microtar: Update to latest upstream commit

This is a major overhaul of the library with some API
changes and ease of use improvements, particularly for
creating new archives.

The updated functionality is intended to support a new
X1000 installer framework.

Change-Id: Icf192bb546831231d49303fbf529ef1c1ce8905c

12 files changed, 1415 insertions, 558 deletions

diff --git a/lib/microtar/.gitignore b/lib/microtar/.gitignore
new file mode 100644
index 0000000000..cccd994a85
--- /dev/null
+++ b/lib/microtar/.gitignore
@@ -0,0 +1,3 @@
+*.o
+*.a
+/mtar
diff --git a/lib/microtar/LICENSE b/lib/microtar/LICENSE
index 7e3bf17ccb..72cf80d63b 100644
--- a/lib/microtar/LICENSE
+++ b/lib/microtar/LICENSE
@@ -1,4 +1,5 @@
 Copyright (c) 2017 rxi
+Copyright (c) 2021 Aidan MacDonald
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of
 this software and associated documentation files (the "Software"), to deal in
diff --git a/lib/microtar/Makefile b/lib/microtar/Makefile
new file mode 100644
index 0000000000..ae2c4f6d6e
--- /dev/null
+++ b/lib/microtar/Makefile
@@ -0,0 +1,25 @@
+CPPFLAGS = -Isrc
+CFLAGS = -std=c99 -Wall -Wextra -O2
+
+MTAR_OBJ = mtar.o
+MTAR_BIN = mtar
+
+MICROTAR_OBJ = src/microtar.o src/microtar-stdio.o
+MICROTAR_LIB = libmicrotar.a
+
+$(MTAR_BIN): $(MTAR_OBJ) $(MICROTAR_LIB)
+        $(CC) $(CFLAGS) $(CPPFLAGS) -o $@ $^
+
+$(MICROTAR_LIB): $(MICROTAR_OBJ)
+        $(AR) cr $@ $^
+
+%.o: %.c
+        $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $@
+
+src/microtar.o: src/microtar.h
+src/microtar-stdio.o: src/microtar.h src/microtar-stdio.h
+mtar.o: src/microtar.h src/microtar-stdio.h
+
+clean:
+        rm -f $(MICROTAR_LIB) $(MICROTAR_OBJ)
+        rm -f $(MTAR_BIN) $(MTAR_OBJ)
diff --git a/lib/microtar/README.md b/lib/microtar/README.md
index 18153caa21..109626cdd4 100644
--- a/lib/microtar/README.md
+++ b/lib/microtar/README.md
@@ -1,128 +1,268 @@
 # microtar
-A lightweight tar library written in ANSI C
 
+A lightweight tar library written in ANSI C.
 
-## Modifications from upstream
+This version is a fork of [rxi's microtar](https://github.com/rxi/microtar)
+with bugfixes and API changes aimed at improving usability, but still keeping
+with the minimal design of the original library.
 
-[Upstream](https://github.com/rxi/microtar) has numerous bugs and gotchas,
-which I fixed in order to improve the overall robustness of the library.
+## License
+
+This library is free software; you can redistribute it and/or modify it under
+the terms of the MIT license. See [LICENSE](LICENSE) for details.
 
-A summary of my changes, in no particular order:
 
-- Fix possible sscanf beyond the bounds of the input buffer
-- Fix possible buffer overruns due to strcpy on untrusted input
-- Fix incorrect octal formatting by sprintf and possible output overrruns
-- Catch read/writes which are too big and handle them gracefully
-- Handle over-long names in `mtar_write_file_header` / `mtar_write_dir_header`
-- Ensure strings in `mtar_header_t` are always null-terminated
-- Save and load group information so we don't lose information
-- Move `mtar_open()` to `microtar-stdio.c` so `microtar.c` can be used in
-  a freestanding environment
-- Allow control of stack usage by moving temporary variables into `mtar_t`,
-  so the caller can decide whether to use the stack or heap
+## Supported format variants
 
-An up-to-date copy of this modified version can be found
-[here](https://github.com/amachronic/microtar).
+No effort has been put into handling every tar format variant. Basically
+what is accepted is the "old-style" format, which appears to work well
+enough to access basic archives created by GNU `tar`.
 
 
-## Modifications for Rockbox
+## Basic usage
 
-Added file `microtar-rockbox.c` implementing `mtar_open()` with native
-Rockbox filesystem API.
+The library consists of two files, `microtar.c` and `microtar.h`, which only
+depend on a tiny part of the standard C library & can be easily incorporated
+into a host project's build system.
 
+The core library does not include any I/O hooks as these are supposed to be
+provided by the host application. If the C library's `fopen` and friends is
+good enough, you can use `microtar-stdio.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.
 
+### Initialization
+
+Initialization is very simple. Everything the library needs is contained in
+the `mtar_t` struct; there is no memory allocation and no global state. It is
+enough to zero-initialize an `mtar_t` object to put it into a "closed" state.
+You can use `mtar_is_open()` to query whether the archive is open or not.
+
+An archive can be opened for reading _or_ writing, but not both. You have to
+specify which access mode you're using when you create the archive.
 
-#### Reading
 ```c
 mtar_t tar;
-mtar_header_t h;
-char *p;
+mtar_init(&tar, MTAR_READ, my_io_ops, my_stream);
+```
 
-/* Open archive for reading */
-mtar_open(&tar, "test.tar", "r");
+Or if using `microtar-stdio.c`:
 
-/* 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);
+```c
+int error = mtar_open(&tar, "file.tar", "rb");
+if(error) {
+    /* do something about it */
 }
+```
 
-/* 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);
+Note that `mtar_init()` is called for you in this case and the access mode is
+deduced from the mode flags.
 
-/* Close archive */
-mtar_close(&tar);
-```
 
-#### Writing
+### Iterating and locating files
+
+If you opened an archive for reading, you'll likely want to iterate over
+all the files. Here's the long way of doing it:
+
 ```c
 mtar_t tar;
-const char *str1 = "Hello world";
-const char *str2 = "Goodbye world";
+int err;
+
+/* Go to the start of the archive... Not necessary if you've
+ * just opened the archive and are already at the beginning.
+ * (And of course you normally want to check the return value.) */
+mtar_rewind(&tar);
 
-/* Open archive for writing */
-mtar_open(&tar, "test.tar", "w");
+/* Iterate over the archive members */
+while((err = mtar_next(&tar)) == MTAR_ESUCCESS) {
+    /* Get a pointer to the current file header. It will
+     * remain valid until you move to another record with
+     * mtar_next() or call mtar_rewind() */
+    const mtar_header_t* header = mtar_get_header(&tar);
 
-/* 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));
+    printf("%s (%d bytes)\n", header->name, header->size);
+}
+
+if(err != MTAR_ENULLRECORD) {
+    /* ENULLRECORD means we hit end of file; any
+     * other return value is an actual error. */
+}
+```
 
-/* Finalize -- this needs to be the last thing done before closing */
-mtar_finalize(&tar);
+There's a useful shortcut for this type of iteration which removes the
+loop boilerplate, replacing it with another kind of boilerplate that may
+be more palatable in some cases.
+
+```c
+/* Will be called for each archive member visited by mtar_foreach().
+ * The member's header is passed in as an argument so you don't need
+ * to fetch it manually with mtar_get_header(). You can freely read
+ * data (if present) and seek around. There is no special cleanup
+ * required and it is not necessary to read to the end of the stream.
+ *
+ * The callback should return zero (= MTAR_SUCCESS) to continue the
+ * iteration or return nonzero to abort. On abort, the value returned
+ * by the callback will be returned from mtar_foreach(). Since it may
+ * also return normal microtar error codes, it is suggested to use a
+ * positive value or pass the result via 'arg'.
+ */
+int foreach_cb(mtar_t* tar, const mtar_header_t* header, void* arg)
+{
+    // ...
+    return 0;
+}
 
