add beginnings of StreamAPI

src/mesh/PhoneAPI.cpp

@@ -5,9 +5,8 @@
 
 PhoneAPI::PhoneAPI()
 {
-    // Make sure that we never let our packets grow too large for one BLE packet
-    assert(FromRadio_size <= 512);
-    assert(ToRadio_size <= 512);
+    assert(FromRadio_size <= MAX_TO_FROM_RADIO_SIZE);
+    assert(ToRadio_size <= MAX_TO_FROM_RADIO_SIZE);
 }
 
 void PhoneAPI::init()

src/mesh/PhoneAPI.h

@@ -5,6 +5,9 @@
 #include "mesh.pb.h"
 #include <string>
 
+// Make sure that we never let our packets grow too large for one BLE packet
+#define MAX_TO_FROM_RADIO_SIZE 512
+
 /**
  * Provides our protobuf based API which phone/PC clients can use to talk to our device
  * over UDP, bluetooth or serial.

src/mesh/StreamAPI.cpp

@@ -0,0 +1 @@
+#include "StreamAPI.h"

src/mesh/StreamAPI.h

@@ -0,0 +1,51 @@
+#pragma once
+
+#include "PhoneAPI.h"
+#include "Stream.h"
+
+// A To/FromRadio packet + our 32 bit header
+#define MAX_STREAM_BUF_SIZE (MAX_TO_FROM_RADIO_SIZE + sizeof(uint32_t))
+
+/**
+ * A version of our 'phone' API that talks over a Stream.  So therefore well suited to use with serial links
+ * or TCP connections.
+ *
+ * ## Wire encoding
+
+When sending protobuf packets over serial or TCP each packet is preceded by uint32 sent in network byte order (big endian).
+The upper 16 bits must be 0x94C3. The lower 16 bits are packet length (this encoding gives room to eventually allow quite large
+packets).
+
+Implementations validate length against the maximum possible size of a BLE packet (our lowest common denominator) of 512 bytes. If
+the length provided is larger than that we assume the packet is corrupted and begin again looking for 0x4403 framing.
+
+The packets flowing towards the device are ToRadio protobufs, the packets flowing from the device are FromRadio protobufs.
+The 0x94C3 marker can be used as framing to (eventually) resync if packets are corrupted over the wire.
+
+Note: the 0x94C3 framing was chosen to prevent confusion with the 7 bit ascii character set. It also doesn't collide with any
+valid utf8 encoding. This makes it a bit easier to start a device outputting regular debug output on its serial port and then only
+after it has received a valid packet from the PC, turn off unencoded debug printing and switch to this packet encoding.
+
+ */
+class StreamAPI : public PhoneAPI
+{
+    /**
+     * The stream we read/write from
+     */
+    Stream *stream;
+
+    uint8_t rxBuf[MAX_STREAM_BUF_SIZE];
+    size_t rxPtr = 0;
+
+  public:
+    StreamAPI(Stream *_stream) : stream(_stream) {}
+
+    /**
+     * Currently we require frequent invocation from loop() to check for arrived serial packets.
+     * FIXME, to support better power behavior instead move to a thread and block on serial reads.
+     */
+    void loop();
+
+  private:
+    void readStream();
+};