libsigrok-internal.h: add length checking endianess helpers

Introduce the read_u8_inc_len() and read_u16le_inc_len() routines which
read the respective numbers from binary input, advance the current read
position, and also track the remaining length of input data. Call sites
need not duplicate the data field width they advanced over.

The input stream is considered exhausted when there is insufficient data
to read another field. All subsequent reads will also terminate. Calling
applications need to check before reading when they expect specific sets
of adjacent fields to be available. It is assumed that most call sites
already do this (once for the whole input stream, not individually for
each conversion call of a field).

diff --git a/src/libsigrok-internal.h b/src/libsigrok-internal.h
index 7499e15f547d1e131c88d9487ea2f0015ac16ff6..06c227bb5b4ceb2d150b8cd06ffc2db4364f7cda 100644 (file)
--- a/src/libsigrok-internal.h
+++ b/src/libsigrok-internal.h
@@ -615,6 +615,30 @@ static inline uint8_t read_u8_inc(const uint8_t **p)
        return v;
 }
 
+/**
+ * Read unsigned 8bit integer, check length, increment read position.
+ * @param[in, out] p Pointer into byte stream.
+ * @param[in, out] l Remaining input payload length.
+ * @return Retrieved integer value, unsigned.
+ */
+static inline uint8_t read_u8_inc_len(const uint8_t **p, size_t *l)
+{
+       uint8_t v;
+
+       if (!p || !*p)
+               return 0;
+       if (l && *l < sizeof(v)) {
+               *l = 0;
+               return 0;
+       }
+       v = read_u8(*p);
+       *p += sizeof(v);
+       if (l)
+               *l -= sizeof(v);
+
+       return v;
+}
+
 /**
  * Read signed 8bit integer from raw memory, increment read position.
  * @param[in, out] p Pointer into byte stream.
@@ -666,6 +690,30 @@ static inline uint16_t read_u16le_inc(const uint8_t **p)
        return v;
 }
 
+/**
+ * Read unsigned 16bit integer (LE format), check length, increment position.
+ * @param[in, out] p Pointer into byte stream.
+ * @param[in, out] l Remaining input payload length.
+ * @return Retrieved integer value, unsigned.
+ */
+static inline uint16_t read_u16le_inc_len(const uint8_t **p, size_t *l)
+{
+       uint16_t v;
+
+       if (!p || !*p)
+               return 0;
+       if (l && *l < sizeof(v)) {
+               *l = 0;
+               return 0;
+       }
+       v = read_u16le(*p);
+       *p += sizeof(v);
+       if (l)
+               *l -= sizeof(v);
+
+       return v;
+}
+
 /**
  * Read signed 16bit integer from raw memory (big endian format), increment read position.
  * @param[in, out] p Pointer into byte stream.