bind/java: ensure there is enough capacity for writing seq

The new testLongString triggers the bug without this change.

Fixes golang/go#9251.

Change-Id: I463e2897b5b08f53801f151c7311d591546c0719
Reviewed-on: https://go-review.googlesource.com/1373
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

bind/java/SeqTest.java

@@ -16,6 +16,28 @@ public class SeqTest extends TestCase {
     assertEquals("Unexpected arithmetic failure", 7, res);
   }
 
+  public void testShortString() {
+    String want = "a short string";
+    String got = Testpkg.StrDup(want);
+    assertEquals("Strings should match", want, got);
+  }
+
+  public void testLongString() {
+    StringBuilder b = new StringBuilder();
+    for (int i = 0; i < 128*1024; i++) {
+      b.append("0123456789");
+    }
+    String want = b.toString();
+    String got = Testpkg.StrDup(want);
+    assertEquals("Strings should match", want, got);
+  }
+
+  public void testUnicode() {
+    String want = "Hello, 世界";
+    String got = Testpkg.StrDup(want);
+    assertEquals("Strings should match", want, got);
+  }
+
   public void testGoRefGC() {
     Testpkg.S s = Testpkg.New();
     runGC();

bind/java/seq_android.c

@@ -30,21 +30,27 @@ typedef struct mem {
 	uint32_t cap;
 } mem;
 
-static mem *mem_resize(mem *m, uint32_t size) {
+// mem_ensure ensures that m has at least size bytes free.
+// If m is NULL, it is created.
+static mem *mem_ensure(mem *m, uint32_t size) {
 	if (m == NULL) {
 		m = (mem*)malloc(sizeof(mem));
 		if (m == NULL) {
-			LOG_FATAL("mem_resize malloc failed");
+			LOG_FATAL("mem_ensure malloc failed");
 		}
+		m->cap = 0;
 		m->off = 0;
 		m->len = 0;
 		m->buf = NULL;
 	}
-	m->buf = (uint8_t*)realloc((void*)m->buf, size);
-	if (m->buf == NULL) {
-		LOG_FATAL("mem_resize realloc failed, size=%d", size);
+	if (m->cap > m->off+size) {
+		return m;
 	}
-	m->cap = size;
+	m->buf = (uint8_t*)realloc((void*)m->buf, m->off+size);
+	if (m->buf == NULL) {
+		LOG_FATAL("mem_ensure realloc failed, off=%d, size=%d", m->off, size);
+	}
+	m->cap = m->off+size;
 	return m;
 }
 
@@ -78,9 +84,11 @@ uint8_t *mem_write(JNIEnv *env, jobject obj, uint32_t size) {
 	if (m->off != m->len) {
 		LOG_FATAL("write can only append to seq, size: (off=%d, len=%d, size=%d", m->off, m->len, size);
 	}
-	if (m->off+size > m->cap) {
-		m = mem_resize(m, 2*m->cap);
+	uint32_t cap = m->cap;
+	while (m->off+size > cap) {
+		cap *= 2;
 	}
+	m = mem_ensure(m, cap);
 	uint8_t *res = m->buf+m->off;
 	m->off += size;
 	m->len += size;
@@ -130,8 +138,8 @@ void init_seq(void *javavm) {
 JNIEXPORT void JNICALL
 Java_go_Seq_ensure(JNIEnv *env, jobject obj, jint size) {
 	mem *m = mem_get(env, obj);
-	if (m == NULL || size > m->cap - m->off) {
-		m = mem_resize(m, size);
+	if (m == NULL || m->off+size > m->cap) {
+		m = mem_ensure(m, size);
 		(*env)->SetLongField(env, obj, memptr_id, (jlong)(uintptr_t)m);
 	}
 }

bind/java/testpkg/Testpkg.java

@@ -23,7 +23,6 @@ public abstract class Testpkg {
     public static void Call(I i) {
         go.Seq _in = new go.Seq();
         go.Seq _out = new go.Seq();
-        System.out.println("Call!");
         _in.writeRef(i.ref());
         Seq.send(DESCRIPTOR, CALL_Call, _in, _out);
     }
@@ -150,11 +149,22 @@ public abstract class Testpkg {
         
     }
     
+    public static String StrDup(String s) {
+        go.Seq _in = new go.Seq();
+        go.Seq _out = new go.Seq();
+        String _result;
+        _in.writeUTF16(s);
+        Seq.send(DESCRIPTOR, CALL_StrDup, _in, _out);
+        _result = _out.readUTF16();
+        return _result;
+    }
+    
     private static final int CALL_Add = 1;
     private static final int CALL_Call = 2;
     private static final int CALL_GC = 3;
     private static final int CALL_Keep = 4;
     private static final int CALL_New = 5;
     private static final int CALL_NumSCollected = 6;
+    private static final int CALL_StrDup = 7;
     private static final String DESCRIPTOR = "testpkg";
 }

bind/java/testpkg/go_testpkg/go_testpkg.go

@@ -81,6 +81,12 @@ func init() {
 	seq.Register(proxySDescriptor, proxySFCode, proxySF)
 }
 
+func proxy_StrDup(out, in *seq.Buffer) {
+	param_s := in.ReadUTF16()
+	res := testpkg.StrDup(param_s)
+	out.WriteUTF16(res)
+}
+
 func init() {
 	seq.Register("testpkg", 1, proxy_Add)
 	seq.Register("testpkg", 2, proxy_Call)
@@ -88,4 +94,5 @@ func init() {
 	seq.Register("testpkg", 4, proxy_Keep)
 	seq.Register("testpkg", 5, proxy_New)
 	seq.Register("testpkg", 6, proxy_NumSCollected)
+	seq.Register("testpkg", 7, proxy_StrDup)
 }

bind/java/testpkg/testpkg.go

@@ -56,3 +56,7 @@ func Add(x, y int) int {
 func NumSCollected() int {
 	return numSCollected
 }
+
+func StrDup(s string) string {
+	return s
+}