-/* Close archive */
-mtar_close(&tar);
+void main()
+{
+    mtar_t tar;
+
+    // ...
+
+    int ret = mtar_foreach(&tar, foreach_cb, NULL);
+    if(ret < 0) {
+        /* Microtar error codes are negative and may be returned if
+         * there is a problem with the iteration. */
+    } else if(ret == MTAR_ESUCCESS) {
+        /* If the iteration reaches the end of the archive without
+         * errors, the return code is MTAR_ESUCCESS. */
+    } else if(ret > 0) {
+        /* Positive values might be returned by the callback to
+         * signal some condition was met; they'll never be returned
+         * by microtar */
+    }
+}
+```
+
+The other thing you're likely to do is look for a specific file:
+
+```c
+/* Seek to a specific member in the archive */
+int err = mtar_find(&tar, "foo.txt");
+if(err == MTAR_ESUCCESS) {
+    /* File was found -- read the header with mtar_get_header() */
+} else if(err == MTAR_ENOTFOUND) {
+    /* File wasn't in the archive */
+} else {
+    /* Some error occurred */
+}
 ```
 
+Note this isn't terribly efficient since it scans the entire archive
+looking for the file.
+
+
+### Reading file data
+
+Once pointed at a file via `mtar_next()` or `mtar_find()` you can read the
+data with a simple POSIX-like API.
+
+- `mtar_read_data(tar, buf, count)` reads up to `count` bytes into `buf`,
+  returning the actual number of bytes read, or a negative error value.
+  If at EOF, this returns zero.
+
+- `mtar_seek_data(tar, offset, whence)` works exactly like `fseek()` with
+  `whence` being one of `SEEK_SET`, `SEEK_CUR`, or `SEEK_END` and `offset`
+  indicating a point relative to the beginning, current position, or end
+  of the file. Returns zero on success, or a negative error code.
+
+- `mtar_eof_data(tar)` returns nonzero if the end of the file has been
+  reached. It is possible to seek backward to clear this condition.
+
+
+### Writing archives
+
+Microtar has limited support for creating archives. When an archive is opened
+for writing, you can add new members using `mtar_write_header()`.
+
+- `mtar_write_header(tar, header)` writes out the header for a new member.
+  The amount of data that follows is dictated by `header->size`, though if
+  the underlying stream supports seeking and re-writing data, this size can
+  be updated later with `mtar_update_header()` or `mtar_update_file_size()`.
+
+- `mtar_update_header(tar, header)` will re-write the previously written
+  header. This may be used to change any header field. The underlying stream
+  must support seeking. On a successful return the stream will be returned
+  to the position it was at before the call.
+
+File data can be written with `mtar_write_data()`, and if the underlying stream
+supports seeking, you can seek with `mtar_seek_data()` and read back previously
+written data with `mtar_read_data()`. Note that it is not possible to truncate
+the file stream by any means.
+
+- `mtar_write_data(tar, buf, count)` will write up to `count` bytes from
+  `buf` to the current member's data. Returns the number of bytes actually
+  written or a negative error code.
+
+- `mtar_update_file_size(tar)` will update the header size to reflect the
+  actual amount of written data. This is intended to be called right before
+  `mtar_end_data()` if you are not declaring file sizes in advance.
+
+- `mtar_end_data(tar)` will end the current member. It will complain if you
+  did not write the correct amount data provided in the header. This must be
+  called before writing the next header.
+
+- `mtar_finalize(tar)` is called after you have written all members to the
+  archive. It writes out some null records which mark the end of the archive,
+  so you cannot write any more archive members after this.
+
+Note that `mtar_close()` can fail if there was a problem flushing buffered
+data to disk, so its return value should always be checked.
+
 
 ## 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.
 
+Most functions that return `int` return an error code from `enum mtar_error`.
+Zero is success and all other error codes are negative. `mtar_strerror()` can
+return a string describing the error code.
 
-## 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.
+A couple of functions use a different return value convention:
 
-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.
+- `mtar_foreach()` may error codes or an arbitrary nonzero value provided
+  by the callback.
+- `mtar_read_data()` and `mtar_write_data()` returns the number of bytes read
+  or written, or a negative error code. In particular zero means that no bytes
+  were read or written.
+- `mtar_get_header()` may return `NULL` if there is no valid header.
+  It is only possible to see a null pointer if misusing the API or after
+  a previous error so checking for this is usually not necessary.
 
-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.
+There is essentially no support for error recovery. After an error you can
+only do two things reliably: close the archive with `mtar_close()` or try
+rewinding to the beginning with `mtar_rewind()`.
 
-#### 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
+## I/O hooks
 
-#### Writing
-The following callbacks should be set for writing an archive to a stream:
+You can provide your own I/O hooks in a `mtar_ops_t` struct. The same ops
+struct can be shared among multiple `mtar_t` objects but each object gets
+its own `void* stream` pointer.
 
-Name    | Arguments                                      | Description
---------|------------------------------------------------|---------------------
-`write` | `mtar_t *tar, const void *data, unsigned size` | Write data to the stream
+Name    | Arguments                                 | Required
+--------|-------------------------------------------|------------
+`read`  | `void* stream, void* data, unsigned size` | If reading
+`write` | `void* stream, void* data, unsigned size` | If writing
+`seek`  | `void* stream, unsigned pos`              | If reading
+`close` | `void* stream`                            | Always
 
+`read` and `write` should transfer the number of bytes indicated
+and return the number of bytes actually read or written, or a negative
+`enum mtar_error` code on error.
 
-## License
-This library is free software; you can redistribute it and/or modify it under
-the terms of the MIT license. See [LICENSE](LICENSE) for details.
+`seek` must have semantics like `lseek(..., pos, SEEK_SET)`; that is,
+the position is an absolute byte offset in the stream. Seeking is not
+optional for read support, but the library only performs backward
+seeks under two circumstances:
+
+- `mtar_rewind()` seeks to position 0.
+- `mtar_seek_data()` may seek backward if the user requests it.
+
+Therefore, you will be able to get away with a limited forward-only
+seek function if you're able to read everything in a single pass use
+the API carefully. Note `mtar_find()` and `mtar_foreach()` will call
+`mtar_rewind()`.
+
+`close` is called by `mtar_close()` to clean up the stream. Note the
+library assumes that the stream handle is cleaned up by `close` even
+if an error occurs.
+
+`seek` and `close` should return an `enum mtar_error` code, either
+`MTAR_SUCCESS`, or a negative value on error.
diff --git a/lib/microtar/README.rockbox b/lib/microtar/README.rockbox
new file mode 100644
index 0000000000..944f792996
--- /dev/null
+++ b/lib/microtar/README.rockbox
@@ -0,0 +1,14 @@
+Upstream commit/repo
+  1e921369b2c92bb219fcef84a37d4d2347794c0f
+  https://github.com/amachronic/microtar
+
+Summary of Rockbox-specific changes:
+
+- microtar.make, SOURCES
+  Target build system integration.
+
+- microtar-rockbox.c, microtar-rockbox.h
+  Implements mtar ops with Rockbox filesystem API.
+
+- microtar.c
+  Define strncpy since Rockbox's libc doesn't define it.
diff --git a/lib/microtar/mtar.c b/lib/microtar/mtar.c
new file mode 100644
