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* Improve asset caching readme * Update assetcaching.md Co-authored-by: Robert Schumacher <roschuma@microsoft.com>
59 lines
2.3 KiB
Markdown
59 lines
2.3 KiB
Markdown
# Asset Caching
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**The latest version of this documentation is available on [GitHub](https://github.com/Microsoft/vcpkg/tree/master/docs/users/assetcaching.md).**
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**Experimental feature: this may change or be removed at any time**
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Vcpkg can utilize mirrors to cache downloaded assets, ensuring continued operation even if the original source changes
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or disappears.
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In-tool help is available via `vcpkg help assetcaching`.
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## Configuration
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Asset caching can be configured by setting the environment variable `X_VCPKG_ASSET_SOURCES` to a semicolon-delimited
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list of source strings. Characters can be escaped using backtick (\`).
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### Valid source strings
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The `<rw>` optional parameter for certain strings controls how they will be accessed. It can be specified as `read`,
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`write`, or `readwrite` and defaults to `read`.
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#### `clear`
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Syntax: `clear`
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Removes all previous sources
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#### `x-azurl`
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Syntax: `x-azurl,<url>[,<sas>[,<rw>]]`
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Adds an Azure Blob Storage source, optionally using Shared Access Signature validation. URL should include the container
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path and be terminated with a trailing `/`. SAS, if defined, should be prefixed with a `?`. Non-Azure servers will also
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work if they respond to GET and PUT requests of the form: `<url><sha512><sas>`. As an example, if you set
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`X_VCPKG_ASSET_SOURCES` to `x-azurl,https://mydomain.com/vcpkg/,token=abc123,readwrite` your server should respond to
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`GET` and `PUT` requests of the form `https://mydomain.com/vcpkg/<sha512>?token=abc123`.
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You can also use the filesystem (e.g. a network drive) via `file://` as asset cache. For example you then set
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`X_VCPKG_ASSET_SOURCES` to `x-azurl,file:///Z:/vcpkg/assetcache/,,readwrite` when you have a network folder mounted at
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`Z:/`.
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The workflow of this asset source is:
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1. Attemp to read from the mirror
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2. (If step 1 failed) Read from the original url
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3. (If step 2 succeeded) Write back to the mirror
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You can enable/disable steps 1 and 3 via the [`<rw>`](#valid-source-strings) specifier and you can disable step 2 via
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`x-block-origin` below.
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See also the [binary caching documentation for Azure Blob Storage](binarycaching.md#azure-blob-storage-experimental) for
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more information on how to set up an `x-azurl` source.
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#### `x-block-origin`
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Syntax: `x-block-origin`
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Disables use of the original URLs in case the mirror does not have the file available.
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