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0.6.2 Apr 25, 2024
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0.6.0 Feb 23, 2024
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#192 in Database interfaces

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MPL-2.0 license



Mapiproxy is a tool for inspecting MonetDB network traffic by acting as a proxy between clients and servers.

The MonetDB network protocol is called MAPI, hence the name.

The proxy can work with TCP sockets, Unix Domain sockets or both at the same time. The MAPI protocol is slightly different between TCP and Unix sockets, the proxy will automatically adjust it when proxying between the two.

Additionally, Mapiproxy offers experimental support for reading PCAP files: captured network traffic files, often generated by tools like tcpdump and Wireshark. However, this feature is still in its early stages and may not be fully functional in practice.


The following is a summary of Mapiproxy's usage:

       mapiproxy [OPTIONS] --pcap PCAP_FILE

    PORT, for example, 50000
    HOST:PORT, for example, localhost:50000 or
    /path/to/unixsock, for example, /tmp/.s.monetdb.50000

    -o, --output=FILE    Write output to this file
    -m, --messages       Dump whole messages
    -b, --blocks         Dump individual blocks
    -r, --raw            Dump bytes as they come in
    -B, --binary         Force dumping as binary
    --color=WHEN         Colorize output (Options: 'always', 'auto', 'never')
    --help               Display this help message
    --version            Show version information

Experimental options:
    --pcap=FILE          Read network capture data from FILE (use '-' for stdin)


Source code is available on GitHub.

Pre-built binaries for x86-64 Linux, MacOS, and Windows are available on the Releases page of the GitHub repository.

Mapiproxy is written in Rust. If you want to build from source and don't have the Rust compiler installed, visit rustup.rs.

With Rust installed, simply execute cargo install mapiproxy. This will download the source, compile and install it. Alternatively, clone the repository from GitHub and build using cargo build --release.

Output Modes

Mapiproxy offers three output modes, corresponding to the layers of the MAPI protocol. In a nutshell, MAPI communication consists of a series of messages. Each message is sent as of one or more blocks. Each block is preceded by a two-byte block header.

Mapiproxy output consists of a mix of single-line informational messages and multi-line frames that display the captured data. For example, in the single-line message

‣ #10 UPSTREAM client stopped sending

we see a connection id, a direction marker (UPSTREAM for client to server and DOWNSTREAM for server to client), and an informational message.

Frames display the data either as a hex dump, like this,

┌ #10 UPSTREAM binary, message, 13 bytes
│ 73 73 65 6c  65 63 74 20   34 32 0a 3b  0a __ __ __     sselect·42↵;↵

or they display it as text, like this:

┌ #10 UPSTREAM text, message, 13 bytes
│sselect 42↵

Mapiproxy generally prefers text output over binary, but will render a frame in binary when at least one of the following conditions holds true:

  • the data is not valid UTF-8 encoded text

  • the data contains control characters other than newline and tab

  • Mapiproxy is running in --raw mode

  • binary output is forced using the -B or --binary flag

When Mapiproxy is in --messages mode, it collects all bytes of a whole message and prints them as a single frame, skipping the block headers. In --blocks mode, it collects whole blocks and prints one block per frame, also without the block header.

Because of the above rules it may happen in --blocks mode that a multi-byte character spans across a block boundary. In that case both blocks are considered to be not valid UTF-8 encoded text so they will be displayed in binary even though other blocks in the message are still rendered as text.

In --raw mode, all bytes are printed as they are received, including the block headers. This means that a single printed chunk may contain parts of multiple blocks and even parts of multiple messages. Conversely, a block or message is often spread across multiple chunks of received bytes.

The --raw mode is the only mode in which block headers are included in the output. They are marked with angle brackets '⟨' and '⟩'. For example:

┌ #20 DOWNSTREAM 42 bytes
│⟨51 00⟩5e 6d  61 70 69 3a   6d 65 72 6f  76 69 6e 67     Q░^mapi:meroving
│ 69 61 6e 3a  2f 2f 70 72   6f 78 79 3f  64 61 74 61     ian://proxy?data
│ 62 61 73 65  3d 64 65 6d   6f 0a __ __  __ __ __ __     base=demo↵

Special characters and color escapes

Mapiproxy output contains some non-ASCII Unicode characters. This cannot currently be disabled. While this is typically not problem on Linux and MacOS, users on Windows platforms may encounter issues. Please share you experiences.

This is a list of the non-ASCII characters used by Mapiproxy:

Character Meaning When
‣, ┌, └, │ Frame boundary always
↵, → newline and tab always
⟨, ⟩ block header markers raw mode
·, ░, ▒ space, NUL byte, any unprintable byte hexdump only

When writing to a terminal or when explicitly enabled with --color=always, Mapiproxy uses VT-100/ANSI color escape sequences for enhanced readability, especially of the hex dumps. This behavior can be disabled by passing the flag --color=never.


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