Use the /dbfs/put API endpoint to upload smaller DBFS files

libs/filer/dbfs_client.go

@@ -1,11 +1,15 @@
 package filer
 
 import (
+	"bytes"
 	"context"
 	"errors"
+	"fmt"
 	"io"
 	"io/fs"
+	"mime/multipart"
 	"net/http"
+	"os"
 	"path"
 	"slices"
 	"sort"
@@ -14,6 +18,7 @@ import (
 
 	"github.com/databricks/databricks-sdk-go"
 	"github.com/databricks/databricks-sdk-go/apierr"
+	"github.com/databricks/databricks-sdk-go/client"
 	"github.com/databricks/databricks-sdk-go/service/files"
 )
 
@@ -63,22 +68,118 @@ func (info dbfsFileInfo) Sys() any {
 	return info.fi
 }
 
+// Interface to allow mocking of the Databricks API client.
+type databricksClient interface {
+	Do(ctx context.Context, method, path string, headers map[string]string,
+		requestBody any, responseBody any, visitors ...func(*http.Request) error) error
+}
+
 // DbfsClient implements the [Filer] interface for the DBFS backend.
 type DbfsClient struct {
 	workspaceClient *databricks.WorkspaceClient
 
+	apiClient databricksClient
+
 	// File operations will be relative to this path.
 	root WorkspaceRootPath
 }
 
 func NewDbfsClient(w *databricks.WorkspaceClient, root string) (Filer, error) {
+	apiClient, err := client.New(w.Config)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create API client: %w", err)
+	}
+
 	return &DbfsClient{
 		workspaceClient: w,
+		apiClient:       apiClient,
 
 		root: NewWorkspaceRootPath(root),
 	}, nil
 }
 
+func (w *DbfsClient) uploadUsingDbfsPutApi(ctx context.Context, path string, overwrite bool, file *os.File) error {
+	overwriteField := "False"
+	if overwrite {
+		overwriteField = "True"
+	}
+
+	buf := &bytes.Buffer{}
+	writer := multipart.NewWriter(buf)
+	err := writer.WriteField("path", path)
+	if err != nil {
+		return err
+	}
+	err = writer.WriteField("overwrite", overwriteField)
+	if err != nil {
+		return err
+	}
+	contents, err := writer.CreateFormFile("contents", "")
+	if err != nil {
+		return err
+	}
+
+	_, err = io.Copy(contents, file)
+	if err != nil {
+		return err
+	}
+
+	err = writer.Close()
+	if err != nil {
+		return err
+	}
+
+	// Request bodies of Content-Type multipart/form-data must are not supported by
+	// the Go SDK directly for DBFS. So we use the Do method directly.
+	return w.apiClient.Do(ctx, http.MethodPost, "/api/2.0/dbfs/put", map[string]string{
+		"Content-Type": writer.FormDataContentType(),
+	}, buf.Bytes(), nil)
+}
+
+func (w *DbfsClient) uploadUsingDbfsStreamingApi(ctx context.Context, path string, overwrite bool, reader io.Reader) error {
+	fileMode := files.FileModeWrite
+	if overwrite {
+		fileMode |= files.FileModeOverwrite
+	}
+
+	handle, err := w.workspaceClient.Dbfs.Open(ctx, path, fileMode)
+	if err != nil {
+		var aerr *apierr.APIError
+		if !errors.As(err, &aerr) {
+			return err
+		}
+
+		// This API returns a 400 if the file already exists.
+		if aerr.StatusCode == http.StatusBadRequest {
+			if aerr.ErrorCode == "RESOURCE_ALREADY_EXISTS" {
+				return FileAlreadyExistsError{path}
+			}
+		}
+
+		return err
+	}
+
+	_, err = io.Copy(handle, reader)
+	cerr := handle.Close()
+	if err == nil {
+		err = cerr
+	}
+	return err
+}
+
+// TODO CONTINUE:
+// 1. Write the unit tests that make sure the filer write method works correctly
+//    in either case.
+// 2. Write a intergration test that asserts write continues works for big file
+//    uploads. Also test the overwrite flag in the integration test.
+//    We can change MaxDbfsUploadLimitForPutApi in the test to avoid creating
+//    massive test fixtures.
+
+// MaxUploadLimitForPutApi is the maximum size in bytes of a file that can be uploaded
+// using the /dbfs/put API. If the file is larger than this limit, the streaming
+// API (/dbfs/create and /dbfs/add-block) will be used instead.
+var MaxDbfsUploadLimitForPutApi int64 = 2 * 1024 * 1024
+
 func (w *DbfsClient) Write(ctx context.Context, name string, reader io.Reader, mode ...WriteMode) error {
 	absPath, err := w.root.Join(name)
 	if err != nil {
@@ -114,30 +215,27 @@ func (w *DbfsClient) Write(ctx context.Context, name string, reader io.Reader, m
 		}
 	}
 
-	handle, err := w.workspaceClient.Dbfs.Open(ctx, absPath, fileMode)
-	if err != nil {
-		var aerr *apierr.APIError
-		if !errors.As(err, &aerr) {
-			return err
-		}
+	localFile, ok := reader.(*os.File)
 
-		// This API returns a 400 if the file already exists.
-		if aerr.StatusCode == http.StatusBadRequest {
-			if aerr.ErrorCode == "RESOURCE_ALREADY_EXISTS" {
-				return FileAlreadyExistsError{absPath}
-			}
-		}
+	// If the source is not a local file, we'll always use the streaming API endpoint.
+	if !ok {
+		return w.uploadUsingDbfsStreamingApi(ctx, absPath, slices.Contains(mode, OverwriteIfExists), reader)
+	}
 
-		return err
+	stat, err := localFile.Stat()
+	if err != nil {
+		return fmt.Errorf("failed to stat file: %w", err)
 	}
 
-	_, err = io.Copy(handle, reader)
-	cerr := handle.Close()
-	if err == nil {
-		err = cerr
+	// If the source is a local file, but is too large then we'll use the streaming API endpoint.
+	if stat.Size() > MaxDbfsUploadLimitForPutApi {
+		return w.uploadUsingDbfsStreamingApi(ctx, absPath, slices.Contains(mode, OverwriteIfExists), localFile)
 	}
 
-	return err
+	// Use the /dbfs/put API when the file is on the local filesystem
+	// and is small enough. This is the most common case when users use the
+	// `databricks fs cp` command.
+	return w.uploadUsingDbfsPutApi(ctx, absPath, slices.Contains(mode, OverwriteIfExists), localFile)
 }
 
 func (w *DbfsClient) Read(ctx context.Context, name string) (io.ReadCloser, error) {