From e724e21f9e0b6b67c5f436c3919a0fe2e1a5c4b1 Mon Sep 17 00:00:00 2001
From: Michael Krayer <michael.krayer@posteo.de>
Date: Tue, 16 Feb 2021 17:35:07 +0100
Subject: [PATCH] initial commit

---
 README.md          |  10 ++++
 build              |   2 +
 src/partialdump.cc | 119 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 131 insertions(+)
 create mode 100644 README.md
 create mode 100755 build
 create mode 100644 src/partialdump.cc

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..44f6266
--- /dev/null
+++ b/README.md
@@ -0,0 +1,10 @@
+patialdump
+---
+Extracts a given number of bytes from a file at a given offset.
+
+Usage:
+```bash
+partialdump [-j nbytes] [-N nbytes] file
+ -j nbytes           number of bytes to skip from the beginning of file (default: 0)
+ -N nbytes           number of bytes to read (default: -1, until EOF)
+```
diff --git a/build b/build
new file mode 100755
index 0000000..a48da31
--- /dev/null
+++ b/build
@@ -0,0 +1,2 @@
+#!/bin/bash
+g++ -o partialdump src/partialdump.cc
diff --git a/src/partialdump.cc b/src/partialdump.cc
new file mode 100644
index 0000000..7f9917c
--- /dev/null
+++ b/src/partialdump.cc
@@ -0,0 +1,119 @@
+#include <iostream>
+#include <algorithm>
+#include <fstream>
+#include <string>
+using namespace std;
+
+const long IO_BUFFSIZE=(long)1024*1024;  // read 1 KiB at a time
+
+/*
+ * Command line parsing routines
+ * https://stackoverflow.com/questions/865668/parsing-command-line-arguments-in-c
+ */
+char* getCmdOption(char** begin, char** end, const std::string& option){
+  char ** itr = std::find(begin, end, option);
+  if(itr!=end && ++itr!=end)
+  {
+    return *itr;
+  }
+  return 0;
+}
+
+bool cmdOptionExists(char** begin, char** end, const std::string& option){
+  return std::find(begin,end,option)!=end;
+}
+
+void print_usage(char* argv[]){
+  cerr << "Usage: " << argv[0] << " [-j nbytes] [-N nbytes] file" << endl;
+  cerr << "Extracts a given number of bytes from a file at a given offset." << endl;
+  cerr << " -j nbytes           number of bytes to skip from the beginning of file (default: 0)" << endl;
+  cerr << " -N nbytes           number of bytes to read (default: -1, until EOF)" << endl;
+  return;
+}
+
+/*
+ * Main program
+ */
+
+int main(int argc,char *argv[]){
+  int iblock;
+  char* buffer = new char[IO_BUFFSIZE];
+  long filesize, iosize;
+
+  if(argc==1){
+    print_usage(argv);
+    return 0;
+  }
+
+  // We expect the following command line arguments
+  // -h            print help
+  // -j nbytes     skip the first nbytes
+  // -N nbytes     read nbytes
+  // 1 positional argument: filename
+  int argc_opt = argc-1;
+  if(cmdOptionExists(argv,argv+argc,"-h")){
+    print_usage(argv);
+    return 0;
+  }
+  char* arg_jump = getCmdOption(argv,argv+argc_opt,"-j");
+  char* arg_size = getCmdOption(argv,argv+argc_opt,"-N");
+  long ijump=0, isize=-1;
+  if(arg_jump){
+    try{
+      ijump = stol(arg_jump);
+    }
+    catch(const invalid_argument& ia){
+      cerr << "Invalid argument to " << ia.what() << ": " << arg_jump << endl;
+      return 2;
+    }
+  }
+  if(arg_size){
+    try{
+      isize = stol(arg_size);
+    }
+    catch(const invalid_argument& ia){
+      cerr << "Invalid argument to " << ia.what() << ": " << arg_size << endl;
+      return 2;
+    }
+  }
+  string filename=argv[argc-1];
+
+  ifstream file(filename,ios::in|ios::binary);
+  if(!file){
+    cerr << "Cannot open file: " << filename << endl;
+    return 3;
+  }
+
+  // If we are supposed to read until the end of file, determine
+  // the file size.
+  if(isize==-1){
+    file.seekg(0,ios::end);
+    filesize = (long)file.tellg();
+    isize = filesize-ijump;
+  }    
+
+  // Seek to beginning of partition to read
+  file.seekg(ijump,ios::beg);
+
+  // Read block by block
+  iblock=0;
+  bool trunc = false;
+  while(!trunc){
+    trunc = (isize-iblock*IO_BUFFSIZE)<IO_BUFFSIZE;
+    if(trunc)
+    	iosize = isize-iblock*IO_BUFFSIZE;
+    else
+    	iosize = IO_BUFFSIZE;
+    file.read(buffer,iosize);
+    if(file.fail()){
+      cerr << "I/O Error: " << filename << " @ " << file.tellg() << endl;
+	    break;
+    }
+    fwrite(buffer,1,iosize,stdout);
+    iblock++;
+  }
+  fflush(stdout);
+  file.close();
+  delete[] buffer;	
+  return 0;
+}