From fff138400cc21c07e4431caa7cb2591f16148643 Mon Sep 17 00:00:00 2001
From: Michael Zimmermann <michael.zimmermann@grandcentrix.net>
Date: Wed, 6 Nov 2024 13:16:54 +0100
Subject: [PATCH] stream: support decoding multiple bytes at once

---
 include/cobs/stream.h | 21 +++++++++++++++++++--
 stream.c              | 36 ++++++++++++++++++++++++++++++++++--
 testutils/common.c    |  4 ++--
 3 files changed, 55 insertions(+), 6 deletions(-)

diff --git a/include/cobs/stream.h b/include/cobs/stream.h
index e4cad68..26369be 100644
--- a/include/cobs/stream.h
+++ b/include/cobs/stream.h
@@ -129,8 +129,25 @@ struct cobs_encode {
  * A frame is only fully received and decoded when the mentioned zero byte was
  * received and the decoder is in the finished state.
  */
-enum cobs_decode_result cobs_decode_stream(struct cobs_decode *decode, uint8_t input_byte,
-					   uint8_t *output_byte, bool *output_available);
+enum cobs_decode_result cobs_decode_stream_single(struct cobs_decode *decode, uint8_t input_byte,
+						  uint8_t *output_byte, bool *output_available);
+
+/**
+ * Pass multiple bytes to the decoder.
+ *
+ * This calls #cobs_decode_stream_single in a loop, but it's more efficient
+ * thanks to inlining. This function will stop the loop if:
+ * - The current frame is complete.
+ * - All input bytes where consumed.
+ * - We need to write to the output buffer but there is no space left.
+ *
+ * That means, you can't expect this function to consume all input bytes. You
+ * have to possibly reset the decoder or allocate more data and call this
+ * function again with the rest of the data.
+ */
+enum cobs_decode_result cobs_decode_stream(struct cobs_decode *decode, const uint8_t *input,
+					   size_t input_size, uint8_t *output, size_t output_size,
+					   size_t *num_read, size_t *num_written);
 
 /**
  * Reset decoder.
diff --git a/stream.c b/stream.c
index 3bc66f2..4146081 100644
--- a/stream.c
+++ b/stream.c
@@ -81,8 +81,10 @@ static int cursor_find_zero(struct cobs_buf_cursor *cursor, size_t *num_processe
 	return -ENOENT;
 }
 
-enum cobs_decode_result cobs_decode_stream(struct cobs_decode *decode, uint8_t input_byte,
-					   uint8_t *output_byte, bool *output_available)
+/* NOTE: It's important to inline this, to make cobs_decode_stream faster. */
+ALWAYS_INLINE
+enum cobs_decode_result cobs_decode_stream_single(struct cobs_decode *decode, uint8_t input_byte,
+						  uint8_t *output_byte, bool *output_available)
 {
 	*output_available = false;
 
@@ -131,6 +133,36 @@ enum cobs_decode_result cobs_decode_stream(struct cobs_decode *decode, uint8_t i
 	}
 }
 
+enum cobs_decode_result cobs_decode_stream(struct cobs_decode *decode, const uint8_t *input,
+					   size_t input_size, uint8_t *output, size_t output_size,
+					   size_t *num_read, size_t *num_written)
+{
+	*num_read = 0;
+	*num_written = 0;
+
+	while (input_size > 0 && (output_size > 0 || input[0] == 0)) {
+		bool output_available = false;
+		enum cobs_decode_result result =
+			cobs_decode_stream_single(decode, input[0], output, &output_available);
+
+		*num_read += 1;
+		input++;
+		input_size -= 1;
+
+		if (output_available) {
+			*num_written += 1;
+			output++;
+			output_size -= 1;
+		}
+
+		if (result != COBS_DECODE_RESULT_CONSUMED) {
+			return result;
+		}
+	}
+
+	return COBS_DECODE_RESULT_CONSUMED;
+}
+
 void cobs_encode_stream_init(struct cobs_encode *encode, struct net_buf *buf)
 {
 	*encode = (struct cobs_encode){
diff --git a/testutils/common.c b/testutils/common.c
index 2b97d5e..787a5f5 100644
--- a/testutils/common.c
+++ b/testutils/common.c
@@ -66,8 +66,8 @@ int cobs_decode_stream_simple(const uint8_t *const input, const size_t input_len
 			 output_length);
 
 		bool available = false;
-		const enum cobs_decode_result res =
-			cobs_decode_stream(&decode, input[i], &output[output_length], &available);
+		const enum cobs_decode_result res = cobs_decode_stream_single(
+			&decode, input[i], &output[output_length], &available);
 
 		if (available) {
 			output_length += 1;