Memfault Compact Log Library

This library enables decoding Memfault-flavored compact logs. For background information on compact logs, see here:

https://mflt.io/compact-logs

Usage

Some brief usage information below. See the source for detailed usage.

Extracting compact log format strings from .elf

To extract the format strings from the symbol file:

from mflt_compact_log.log_fmt import LogFormatElfSectionParser

elf = "path to elf file"
# parse the elf file
mappings = LogFormatElfSectionParser.get_mapping_from_elf_file(elf)
# 'mappings' is a dictionary mapping log id to LogFormatInfo data
print(mappings)

>>> {8: LogFormatInfo(filename='./main/console_example_main.c', line=245, n_args=0, fmt='This is a compact log example')}

Decoding compact logs

To apply the format string to raw compact log data:

from mflt_compact_log import CompactLogDecoder

# example format string; this could instead be retrieved from the elf file
fmt = "An Integer Format String: %d"

# compact log hex encoded raw data
compact_log = "820A0B"

# decode the log!
compact_log_as_bytes = bytes.fromhex(compact_log)
log = CompactLogDecoder.from_cbor_array(fmt, compact_log_as_bytes)
log.decode()
>>> 'An Integer Format String: 11'

Changes

[0.2.1] - 2026-01-20

• Add project description to pyproject.toml

[0.2.0] - 2025-11-17

• Remove support for Python < 3.10

• Remove click dependency

• Add support for Truncated Compact Log entries

• The command line tools, mflt-compact-log.log_fmt and mflt-compact-log.decode_compact_log, have been moved into subcommands under mflt-compact-log:

  • mflt-compact-log log-fmt
  • mflt-compact-log decode

  See mflt-compact-log --help for details.

[0.1.1] - 2024-11-14

• Fix some missing dependencies that are required as of the 0.1.0 release.

[0.1.0] - 2024-11-08

• Replace the wasmer-based decoder with a pure Python implementation

[0.0.5] - 2024-08-29

• Improve the output of mflt-compact-log.log_fmt for log format strings containing non-printable characters

[0.0.4] - 2024-06-13

• Source pyelftools from https://pypi.org/project/pyelftools/ again, as the required bugfixes have been merged upstream. See notes of 0.0.3 below.

[0.0.3] - 2024-01-30

• Source pyelftools from https://github.com/memfault/pyelftools while we are waiting for 2 bugfixes to get merged upstream (https://github.com/eliben/pyelftools/pull/537 and https://github.com/eliben/pyelftools/pull/538).

0.0.2

• support Python 3.9 and 3.10
• update prettytable dependency from 0.7.2 to 3.4.1
• update pyelftools dependency from ^0.28.0 to ^0.29.0