net: buf: add function to match buffer's content with a given data

This commit adds a new function the net_buf's API that allow an user
to match the net_buf's content with a data without copying it to a
temporary buffer.

Signed-off-by: Konrad Derda <konrad.derda@nordicsemi.no>

include/zephyr/net/buf.h

@@ -2414,6 +2414,22 @@ size_t net_buf_append_bytes(struct net_buf *buf, size_t len,
 			    const void *value, k_timeout_t timeout,
 			    net_buf_allocator_cb allocate_cb, void *user_data);
 
+/**
+ * @brief Match data with a net_buf's content
+ *
+ * @details Compare data with a content of a net_buf. Provide information about
+ * the number of bytes matching between both. If needed, traverse
+ * through multiple buffer fragments.
+ *
+ * @param buf Network buffer
+ * @param offset Starting offset to compare from
+ * @param data Data buffer for comparison
+ * @param len Number of bytes to compare
+ *
+ * @return The number of bytes compared before the first difference.
+ */
+size_t net_buf_data_match(const struct net_buf *buf, size_t offset, const void *data, size_t len);
+
 /**
  * @brief Skip N number of bytes in a net_buf
  *

subsys/net/buf.c

@@ -694,3 +694,39 @@ size_t net_buf_append_bytes(struct net_buf *buf, size_t len,
 	/* Unreachable */
 	return 0;
 }
+
+size_t net_buf_data_match(const struct net_buf *buf, size_t offset, const void *data, size_t len)
+{
+	const uint8_t *dptr = data;
+	const uint8_t *bptr;
+	size_t compared = 0;
+	size_t to_compare;
+
+	if (!buf || !data) {
+		return compared;
+	}
+
+	/* find the right fragment to start comparison */
+	while (buf && offset >= buf->len) {
+		offset -= buf->len;
+		buf = buf->frags;
+	}
+
+	while (buf && len > 0) {
+		bptr = buf->data + offset;
+		to_compare = MIN(len, buf->len - offset);
+
+		for (size_t i = 0; i < to_compare; ++i) {
+			if (dptr[compared] != bptr[i]) {
+				return compared;
+			}
+			compared++;
+		}
+
+		len -= to_compare;
+		buf = buf->frags;
+		offset = 0;
+	}
+
+	return compared;
+}