AP_HAL: BetterStream add a read(uint8_t*buffer, uint16_t count method

libraries/AP_HAL/utility/BetterStream.cpp

@@ -19,3 +19,15 @@ size_t AP_HAL::BetterStream::write(const char *str)
 {
     return write((const uint8_t *)str, strlen(str));
 }
+
+ssize_t AP_HAL::BetterStream::read(uint8_t *buffer, uint16_t count) {
+    uint16_t offset = 0;
+    while (count--) {
+        const int16_t x = read();
+        if (x == -1) {
+            return offset;
+        }
+        buffer[offset++] = (uint8_t)x;
+    }
+    return offset;
+}

libraries/AP_HAL/utility/BetterStream.h

@@ -19,11 +19,12 @@
 //
 #pragma once
 
-#include <stdarg.h>
-
 #include <AP_Common/AP_Common.h>
 #include <AP_HAL/AP_HAL_Namespace.h>
 
+#include <stdarg.h>
+#include <unistd.h>
+
 class AP_HAL::BetterStream {
 public:
 
@@ -48,6 +49,10 @@ public:
     // returns false if discard failed (e.g. port locked)
     virtual bool discard_input() = 0; // discard all bytes available for reading
 
+    // returns -1 on error (e.g. port locked), number of bytes read
+    // otherwise
+    virtual ssize_t read(uint8_t *buffer, uint16_t count);
+
     /* NB txspace was traditionally a member of BetterStream in the
      * FastSerial library. As far as concerns go, it belongs with available() */
     virtual uint32_t txspace() = 0;