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Identifying channels

A conda channel is defined as a URL where one can find one or more repodata.json files arranged in one subdirectory (subdir) each. noarch/repodata.json MUST be present to consider the parent location a channel.

Channel base URLs​

The base URL for the arbitrary location of a repodata file is defined as:

<scheme>://[<authority>][/<path>/][/label/<label name>]/<subdir>/repodata.json

with <scheme>, <authority> and <path> defined by RFC 3986.

Given the channel definition above, the base URL without trailing slashes is thus:

<scheme>://[<authority>][/<path>/][/label/<label name>]

For example, given https://conda.anaconda.org/conda-forge/noarch/repodata.json, the part leading to noarch/repodata.json and thus base URL is https://conda.anaconda.org/conda-forge. For local repodata such as file:///home/username/channel/noarch/repodata.json, the channel base URL is file:///home/username/channel.

When present, each path component MUST only contain lowercase ASCII letters, numbers, underscores, periods, and dashes. They MUST NOT start with a period or a dash. They SHOULD start and end with a letter or a number. If present, each path component MUST match this regex:

^[a-z0-9_][a-z0-9_.-]*$

For file://-based channel URLs, the path component rules MAY be understood as recommendations only.

The maximum length of an individual path component in a channel base URL MUST NOT exceed 128 characters. The maximum length of a channel base URL SHOULD NOT exceed 256 characters.

To avoid ambiguous MatchSpec grammar, the last path component of a channel base URL SHOULD NOT match any subdir identifiers. If it does, the behavior in this ambiguous case is not defined and implementation dependent.

Channel names​

For convenience, the channel name is defined as the concatenation of scheme, authority and path components of a channel URL. At least one of authority or path SHOULD be present. In their absence, the channel name MUST be considered empty, regardless the scheme. Empty channel names SHOULD NOT be used.

When the scheme and authority fields are missing, the full URL can be inferred with these rules:

  • If the channel name matches the regex ^\.{0,2}[/\\].*$, or if it matches the regex ^[A-Z]:([\\/].*)?$ (for Windows drives), it SHOULD be understood as the path component of a file:// URL.
  • Otherwise, the tool SHOULD provide a user-configurable mechanism to use a default scheme and authority, with the provided channel name taken as the rest of the path component. At the time of this CEP's writing, most tools assume the default URL scheme and authority to be https://conda.anaconda.org.

Subdir names​

Channel subdir names MUST either be the literal noarch or a string following the syntax {os}-{arch}, where {os} and {arch} MUST only consist of lowercase ASCII letters and numbers. Non-noarch subdirs MUST match this regex:

^[a-z0-9]+-[a-z0-9]+$

The maximum length of a subdir name MUST NOT exceed 32 characters.

Label names​

Channel label names MUST only consist of ASCII letters, digits, underscores, hyphens, forward slashes, periods, and whitespace. They MUST start with a letter. They MUST match this regex:

^[a-zA-Z][0-9a-zA-Z_\-\./]*$

The last /-delimited component of a label SHOULD NOT match any subdir identifier. If it does, the behavior in this ambiguous case is undefined and implementation dependent.

The label nolabel is reserved and MUST only be used for conda packages which have no other labels. In other words, in the space of labels, the empty set is represented by the labels nolabel.

A URL for a package, repodata, etc. without a label component MUST be assumed to have the default label main.

The maximum length of a label name MUST NOT exceed 128 characters.

History​

  • 2025-04-17: Channel identifiers were first standardized by CEP 26.