ESP8266lib/data/ChunkBuffer.h

#ifndef CHUNK_BUFFER_H
#define CHUNK_BUFFER_H

#include "../Debug.h"

/**
 * linked list of several chunks that are either managed or unmanaged
 */
class ChunkBuffer {

public:

	/** data of certain length */
	struct Data {
		const uint8_t* ptr;
		const uint16_t size;
		Data(const uint8_t* ptr, const uint16_t size) : ptr(ptr), size(size) {;}
	};

	/** one data chunk within the buffer */
	struct Chunk {

		bool managed;
		uint8_t* base;	// do not modify this one!

		uint8_t* ptr;
		uint16_t len;

		Chunk* next = nullptr;

		~Chunk() {
			debugMod("ChunkBuffer::Chunk", "dtor");
			if (managed) {
				free(base);
				base = nullptr;
			}
		}

		/** allocate a new managed chunk */
		static Chunk* alloc(const uint16_t size) {
			debugMod1("ChunkBuffer::Chunk", "alloc(%d)", size);
			Chunk* chunk = new Chunk();
			chunk->base = (uint8_t*)malloc(size);
			chunk->ptr = chunk->base;
			chunk->len = size;
			chunk->managed = true;
			return chunk;
		}

		/** allocate a new wrapped chunk */
		static Chunk* wrap(uint8_t* ptr, const uint16_t size) {
			debugMod1("ChunkBuffer::Chunk", "alloc(%d)", size);
			Chunk* chunk = new Chunk();
			chunk->base = ptr;
			chunk->ptr = chunk->base;
			chunk->len = size;
			chunk->managed = false;
			return chunk;
		}

		/** consume max(!) size bytes from this chunk */
		Data consume(const uint16_t size) {
			debugMod1("ChunkBuffer::Chunk", "consume(%d)", size);
			const uint16_t useBytes = min(size, this->len);
			Data res(ptr, useBytes);
			ptr += useBytes;	// adjust pointer for next consume() call
			len -= useBytes;	// adjuste len for next consume() call;
			return res;
		}

		/** consume one byte, if available */
		int consumeByte() {
			if (len) {
				uint8_t res = *ptr;
				ptr += 1;
				len -= 1;
				return res;
			}
			return -1;
		}

		bool empty() const {
			return len == 0;
		}

	private:
		Chunk() {;}

	};

	static uint16_t min(const uint16_t a, const uint16_t b) {
		return (a<b) ? (a) : (b);
	}

private:

	Chunk* root;

public:

	ChunkBuffer() : root(nullptr) {
		debugMod("ChunkBuffer", "ctor()");
	}

	/** get a block of max(!) size bytes from the buffer. might return less */
	Data get(const uint16_t size) {

		cleanup();

		// something available?
		if (!root) {
			return Data(0,0);
		} else {
			return root->consume(size);
		}

	}

	int getByte() {

		cleanup();

		if (root && !root->empty()) {
			return root->consumeByte();
		}
		return -1;
	}

	/** append the given chunk to the buffer */
	void append(Chunk* c) {

		debugMod("ChunkBuffer", "append()");

		if (!root) {

			// new chunk is the root
			root = c;

		} else {

			// append new chunk at the end
			Chunk* x = root;
			while (x->next) {x = x->next;}
			x->next = c;

		}

	}

	/** allocate a new managed chunk of the given size */
	Chunk* alloc(const uint16_t size) {
		debugMod1("ChunkBuffer", "alloc(%d)", size);
		return Chunk::alloc(size);
	}

	/** get a new unmanaged wrapper chunk for the given data */
	Chunk* wrap(const uint8_t* data, const uint16_t size) {
		debugMod1("ChunkBuffer", "wrap(%d)", size);
		return Chunk::wrap((uint8_t*) data, size);
	}

	/** number of available bytes */
	uint32_t available() const {
		uint32_t s = 0;
		Chunk* c = root;
		while(c) {
			s += c->len;
			c = c->next;
		}
		return s;
	}

	/** nothing available? */
	bool empty() const {
		return (!root || root->len == 0);
	}

private:

	void cleanup() {

		// current chunk empty? -> cleanup and proceed with next chunk
		if (root && root->empty()) {
			Chunk* old = root;
			root = old->next;			// next chunk is the chunk (if any) after the current (empty) one
			delete old;					// delete the empty chunk and free the data
		}

	}

};

#endif // CHUNK_BUFFER_H