sqlite: implement write. simple test passes now!

Change-Id: I260c71bdf4fcf6c35cb9caf73f430a31cdeebb78

misc/sqlite/sqlite3_os_go.c

@@ -28,8 +28,7 @@ static int go_file_read(sqlite3_file* file, void* dest, int iAmt, sqlite3_int64
 }
 
 static int go_file_write(sqlite3_file* file, const void* src, int iAmt, sqlite3_int64 iOfst) {
-  fprintf(stderr, "write\n");
-  return 0;
+  return GoFileWrite(((GoFile*) file)->fd, src, iAmt, iOfst);
 }
 
 static int go_file_truncate(sqlite3_file* file, sqlite3_int64 size) {

misc/sqlite/vfs.go

@@ -34,7 +34,7 @@ func GoFileClose(fd C.int) (int) {
 }
 
 //export GoFileRead
-// Returns SQLite error codes to be returned by xRead:
+// Returns SQLite error code to be returned by xRead:
 //   SQLITE_OK: read n bytes
 //   SQLITE_IOERR_READ: got error while reading
 //   SQLITE_IOERR_SHORT_READ: read fewer than n bytes; rest will be zeroed
@@ -71,6 +71,40 @@ func GoFileRead(fd C.int, dst *C.char, n C.int, offset C.long) (rv int) {
 	return C.SQLITE_OK
 }
 
+//export GoFileWrite
+// Returns SQLite error code to be returned by xWrite:
+//   SQLITE_OK: wrote n bytes
+//   SQLITE_IOERR_WRITE: got error while writing
+//   SQLITE_FULL: partial write
+func GoFileWrite(fd C.int, src *C.char, n C.int, offset C.long) (rv int) {
+	println("writing", n, "bytes at offset", offset, "to fd", fd);
+	defer func() {
+		println("write returning", rv);
+	}()
+
+	file := GetFile(int(fd))
+	if file == nil {
+		return C.SQLITE_IOERR_WRITE
+	}
+
+	// TODO: avoid this copy
+	buf := make([]byte, n)
+	C.memcpy(unsafe.Pointer(&buf[0]), unsafe.Pointer(src), C.size_t(len(buf)))
+
+	nwritten, err := file.WriteAt(buf, int64(offset))
+	if err != nil {
+		if err == os.ENOSPC {
+			return C.SQLITE_FULL
+		}
+		return C.SQLITE_IOERR_WRITE
+	}
+	if nwritten != int(n) {
+		return C.SQLITE_IOERR_WRITE
+	}
+
+	return C.SQLITE_OK
+}
+
 //export GoFileFileSize
 // return[0]: 0 on success and -1 on error.
 // return[1]: size