index 0000000000..4a9a27b782
--- /dev/null
+++ b/lib/microtar/mtar.c
@@ -0,0 +1,243 @@
+/*
+ * Copyright (c) 2021 Aidan MacDonald
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include "microtar-stdio.h"
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <unistd.h>
+
+/* exit codes */
+#define E_TAR   1
+#define E_FS    2
+#define E_OTHER 4
+#define E_ARGS  8
+
+enum {
+    OP_LIST,
+    OP_CREATE,
+    OP_EXTRACT,
+};
+
+void die(int err, const char* msg, ...)
+{
+    fprintf(stderr, "mtar: ");
+
+    va_list ap;
+    va_start(ap, msg);
+    vfprintf(stderr, msg, ap);
+    va_end(ap);
+
+    fprintf(stderr, "\n");
+    exit(err);
+}
+
+int list_foreach_cb(mtar_t* tar, const mtar_header_t* h, void* arg)
+{
+    (void)tar;
+    (void)arg;
+    printf("%s\n", h->name);
+    return 0;
+}
+
+void list_files(mtar_t* tar)
+{
+    int err = mtar_foreach(tar, list_foreach_cb, NULL);
+    if(err)
+        die(E_TAR, "listing failed: %s", mtar_strerror(err));
+}
+
+struct extract_args {
+    char** names;
+    int count;
+};
+
+int extract_foreach_cb(mtar_t* tar, const mtar_header_t* h, void* arg)
+{
+    struct extract_args* args = arg;
+    (void)args; /* TODO */
+
+    if(h->type == MTAR_TDIR) {
+        if(mkdir(h->name, h->mode) != 0)
+            die(E_FS, "cannot create directory \"%s\"", h->name);
+        return 0;
+    }
+
+    if(h->type != MTAR_TREG) {
+        fprintf(stderr, "warning: not extracting unsupported type \"%s\"", h->name);
+        return 0;
+    }
+
+    int fd = open(h->name, O_CREAT|O_WRONLY|O_TRUNC, h->mode);
+    if(fd < 0)
+        die(E_FS, "extracting \"%s\" failed: %s", h->name, strerror(errno));
+
+    char iobuf[1024];
+    while(!mtar_eof_data(tar)) {
+        int rcount = mtar_read_data(tar, iobuf, sizeof(iobuf));
+        if(rcount < 0)
+            die(E_TAR, "extracting \"%s\" failed: %s", h->name, mtar_strerror(rcount));
+
+        int wcount = write(fd, iobuf, rcount);
+        if(wcount != rcount)
+            die(E_FS, "extracting \"%s\" failed: %s", h->name, strerror(errno));
+    }
+
+    close(fd);
+    return 0;
+}
+
+void extract_files(mtar_t* tar, char** files, int num_files)
+{
+    struct extract_args args;
+    args.names = files;
+    args.count = num_files;
+
+    int err = mtar_foreach(tar, extract_foreach_cb, &args);
+    if(err)
+        die(E_TAR, "extraction failed: %s", mtar_strerror(err));
+}
+
+void add_files(mtar_t* tar, char** files, int num_files)
+{
+    for(int i = 0; i < num_files; ++i) {
+        int fd = open(files[i], O_RDONLY);
+        if(fd < 0)
+            die(E_FS, "adding \"%s\" failed: %s", files[i], strerror(errno));
+
+        off_t off = lseek(fd, 0, SEEK_END);
+        if(off < 0)
+            die(E_FS, "adding \"%s\" failed: %s", files[i], strerror(errno));
+
+        unsigned filesize = off;
+        lseek(fd, 0, SEEK_SET);
+
+        int err = mtar_write_file_header(tar, files[i], filesize);
+        if(err)
+            die(E_TAR, "adding \"%s\" failed: %s", files[i], mtar_strerror(err));
+
+        char iobuf[1024];
+        while(1) {
+            int rcount = read(fd, iobuf, sizeof(iobuf));
+            if(rcount < 0)
+                die(E_FS, "adding \"%s\" failed: %s", files[i], strerror(errno));
+            if(rcount == 0)
+                break;
+
+            int wcount = mtar_write_data(tar, iobuf, rcount);
+            if(wcount < 0)
+                die(E_TAR, "adding \"%s\" failed: %s", files[i], mtar_strerror(wcount));
+            if(wcount != rcount)
+                die(E_TAR, "adding \"%s\" failed: write too short %d/%d", files[i], wcount, rcount);
+        }
+
+        close(fd);
+
+        err = mtar_end_data(tar);
+        if(err)
+            die(E_TAR, "adding \"%s\" failed: %s", files[i], mtar_strerror(err));
+    }
+}
+
+int main(int argc, char* argv[])
+{
+    ++argv, --argc;
+    if(argc == 0)
+        die(E_ARGS, "no input files");
+
+    if(!strcmp(*argv, "--help")) {
+        printf(
+"usage:\n"
+"  mtar list tar-file\n"
+"    List the members of the given tar archive, one filename per line.\n"
+"\n"
+"  mtar create tar-file members...\n"
+"  mtar add tar-file members...\n"
+"    Create a new tar archive from the files listed on the command line.\n"
+"    WARNING: Any existing file at tar-file will be overwritten!\n"
+"\n"
+"  mtar extract tar-file [members...]\n"
+"    Extract the contents of the tar archive to the current directory.\n"
+"    If filenames are given, only the named members will be extracted.\n"
+"\n");
+        exit(E_ARGS);
+    }
+
+    int op;
+    if(!strcmp(*argv, "list"))
+        op = OP_LIST;
+    else if(!strcmp(*argv, "create"))
+        op = OP_CREATE;
+    else if(!strcmp(*argv, "extract"))
+        op = OP_EXTRACT;
+    else
+        die(E_ARGS, "invalid operation \"%s\"", *argv);
+    ++argv, --argc;
+
+    if(argc == 0)
+        die(E_ARGS, "missing archive name");
+    const char* archive_name = *argv;
+    ++argv, --argc;
+
+    if(op == OP_LIST && argc != 0)
+        die(E_ARGS, "excess arguments on command line");
+
+    const char* mode = "rb";
+    if(op == OP_CREATE)
+        mode = "wb";
+
+    mtar_t tar;
+    int err = mtar_open(&tar, archive_name, mode);
+    if(err)
+        die(E_TAR, "can't open archive: %s", mtar_strerror(err));
+
+    switch(op) {
+    case OP_LIST:
+        list_files(&tar);
+        break;
+
+    case OP_EXTRACT:
+        extract_files(&tar, argv, argc);
+        break;
+
+    case OP_CREATE:
+        add_files(&tar, argv, argc);
+        err = mtar_finalize(&tar);
+        if(err)
+            die(E_TAR, "failed to finalize archive: %s", mtar_strerror(err));
+        break;
+
+    default:
+        die(E_OTHER, "not implemented");
+        break;
+    }
+
+    err = mtar_close(&tar);
+    if(err)
+        die(E_TAR, "failed to close archive: %s", mtar_strerror(err));
+
+    return 0;
+}
diff --git a/lib/microtar/src/microtar-rockbox.c b/lib/microtar/src/microtar-rockbox.c
index 04ba93cc42..d0f579fefb 100644
--- a/lib/microtar/src/microtar-rockbox.c
+++ b/lib/microtar/src/microtar-rockbox.c
@@ -20,81 +20,72 @@
  ****************************************************************************/
 
 #include "file.h"
-#include "microtar.h"
+#include "microtar-rockbox.h"
 #include <stdint.h>
 
-static int fd_write(mtar_t *tar, const void *data, unsigned size) {
-  intptr_t fd = (intptr_t)tar->stream;
-  ssize_t res = write(fd, data, size);
-  if(res < 0 || ((unsigned)res != size))
-    return MTAR_EWRITEFAIL;
-  else
-    return MTAR_ESUCCESS;
-}
+static int fd_read(void* stream, void* data, unsigned size)
+{
+    ssize_t res = read((intptr_t)stream, data, size);
+    if(res < 0)
+        return MTAR_EREADFAIL;
 
-static int fd_read(mtar_t *tar, void *data, unsigned size) {
-  intptr_t fd = (intptr_t)tar->stream;
-  ssize_t res = read(fd, data, size);
-  if(res < 0 || ((unsigned)res != size))
-    return MTAR_EREADFAIL;
-  else
-    return MTAR_ESUCCESS;
+    return res;
 }
 
-static int fd_seek(mtar_t *tar, unsigned offset) {
-  intptr_t fd = (intptr_t)tar->stream;
-  off_t res = lseek(fd, offset, SEEK_SET);
-  if(res < 0 || ((unsigned)res != offset))
-    return MTAR_ESEEKFAIL;
-  else
-    return MTAR_ESUCCESS;
-}
+static int fd_write(void* stream, const void* data, unsigned size)
+{
+    ssize_t res = write((intptr_t)stream, data, size);
+    if(res < 0)
+        return MTAR_EWRITEFAIL;
 
-static int fd_close(mtar_t *tar) {
-  intptr_t fd = (intptr_t)tar->stream;
-  close(fd);
-  return MTAR_ESUCCESS;
+    return res;
 }
 
+static int fd_seek(void* stream, unsigned offset)
+{
+    off_t res = lseek((intptr_t)stream, offset, SEEK_SET);
+    if(res < 0 || ((unsigned)res != offset))
+        return MTAR_ESEEKFAIL;
+    else
+        return MTAR_ESUCCESS;
+}
 
-int mtar_open(mtar_t *tar, const char *filename, const char *mode) {
-  int err;
-  int openmode;
