Support writing large raw String content without expanding the underlying buffer (#398)

Currently, the underlying buffer will expand when writing raw String content that is larger that the buffer. This change writes that as chunks instead.

Author: rob-bygrave

json-core/src/main/java/io/avaje/json/stream/core/JGenerator.java

@@ -57,6 +57,7 @@ class JGenerator implements JsonGenerator {
 
   private final Grisu3.FastDtoaBuilder doubleBuilder = new Grisu3.FastDtoaBuilder();
   private final int largeStringMax;
+  private final int largeAsciiMax;
   private byte[] buffer;
   private JsonOutput target;
   private int lastOp;
@@ -80,6 +81,7 @@ class JGenerator implements JsonGenerator {
     this.buffer = buffer;
     // each char can take up to 6 bytes when Unicode escaped, round down 1/8 number of chars
     this.largeStringMax = buffer.length >> 3;
+    this.largeAsciiMax = buffer.length - 10;
   }
 
   @Override
@@ -360,13 +362,33 @@ private void writeStringEscape(final String str, int i, int cur, final int len)
   @SuppressWarnings("deprecation")
   private void writeAscii(final String value) {
     final int len = value.length();
+    if (len > largeAsciiMax) {
+      writeLargeAscii(value);
+      return;
+    }
     if (position + len >= buffer.length) {
       enlargeOrFlush(position, len);
     }
     value.getBytes(0, len, buffer, position);
     position += len;
   }
 
+  /** Break a large ascii into segments and flush when necessary */
+  private void writeLargeAscii(String value) {
+    int left = value.length();
+    int offset = 0;
+    while (left > 0) {
+      final int len = Math.min(largeAsciiMax, left);
+      if (position + len >= buffer.length) {
+        enlargeOrFlush(position, 0); // just flush
+      }
+      value.getBytes(offset, offset + len, buffer, position);
+      position += len;
+      offset += len;
+      left -= len;
+    }
+  }
+
   private void writeAscii(final byte[] buf) {
     final int len = buf.length;
     if (position + len >= buffer.length) {

json-core/src/test/java/io/avaje/json/stream/core/JsonWriterTest.java

@@ -192,4 +192,29 @@ void largeStringUnicode() {
       .describedAs("internal buffer should not grow")
       .isEqualTo(100);
   }
+
+  @Test
+  void largeStringAscii() {
+    ByteArrayOutputStream os = new ByteArrayOutputStream();
+    JGenerator dJsonWriter = new JGenerator(100);
+    dJsonWriter.prepare(JsonOutput.ofStream(os));
+
+    JsonWriteAdapter fw = new JsonWriteAdapter(dJsonWriter, HybridBufferRecycler.shared(), true, true);
+
+    String largeValue = '"' + "_1234567890123456789".repeat(21) + '"';
+
+    fw.beginObject();
+    fw.name("key");
+    fw.rawValue(largeValue);
+    fw.endObject();
+    fw.close();
+
+    String jsonResult = new String(os.toByteArray(), 0, os.toByteArray().length);
+    assertThat(jsonResult).isEqualTo("{\"key\":" + largeValue + "}");
+
+    byte[] effectiveBufferSize = dJsonWriter.ensureCapacity(0);
+    assertThat(effectiveBufferSize.length)
+      .describedAs("internal buffer should not grow")
+      .isEqualTo(100);
+  }
 }