Import of the watch repository from Pebble

src/fw/console/cobs.h

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+/*
+ * Copyright 2024 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+//! An implementation of Consistent Overhead Byte Stuffing
+//!
+//! http://conferences.sigcomm.org/sigcomm/1997/papers/p062.pdf
+//! http://en.wikipedia.org/wiki/Consistent_Overhead_Byte_Stuffing
+
+//! Evaluates to the offset required when encoding in-place
+#define COBS_OVERHEAD(n) (((n) + 253) / 254)
+//! Evaluates to the maximum buffer size required to hold n bytes of data
+//! after COBS encoding.
+#define MAX_SIZE_AFTER_COBS_ENCODING(n) ((n) + COBS_OVERHEAD(n))
+
+typedef struct CobsDecodeContext {
+  char *output;
+  size_t output_length;
+  size_t decoded_length;
+  uint8_t payload_remaining;
+  bool block_is_terminated;
+} CobsDecodeContext;
+
+//! Initialize the COBS decoding context.
+void cobs_streaming_decode_start(CobsDecodeContext * restrict ctx,
+                                 void * restrict output_buffer,
+                                 size_t length);
+
+//! Decode a byte in the COBS stream.
+//!
+//! @return false if decoding has failed.
+bool cobs_streaming_decode(CobsDecodeContext * restrict ctx, char in);
+
+//! Complete a COBS stream.
+//!
+//! @return length of decoded stream, or SIZE_MAX if decoding has failed.
+size_t cobs_streaming_decode_finish(CobsDecodeContext * restrict ctx);
+
+//! COBS-encode a buffer out to another buffer.
+//!
+//! @param [out] dst destination buffer. The buffer must be at least
+//!                 MAX_SIZE_AFTER_COBS_ENCODING(length) bytes long.
+//! @param [in] src source buffer
+//! @param      length length of src
+size_t cobs_encode(void * restrict dst, const void * restrict src,
+                   size_t length);