Vercel Global Config

Load a value from Vercel Global Config (formerly Edge Config), Vercel’s globally replicated key-value store for feature flags, redirect maps, and experimentation settings. Pure net/http, no third-party SDK.

Install

go get github.com/xavidop/mamori/providers/vercel-gc

import _ "github.com/xavidop/mamori/providers/vercel-gc"

Using the ref

A vercel-gc:// ref points at one key in a Global Config store, optionally selecting a field from a JSON value stored there.

vercel-gc://<key>
vercel-gc://<store-id>/<key>[#field-or-pointer]

Examples

• vercel-gc://log-level reads key log-level from the store named by GLOBAL_CONFIG/EDGE_CONFIG.
• vercel-gc://ecfg_abc123/log-level reads the same key from an explicit store.
• vercel-gc://api-config#timeout reads field timeout of the JSON-valued key api-config.
• vercel-gc://api-config#/retry/maxAttempts reads a nested field by JSON Pointer.

type Config struct {
	LogLevel   string `source:"vercel-gc://log-level"`
	MaxRetries int    `source:"vercel-gc://max-retries"`
	APITimeout string `source:"vercel-gc://api-config#timeout"`
}

A stored JSON string is unwrapped to its raw text; every other JSON type (boolean, number, object, array) passes through as its own compacted JSON encoding, so a number is exactly what the store holds rather than what a float64 round trip would produce - a deliberate difference from the LaunchDarkly provider, which evaluates flags through an SDK value type backed by float64. A key stored as null exists and resolves to the four bytes null; only an absent key is not-found. Value.Sensitive is always false (Global Config holds flags and redirects, not managed secrets - wrap a field in secret.String for redaction anyway), and Value.Version is a content hash rather than the store’s digest, because the digest moves on every edit to any key in the store.

Error classification

A missing store is detected as a 404 before status classification runs, and reports not_found directly. A missing key in a store that does exist is detected by its absence from the fetched items, not a status code, and also reports not_found. Beyond those two cases, failures are classified by HTTP status:

A 403 is not always an insufficient credential: Vercel’s documented error body for a request missing a token also carries "code": "forbidden", and Vercel has not published its full error-code vocabulary, so the mapping keys on status rather than guessing at a body it cannot rely on.

Watch

Vercel exposes no streaming or blocking read for Global Config, so this provider does not implement WatchableProvider - mamori polls it instead (WithPollInterval + jitter). Each Resolve requests the store’s cheap /digest endpoint and refetches the full /items body only when the digest moved, so an unchanged poll tick costs one small request per field and no body fetch.

Configuration

import vercelgc "github.com/xavidop/mamori/providers/vercel-gc"

mamori.WithProvider(vercelgc.New(vercelgc.WithConnectionString(os.Getenv("GLOBAL_CONFIG"))))

GLOBAL_CONFIG (falling back to EDGE_CONFIG for stores connected before Vercel’s rename) is read lazily at resolve time, so a blank import alone is enough once the environment variable is set. The token always travels as an Authorization: Bearer header, never a URL query parameter, so a request to the Global Config API cannot leak it into a log line, a trace span, or an error message. That guarantee is about requests, not about parsing the connection string itself: a malformed connection string (a trailing newline is the realistic case) can otherwise surface inside a url.Parse diagnostic, so this provider strips the URL from that error before returning it. Passing a full connection string to WithBaseURL by mistake is the other way the token can end up in a transport error, since it redirects every request to the host it names.

Verified with an in-memory fake HTTP transport (digest-gated fetching, value mapping, error classification, batch resolution, concurrent resolve), so the conformance kit runs without a live Vercel store. A //go:build integration test exercises a real store when GLOBAL_CONFIG/EDGE_CONFIG and VERCEL_GC_TEST_KEY are set.