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dotnet-install url lookup scheme docs
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dotnet-install-urls.md

.NET Install Script URL Lookup Scheme

This document summarizes how the dotnet-install.sh script determines the download URLs for .NET SDKs and runtimes.

1. Primary Lookup: aka.ms Short URL Redirection

  • When Used:
    This is the preferred and first method for obtaining download URLs, especially for the latest releases and common channels (like LTS/STS).

  • How It Works:

    • The script constructs a URL of the form: 
      https://aka.ms/dotnet/<channel>/<quality>/<product>-<os>-<architecture>.tar.gz
      • <channel>: e.g., LTS, STS, or a version like 8.0
      • <quality>: daily, preview (optional, not for LTS/STS)
      • <product>: dotnet-sdk, dotnet-runtime, aspnetcore-runtime
      • <os>: linux, linux-musl, osx, freebsd, rhel.6, etc.
      • <architecture>: x64, arm64, etc.
    • The script follows HTTP 301 redirects to the real storage endpoint, resolving the actual artifact location.
    • The download link obtained is used to fetch the installer package.

2. Fallback: Feed-Based Direct Lookups

If the aka.ms approach fails (e.g., for older versions or if a specific version is requested), the script falls back to constructing direct URLs to known feeds:

  • Feeds Used:

    • Public:
      • https://builds.dotnet.microsoft.com/dotnet
      • https://ci.dot.net/public
    • Custom feeds can be specified via --azure-feed or --uncached-feed.

  • Version Determination:

    • If latest is requested, the script fetches a latest.version file from the feed to determine the most recent version for a channel.
    • If a specific version is given, that version is used directly.

  • URL Construction:
    The script generates URLs based on the required asset:

    <feed>/<Type>/<Channel or Version>/<Package File>
    • Type: Sdk, Runtime, or aspnetcore/Runtime
    • Package File:
      • For SDK: dotnet-sdk-<version>-<os>-<arch>.tar.gz
      • For Runtime: dotnet-runtime-<version>-<os>-<arch>.tar.gz
      • For aspnetcore: aspnetcore-runtime-<version>-<os>-<arch>.tar.gz

  • Legacy Fallback:
    For some very old versions or specific distros, the script constructs "legacy" URLs using different file naming conventions and OS identifiers (e.g., dotnet-dev-ubuntu.16.04-x64.<version>.tar.gz).

3. Other Details

  • Version Selection from global.json:
    If a global.json file is provided, the script tries to parse the version from it.
  • Internal Builds:
    If --internal is specified, it uses internal feeds and requires credentials.
  • Validation:
    The script checks if the required version is already installed and skips downloading if so.

Summary Table

Step URL Pattern/Source Used For
aka.ms redirect https://aka.ms/dotnet/<channel>/<quality>/<product>-<os>-<arch>.tar.gz Latest/standard downloads
Feed direct lookup <feed>/<Type>/<Channel or Version>/<Package File> (see above for specifics) Specific/older versions
Legacy fallback <feed>/<Type>/<Version>/<legacy file> (OS/distro-specific) Ancient distros/versions

In summary:
The script first attempts to use a short aka.ms URL, following redirects to the official Microsoft blob storage. If that fails or for specific versions, it falls back to constructing direct URLs to dotnet feeds, and as a last resort, uses legacy URL patterns, all determined dynamically based on user input, system architecture, and OS.

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