-  int fd;
-
-  /* Init tar struct and functions */
-  memset(tar, 0, sizeof(*tar));
-  tar->write = fd_write;
-  tar->read = fd_read;
-  tar->seek = fd_seek;
-  tar->close = fd_close;
+static int fd_close(void* stream)
+{
+    close((intptr_t)stream);
+    return MTAR_ESUCCESS;
+}
 
-  /* Get correct mode flags */
-  if ( strchr(mode, 'r') )
-      openmode = O_RDONLY;
-  else if ( strchr(mode, 'w') )
-      openmode = O_CREAT|O_TRUNC|O_WRONLY;
-  else if ( strchr(mode, 'a') )
-      openmode = O_WRONLY|O_APPEND;
-  else
-      return MTAR_EFAILURE;
+static const mtar_ops_t fd_ops = {
+    .read = fd_read,
+    .write = fd_write,
+    .seek = fd_seek,
+    .close = fd_close,
+};
 
-  /* Open file */
-  fd = open(filename, openmode);
-  if(fd < 0)
-    return MTAR_EOPENFAIL;
+int mtar_open(mtar_t* tar, const char* filename, int flags)
+{
+    /* Determine access mode */
+    int access;
+    switch(flags & O_ACCMODE) {
+    case O_RDONLY:
+        access = MTAR_READ;
+        break;
 
-  tar->stream = (void*)(intptr_t)fd;
+    case O_WRONLY:
+        access = MTAR_WRITE;
+        break;
 
-  /* Read first header to check it is valid if mode is `r` */
-  if ( openmode & O_RDONLY ) {
-    err = mtar_read_header(tar, &tar->header);
-    if (err != MTAR_ESUCCESS) {
-      mtar_close(tar);
-      return err;
+    default:
+        /* Note - O_RDWR isn't very useful so we don't allow it */
+        return MTAR_EAPI;
     }
-  }
 
-  /* Return ok */
-  return MTAR_ESUCCESS;
+    int fd = open(filename, flags);
+    if(fd < 0)
+        return MTAR_EOPENFAIL;
+
+    /* Init tar struct and functions */
+    mtar_init(tar, access, &fd_ops, (void*)(intptr_t)fd);
+    return MTAR_ESUCCESS;
 }
diff --git a/lib/microtar/src/microtar-rockbox.h b/lib/microtar/src/microtar-rockbox.h
new file mode 100644
index 0000000000..36acbb2bfe
--- /dev/null
+++ b/lib/microtar/src/microtar-rockbox.h
@@ -0,0 +1,29 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2021 Aidan MacDonald
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+
+#ifndef MICROTAR_ROCKBOX_H
+#define MICROTAR_ROCKBOX_H
+
+#include "microtar.h"
+
+int mtar_open(mtar_t* tar, const char* filename, int flags);
+
+#endif
diff --git a/lib/microtar/src/microtar-stdio.c b/lib/microtar/src/microtar-stdio.c
index 215000aa98..2697d005cd 100644
--- a/lib/microtar/src/microtar-stdio.c
+++ b/lib/microtar/src/microtar-stdio.c
@@ -1,65 +1,88 @@
-/**
+/*
  * Copyright (c) 2017 rxi
+ * Copyright (c) 2021 Aidan MacDonald
  *
- * This library is free software; you can redistribute it and/or modify it
- * under the terms of the MIT license. See `microtar.c` for details.
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
  */
 
+#include "microtar-stdio.h"
 #include <stdio.h>
 #include <string.h>
 
-#include "microtar.h"
+static int file_read(void* stream, void* data, unsigned size)
+{
+    unsigned res = fread(data, 1, size, (FILE*)stream);
+    if(res != size && ferror((FILE*)stream))
+        return MTAR_EREADFAIL;
 
-static int file_write(mtar_t *tar, const void *data, unsigned size) {
-  unsigned res = fwrite(data, 1, size, tar->stream);
-  return (res == size) ? MTAR_ESUCCESS : MTAR_EWRITEFAIL;
+    return res;
 }
 
-static int file_read(mtar_t *tar, void *data, unsigned size) {
-  unsigned res = fread(data, 1, size, tar->stream);
-  return (res == size) ? MTAR_ESUCCESS : MTAR_EREADFAIL;
-}
+static int file_write(void* stream, const void* data, unsigned size)
+{
+    unsigned res = fwrite(data, 1, size, (FILE*)stream);
+    if(res != size && ferror((FILE*)stream))
+       return MTAR_EWRITEFAIL;
 
-static int file_seek(mtar_t *tar, unsigned offset) {
-  int res = fseek(tar->stream, offset, SEEK_SET);
-  return (res == 0) ? MTAR_ESUCCESS : MTAR_ESEEKFAIL;
+    return res;
 }
 
-static int file_close(mtar_t *tar) {
-  fclose(tar->stream);
-  return MTAR_ESUCCESS;
+static int file_seek(void* stream, unsigned offset)
+{
+    int res = fseek((FILE*)stream, offset, SEEK_SET);
+    return (res == 0) ? MTAR_ESUCCESS : MTAR_ESEEKFAIL;
 }
 
+static int file_close(void* stream)
+{
+    int err = fclose((FILE*)stream);
+    return (err == 0 ? MTAR_ESUCCESS : MTAR_EFAILURE);
+}
 
-int mtar_open(mtar_t *tar, const char *filename, const char *mode) {
-  int err;
-  mtar_header_t h;
-
-  /* Init tar struct and functions */
-  memset(tar, 0, sizeof(*tar));
-  tar->write = file_write;
-  tar->read = file_read;
-  tar->seek = file_seek;
-  tar->close = file_close;
+static const mtar_ops_t file_ops = {
+    .read = file_read,
+    .write = file_write,
+    .seek = file_seek,
+    .close = file_close,
+};
 
-  /* Assure mode is always binary */
-  if ( strchr(mode, 'r') ) mode = "rb";
-  if ( strchr(mode, 'w') ) mode = "wb";
-  if ( strchr(mode, 'a') ) mode = "ab";
-  /* Open file */
-  tar->stream = fopen(filename, mode);
-  if (!tar->stream) {
-    return MTAR_EOPENFAIL;
-  }
-  /* Read first header to check it is valid if mode is `r` */
-  if (*mode == 'r') {
-    err = mtar_read_header(tar, &h);
-    if (err != MTAR_ESUCCESS) {
-      mtar_close(tar);
-      return err;
+int mtar_open(mtar_t* tar, const char* filename, const char* mode)
+{
+    /* Determine access mode */
+    int access;
+    char* read = strchr(mode, 'r');
+    char* write = strchr(mode, 'w');
+    if(read) {
+        if(write)
+            return MTAR_EAPI;
+        access = MTAR_READ;
+    } else if(write) {
+        access = MTAR_WRITE;
+    } else {
+        return MTAR_EAPI;
     }
-  }
 
-  /* Return ok */
-  return MTAR_ESUCCESS;
+    /* Open file */
+    FILE* file = fopen(filename, mode);
+    if(!file)
+        return MTAR_EOPENFAIL;
+
+    mtar_init(tar, access, &file_ops, file);
+    return MTAR_ESUCCESS;
 }
diff --git a/lib/microtar/src/microtar-stdio.h b/lib/microtar/src/microtar-stdio.h
new file mode 100644
index 0000000000..ad46af0390
--- /dev/null
+++ b/lib/microtar/src/microtar-stdio.h
@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2017 rxi
+ * Copyright (c) 2021 Aidan MacDonald
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#ifndef MICROTAR_STDIO_H
+#define MICROTAR_STDIO_H
+
+#include "microtar.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+int mtar_open(mtar_t* tar, const char* filename, const char* mode);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/lib/microtar/src/microtar.c b/lib/microtar/src/microtar.c
index 04cd4ea132..8ab9a8c5f4 100644
--- a/lib/microtar/src/microtar.c
+++ b/lib/microtar/src/microtar.c
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2017 rxi
+ * Copyright (c) 2021 Aidan MacDonald
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to
@@ -20,16 +21,14 @@
  * IN THE SOFTWARE.
  */
 
-#include <stdlib.h>
-#include <stddef.h>
+#include "microtar.h"
 #include <limits.h>
 #include <string.h>
 
-#include "microtar.h"
-
 #ifdef ROCKBOX
 /* Rockbox lacks strncpy in its libc */
-static char* strncpy(char* dest, const char* src, size_t n) {
+#define strncpy my_strncpy
+static char* my_strncpy(char* dest, const char* src, size_t n) {
     size_t i;
 
     for(i = 0; i < n && *src; ++i)
@@ -42,362 +41,685 @@ static char* strncpy(char* dest, const char* src, size_t n) {
 }
 #endif
 
+enum {
+    S_HEADER_VALID   = 1 << 0,
+    S_WROTE_HEADER   = 1 << 1,
+    S_WROTE_DATA     = 1 << 2,
+    S_WROTE_DATA_EOF = 1 << 3,
+    S_WROTE_FINALIZE = 1 << 4,
+};
+
+enum {
+    NAME_OFF     = 0,                           NAME_LEN = 100,
+    MODE_OFF     = NAME_OFF+NAME_LEN,           MODE_LEN = 8,
+    OWNER_OFF    = MODE_OFF+MODE_LEN,           OWNER_LEN = 8,
+    GROUP_OFF    = OWNER_OFF+OWNER_LEN,         GROUP_LEN = 8,
+    SIZE_OFF     = GROUP_OFF+GROUP_LEN,         SIZE_LEN = 12,
+    MTIME_OFF    = SIZE_OFF+SIZE_LEN,           MTIME_LEN = 12,
+    CHKSUM_OFF   = MTIME_OFF+MTIME_LEN,         CHKSUM_LEN = 8,
+    TYPE_OFF     = CHKSUM_OFF+CHKSUM_LEN,
+    LINKNAME_OFF = TYPE_OFF+1,                  LINKNAME_LEN = 100,
