fix: connection early termination resulting in internal error

When the connection terminates before all bytes read, we were
getting an io.ErrUnexpectedEOF that was not being handled as
a standard io.EOF resulting in an internal error being raised.
Translate io.ErrUnexpectedEOF to io.EOF so that we return the
normal errors for unexpected content. Add a log message so
that its clear the error is due to the connection being
terminated before all data sent and not the fault of the
gateway.

s3api/utils/csum-reader.go

@@ -30,6 +30,7 @@ import (
 
 	"github.com/aws/aws-sdk-go-v2/service/s3/types"
 	"github.com/cespare/xxhash/v2"
+	"github.com/versity/versitygw/debuglogger"
 	"github.com/versity/versitygw/s3err"
 	"github.com/zeebo/xxh3"
 )
@@ -127,6 +128,13 @@ func NewHashReader(r io.Reader, expectedSum string, ht HashType) (*HashReader, e
 // Read allows *HashReader to be used as an io.Reader
 func (hr *HashReader) Read(p []byte) (int, error) {
 	n, readerr := hr.r.Read(p)
+	// Treat ErrUnexpectedEOF as EOF so a truncated body triggers checksum
+	// validation (which will fail on partial data) rather than leaking a
+	// raw Go error as an internal server error.
+	if readerr == io.ErrUnexpectedEOF {
+		debuglogger.Logf("client connection terminated early")
+		readerr = io.EOF
+	}
 	_, err := hr.hash.Write(p[:n])
 	if err != nil {
 		return n, err

s3api/utils/signed-chunk-reader.go

@@ -124,6 +124,14 @@ func NewSignedChunkReader(r io.Reader, authdata AuthData, canonicalString, secre
 // Read satisfies the io.Reader for this type
 func (cr *ChunkReader) Read(p []byte) (int, error) {
 	n, err := cr.r.Read(p)
+	// Treat ErrUnexpectedEOF as EOF so a connection that closes before
+	// all Content-Length bytes arrive follows the normal EOF path and
+	// returns a proper S3 error (e.g. ErrContentLengthMismatch or
+	// SignatureDoesNotMatch) instead of leaking an internal Go error.
+	if err == io.ErrUnexpectedEOF {
+		debuglogger.Logf("client connection terminated early")
+		err = io.EOF
+	}
 	if err != nil && err != io.EOF {
 		return 0, err
 	}