IO: Ensure parent directory exists before writing file (#34)

* [FileSystemByteSink] Ensure the parent directory exists

* Dumper: Hide prepare() call in FileSystemByteSink.

Co-authored-by: Bart Wiegmans <[email protected]>

Author: shevek-google

dumper/app/src/main/java/com/google/edwmigration/dumper/application/dumper/connector/netezza/NetezzaMetadataConnector.java

@@ -172,6 +172,7 @@ public void addTasksTo(List<? super Task<?>> out, ConnectorArguments arguments)
         // Not documented.
         out.add(new JdbcSelectTask("nz.v_objects.csv", "SELECT * FROM system.._v_objects"));
 
+        // TODO; these might be placed in a ParallelTaskGroup?`
         // these neeed to be filtered on WHERE = dbname, or else which DB md table will contain SYSTEM data too
         for (String db : dbs) {
             // The benefit of having this reduces the amount of data in the zip file

dumper/app/src/main/java/com/google/edwmigration/dumper/application/dumper/io/FileSystemOutputHandle.java

@@ -38,6 +38,7 @@ public class FileSystemOutputHandle implements OutputHandle {
     private final Path targetPath;
 
     public FileSystemOutputHandle(@Nonnull Path rootPath, @Nonnull String targetPath) {
+        // Due to the semantics of prepare(), both of these must be within the same subdirectory.
         this.targetPath = rootPath.resolve(targetPath);
         this.temporaryPath = rootPath.resolve(targetPath + ".tmp");
         // LOG.debug("Created " + this);
@@ -50,17 +51,29 @@ public boolean exists() throws IOException {
     }
 
     @Override
-    public ByteSink asByteSink() {
+    public ByteSink asByteSink() throws IOException {
         // LOG.debug("As ByteSink: " + this + " = " + targetPath);
+        prepare();
         return new FileSystemByteSink(targetPath);
     }
 
     @Override
-    public ByteSink asTemporaryByteSink() {
+    public ByteSink asTemporaryByteSink() throws IOException {
         // LOG.debug("As Temporary ByteSink: " + this + " = " + temporaryPath);
+        prepare();
         return new FileSystemByteSink(temporaryPath);
     }
 
+    /**
+     * Ensures that the target file can be written.
+     *
+     * Must be called before calling openStream() on a ByteStream acquired from this object.
+     */
+    private void prepare() throws IOException {
+        // Ensures that the directory to which we want to write exists
+        Files.createDirectories(targetPath.getParent());
+    }
+
     @Override
     public void commit() throws IOException {
         if (!Files.exists(temporaryPath))

dumper/app/src/main/java/com/google/edwmigration/dumper/application/dumper/io/OutputHandle.java

@@ -33,17 +33,17 @@ public interface OutputHandle {
 
     /** Returns a ByteSink on the target file. */
     @Nonnull
-    public ByteSink asByteSink();
+    public ByteSink asByteSink() throws IOException;
 
     /** Returns a CharSink on the target file. */
     @Nonnull
-    default public CharSink asCharSink(@Nonnull Charset charset) {
+    default public CharSink asCharSink(@Nonnull Charset charset) throws IOException {
         return asByteSink().asCharSink(charset);
     }
 
     /** Returns a ByteSink on the temporary file. */
     @Nonnull
-    public ByteSink asTemporaryByteSink();
+    public ByteSink asTemporaryByteSink() throws IOException;
 
     /**
      * Renames the temporary file to the final file.