+
+    HEADER_LEN   = 512,
+};
+
+static int parse_octal(const char* str, size_t len, unsigned* ret)
+{
+    unsigned n = 0;
+
+    while(len-- > 0 && *str != 0) {
+        if(*str < '0' || *str > '9')
+            return MTAR_EOVERFLOW;
+
+        if(n > UINT_MAX/8)
+            return MTAR_EOVERFLOW;
+        else
+            n *= 8;
+
+        char r = *str++ - '0';
+
+        if(n > UINT_MAX - r)
+            return MTAR_EOVERFLOW;
+        else
+            n += r;
+    }
 
-static int parse_octal(const char* str, size_t len, unsigned* ret) {
-  unsigned n = 0;
-  while(len-- > 0 && *str != 0) {
-    if(*str < '0' || *str > '9')
-      return MTAR_EOVERFLOW;
-
-    if(n > UINT_MAX/8)
-      return MTAR_EOVERFLOW;
-    else
-      n *= 8;
-
-    char r = *str++ - '0';
-    if(n > UINT_MAX - r)
-      return MTAR_EOVERFLOW;
-    else
-      n += r;
-  }
-
-  *ret = n;
-  return MTAR_ESUCCESS;
+    *ret = n;
+    return MTAR_ESUCCESS;
 }
 
+static int print_octal(char* str, size_t len, unsigned value)
+{
+    /* move backwards over the output string */
+    char* ptr = str + len - 1;
+    *ptr = 0;
 
-static int print_octal(char* str, size_t len, unsigned value) {
-  /* move backwards over the output string */
-  char* ptr = str + len - 1;
-  *ptr = 0;
+    /* output the significant digits */
+    while(value > 0) {
+        if(ptr == str)
+            return MTAR_EOVERFLOW;
 
-  /* output the significant digits */
-  while(value > 0) {
-    if(ptr == str)
-      return MTAR_EOVERFLOW;
+        --ptr;
+        *ptr = '0' + (value % 8);
+        value /= 8;
+    }
 
-    --ptr;
-    *ptr = '0' + (value % 8);
-    value /= 8;
-  }
+    /* pad the remainder of the field with zeros */
+    while(ptr != str) {
+        --ptr;
+        *ptr = '0';
+    }
 
-  /* pad the remainder of the field with zeros */
-  while(ptr != str) {
-    --ptr;
-    *ptr = '0';
-  }
+    return MTAR_ESUCCESS;
+}
 
-  return MTAR_ESUCCESS;
+static unsigned round_up_512(unsigned n)
+{
+    return (n + 511u) & ~511u;
 }
 
+static int tread(mtar_t* tar, void* data, unsigned size)
+{
+    int ret = tar->ops->read(tar->stream, data, size);
+    if(ret >= 0)
+        tar->pos += ret;
 
-static unsigned round_up(unsigned n, unsigned incr) {
-  return n + (incr - n % incr) % incr;
+    return ret;
 }
 
+static int twrite(mtar_t* tar, const void* data, unsigned size)
+{
+    int ret = tar->ops->write(tar->stream, data, size);
+    if(ret >= 0)
+        tar->pos += ret;
 
-static unsigned checksum(const mtar_raw_header_t* rh) {
-  unsigned i;
-  unsigned char *p = (unsigned char*) rh;
-  unsigned res = 256;
-  for (i = 0; i < offsetof(mtar_raw_header_t, checksum); i++) {
-    res += p[i];
-  }
-  for (i = offsetof(mtar_raw_header_t, type); i < sizeof(*rh); i++) {
-    res += p[i];
-  }
-  return res;
+    return ret;
 }
 
-
-static int tread(mtar_t *tar, void *data, unsigned size) {
-  int err = tar->read(tar, data, size);
-  tar->pos += size;
-  return err;
+static int tseek(mtar_t* tar, unsigned pos)
+{
+    int err = tar->ops->seek(tar->stream, pos);
+    tar->pos = pos;
+    return err;
 }
 
+static int write_null_bytes(mtar_t* tar, size_t count)
+{
+    int ret;
+    size_t n;
+
+    memset(tar->buffer, 0, sizeof(tar->buffer));
+    while(count > 0) {
+        n = count < sizeof(tar->buffer) ? count : sizeof(tar->buffer);
+        ret = twrite(tar, tar->buffer, n);
+        if(ret < 0)
+            return ret;
+        if(ret != (int)n)
+            return MTAR_EWRITEFAIL;
+
+        count -= n;
+    }
 
-static int twrite(mtar_t *tar, const void *data, unsigned size) {
-  int err = tar->write(tar, data, size);
-  tar->pos += size;
-  return err;
+    return MTAR_ESUCCESS;
 }
 
+static unsigned checksum(const char* raw)
+{
+    unsigned i;
+    unsigned char* p = (unsigned char*)raw;
+    unsigned res = 256;
 
-static int write_null_bytes(mtar_t *tar, int n) {
-  int i, err;
-  char nul = '\0';
-  for (i = 0; i < n; i++) {
-    err = twrite(tar, &nul, 1);
-    if (err) {
-      return err;
-    }
-  }
-  return MTAR_ESUCCESS;
+    for(i = 0; i < CHKSUM_OFF; i++)
+        res += p[i];
+    for(i = TYPE_OFF; i < HEADER_LEN; i++)
+        res += p[i];
+
+    return res;
 }
 
+static int raw_to_header(mtar_header_t* h, const char* raw)
+{
+    unsigned chksum;
+    int rc;
+
+    /* If the checksum starts with a null byte we assume the record is NULL */
+    if(raw[CHKSUM_OFF] == '\0')
+        return MTAR_ENULLRECORD;
+
+    /* Compare the checksum */
+    if((rc = parse_octal(&raw[CHKSUM_OFF], CHKSUM_LEN, &chksum)))
+       return rc;
+    if(chksum != checksum(raw))
+        return MTAR_EBADCHKSUM;
+
+    /* Load raw header into header */
+    if((rc = parse_octal(&raw[MODE_OFF], MODE_LEN, &h->mode)))
+        return rc;
+    if((rc = parse_octal(&raw[OWNER_OFF], OWNER_LEN, &h->owner)))
+        return rc;
+    if((rc = parse_octal(&raw[GROUP_OFF], GROUP_LEN, &h->group)))
+        return rc;
+    if((rc = parse_octal(&raw[SIZE_OFF], SIZE_LEN, &h->size)))
+        return rc;
+    if((rc = parse_octal(&raw[MTIME_OFF], MTIME_LEN, &h->mtime)))
+        return rc;
+
+    h->type = raw[TYPE_OFF];
+    if(!h->type)
+        h->type = MTAR_TREG;
+
+    memcpy(h->name, &raw[NAME_OFF], NAME_LEN);
+    h->name[sizeof(h->name) - 1] = 0;
+
+    memcpy(h->linkname, &raw[LINKNAME_OFF], LINKNAME_LEN);
+    h->linkname[sizeof(h->linkname) - 1] = 0;
+
+    return MTAR_ESUCCESS;
+}
 
-static int raw_to_header(mtar_header_t *h, const mtar_raw_header_t *rh) {
-  unsigned chksum1, chksum2;
-  int rc;
+static int header_to_raw(char* raw, const mtar_header_t* h)
+{
+    unsigned chksum;
+    int rc;
+
+    memset(raw, 0, HEADER_LEN);
+
+    /* Load header into raw header */
+    if((rc = print_octal(&raw[MODE_OFF], MODE_LEN, h->mode)))
+        return rc;
+    if((rc = print_octal(&raw[OWNER_OFF], OWNER_LEN, h->owner)))
+        return rc;
+    if((rc = print_octal(&raw[GROUP_OFF], GROUP_LEN, h->group)))
+        return rc;
+    if((rc = print_octal(&raw[SIZE_OFF], SIZE_LEN, h->size)))
+        return rc;
+    if((rc = print_octal(&raw[MTIME_OFF], MTIME_LEN, h->mtime)))
+        return rc;
+
+    raw[TYPE_OFF] = h->type ? h->type : MTAR_TREG;
+
+#if defined(__GNUC__) && (__GNUC__ >= 8)
+/* Sigh. GCC wrongly assumes the output of strncpy() is supposed to be
+ * a null-terminated string -- which it is not, and we are relying on
+ * that fact here -- and tries to warn about 'string truncation' because
+ * the null terminator might not be copied. Just suppress the warning. */
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wstringop-truncation"
+#endif
 
-  /* If the checksum starts with a null byte we assume the record is NULL */
-  if (*rh->checksum == '\0') {
-    return MTAR_ENULLRECORD;
-  }
+    strncpy(&raw[NAME_OFF], h->name, NAME_LEN);
+    strncpy(&raw[LINKNAME_OFF], h->linkname, LINKNAME_LEN);
 
-  /* Build and compare checksum */
-  chksum1 = checksum(rh);
-  if((rc = parse_octal(rh->checksum, sizeof(rh->checksum), &chksum2)))
-      return rc;
-  if (chksum1 != chksum2) {
-    return MTAR_EBADCHKSUM;
-  }
+#if defined(__GNUC__) && (__GNUC__ >= 8)
+# pragma GCC diagnostic pop
+#endif
 
-  /* Load raw header into header */
-  if((rc = parse_octal(rh->mode, sizeof(rh->mode), &h->mode)))
-    return rc;
-  if((rc = parse_octal(rh->owner, sizeof(rh->owner), &h->owner)))
-    return rc;
-  if((rc = parse_octal(rh->group, sizeof(rh->group), &h->group)))
-    return rc;
-  if((rc = parse_octal(rh->size, sizeof(rh->size), &h->size)))
-    return rc;
-  if((rc = parse_octal(rh->mtime, sizeof(rh->mtime), &h->mtime)))
-    return rc;
+    /* Calculate and write checksum */
+    chksum = checksum(raw);
+    if((rc = print_octal(&raw[CHKSUM_OFF], CHKSUM_LEN-1, chksum)))
+        return rc;
 
-  h->type = rh->type;
+    raw[CHKSUM_OFF + CHKSUM_LEN - 1] = ' ';
 
-  memcpy(h->name, rh->name, sizeof(rh->name));
