Tar handler

.vscode/settings.json

@@ -0,0 +1,16 @@
+{
+    "files.associations": {
+        "array": "cpp",
+        "deque": "cpp",
+        "string": "cpp",
+        "unordered_map": "cpp",
+        "vector": "cpp",
+        "iterator": "cpp",
+        "memory_resource": "cpp",
+        "optional": "cpp",
+        "string_view": "cpp",
+        "initializer_list": "cpp",
+        "type_traits": "cpp",
+        "utility": "cpp"
+    }
+}

Makefile

@@ -9,7 +9,7 @@ CXXFLAGS += -pedantic
 CXXFLAGS += -pedantic-errors
 CXXFLAGS += -ffunction-sections -fdata-sections
 CXXFLAGS += -fno-implicit-inline-templates
-CXXFLAGS += -Iinc
+CXXFLAGS += -Isrc
 
 
 LD_LIBS := -lc -lgcc -lpthread

inc/Buffer.h

@@ -0,0 +1,43 @@
+#ifndef __INC_BUFFER_H__
+#define __INC_BUFFER_H__
+
+template<typename T, std::size_t S>
+class Buffer
+    : std::array<T, S>
+{
+    typedef std::array<T,S> ArrayT;
+    typedef typename ArrayT::reference reference;
+    typedef typename ArrayT::const_reference const_reference;
+    typedef typename ArrayT::size_type size_type;
+    typedef typename ArrayT::value_type value_type;
+    typedef typename ArrayT::iterator iterator;
+    typedef typename ArrayT::const_iterator const_iterator;
+
+public:
+    Buffer() : length(0) {}
+
+    constexpr reference front() noexcept { return ArrayT::front(); }
+    constexpr reference back() noexcept { return *(ArrayT::begin() + length); }
+    constexpr T * data() noexcept { return ArrayT::data(); }
+
+    constexpr iterator begin() noexcept { return ArrayT::begin();}
+    constexpr const_iterator cbegin() const noexcept { return ArrayT::cbegin(); }
+    constexpr iterator end() noexcept { return (ArrayT::begin() + length); }
+    constexpr const_iterator cend() const noexcept { return (ArrayT::cbegin() + length); }
+
+    constexpr size_type size() const noexcept {return length;}
+    constexpr size_type max_size() const noexcept {return ArrayT::max_size();}
+
+    constexpr void push_back(const_reference v) noexcept { *(this->begin() + length++) = v; };
+    constexpr void push_back(value_type&&v) noexcept { *(this->begin() + length++) = std::move(v); }
+
+    inline void fill(const_reference &v){ ArrayT::fill(v); length = ArrayT::max_size(); }
+    inline void fill(const_iterator b, const_iterator e) { std::copy(b, e, ArrayT::begin()); length = e - b; }
+    inline void fill_n(const_iterator b, size_type s) { std::copy(b, b + s, ArrayT::begin()); length = s; }
+    constexpr void clear() noexcept { this->length = 0; }
+
+private:
+    size_type length;
+};
+
+#endif

inc/ringbuffer.h

@@ -1,24 +0,0 @@
-#ifndef __INC_RINGBUFFER_H__
-#define __INC_RINGBUFFER_H__
-
-#include <array>
-
-class ringbuffer
-{
-public:
-    ringbuffer();
-
-    int write(char);
-    int read(char&);
-
-private:
-    enum {
-        MAX_BUFFER_SIZE = 2
-    };
-
-    std::array<char, MAX_BUFFER_SIZE> buffer;
-    std::array<char, MAX_BUFFER_SIZE>::iterator head;
-    std::array<char, MAX_BUFFER_SIZE>::iterator tail;
-};
-
-#endif

