Remove setInjectionBufferLength() for Binary.

Simply pass the length to injectionBuffer() directly,
and refactor BinaryAdapters to wrap a ByteBuffer
for injection (instead of creating a new one).

opentracing-api/src/main/java/io/opentracing/propagation/Binary.java

@@ -33,37 +33,29 @@
  */
 public interface Binary {
     /**
-     * Hints the buffer length required for SpanContext injection.
-     * The user may use this to allocate the ByteBuffer
-     * or resize an existing one. This method is always called
-     * before injectionBuffer().
+     * Gets the buffer used to store data as part of {@link SpanContext} injection.
+     *
+     * The lenght parameter hints the buffer length required for
+     * {@link SpanContext} injection. The user may use this to allocate a new
+     * ByteBuffer or resize an existing one.
      *
      * It is an error to call this method when Binary is used
-     * for SpanContext extraction. It is also an error to call
-     * this method more than one time.
+     * for {@link SpanContext} extraction.
      *
-     * @param length The buffer length required for SpanContext injection.
+     * @param length The buffer length required for {@link SpanContext} injection.
      *               It needs to be larger than zero.
-     */
-    void setInjectionBufferLength(int length);
-
-    /**
-     * Gets the buffer containing the data used for SpanContext injection.
-     *
-     * It is an error to call this method when Binary is used
-     * for SpanContext extraction.
      *
-     * @return The buffer used for SpanContext injection.
+     * @return The buffer used for {@link SpanContext} injection.
      */
-    ByteBuffer injectionBuffer();
+    ByteBuffer injectionBuffer(int lenght);
 
     /**
-     * Gets the buffer containing the data used for SpanContext extraction.
+     * Gets the buffer containing the data used for {@link SpanContext} extraction.
      *
      * It is an error to call this method when Binary is used
-     * for SpanContext injection.
+     * for {@link SpanContext} injection.
      *
-     * @return The buffer used for SpanContext extraction.
+     * @return The buffer used for {@link SpanContext} extraction.
      */
     ByteBuffer extractionBuffer();
 }

opentracing-api/src/main/java/io/opentracing/propagation/BinaryAdapters.java

@@ -25,7 +25,7 @@ private BinaryAdapters() {}
      *
      * @param buffer The ByteBuffer used as input.
      *
-     * @return The new Binary carrier used for extraction.
+     * @return The new {@link Binary} carrier used for extraction.
      */
     public static Binary extractionCarrier(ByteBuffer buffer) {
         if (buffer == null) {
@@ -36,15 +36,18 @@ public static Binary extractionCarrier(ByteBuffer buffer) {
     }
 
     /**
-     * Creates an outbound Binary instance used for injection,
-     * allocating a new ByteBuffer instance when
-     * setInjectBufferLength() is called. The ByteBuffer can
-     * be later retrieved using injectBuffer().
+     * Creates an outbound {@link Binary} instance used for injection with the
+     * specified ByteBuffer as output. ByteBuffer.limit() will be set to the value
+     * of the requested length at {@link Binary#injectionBuffer()} time, and
+     * AssertionError will be thrown if the requested length is larger than
+     * the remaining length of ByteBuffer.
+     *
+     * @param buffer The ByteBuffer used as input.
      *
      * @return The new Binary carrier used for injection.
      */
-    public static Binary injectionCarrier() {
-        return new BinaryInjectAdapter();
+    public static Binary injectionCarrier(ByteBuffer buffer) {
+        return new BinaryInjectAdapter(buffer);
     }
 
     static class BinaryExtractAdapter implements Binary {
@@ -55,12 +58,7 @@ public BinaryExtractAdapter(ByteBuffer buffer) {
         }
 
         @Override
-        public void setInjectionBufferLength(int length) {
-            throw new UnsupportedOperationException();
-        }
-
-        @Override
-        public ByteBuffer injectionBuffer() {
+        public ByteBuffer injectionBuffer(int length) {
             throw new UnsupportedOperationException();
         }
 
@@ -73,24 +71,20 @@ public ByteBuffer extractionBuffer() {
     static class BinaryInjectAdapter implements Binary {
         ByteBuffer buffer;
 