-  h->name[sizeof(h->name) - 1] = 0;
+    return MTAR_ESUCCESS;
+}
 
-  memcpy(h->linkname, rh->linkname, sizeof(rh->linkname));
-  h->linkname[sizeof(h->linkname) - 1] = 0;
+static unsigned data_beg_pos(const mtar_t* tar)
+{
+    return tar->header_pos + HEADER_LEN;
+}
 
-  return MTAR_ESUCCESS;
+static unsigned data_end_pos(const mtar_t* tar)
+{
+    return tar->end_pos;
 }
 
+static int ensure_header(mtar_t* tar)
+{
+    int ret, err;
 
-static int header_to_raw(mtar_raw_header_t *rh, const mtar_header_t *h) {
-  unsigned chksum;
-  int rc;
+    if(tar->state & S_HEADER_VALID)
+        return MTAR_ESUCCESS;
 
-  /* Load header into raw header */
-  memset(rh, 0, sizeof(*rh));
-  if((rc = print_octal(rh->mode, sizeof(rh->mode), h->mode)))
-    return rc;
-  if((rc = print_octal(rh->owner, sizeof(rh->owner), h->owner)))
-    return rc;
-  if((rc = print_octal(rh->group, sizeof(rh->group), h->group)))
-    return rc;
-  if((rc = print_octal(rh->size, sizeof(rh->size), h->size)))
-    return rc;
-  if((rc = print_octal(rh->mtime, sizeof(rh->mtime), h->mtime)))
-    return rc;
-  rh->type = h->type ? h->type : MTAR_TREG;
-  strncpy(rh->name, h->name, sizeof(rh->name));
-  strncpy(rh->linkname, h->linkname, sizeof(rh->linkname));
+    if(tar->pos > UINT_MAX - HEADER_LEN)
+        return MTAR_EOVERFLOW;
 
-  /* Calculate and write checksum */
-  chksum = checksum(rh);
-  if((rc = print_octal(rh->checksum, 7, chksum)))
-     return rc;
-  rh->checksum[7] = ' ';
+    tar->header_pos = tar->pos;
+    tar->end_pos = data_beg_pos(tar);
 
-  return MTAR_ESUCCESS;
-}
+    ret = tread(tar, tar->buffer, HEADER_LEN);
+    if(ret < 0)
+        return ret;
+    if(ret != HEADER_LEN)
+        return MTAR_EREADFAIL;
 
+    err = raw_to_header(&tar->header, tar->buffer);
+    if(err)
+        return err;
 
-const char* mtar_strerror(int err) {
-  switch (err) {
-    case MTAR_ESUCCESS     : return "success";
-    case MTAR_EFAILURE     : return "failure";
-    case MTAR_EOPENFAIL    : return "could not open";
-    case MTAR_EREADFAIL    : return "could not read";
-    case MTAR_EWRITEFAIL   : return "could not write";
-    case MTAR_ESEEKFAIL    : return "could not seek";
-    case MTAR_EBADCHKSUM   : return "bad checksum";
-    case MTAR_ENULLRECORD  : return "null record";
-    case MTAR_ENOTFOUND    : return "file not found";
-    case MTAR_EOVERFLOW    : return "overflow";
-  }
-  return "unknown error";
+    if(tar->end_pos > UINT_MAX - tar->header.size)
+        return MTAR_EOVERFLOW;
+    tar->end_pos += tar->header.size;
+
+    tar->state |= S_HEADER_VALID;
+    return MTAR_ESUCCESS;
 }
 
+const char* mtar_strerror(int err)
+{
+    switch(err) {
+    case MTAR_ESUCCESS:     return "success";
+    case MTAR_EFAILURE:     return "failure";
+    case MTAR_EOPENFAIL:    return "could not open";
+    case MTAR_EREADFAIL:    return "could not read";
+    case MTAR_EWRITEFAIL:   return "could not write";
+    case MTAR_ESEEKFAIL:    return "could not seek";
+    case MTAR_ESEEKRANGE:   return "seek out of bounds";
+    case MTAR_EBADCHKSUM:   return "bad checksum";
+    case MTAR_ENULLRECORD:  return "null record";
+    case MTAR_ENOTFOUND:    return "file not found";
+    case MTAR_EOVERFLOW:    return "overflow";
+    case MTAR_EAPI:         return "API usage error";
+    case MTAR_ENAMETOOLONG: return "name too long";
+    case MTAR_EWRONGSIZE:   return "wrong amount of data written";
+    case MTAR_EACCESS:      return "wrong access mode";
+    default:                return "unknown error";
+    }
+}
 
-int mtar_close(mtar_t *tar) {
-  return tar->close(tar);
+void mtar_init(mtar_t* tar, int access, const mtar_ops_t* ops, void* stream)
+{
+    memset(tar, 0, sizeof(mtar_t));
+    tar->access = access;
+    tar->ops = ops;
+    tar->stream = stream;
 }
 
+int mtar_close(mtar_t* tar)
+{
+    int err = tar->ops->close(tar->stream);
+    tar->ops = NULL;
+    tar->stream = NULL;
+    return err;
+}
 
-int mtar_seek(mtar_t *tar, unsigned pos) {
-  int err = tar->seek(tar, pos);
-  tar->pos = pos;
-  return err;
+int mtar_is_open(mtar_t* tar)
+{
+    return (tar->ops != NULL) ? 1 : 0;
 }
 
+mtar_header_t* mtar_get_header(mtar_t* tar)
+{
+    if(tar->state & S_HEADER_VALID)
+        return &tar->header;
+    else
+        return NULL;
+}
 
-int mtar_rewind(mtar_t *tar) {
-  tar->remaining_data = 0;
-  tar->last_header = 0;
-  return mtar_seek(tar, 0);
+int mtar_access_mode(const mtar_t* tar)
+{
+    return tar->access;
 }
 
+int mtar_rewind(mtar_t* tar)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(tar->access != MTAR_READ)
+        return MTAR_EAPI;
+#endif
 
-int mtar_next(mtar_t *tar) {
-  int err, n;
-  /* Load header */
-  err = mtar_read_header(tar, &tar->header);
-  if (err) {
+    int err = tseek(tar, 0);
+    tar->state = 0;
     return err;
-  }
-  /* Seek to next record */
-  n = round_up(tar->header.size, 512) + sizeof(mtar_raw_header_t);
-  return mtar_seek(tar, tar->pos + n);
 }
 
+int mtar_next(mtar_t* tar)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(tar->access != MTAR_READ)
+        return MTAR_EACCESS;
+#endif
 
-int mtar_find(mtar_t *tar, const char *name, mtar_header_t *h) {
-  int err;
-  /* Start at beginning */
-  err = mtar_rewind(tar);
-  if (err) {
-    return err;
-  }
-  /* Iterate all files until we hit an error or find the file */
-  while ( (err = mtar_read_header(tar, &tar->header)) == MTAR_ESUCCESS ) {
-    if ( !strcmp(tar->header.name, name) ) {
-      if (h) {
-        *h = tar->header;
-      }
-      return MTAR_ESUCCESS;
-    }
-    err = mtar_next(tar);
-    if (err) {
-      return err;
+    if(tar->state & S_HEADER_VALID) {
+        tar->state &= ~S_HEADER_VALID;
+
+        /* seek to the next header */
+        int err = tseek(tar, round_up_512(data_end_pos(tar)));
+        if(err)
+            return err;
     }
-  }
-  /* Return error */
-  if (err == MTAR_ENULLRECORD) {
-    err = MTAR_ENOTFOUND;
-  }
-  return err;
-}
-
-
-int mtar_read_header(mtar_t *tar, mtar_header_t *h) {
-  int err;
-  /* Save header position */
-  tar->last_header = tar->pos;
-  /* Read raw header */
-  err = tread(tar, &tar->raw_header, sizeof(tar->raw_header));
-  if (err) {
+
+    return ensure_header(tar);
+}
+
+int mtar_foreach(mtar_t* tar, mtar_foreach_cb cb, void* arg)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(tar->access != MTAR_READ)
+        return MTAR_EACCESS;
+#endif
+
+    int err = mtar_rewind(tar);
+    if(err)
+        return err;
+
+    while((err = mtar_next(tar)) == MTAR_ESUCCESS)
+        if((err = cb(tar, &tar->header, arg)) != 0)
+            return err;
+
+    if(err == MTAR_ENULLRECORD)
+        err = MTAR_ESUCCESS;
+
     return err;
-  }
-  /* Seek back to start of header */
-  err = mtar_seek(tar, tar->last_header);
-  if (err) {
+}
+
+static int find_foreach_cb(mtar_t* tar, const mtar_header_t* h, void* arg)
+{
+    (void)tar;
+    const char* name = (const char*)arg;
+    return strcmp(name, h->name) ? 0 : 1;
+}
+
+int mtar_find(mtar_t* tar, const char* name)
+{
+    int err = mtar_foreach(tar, find_foreach_cb, (void*)name);
+    if(err == 1)
+        err = MTAR_ESUCCESS;
+    else if(err == MTAR_ESUCCESS)
+        err = MTAR_ENOTFOUND;
+
     return err;
-  }
-  /* Load raw header into header struct and return */
-  return raw_to_header(h, &tar->raw_header);
 }
 
+int mtar_read_data(mtar_t* tar, void* ptr, unsigned size)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(!(tar->state & S_HEADER_VALID))
+        return MTAR_EAPI;
+#endif
 
-int mtar_read_data(mtar_t *tar, void *ptr, unsigned size) {
-  int err;
-  /* If we have no remaining data then this is the first read, we get the size,
-   * set the remaining data and seek to the beginning of the data */
-  if (tar->remaining_data == 0) {
-    /* Read header */
-    err = mtar_read_header(tar, &tar->header);
