new class: ObjectStream

Author: pschatzmann

src/AudioTools/Communication/ObjectStream.h

@@ -0,0 +1,76 @@
+#include "AudioTools/CoreAudio/BaseStream.h"
+namespace audio_tools {
+/**
+ * @brief A Arduino Stream which makes sure that we read back the same size
+ * as we wrote. It adds a size prefix to the data stream.
+ * @author Phil Schatzmann
+ */
+class ObjectStream : public BaseStream {
+  ObjectStream(Stream &stream) {
+    p_in = &stream;
+    p_out = &stream;
+  }
+  ObjectStream(Print &stream) { p_out = &stream; }
+
+  /// reads the data from the input stream: I recommend to set the len to the
+  /// max object size, to avoid that we read only a part of the object.
+  size_t readBytes(uint8_t *data, size_t len) {
+    if (p_in == nullptr) return 0;
+    // read the size prefix if necessary
+    int to_read = available();
+    size_t result = 0;
+    if (to_read > 0) {
+      if (to_read > len) to_read = len;
+      // read the data
+      result = p_in->readBytes(data, to_read);
+      // determe the open number of bytes
+      n_open_read -= result;
+      is_complete = n_open_read == 0;
+      // if we have read all data we need to read the size prefix again
+      if (is_complete) n_open_read = -1;
+    }
+    return result;
+  }
+
+  size_t write(const uint8_t *data, size_t len) {
+    if (p_out == nullptr) return 0;
+    // write the size prefix
+    p_out->write((uint8_t *)&len, sizeof(size_t));
+    // write the data
+    return p_out->write(data, len);
+  }
+
+  int available() {
+    if (p_in == nullptr) return 0;
+    if (n_open_read >= 0) return n_open_read;
+    // make sure that we can read the size prefix
+    if (p_in->available() < sizeof(size_t)) return 0;
+    // read the size prefix
+    p_in->readBytes((uint8_t *)&n_open_read, sizeof(size_t));
+    return n_open_read;
+  }
+
+  // not supported
+  virtual size_t write(uint8_t ch) { return 0; }
+
+  int availableForWrite() override {
+    if (max_object_size > 0) return max_object_size;
+    if (p_out == nullptr) return DEFAULT_BUFFER_SIZE;
+    return p_out->availableForWrite();
+  }
+
+  /// When value is 0 (default) we determine it from the output, otherwise we
+  /// return the defined value.
+  void setMaxObjectSize(size_t size) { max_object_size = size; }
+
+  /// Determine if we processed the complete object
+  bool isObjectComplete() { return is_complete; }
+
+ protected:
+  Stream *p_in = nullptr;
+  Print *p_out = nullptr;
+  int n_open_read = -1;
+  int max_object_size = 0;  // 0 u
+  bool is_complete = true;
+};
+}  // namespace audio_tools