src/TarHandler.cc

@@ -0,0 +1,111 @@
+#include <cstring>
+#include <iostream>
+#include "TarHandler.h"
+
+#define ASCII_TO_NUMBER(num) ((num) - 48) //Converts an ascii digit to the corresponding number
+
+TarHandler::TarHandler()
+    : idle(true)
+    , tar_index(0)
+    , next_tar_header(0)
+    , file_size(0)
+    , read_byte_count(0)
+    , processed_tar_blocks(0)
+    , file_processed_bytes(0)
+{
+}
+
+void TarHandler::tcp_in_handler(char* data, std::size_t size)
+{
+    if(this->idle) {
+        this->idle = false;
+        this->tar_index = 0;
+        this->file_size = 0;
+        this->next_tar_header;
+        this->read_byte_count = 0;
+        this->file_size = 0;
+    }
+
+    // process incoming buffer
+    for(std::size_t i = 0; i < size; i++) {
+        this->tar_block[this->tar_index] = data[i];
+        this->read_byte_count++;
+        if(this->tar_index++ == TAR_BLOCK_SIZE - 1) {
+            this->tar_block_handler();
+            this->tar_index = 0;
+        }
+    }
+}
+
+bool TarHandler::tar_block_handler()
+{
+    this->processed_tar_blocks++;
+    if(this->next_tar_header == (this->read_byte_count) - TAR_BLOCK_SIZE) {
+        // Tar header detected
+        struct tar_file_header tar_header;
+        memcpy(&tar_header, this->tar_block, TAR_BLOCK_SIZE);
+        if(!check_checksum(&tar_header)) {
+            fprintf(stderr, "checksum missmatch\r\n");
+            return false;
+        }
+        this->file_size = decode_tar_octal(tar_header.file_size, sizeof(tar_header.file_size));
+        this->file_processed_bytes = 0;
+        printf("%s - size: %lu\r\n", tar_header.filename, file_size);
+        this->next_tar_header = (file_size / TAR_BLOCK_SIZE + 1) * TAR_BLOCK_SIZE + this->processed_tar_blocks * TAR_BLOCK_SIZE;
+    } else {
+        std::size_t i = 0;
+        if((this->file_size - this->file_processed_bytes) >= TAR_BLOCK_SIZE) {
+            for(i = 0; i < TAR_BLOCK_SIZE; i++) {
+                printf("%c", this->tar_block[i]);
+            }
+        }
+        else {
+            for(i = 0; i < (this->file_size - this->file_processed_bytes); i++) {
+                printf("%c", this->tar_block[i]);
+            }
+        }
+        this->file_processed_bytes += i;
+        printf("processed bytes: %lu\r\n", this->file_processed_bytes);
+    }
+    return true;
+}
+
+uint64_t TarHandler::decode_tar_octal(char* data, std::size_t size)
+{
+    unsigned char *current_ptr = (unsigned char *) data + size;
+    uint64_t sum = 0;
+    uint64_t current_multiplier = 1;
+
+    unsigned char* check_ptr = current_ptr; //This is used to check where the last NUL/space char is
+    for(; check_ptr >= (unsigned char *) data; --check_ptr) {
+        if((*check_ptr) == 0 || (*check_ptr) == ' ') {
+            current_ptr = check_ptr - 1;
+        }
+    }
+    for(; current_ptr >= (unsigned char *) data; --current_ptr) {
+        sum += ASCII_TO_NUMBER(*current_ptr) * current_multiplier;
+        current_multiplier *= 8;
+    }
+    return sum;
+}
+
+bool TarHandler::check_checksum(struct tar_file_header *tar_header)
+{
+    char original_checksum[8];
+    memcpy(original_checksum, tar_header->checksum, 8);
+    memset(tar_header->checksum, ' ', 8);
+
+    int64_t unsigned_sum = 0;
+    int64_t signed_sum = 0;
+    unsigned char *uc_tar = (unsigned char *)tar_header;
+    signed char *sc_tar = (signed char *)tar_header;
+    for(int i = 0; i < TAR_BLOCK_SIZE; i++) {
+        unsigned_sum += uc_tar[i];
+        signed_sum += sc_tar[i];
+    }
+    //Copy back the checksum
+    memcpy(tar_header->checksum, original_checksum, 8);
+    //Decode the original checksum
+    uint64_t reference_checksum = decode_tar_octal(original_checksum, sizeof(original_checksum));
+    return (reference_checksum == unsigned_sum || reference_checksum == signed_sum);
+}