-    if (err) {
-      return err;
-    }
-    /* Seek past header and init remaining data */
-    err = mtar_seek(tar, tar->pos + sizeof(mtar_raw_header_t));
-    if (err) {
-      return err;
+    /* have we reached end of file? */
+    unsigned data_end = data_end_pos(tar);
+    if(tar->pos >= data_end)
+        return 0;
+
+    /* truncate the read if it would go beyond EOF */
+    unsigned data_left = data_end - tar->pos;
+    if(data_left < size)
+        size = data_left;
+
+    return tread(tar, ptr, size);
+}
+
+int mtar_seek_data(mtar_t* tar, int offset, int whence)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(!(tar->state & S_HEADER_VALID))
+        return MTAR_EAPI;
+#endif
+
+    unsigned data_beg = data_beg_pos(tar);
+    unsigned data_end = data_end_pos(tar);
+    unsigned newpos;
+
+    switch(whence) {
+    case SEEK_SET:
+        if(offset < 0)
+            return MTAR_ESEEKRANGE;
+
+        newpos = data_beg + offset;
+        break;
+
+    case SEEK_CUR:
+        if((offset > 0 && (unsigned) offset > data_end - tar->pos) ||
+           (offset < 0 && (unsigned)-offset > tar->pos - data_beg))
+            return MTAR_ESEEKRANGE;
+
+        newpos = tar->pos + offset;
+        break;
+
+    case SEEK_END:
+        if(offset > 0)
+            return MTAR_ESEEKRANGE;
+
+        newpos = data_end + offset;
+        break;
+
+    default:
+        return MTAR_EAPI;
     }
-    tar->remaining_data = tar->header.size;
-  }
-  /* Ensure caller does not read too much */
-  if(size > tar->remaining_data)
-    return MTAR_EOVERFLOW;
-  /* Read data */
-  err = tread(tar, ptr, size);
-  if (err) {
-    return err;
-  }
-  tar->remaining_data -= size;
-  /* If there is no remaining data we've finished reading and seek back to the
-   * header */
-  if (tar->remaining_data == 0) {
-    return mtar_seek(tar, tar->last_header);
-  }
-  return MTAR_ESUCCESS;
+
+    return tseek(tar, newpos);
+}
+
+unsigned mtar_tell_data(mtar_t* tar)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(!(tar->state & S_HEADER_VALID))
+        return MTAR_EAPI;
+#endif
+
+    return tar->pos - data_beg_pos(tar);
 }
 
+int mtar_eof_data(mtar_t* tar)
+{
+    /* API usage error, but just claim EOF. */
+    if(!(tar->state & S_HEADER_VALID))
+        return 1;
 
-int mtar_write_header(mtar_t *tar, const mtar_header_t *h) {
-  /* Build raw header and write */
-  header_to_raw(&tar->raw_header, h);
-  tar->remaining_data = h->size;
-  return twrite(tar, &tar->raw_header, sizeof(tar->raw_header));
+    return tar->pos >= data_end_pos(tar) ? 1 : 0;
 }
 
+int mtar_write_header(mtar_t* tar, const mtar_header_t* h)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(tar->access != MTAR_WRITE)
+        return MTAR_EACCESS;
+    if(((tar->state & S_WROTE_DATA) && !(tar->state & S_WROTE_DATA_EOF)) ||
+       (tar->state & S_WROTE_FINALIZE))
+        return MTAR_EAPI;
+#endif
+
+    tar->state &= ~(S_HEADER_VALID | S_WROTE_HEADER |
+                    S_WROTE_DATA | S_WROTE_DATA_EOF);
+
+    /* ensure we have enough space to write the declared amount of data */
+    if(tar->pos > UINT_MAX - HEADER_LEN - round_up_512(h->size))
+        return MTAR_EOVERFLOW;
+
+    tar->header_pos = tar->pos;
+    tar->end_pos = data_beg_pos(tar);
+
+    if(h != &tar->header)
+        tar->header = *h;
+
+    int err = header_to_raw(tar->buffer, &tar->header);
+    if(err)
+        return err;
+
+    int ret = twrite(tar, tar->buffer, HEADER_LEN);
+    if(ret < 0)
+        return ret;
+    if(ret != HEADER_LEN)
+        return MTAR_EWRITEFAIL;
 
-int mtar_write_file_header(mtar_t *tar, const char *name, unsigned size) {
-  /* Build header */
-  memset(&tar->header, 0, sizeof(tar->header));
-  /* Ensure name fits within header */
-  if(strlen(name) > sizeof(tar->header.name))
-    return MTAR_EOVERFLOW;
-  strncpy(tar->header.name, name, sizeof(tar->header.name));
-  tar->header.size = size;
-  tar->header.type = MTAR_TREG;
-  tar->header.mode = 0664;
-  /* Write header */
-  return mtar_write_header(tar, &tar->header);
+    tar->state |= (S_HEADER_VALID | S_WROTE_HEADER);
+    return MTAR_ESUCCESS;
 }
 
+int mtar_update_header(mtar_t* tar, const mtar_header_t* h)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(tar->access != MTAR_WRITE)
+        return MTAR_EACCESS;
+    if(!(tar->state & S_WROTE_HEADER) ||
+       (tar->state & S_WROTE_DATA_EOF) ||
+       (tar->state & S_WROTE_FINALIZE))
+        return MTAR_EAPI;
+#endif
+
+    unsigned beg_pos = data_beg_pos(tar);
+    if(beg_pos > UINT_MAX - h->size)
+        return MTAR_EOVERFLOW;
+
+    unsigned old_pos = tar->pos;
+    int err = tseek(tar, tar->header_pos);
+    if(err)
+        return err;
+
+    if(h != &tar->header)
+        tar->header = *h;
 
-int mtar_write_dir_header(mtar_t *tar, const char *name) {
-  /* Build header */
-  memset(&tar->header, 0, sizeof(tar->header));
-  /* Ensure name fits within header */
-  if(strlen(name) > sizeof(tar->header.name))
-    return MTAR_EOVERFLOW;
-  strncpy(tar->header.name, name, sizeof(tar->header.name));
-  tar->header.type = MTAR_TDIR;
-  tar->header.mode = 0775;
-  /* Write header */
-  return mtar_write_header(tar, &tar->header);
+    err = header_to_raw(tar->buffer, &tar->header);
+    if(err)
+        return err;
+
+    int len = twrite(tar, tar->buffer, HEADER_LEN);
+    if(len < 0)
+        return len;
+    if(len != HEADER_LEN)
+        return MTAR_EWRITEFAIL;
+
+    return tseek(tar, old_pos);
 }
 
+int mtar_write_file_header(mtar_t* tar, const char* name, unsigned size)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(tar->access != MTAR_WRITE)
+        return MTAR_EACCESS;
+    if(((tar->state & S_WROTE_DATA) && !(tar->state & S_WROTE_DATA_EOF)) ||
+       (tar->state & S_WROTE_FINALIZE))
+        return MTAR_EAPI;
+#endif
 
-int mtar_write_data(mtar_t *tar, const void *data, unsigned size) {
-  int err;
+    size_t namelen = strlen(name);
+    if(namelen > NAME_LEN)
+        return MTAR_ENAMETOOLONG;
 
-  /* Ensure we are writing the correct amount of data */
-  if(size > tar->remaining_data)
-    return MTAR_EOVERFLOW;
+    tar->header.mode = 0644;
+    tar->header.owner = 0;
+    tar->header.group = 0;
+    tar->header.size = size;
+    tar->header.mtime = 0;
+    tar->header.type = MTAR_TREG;
+    memcpy(tar->header.name, name, namelen + 1);
+    tar->header.linkname[0] = '\0';
+
+    return mtar_write_header(tar, &tar->header);
+}
+
+int mtar_write_dir_header(mtar_t* tar, const char* name)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(tar->access != MTAR_WRITE)
+        return MTAR_EACCESS;
+    if(((tar->state & S_WROTE_DATA) && !(tar->state & S_WROTE_DATA_EOF)) ||
+       (tar->state & S_WROTE_FINALIZE))
+        return MTAR_EAPI;
+#endif
+
+    size_t namelen = strlen(name);
+    if(namelen > NAME_LEN)
+        return MTAR_ENAMETOOLONG;
+
+    tar->header.mode = 0755;
+    tar->header.owner = 0;
+    tar->header.group = 0;
+    tar->header.size = 0;
+    tar->header.mtime = 0;
+    tar->header.type = MTAR_TDIR;
+    memcpy(tar->header.name, name, namelen + 1);
+    tar->header.linkname[0] = '\0';
+
+    return mtar_write_header(tar, &tar->header);
+}
+
+int mtar_write_data(mtar_t* tar, const void* ptr, unsigned size)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(tar->access != MTAR_WRITE)
+        return MTAR_EACCESS;
+    if(!(tar->state & S_WROTE_HEADER) ||
+       (tar->state & S_WROTE_DATA_EOF) ||
+       (tar->state & S_WROTE_FINALIZE))
+        return MTAR_EAPI;
+#endif
+
+    tar->state |= S_WROTE_DATA;
+
+    int err = twrite(tar, ptr, size);
+    if(tar->pos > tar->end_pos)
+        tar->end_pos = tar->pos;
 
-  /* Write data */
-  err = twrite(tar, data, size);
-  if (err) {
     return err;
-  }
-  tar->remaining_data -= size;
-  /* Write padding if we've written all the data for this file */
-  if (tar->remaining_data == 0) {
