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JojoDiff Alternative Patch library - portable C library for memory-efficient binary patching
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Jojo AlterNative Patch (JANPatch)

Memory-efficient library which can apply JojoDiff patch files. Very useful for embedded development, for example for delta firmware updates. Written in C, and can be backed by anything that offers basic I/O primitives.

This is an implementation from scratch, done by reverse engineering the diff file format, and inspecting the diff generation code. It's not a derived work from jptch (the patch application in JojoDiff). The reason for this is that JojoDiff is licensed under GPLv3, which does not allow linking in the library in non-GPL applications. JANPatch is licensed under Apache 2.0.

For an example of using this library on an embedded system, see binary-diff-mbedos5.

Usage (CLI)

On POSIX systems (macOS, Linux, Cygwin under Windows):

  1. Build the CLI, via:

    $ make
  2. Run ./janpatch-cli with the old file, a JojoDiff patch file, and the destination:

    $ ./janpatch-cli demo/blinky-k64f-old.bin demo/blinky-k64f.patch ./blinky-k64f-patched.bin
  3. Verify that the patch was applied successfully:

    $ diff demo/blinky-k64f-new.bin blinky-k64f-patched.bin
    # should return nothing

Usage (library)

JANPatch is implemented in a single header file, which you can copy into your project. For portability to non-POSIX platforms you need to provide the library with function pointers to basic IO operations. These are fread, fwrite, fseek and (optionally) ftell. The file pointer for these functions is of type JANPATCH_STREAM, which you can set when building.

The functions are defined in a context, for example on POSIX systems, you define JANPatch like this:

#define JANPATCH_STREAM     FILE        // use POSIX FILE

#include "janpatch.h"

janpatch_ctx ctx = {
    // fread/fwrite buffers for every file, minimum size is 1 byte
    // when you run on an embedded system with block size flash, set it to the size of a block for best performance
    { (unsigned char*)malloc(1024), 1024 },
    { (unsigned char*)malloc(1024), 1024 },
    { (unsigned char*)malloc(1024), 1024 },

    // define functions which can perform basic IO
    // on POSIX, use:
    &ftell          // NOTE: passing ftell is optional, and only required when you need progress reports

Then create three objects of type JANPATCH_STREAM and call janpatch with the context:

JANPATCH_STREAM *source = fopen("source.bin", "rb");
JANPATCH_STREAM *patch  = fopen("patch", "rb");
JANPATCH_STREAM *target = fopen("target.bin", "wb");

janpatch(ctx, source, patch, target);

For a demonstration of using this library on a non-POSIX system, see binary-diff-mbedos5#xdot.

Reporting progress

Exact progress indication is hard, as the size of the file after patching is not known, but you can get rudimentary progress (based on the pages written to the target stream) by setting the progress property on the context:

void progress(uint8_t percentage) {
    printf("Patch progress: %d%%\n", percentage);

ctx.progress = &progress;

Note that you need to have declared ctx.ftell for this to work.

Generating patch files

To generate patch files you'll need to build JojoDiff or JDiff.js.

  1. Install a recent version of Node.js.

  2. Install JDiff.js:

    $ npm install jdiff-js -g
  3. Generate a patch file via:

    $ jdiff old-file.bin new-file.bin old-to-new-file.patch

Running tests

To test janpatch against a wide variety of outputs you can run the integration tests. The script will generate all possible diffs between files in the integration-tests/source directory, then use janpatch to patch them.

To run:

  1. Install a recent version of Node.js.

  2. Build JojoDiff (see above).

  3. Build janpatch-cli.

  4. Run:

    $ node integration-tests/run-tests.js --jdiff-path "/path/to/jdiff"

Mbed OS 5 - Building without loading UART driver

Error messages are printed over printf, which will automatically load the UART drivers on Mbed OS 5. You can mitigate this by using debug(), which is stripped out when building for a release profile.

You can do this by declaring the JANPATCH_ERROR macro as such:

#define JANPATCH_ERROR(...)  debug(__VA_ARGS__)


Apache License version 2. See LICENSE.

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