From d7dcd97c75113b0723cb3c76a018c19374054a19 Mon Sep 17 00:00:00 2001
From: C-3PO <c-3po@jedipedia.net>
Date: Tue, 24 Jul 2018 17:07:47 +0200
Subject: [PATCH] =?UTF-8?q?=F0=9F=9A=A7=20Implement=20file=20reader?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 src/fileReader.c    | 65 +++++++++++++++++++++++++++++++++++++--------
 src/fileReader.h    |  4 +--
 src/fileUtilities.h | 46 ++++++++++++++++++++++++++++++++
 src/main.c          |  5 ++--
 4 files changed, 105 insertions(+), 15 deletions(-)
 create mode 100644 src/fileUtilities.h

diff --git a/src/fileReader.c b/src/fileReader.c
index e6948ce..2cd5ad4 100644
--- a/src/fileReader.c
+++ b/src/fileReader.c
@@ -4,23 +4,66 @@
 #include <errno.h>
 //for strerror()
 #include <string.h>
+//for malloc
+#include <stdlib.h>
 
 #include "fileReader.h"
+#include "fileUtilities.h"
 
-void initFileReader(char path[], unsigned long offset, unsigned long length) {
-  //Opens the given file at the given address
-  //Returns a function that will read into memory and return that memory.
+//minimum of two integers
+#define min(a,b) \
+  ({ __typeof__ (a) _a = (a); \
+    __typeof__ (b) _b = (b); \
+  _a < _b ? _a : _b; })
 
-  FILE *fileFrom = NULL;
-  char* fileName = path;
 
-  fileFrom = fopen(fileName, "r");
-  if (fileFrom == NULL) {
-    fprintf(stderr, "Could not open file %s for reading: %s\n", fileName, strerror(errno));
-    //error();
+//Opens the given file at the given offset
+void initFileReader(char path[], unsigned long offset) {
+  file.name = path;
+
+  file.filePointer = fopen(file.name, "r");
+  if (file.filePointer == NULL) {
+    fprintf(stderr, "Could not open file %s for reading: %s\n", file.name, strerror(errno));
+    exit(1);
   }
+
+  //get file size
+  fseek(file.filePointer, 0L, SEEK_END);
+  file.size = ftell(file.filePointer);
+
+  //seek to offset
+  if (offset != 0UL) {
+    fseek(file.filePointer, offset, SEEK_SET);
+  } else {
+    rewind(file.filePointer);
+  }
+  file.offset = offset;
 }
 
-unsigned char* readBytes(unsigned long numBytes) {
-  //TODO
+
+//Reads the given amount of bytes from the file and returns them. Automatically opens next file if EOF is reached.
+char* getBytes(unsigned long numBytes) {
+  char* output = malloc(numBytes);
+  if (output == NULL) {
+    fprintf(stderr, "Could not allocate %lu bytes.\n", numBytes);
+    exit(1);
+  }
+  char* bufferPosition = output;
+  unsigned long remainingBytes = numBytes;
+
+  //As long as we still need to read bytes
+  while (remainingBytes > 0) {
+    //Read as many bytes as we can from the current file
+    const unsigned long availableBytes = min(remainingBytes, file.size - file.offset);
+    readBytesIntoBuffer(bufferPosition, availableBytes);
+    bufferPosition += availableBytes;
+    remainingBytes -= availableBytes;
+
+    //If we've reached end of file, close file and open next file
+    if (file.offset == file.size) {
+      openNextFile();
+    }
+  }
+
+  return output;
 }
diff --git a/src/fileReader.h b/src/fileReader.h
index 687cab1..5db6687 100644
--- a/src/fileReader.h
+++ b/src/fileReader.h
@@ -1,5 +1,5 @@
 #pragma once
 
-void initFileReader(char path[], unsigned long offset, unsigned long length);
+void initFileReader(char path[], unsigned long offset);
 
-unsigned char* readBytes(unsigned long numBytes);
+char* getBytes(unsigned long numBytes);
diff --git a/src/fileUtilities.h b/src/fileUtilities.h
new file mode 100644
index 0000000..01f5b6d
--- /dev/null
+++ b/src/fileUtilities.h
@@ -0,0 +1,46 @@
+#pragma once
+
+#include "fileReader.h"
+
+//A structure to store various information needed when reading from a file.
+struct FILE_INFO {
+  char* name;
+  unsigned long size;
+  FILE* filePointer;
+  unsigned long offset;
+};
+
+struct FILE_INFO file;
+
+
+//Reads the given amount of bytes from the currently open file into the given buffer.
+void readBytesIntoBuffer(char* buffer, long numBytes) {
+  const size_t result = fread(buffer, 1, numBytes, file.filePointer);
+  file.offset += result;
+
+  if (result != numBytes) {
+    fprintf(stderr, "Could not read %lu bytes from file: %s\n", numBytes, strerror(errno));
+    exit(1);
+  }
+}
+
+
+//Closes the currently opened file and opens the next file at its beginning.
+void openNextFile() {
+  const int closeResult = fclose(file.filePointer);
+  if (closeResult != 0) {
+    fprintf(stderr, "Could not close file: %s\n", strerror(errno));
+    exit(1);
+  }
+
+  //Open next file
+  const size_t fileNameLength = strlen(file.name);
+  //We need to transfer carry if necessary (e.g. .z09 to .z10), otherwise just increase last digit
+  if (file.name[fileNameLength - 1] == '9') {
+    file.name[fileNameLength - 2] += 1;
+    file.name[fileNameLength - 1] = 0;
+  } else {
+    file.name[fileNameLength - 1] += 1;
+  }
+  initFileReader(file.name, 0UL);
+}
diff --git a/src/main.c b/src/main.c
index edde11a..dab2ccc 100644
--- a/src/main.c
+++ b/src/main.c
@@ -13,10 +13,11 @@ int main(int argc, unsigned char *argv[]) {
   printf("Hello World!\n");
 
   //Initialise file reader
-  initFileReader("1234", 0UL, 10UL);
+  initFileReader("1234", 0UL);
 
   //Skip header (30 bytes + additional length)
-  readBytes(30UL);
+  char* fileHeader = getBytes(30UL);
+  printf(fileHeader);
 
   //Initialise decryption (pass decryption keys)