-    return write_null_bytes(tar, round_up(tar->pos, 512) - tar->pos);
-  }
-  return MTAR_ESUCCESS;
 }
 
+int mtar_update_file_size(mtar_t* tar)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(tar->access != MTAR_WRITE)
+        return MTAR_EACCESS;
+    if(!(tar->state & S_WROTE_HEADER) ||
+       (tar->state & S_WROTE_DATA_EOF) ||
+       (tar->state & S_WROTE_FINALIZE))
+        return MTAR_EAPI;
+#endif
+
+    unsigned new_size = data_end_pos(tar) - data_beg_pos(tar);
+    if(new_size == tar->header.size)
+        return MTAR_ESUCCESS;
+    else {
+        tar->header.size = new_size;
+        return mtar_update_header(tar, &tar->header);
+    }
+}
+
+int mtar_end_data(mtar_t* tar)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(tar->access != MTAR_WRITE)
+        return MTAR_EACCESS;
+    if(!(tar->state & S_WROTE_HEADER) ||
+       (tar->state & S_WROTE_DATA_EOF) ||
+       (tar->state & S_WROTE_FINALIZE))
+        return MTAR_EAPI;
+#endif
+
+    int err;
+
+    /* ensure the caller wrote the correct amount of data */
+    unsigned expected_end = data_beg_pos(tar) + tar->header.size;
+    if(tar->end_pos != expected_end)
+        return MTAR_EWRONGSIZE;
+
+    /* ensure we're positioned at the end of the stream */
+    if(tar->pos != tar->end_pos) {
+        err = tseek(tar, tar->end_pos);
+        if(err)
+            return err;
+    }
+
+    /* write remainder of the 512-byte record */
+    err = write_null_bytes(tar, round_up_512(tar->pos) - tar->pos);
+    if(err)
+        return err;
+
+    tar->state |= S_WROTE_DATA_EOF;
+    return MTAR_ESUCCESS;
+}
+
+int mtar_finalize(mtar_t* tar)
+{
+#ifndef MICROTAR_DISABLE_API_CHECKS
+    if(tar->access != MTAR_WRITE)
+        return MTAR_EACCESS;
+    if(((tar->state & S_WROTE_DATA) && !(tar->state & S_WROTE_DATA_EOF)) ||
+       (tar->state & S_WROTE_FINALIZE))
+        return MTAR_EAPI;
+#endif
 
-int mtar_finalize(mtar_t *tar) {
-  /* Write two NULL records */
-  return write_null_bytes(tar, sizeof(mtar_raw_header_t) * 2);
+    tar->state |= S_WROTE_FINALIZE;
+    return write_null_bytes(tar, 1024);
 }
diff --git a/lib/microtar/src/microtar.h b/lib/microtar/src/microtar.h
index d30c829521..7a9be2ac92 100644
--- a/lib/microtar/src/microtar.h
+++ b/lib/microtar/src/microtar.h
@@ -1,105 +1,132 @@
-/**
+/*
  * Copyright (c) 2017 rxi
+ * Copyright (c) 2021 Aidan MacDonald
  *
- * This library is free software; you can redistribute it and/or modify it
- * under the terms of the MIT license. See `microtar.c` for details.
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
  */
 
 #ifndef MICROTAR_H
 #define MICROTAR_H
 
 #ifdef __cplusplus
-extern "C"
-{
+extern "C" {
 #endif
 
-#include <stdio.h>
-#include <stdlib.h>
-
-#define MTAR_VERSION "0.1.0"
-
-enum {
-  MTAR_ESUCCESS     =  0,
-  MTAR_EFAILURE     = -1,
-  MTAR_EOPENFAIL    = -2,
-  MTAR_EREADFAIL    = -3,
-  MTAR_EWRITEFAIL   = -4,
-  MTAR_ESEEKFAIL    = -5,
-  MTAR_EBADCHKSUM   = -6,
-  MTAR_ENULLRECORD  = -7,
-  MTAR_ENOTFOUND    = -8,
-  MTAR_EOVERFLOW    = -9,
+#include <stdio.h>  /* SEEK_SET et al. */
+
+enum mtar_error {
+    MTAR_ESUCCESS     =  0,
+    MTAR_EFAILURE     = -1,
+    MTAR_EOPENFAIL    = -2,
+    MTAR_EREADFAIL    = -3,
+    MTAR_EWRITEFAIL   = -4,
+    MTAR_ESEEKFAIL    = -5,
+    MTAR_ESEEKRANGE   = -6,
+    MTAR_EBADCHKSUM   = -7,
+    MTAR_ENULLRECORD  = -8,
+    MTAR_ENOTFOUND    = -9,
+    MTAR_EOVERFLOW    = -10,
+    MTAR_EAPI         = -11,
+    MTAR_ENAMETOOLONG = -12,
+    MTAR_EWRONGSIZE   = -13,
+    MTAR_EACCESS      = -14,
+};
+
+enum mtar_type {
+    MTAR_TREG   = '0',
+    MTAR_TLNK   = '1',
+    MTAR_TSYM   = '2',
+    MTAR_TCHR   = '3',
+    MTAR_TBLK   = '4',
+    MTAR_TDIR   = '5',
+    MTAR_TFIFO  = '6',
 };
 
-enum {
-  MTAR_TREG   = '0',
-  MTAR_TLNK   = '1',
-  MTAR_TSYM   = '2',
-  MTAR_TCHR   = '3',
-  MTAR_TBLK   = '4',
-  MTAR_TDIR   = '5',
-  MTAR_TFIFO  = '6'
+enum mtar_access {
+    MTAR_READ,
+    MTAR_WRITE,
 };
 
-typedef struct {
-  unsigned mode;
-  unsigned owner;
-  unsigned group;
-  unsigned size;
-  unsigned mtime;
-  unsigned type;
-  char name[101]; /* +1 byte in order to ensure null termination */
-  char linkname[101];
-} mtar_header_t;
-
-
-typedef struct {
-  char name[100];
-  char mode[8];
-  char owner[8];
-  char group[8];
-  char size[12];
-  char mtime[12];
-  char checksum[8];
-  char type;
-  char linkname[100];
-  char _padding[255];
-} mtar_raw_header_t;
-
-
-typedef struct mtar_t mtar_t;
-
-struct mtar_t {
-  int (*read)(mtar_t *tar, void *data, unsigned size);
-  int (*write)(mtar_t *tar, const void *data, unsigned size);
-  int (*seek)(mtar_t *tar, unsigned pos);
-  int (*close)(mtar_t *tar);
-  void *stream;
-  unsigned pos;
-  unsigned remaining_data;
-  unsigned last_header;
-  mtar_header_t header;
-  mtar_raw_header_t raw_header;
+typedef struct mtar_header mtar_header_t;
+typedef struct mtar mtar_t;
+typedef struct mtar_ops mtar_ops_t;
+
+typedef int(*mtar_foreach_cb)(mtar_t*, const mtar_header_t*, void*);
+
+struct mtar_header {
+    unsigned mode;
+    unsigned owner;
+    unsigned group;
+    unsigned size;
+    unsigned mtime;
+    unsigned type;
+    char name[101]; /* +1 byte in order to ensure null termination */
+    char linkname[101];
 };
 
+struct mtar_ops {
+    int(*read)(void* stream, void* data, unsigned size);
+    int(*write)(void* stream, const void* data, unsigned size);
+    int(*seek)(void* stream, unsigned pos);
+    int(*close)(void* stream);
+};
+
+struct mtar {
+    char buffer[512];       /* IO buffer, put first to allow library users to
+                             * control its alignment */
+    int state;              /* Used to simplify the API and verify API usage */
+    int access;             /* Access mode */
+    unsigned pos;           /* Current position in file */
+    unsigned end_pos;       /* End position of the current file */
+    unsigned header_pos;    /* Position of the current header */
+    mtar_header_t header;   /* Most recently parsed header */
+    const mtar_ops_t* ops;  /* Stream operations */
+    void* stream;           /* Stream handle */
+};
 
 const char* mtar_strerror(int err);
 
-int mtar_open(mtar_t *tar, const char *filename, const char *mode);
-int mtar_close(mtar_t *tar);
-
-int mtar_seek(mtar_t *tar, unsigned pos);
-int mtar_rewind(mtar_t *tar);
-int mtar_next(mtar_t *tar);
-int mtar_find(mtar_t *tar, const char *name, mtar_header_t *h);
-int mtar_read_header(mtar_t *tar, mtar_header_t *h);
-int mtar_read_data(mtar_t *tar, void *ptr, unsigned size);
-
-int mtar_write_header(mtar_t *tar, const mtar_header_t *h);
-int mtar_write_file_header(mtar_t *tar, const char *name, unsigned size);
-int mtar_write_dir_header(mtar_t *tar, const char *name);
-int mtar_write_data(mtar_t *tar, const void *data, unsigned size);
-int mtar_finalize(mtar_t *tar);
+void mtar_init(mtar_t* tar, int access, const mtar_ops_t* ops, void* stream);
+int mtar_close(mtar_t* tar);
+int mtar_is_open(mtar_t* tar);
+
+mtar_header_t* mtar_get_header(mtar_t* tar);
+int mtar_access_mode(const mtar_t* tar);
+
+int mtar_rewind(mtar_t* tar);
+int mtar_next(mtar_t* tar);
+int mtar_foreach(mtar_t* tar, mtar_foreach_cb cb, void* arg);
+int mtar_find(mtar_t* tar, const char* name);
+
+int mtar_read_data(mtar_t* tar, void* ptr, unsigned size);
+int mtar_seek_data(mtar_t* tar, int offset, int whence);
+unsigned mtar_tell_data(mtar_t* tar);
+int mtar_eof_data(mtar_t* tar);
+
+int mtar_write_header(mtar_t* tar, const mtar_header_t* h);
+int mtar_update_header(mtar_t* tar, const mtar_header_t* h);
+int mtar_write_file_header(mtar_t* tar, const char* name, unsigned size);
+int mtar_write_dir_header(mtar_t* tar, const char* name);
+int mtar_write_data(mtar_t* tar, const void* ptr, unsigned size);
+int mtar_update_file_size(mtar_t* tar);
+int mtar_end_data(mtar_t* tar);
+int mtar_finalize(mtar_t* tar);
 
 #ifdef __cplusplus
 }