src/TarHandler.h

@@ -0,0 +1,53 @@
+#pragma once
+
+#include <cstdint>
+
+class TarHandler
+{
+public:
+    struct tar_file_header {
+        char filename[100];
+        char mode[8];
+        char uid[8];
+        char gid[8];
+        char file_size[12];
+        char last_modification[12];
+        char checksum[8];
+        char type_flag;
+        char linked_file_name[100];
+        char ustar_indicator[6];
+        char ustar_version[2];
+        char owner_user_name[32];
+        char owner_group_name[32];
+        char device_major_number[8];
+        char device_minor_number[8];
+        char filename_prefix[155];
+        char padding[12];
+    };
+
+public:
+    TarHandler();
+
+    void tcp_in_handler(char* data, std::size_t size);
+
+private:
+    uint64_t decode_tar_octal(char* data, std::size_t size);
+
+    bool check_checksum(struct tar_file_header *tar_header);
+
+    bool tar_block_handler();
+
+    enum {
+        TAR_BLOCK_SIZE = 512
+    };
+
+    char tar_block[TAR_BLOCK_SIZE];
+    std::size_t tar_index;
+    std::size_t next_tar_header;
+    std::size_t file_size;
+    std::size_t read_byte_count;
+    std::size_t processed_tar_blocks;
+    std::size_t file_processed_bytes;
+
+    bool idle;
+};

src/main.cc

@@ -1,23 +1,38 @@
-#include <iostream>
+#include <stdio.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include "TarHandler.h"
 
-#include "ringbuffer.h"
 
-ringbuffer buf;
+#define TAR_FILE "test.tar"
 
-int main(void) {
-    buf.write('a');
-    buf.write('b');
-    buf.write('c');
+#define BLOCK_SIZE 1522
 
-    char c;
-    if(buf.read(c)) {
-        std::cout << c;
-    }
-    if(buf.read(c)) {
-        std::cout << c;
-    }
-    if(buf.read(c)) {
-        std::cout << c;
+
+int main(void)
+{
+    int fd = open(TAR_FILE, O_RDONLY);
+    if(fd < 0) {
+        fprintf(stderr, "Unable to open %s\r\n", TAR_FILE);
+        return fd;
     }
+
+    int res;
+    char block[BLOCK_SIZE];
+    size_t processed_blocks = 0;
+    TarHandler tar_handler;
+    do {
+        res = read(fd, block, sizeof(block));
+        tar_handler.tcp_in_handler(block, res);
+        processed_blocks++;
+    } while(res > 0);
+    printf("processed blocks: %lu\r\n", processed_blocks);
+
+    close(fd);
+
     return 0;
 }

src/ringbuffer.cc

@@ -1,39 +0,0 @@
-#include "ringbuffer.h"
-
-ringbuffer::ringbuffer()
-{
-    head = buffer.begin();
-    tail = buffer.begin();
-}
-
-int ringbuffer::write(char c)
-{
-    if(head - tail == MAX_BUFFER_SIZE) {
-        return 0;
-    }
-
-    if(head == buffer.end()) {
-        head = buffer.begin();
-    }
-
-    *head = c;
-    head++;
-
-    return 1;
-}
-
-int ringbuffer::read(char& c)
-{
-    if(head - tail == 0) {
-        return 0;
-    }
-
-    if(tail == buffer.end()) {
-        tail = buffer.begin();
-    }
-
-    c = *tail;
-    tail++;
-
-    return 1;
-}