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.

Close() is idempotent and terminal: after it returns, every Resolve reports errors.Is(err, mamori.ErrUnavailable) locally, without contacting Vercel. It also returns its own idle HTTP connections to the pool, and leaves connections belonging to the rest of your process alone. A client injected with WithHTTPClient is never closed, so it stays usable for whatever else holds it.

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.