+        public BinaryInjectAdapter(ByteBuffer buffer) {
+            this.buffer = buffer;
+        }
+
         @Override
-        public void setInjectionBufferLength(int length) {
+        public ByteBuffer injectionBuffer(int length) {
             if (length < 1) {
                 throw new IllegalArgumentException("length needs to be larger than 0");
             }
-            if (buffer != null) {
-                throw new IllegalStateException("injectBuffer() length has already been set.");
-            }
-
-            buffer = ByteBuffer.allocate(length);
-        }
-
-        @Override
-        public ByteBuffer injectionBuffer() {
-            if (buffer == null) {
-                throw new IllegalStateException("setInjectBufferLength() needs to be called before injectBuffer()");
+            if (length > buffer.remaining()) {
+                throw new AssertionError("length is larger than the backing ByteBuffer remaining length");
             }
 
+            buffer.limit(buffer.position() + length);
             return buffer;
         }
 

opentracing-api/src/test/java/io/opentracing/propagation/BinaryAdaptersTest.java

@@ -37,33 +37,32 @@ public void testExtractBinaryNull() {
     @Test(expected = UnsupportedOperationException.class)
     public void testExtractBinaryInjectBuffer() {
         Binary binary = BinaryAdapters.extractionCarrier(ByteBuffer.allocate(1));
-        binary.injectionBuffer();
+        binary.injectionBuffer(1);
     }
 
     @Test
     public void testInjectBinary() {
-        Binary binary = BinaryAdapters.injectionCarrier();
-        binary.setInjectionBufferLength(1);
-        assertNotNull(binary.injectionBuffer());
-        assertEquals(0, binary.injectionBuffer().position());
-        assertEquals(1, binary.injectionBuffer().capacity());
+        ByteBuffer buffer = ByteBuffer.allocate(1);
+        Binary binary = BinaryAdapters.injectionCarrier(buffer);
+        assertEquals(buffer, binary.injectionBuffer(1));
+        assertEquals(0, buffer.position());
     }
 
     @Test(expected = IllegalArgumentException.class)
     public void testInjectBinaryInvalidLength() {
-        Binary binary = BinaryAdapters.injectionCarrier();
-        binary.setInjectionBufferLength(0);
+        Binary binary = BinaryAdapters.injectionCarrier(ByteBuffer.allocate(1));
+        binary.injectionBuffer(0);
     }
 
-    @Test(expected = IllegalStateException.class)
-    public void testInjectBinaryNoLength() {
-        Binary binary = BinaryAdapters.injectionCarrier();
-        binary.injectionBuffer();
+    @Test(expected = AssertionError.class)
+    public void testInjectBinaryLargerLength() {
+        Binary binary = BinaryAdapters.injectionCarrier(ByteBuffer.allocate(1));
+        binary.injectionBuffer(2);
     }
 
     @Test(expected = UnsupportedOperationException.class)
     public void testInjectBinaryExtractBuffer() {
-        Binary binary = BinaryAdapters.injectionCarrier();
+        Binary binary = BinaryAdapters.injectionCarrier(ByteBuffer.allocate(1));
         binary.extractionBuffer();
     }
 }

opentracing-mock/src/main/java/io/opentracing/mock/MockTracer.java

@@ -143,8 +143,7 @@ public <C> void inject(MockSpan.MockContext ctx, Format<C> format, C carrier) {
                     objStream.flush(); // *need* to flush ObjectOutputStream.
 
                     byte[] buff = stream.toByteArray();
-                    binary.setInjectionBufferLength(buff.length);
-                    binary.injectionBuffer().put(buff);
+                    binary.injectionBuffer(buff.length).put(buff);
 
                 } catch (IOException e) {
                     throw new RuntimeException("Corrupted state", e);

opentracing-mock/src/test/java/io/opentracing/mock/MockTracerTest.java

@@ -214,10 +214,10 @@ public void testBinaryPropagator() {
             parentSpan.setBaggageItem("foobag", "fooitem");
             parentSpan.finish();
 
-            Binary binary = BinaryAdapters.injectionCarrier();
+            ByteBuffer buffer = ByteBuffer.allocate(128);
+            Binary binary = BinaryAdapters.injectionCarrier(buffer);
             tracer.inject(parentSpan.context(), Format.Builtin.BINARY, binary);
 
-            ByteBuffer buffer = binary.injectionBuffer();
             buffer.rewind();
             SpanContext extract = tracer.extract(Format.Builtin.BINARY, BinaryAdapters.extractionCarrier(buffer));