is
extracted in `s3api/controllers/base.go`. This ensures that the
`CopySource` argument passed to the backend functions UploadPartCopy()
and CopyObject() does not start with '/'. Since the backends no longer
need to strip away any leading '/' in `CopySource`, the parts of
commit 5e484f2 modifying the Posix and Azure backends are reverted.

Fixes issue #773.

Signed-off-by: Christophe Vu-Brugier <christophe.vu-brugier@seagate.com>

backend/azure/azure.go

@@ -692,12 +692,7 @@ func (az *Azure) CopyObject(ctx context.Context, input *s3.CopyObjectInput) (*s3
 		return nil, err
 	}
 
-	cpSrc := *input.CopySource
-	if cpSrc[0] == '/' {
-		cpSrc = cpSrc[1:]
-	}
-
-	if strings.Join([]string{*input.Bucket, *input.Key}, "/") == cpSrc && isMetaSame(mdmap, input.Metadata) {
+	if strings.Join([]string{*input.Bucket, *input.Key}, "/") == *input.CopySource && isMetaSame(mdmap, input.Metadata) {
 		return nil, s3err.GetAPIError(s3err.ErrInvalidCopyDest)
 	}
 
@@ -711,7 +706,7 @@ func (az *Azure) CopyObject(ctx context.Context, input *s3.CopyObjectInput) (*s3
 		return nil, err
 	}
 
-	resp, err := bclient.CopyFromURL(ctx, az.serviceURL+"/"+cpSrc, &blob.CopyFromURLOptions{
+	resp, err := bclient.CopyFromURL(ctx, az.serviceURL+"/"+*input.CopySource, &blob.CopyFromURLOptions{
 		BlobTags: tags,
 		Metadata: parseMetadata(input.Metadata),
 	})

backend/posix/posix.go

@@ -1983,13 +1983,7 @@ func (p *Posix) CopyObject(ctx context.Context, input *s3.CopyObjectInput) (*s3.
 	if input.ExpectedBucketOwner == nil {
 		return nil, s3err.GetAPIError(s3err.ErrInvalidRequest)
 	}
-
-	cpSrc := *input.CopySource
-	if cpSrc[0] == '/' {
-		cpSrc = cpSrc[1:]
-	}
-
-	srcBucket, srcObject, ok := strings.Cut(cpSrc, "/")
+	srcBucket, srcObject, ok := strings.Cut(*input.CopySource, "/")
 	if !ok {
 		return nil, s3err.GetAPIError(s3err.ErrInvalidCopySource)
 	}

s3api/controllers/base.go

@@ -1535,6 +1535,9 @@ func (c S3ApiController) PutActions(ctx *fiber.Ctx) error {
 
 	// Copy source headers
 	copySource := ctx.Get("X-Amz-Copy-Source")
+	if len(copySource) > 0 && copySource[0] == '/' {
+		copySource = copySource[1:]
+	}
 	copySrcIfMatch := ctx.Get("X-Amz-Copy-Source-If-Match")
 	copySrcIfNoneMatch := ctx.Get("X-Amz-Copy-Source-If-None-Match")
 	copySrcModifSince := ctx.Get("X-Amz-Copy-Source-If-Modified-Since")