feat: implement cross-protocol checksum verification for file transfers

internal/protocols/ftp/ftp.go

@@ -1,7 +1,9 @@
 package ftp
 
 import (
+	"crypto/md5"
 	"crypto/tls"
+	"encoding/hex"
 	"fmt"
 	"io"
 	"path/filepath"
@@ -177,3 +179,16 @@ func (e *FTPExplorer) ReadFile(path string) (io.ReadCloser, error) {
 func (e *FTPExplorer) WriteFile(path string, r io.Reader, size int64) error {
 	return e.client.Stor(path, r)
 }
+
+func (e *FTPExplorer) Checksum(path string) (string, error) {
+	r, err := e.ReadFile(path)
+	if err != nil {
+		return "", err
+	}
+	defer r.Close()
+	h := md5.New()
+	if _, err := io.Copy(h, r); err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(h.Sum(nil)), nil
+}

internal/protocols/local/local.go

@@ -1,6 +1,8 @@
 package local
 
 import (
+	"crypto/md5"
+	"encoding/hex"
 	"io"
 	"os"
 	"path/filepath"
@@ -82,6 +84,19 @@ func (e *LocalExplorer) Rename(src, dst string) error {
 	return os.Rename(src, dst)
 }
 
+func (e *LocalExplorer) Checksum(path string) (string, error) {
+	r, err := e.ReadFile(path)
+	if err != nil {
+		return "", err
+	}
+	defer r.Close()
+	h := md5.New()
+	if _, err := io.Copy(h, r); err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(h.Sum(nil)), nil
+}
+
 func (e *LocalExplorer) ReadFile(path string) (io.ReadCloser, error) {
 	return os.Open(path)
 }

internal/protocols/nfs/nfs_unix.go

@@ -3,6 +3,8 @@
 package nfs
 
 import (
+	"crypto/md5"
+	"encoding/hex"
 	"fmt"
 	"io"
 	"path/filepath"
@@ -125,3 +127,16 @@ func (e *NFSExplorer) WriteFile(path string, r io.Reader, size int64) error {
 	_, err = io.Copy(f, r)
 	return err
 }
+
+func (e *NFSExplorer) Checksum(path string) (string, error) {
+	r, err := e.ReadFile(path)
+	if err != nil {
+		return "", err
+	}
+	defer r.Close()
+	h := md5.New()
+	if _, err := io.Copy(h, r); err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(h.Sum(nil)), nil
+}

internal/protocols/nfs/nfs_windows.go

@@ -25,3 +25,4 @@ func (e *NFSExplorer) Delete(path string) error { return nil }
 func (e *NFSExplorer) Rename(src, dst string) error { return nil }
 func (e *NFSExplorer) ReadFile(path string) (io.ReadCloser, error) { return nil, nil }
 func (e *NFSExplorer) WriteFile(path string, r io.Reader, size int64) error { return nil }
+func (e *NFSExplorer) Checksum(path string) (string, error) { return "", nil }

internal/protocols/s3/s3.go

@@ -307,3 +307,28 @@ func (e *S3Explorer) WriteFile(path string, r io.Reader, size int64) error {
 	})
 	return err
 }
+
+func (e *S3Explorer) Checksum(path string) (string, error) {
+	bucket, subpath, _, err := e.getBucketAndPath(path)
+	if err != nil {
+		return "", err
+	}
+	
+	if subpath == "" {
+		return "", fmt.Errorf("cannot calculate checksum of bucket")
+	}
+
+	input := &s3.HeadObjectInput{
+		Bucket: aws.String(bucket),
+		Key:    aws.String(subpath),
+	}
+	head, err := e.client.HeadObject(context.TODO(), input)
+	if err != nil {
+		return "", err
+	}
+
+	if head.ETag != nil {
+		return strings.Trim(*head.ETag, "\""), nil
+	}
+	return "", fmt.Errorf("no etag found")
+}

internal/protocols/sftp/sftp.go

@@ -1,6 +1,8 @@
 package sftp
 
 import (
+	"crypto/md5"
+	"encoding/hex"
 	"fmt"
 	"io"
 	"path/filepath"
@@ -162,3 +164,16 @@ func (e *SFTPExplorer) WriteFile(path string, r io.Reader, size int64) error {
 	_, err = io.Copy(f, r)
 	return err
 }
+
+func (e *SFTPExplorer) Checksum(path string) (string, error) {
+	r, err := e.ReadFile(path)
+	if err != nil {
+		return "", err
+	}
+	defer r.Close()
+	h := md5.New()
+	if _, err := io.Copy(h, r); err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(h.Sum(nil)), nil
+}

internal/protocols/smb/smb.go

@@ -1,6 +1,8 @@
 package smb
 
 import (
+	"crypto/md5"
+	"encoding/hex"
 	"fmt"
 	"io"
 	"net"
@@ -243,3 +245,16 @@ func (e *SMBExplorer) WriteFile(path string, r io.Reader, size int64) error {
 	_, err = io.Copy(f, r)
 	return err
 }
+
+func (e *SMBExplorer) Checksum(path string) (string, error) {
+	r, err := e.ReadFile(path)
+	if err != nil {
+		return "", err
+	}
+	defer r.Close()
+	h := md5.New()
+	if _, err := io.Copy(h, r); err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(h.Sum(nil)), nil
+}

internal/protocols/webdav/webdav.go

@@ -1,6 +1,8 @@
 package webdav
 
 import (
+	"crypto/md5"
+	"encoding/hex"
 	"fmt"
 	"io"
 	"strings"
@@ -102,3 +104,16 @@ func (e *WebDAVExplorer) ReadFile(path string) (io.ReadCloser, error) {
 func (e *WebDAVExplorer) WriteFile(path string, r io.Reader, size int64) error {
 	return e.client.WriteStream(path, r, 0644)
 }
+
+func (e *WebDAVExplorer) Checksum(path string) (string, error) {
+	r, err := e.ReadFile(path)
+	if err != nil {
+		return "", err
+	}
+	defer r.Close()
+	h := md5.New()
+	if _, err := io.Copy(h, r); err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(h.Sum(nil)), nil
+}