microtar

A lightweight tar library written in ANSI C

Basic Usage

The library consists of microtar.c and microtar.h. These two files can be dropped into an existing project and compiled along with it.

On POSIX-compliant systems (MacOS/BSD/Linux), an implementation using mmap can be used via microtar-mmap.c and microtar-mmap.h (you still need to include microtar.c and microtar.h). This can be faster for reads, as it greatly reduces the amount of copying.

Reading

mtar_t tar;
mtar_header_t h;
char *p;

/* Open archive for reading */
mtar_open(&tar, "test.tar", "r");

/* Print all file names and sizes */
while ( (mtar_read_header(&tar, &h)) != MTAR_ENULLRECORD ) {
  printf("%s (%d bytes)\n", h.name, h.size);
  mtar_next(&tar);
}

/* Load and print contents of file "test.txt" */
mtar_find(&tar, "test.txt", &h);
p = calloc(1, h.size + 1);
mtar_read_data(&tar, p, h.size);
printf("%s", p);
free(p);

/* Close archive */
mtar_close(&tar);

or, using the mmap-based implementation:

mtar_t tar;
const char *str;
mtar_header_t h;

/* Open the file and map its contents */
mtar_open_mapped(&tar, "test.tar");

/* Print all file names and sizes */
while ( (mtar_read_header(&tar, &h)) != MTAR_ENULLRECORD ) {
  const char *data;
  printf("%s (%d bytes)\n", h.name, h.size);
  /* Get file pointer and bump to next header */
  mtar_get_pointer(&tar, (const void**) &data);
}

/* Get mapped pointer to "test.txt" */
mtar_get_mapped(&tar, "test.txt", &str);
/* Directly print contents */
printf("%s", str);
mtar_close(&tar);

Writing

mtar_t tar;
const char *str1 = "Hello world";
const char *str2 = "Goodbye world";

/* Open archive for writing */
mtar_open(&tar, "test.tar", "w");

/* Write strings to files `test1.txt` and `test2.txt` */
mtar_write_file_header(&tar, "test1.txt", strlen(str1));
mtar_write_data(&tar, str1, strlen(str1));
mtar_write_file_header(&tar, "test2.txt", strlen(str2));
mtar_write_data(&tar, str2, strlen(str2));

/* Finalize -- this needs to be the last thing done before closing */
mtar_finalize(&tar);

/* Close archive */
mtar_close(&tar);

Writing to memory

mtar_t tar;
mtar_mem_stream_t mem;
char buffer[4096];
const char *str1 = "Hello world";
const char *str2 = "Goodbye world";

/* Initialize memory stream object */
mtar_init_mem_stream(&mem, buffer, sizeof(buffer));
/* Open archive for writing */
mtar_open_mem(&tar, &mem);

/* Write strings to files `test1.txt` and `test2.txt` */
mtar_write_file_header(&tar, "test1.txt", strlen(str1));
mtar_write_data(&tar, str1, strlen(str1));
mtar_write_file_header(&tar, "test2.txt", strlen(str2));
mtar_write_data(&tar, str2, strlen(str2));

/* Finalize -- this needs to be the last thing done before closing */
mtar_finalize(&tar);

/* Close archive */
mtar_close(&tar);

/* Now you can process the buffer */
size_t data_len = mem.pos;
FILE *fp = fopen("output.tar", "wb");
fwrite(buffer, data_len, 1, fp);
fclose(fp);

Error handling

All functions which return an int will return MTAR_ESUCCESS if the operation is successful. If an error occurs an error value less-than-zero will be returned; this value can be passed to the function mtar_strerror() to get its corresponding error string.

Wrapping a stream

If you want to read or write from something other than a file, the mtar_t struct can be manually initialized with your own callback functions and a stream pointer.

All callback functions are passed a pointer to the mtar_t struct as their first argument. They should return MTAR_ESUCCESS if the operation succeeds without an error, or an integer below zero if an error occurs.

After the stream field has been set, all required callbacks have been set and all unused fields have been zeroset the mtar_t struct can be safely used with the microtar functions. mtar_open should not be called if the mtar_t struct was initialized manually.

Reading

The following callbacks should be set for reading an archive from a stream:

Name	Arguments	Description
read	mtar_t *tar, void *data, unsigned size	Read data from the stream
seek	mtar_t *tar, unsigned pos	Set the position indicator
close	mtar_t *tar	Close the stream

Writing

The following callbacks should be set for writing an archive to a stream:

Name	Arguments	Description
write	mtar_t *tar, const void *data, unsigned size	Write data to the stream

License

This library is free software; you can redistribute it and/or modify it under the terms of the MIT license. See LICENSE for details.