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Chimera can automatically download maps you don’t have when joining multiplayer servers. This feature eliminates the need to manually search for and download maps, streamlining the multiplayer experience.

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Overview

When you attempt to join a server that’s running a map you don’t have, Chimera will:
  1. Detect that the map is missing
  2. Automatically begin downloading it from a configured repository
  3. Display download progress with speed and file size information
  4. Complete the download and join the server
By default, maps are downloaded from the HAC2 Map Repository.

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Default Configuration

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Download Source

Chimera downloads maps from the HAC2/HaloNet repository by default: 
http://maps.halonet.net/maplist.php
This repository contains a large collection of community-created Custom Edition maps.

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Download Location

Downloaded maps are stored in: 
%USERPROFILE%\Documents\My Games\Halo CE\chimera\maps
This keeps downloaded maps separate from your main maps folder by default.

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Configuration

Map downloading can be customized in chimera.ini under the [memory] section:

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Download Path

Change where downloaded maps are saved: 
[memory]
; Custom download path (relative to Halo profiles folder)
download_map_path=chimera/maps

; Or use an absolute path
download_map_path=C:\CustomMaps\Downloaded

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Download Template

Customize the download URL template: 
[memory]
; URL template with placeholders
download_template=http://{mirror<repo.halomaps.org,maps.halonet.net>}/maps/{map}.map?server={server}&password={password}

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Template Placeholders

The download URL template supports several placeholders:
PlaceholderDescriptionExample
{map}Map name (URL encoded)bloodgulch
{game}Game engine typeretail or custom
{server}Server address192.168.1.100:2302
{password}Server password (URL encoded)mypassword
{mirror<list>}Mirror list (comma-separated)server1.com,server2.com

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Mirror Failover

The {mirror<>} placeholder supports multiple mirrors with automatic failover: 
download_template=http://{mirror<repo.halomaps.org,maps.halonet.net,mirror3.com>}/maps/{map}.map
Chimera will try each mirror in order until a successful download occurs.

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Retail Map Downloads

Security Warning: Downloading retail Halo PC maps is disabled by default for security reasons.
Retail maps can be modified to contain malicious content. Only enable if you trust the download source: 
[memory]
; UNSAFE - only enable if you trust the source
download_retail_maps=1

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Download Font

Customize the font used for download progress display: 
[memory]
; Font for download progress overlay
download_font=console

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Download Process

1

Server connection attempt

When you try to join a server, Chimera checks if you have the required map.
2

Download initiation

If the map is missing and downloading is enabled:
  • Chimera constructs the download URL using the template
  • A download thread is spawned to fetch the map
  • Progress is displayed on-screen
3

Download progress

During download, you’ll see:
  • Map name being downloaded
  • Current download speed (KB/s or MB/s)
  • Downloaded size / total size
  • Progress percentage
4

Validation

Once downloaded:
  • Chimera validates the map file header (checks for ‘head’ and ‘foot’ magic values)
  • Invalid or corrupted downloads are rejected
  • Successful downloads are saved to the configured location
5

Server join

After successful validation, Chimera automatically proceeds to join the server with the newly downloaded map.

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Technical Details

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Implementation

Chimera’s map downloader uses:
  • libcurl - For HTTP/HTTPS downloads
  • Multi-threading - Downloads occur in a background thread
  • Buffering - 1 MiB memory buffer for efficient I/O
  • Timeout - 10 second connection timeout
  • User Agent - Chimera MapDownloader/1.0

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Download Validation

Map files are validated by checking magic values: Standard maps (retail/Custom Edition): 
header[0x000] == 0x68656164 ("head")
header[0x7FC] == 0x666F6F74 ("foot")
Demo maps (trial): 
header[0x2C0] == 0x45686564 ("Ehed")
header[0x5F0] == 0x47666F74 ("Gfot")
Downloads with invalid headers (e.g., HTML error pages) are automatically rejected.

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Security Considerations

Chimera implements several security measures:
  1. Header validation - Ensures downloaded files are valid map files
  2. Minimum size check - Files must be at least 2048 bytes (0x800)
  3. Retail map blocking - Retail maps blocked by default to prevent replacement attacks
  4. URL encoding - Map names and passwords are properly URL-encoded
  5. HTTPS support - Supports secure downloads when configured

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Custom Download Servers

You can set up your own map download server and point Chimera to it:

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Simple HTTP Server

[memory]
download_template=http://mymapserver.com/maps/{map}.map
Your server should:
  • Respond to GET requests for /{map}.map
  • Return 404 for missing maps
  • Support HTTP/1.1

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Advanced Template

For more complex setups: 
[memory]
download_template=https://api.mymaps.com/download?name={map}&game={game}&srv={server}
This allows your server to:
  • Log download statistics
  • Implement access control
  • Serve different map versions based on game type
  • Track which servers are requesting maps

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Troubleshooting

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Download fails to start

  • Check that download_template is configured in chimera.ini
  • Verify you have write permissions to the download path
  • Ensure your internet connection is active

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Download times out

  • The default timeout is 10 seconds for connection establishment
  • Check your firewall settings
  • Verify the download server is online
  • Try a different mirror if using multiple mirrors

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Invalid map file error

  • The downloaded file is not a valid map (likely an error page)
  • Check that the download URL template is correct
  • Verify the map exists on the server
  • Try downloading the map manually to test the URL

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Wrong map downloaded

  • Ensure the {map} placeholder is in the correct position in your template
  • Check that the server is returning the correct map for the requested name
  • Map names are case-insensitive (automatically converted to lowercase)

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Downloaded maps not loading

  • Check that the maps are in the correct folder
  • Verify the download path setting in chimera.ini
  • Ensure Chimera has read access to the download folder
  • The map may be corrupted - try deleting and re-downloading

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Performance Tips

  1. Use local mirrors - Host frequently used maps on a local network server for faster downloads
  2. Enable compression - Serve compressed maps if your server supports it
  3. Increase buffer size - The default 1 MiB buffer works well for most connections
  4. Use HTTPS - Provides security but may be slightly slower than HTTP
  5. Pre-download maps - For frequently played servers, manually download maps ahead of time

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Best Practices

  1. Organize downloads - Use a separate folder for auto-downloaded maps
  2. Regular cleanup - Periodically review and remove unused maps
  3. Mirror redundancy - Configure multiple mirrors for reliability
  4. Trust your sources - Only download from trusted repositories
  5. Monitor disk space - Auto-downloading can fill disk space over time

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