Build a cache key

A stable lowercase-hex hash. cachem keys may contain only lowercase letters and numbers, so a URL cannot be one directly and the inputs are hashed instead. rlang::hash() returns lowercase hex, which satisfies the rule.

Usage

cache_key(source, key, params = NULL)

Arguments

source

A friendly label for the service.

key

Something identifying the call, usually the method and URL.

params

Anything else that changes the answer, such as a POST body.

Value

A single string.

Details

The salt and the schema version are inside the hash, so changing either yields a fresh keyspace. Set BIOHTTP_CACHE_SALT per deployment: a shared disk cache would otherwise collide across app versions, and it would leak which queries were run to anyone able to probe it.

Put anything that changes the answer into params, credentials included. The wrappers pass their headers through, because two callers hitting the same URL with different tokens can legitimately get different responses, and keying on the URL alone would serve one caller's data to the other. The cost is that rotating a token misses the cache once, which is the right trade.

Examples

cache_key("gnomAD", "GET https://example.org/v1/gene/BRCA1")
#> [1] "c78efd8b2316b27f48b66212054e32cd"
cache_key("gnomAD", "POST https://example.org/graphql", list(q = "BRCA1"))
#> [1] "572c652c8a78fbd9e901acfb4b49c691"