feat: add SsFormat encoding library

google-cloud-spanner/src/main/java/com/google/cloud/spanner/spi/v1/GrowableByteArrayOutputStream.java

@@ -0,0 +1,105 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.cloud.spanner.spi.v1;
+
+import com.google.api.core.InternalApi;
+import java.util.Arrays;
+
+/**
+ * A simple, unsynchronized byte array output stream optimized for key encoding.
+ *
+ * <p>Unlike {@link java.io.ByteArrayOutputStream}, this class is not thread-safe and does not incur
+ * synchronization overhead. This provides better performance for single-threaded key encoding
+ * operations where synchronization is not required.
+ */
+@InternalApi
+public final class GrowableByteArrayOutputStream {
+
+  private byte[] buf;
+  private int count;
+
+  /** Creates a new output stream with a default initial capacity of 32 bytes. */
+  public GrowableByteArrayOutputStream() {
+    this(32);
+  }
+
+  /**
+   * Creates a new output stream with the specified initial capacity.
+   *
+   * @param initialCapacity the initial buffer size
+   * @throws IllegalArgumentException if initialCapacity is negative
+   */
+  public GrowableByteArrayOutputStream(int initialCapacity) {
+    if (initialCapacity < 0) {
+      throw new IllegalArgumentException("Negative initial capacity: " + initialCapacity);
+    }
+    this.buf = new byte[initialCapacity];
+  }
+
+  private void ensureCapacity(int minCapacity) {
+    if (minCapacity > buf.length) {
+      int newCapacity = Math.max(buf.length << 1, minCapacity);
+      buf = Arrays.copyOf(buf, newCapacity);
+    }
+  }
+
+  /**
+   * Writes the specified byte to this output stream.
+   *
+   * @param b the byte to write (only the low 8 bits are used)
+   */
+  public void write(int b) {
+    ensureCapacity(count + 1);
+    buf[count++] = (byte) b;
+  }
+
+  /**
+   * Writes a portion of a byte array to this output stream.
+   *
+   * @param b the source byte array
+   * @param off the start offset in the array
+   * @param len the number of bytes to write
+   */
+  public void write(byte[] b, int off, int len) {
+    ensureCapacity(count + len);
+    System.arraycopy(b, off, buf, count, len);
+    count += len;
+  }
+
+  /**
+   * Returns a copy of the buffer contents as a new byte array.
+   *
+   * @return a new byte array containing the written bytes
+   */
+  public byte[] toByteArray() {
+    return Arrays.copyOf(buf, count);
+  }
+
+  /** Resets the buffer so that it can be reused. The underlying buffer is retained. */
+  public void reset() {
+    count = 0;
+  }
+
+  /**
+   * Returns the current number of bytes written to this stream.
+   *
+   * @return the number of valid bytes in the buffer
+   */
+  public int size() {
+    return count;
+  }
+}