From 9b4b53739e6e77ba987d91d35fc1e365fcf3bcc0 Mon Sep 17 00:00:00 2001
From: Christopher Pruijsen <christopher.pruijsen@gmail.com>
Date: Sun, 13 Sep 2026 09:19:12 +0000
Subject: [PATCH] fix: preserve concurrency: 0 so it disables the limit as
 documented

expandConfig normalized the option with `concurrency || 20`, which turns
the documented "0 disables concurrency limits" into the default of 20.
Use `??` so only a missing value falls back to the default.

The sqlite3 client sizes its connection pool from the same config value;
map a preserved 0 to an unbounded pool there too, matching the http and
ws clients where promise-limit treats a falsy limit as pass-through.

Fixes #351
---
 .../src/__tests__/config.test.ts              | 37 +++++++++++++++++++
 packages/libsql-client/src/sqlite3.ts         |  6 ++-
 packages/libsql-core/src/config.ts            |  2 +-
 3 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/packages/libsql-client/src/__tests__/config.test.ts b/packages/libsql-client/src/__tests__/config.test.ts
index 30fd41f..9c86ae5 100644
--- a/packages/libsql-client/src/__tests__/config.test.ts
+++ b/packages/libsql-client/src/__tests__/config.test.ts
@@ -232,3 +232,40 @@ describe("expandConfig - parsing of valid arguments", () => {
         });
     }
 });
+
+describe("expandConfig - concurrency", () => {
+    const cases = [
+        {
+            name: "default",
+            config: { url: "file://local.db" },
+            concurrency: 20,
+        },
+        {
+            name: "explicit limit",
+            config: { url: "file://local.db", concurrency: 42 },
+            concurrency: 42,
+        },
+        {
+            name: "zero disables the limit",
+            config: { url: "file://local.db", concurrency: 0 },
+            concurrency: 0,
+        },
+        {
+            name: "negative clamps to zero",
+            config: { url: "file://local.db", concurrency: -5 },
+            concurrency: 0,
+        },
+        {
+            name: "in-memory zero disables the limit",
+            config: { url: ":memory:", concurrency: 0 },
+            concurrency: 0,
+        },
+    ];
+    for (const { name, config, concurrency } of cases) {
+        test(name, () => {
+            expect(expandConfig(config, false).concurrency).toEqual(
+                concurrency,
+            );
+        });
+    }
+});
diff --git a/packages/libsql-client/src/sqlite3.ts b/packages/libsql-client/src/sqlite3.ts
index 3044da3..be852dc 100644
--- a/packages/libsql-client/src/sqlite3.ts
+++ b/packages/libsql-client/src/sqlite3.ts
@@ -82,8 +82,12 @@ export function _createClient(config: ExpandedConfig): Client {
     // second connection would be a second, empty database rather than another
     // way into the same one. Each connection to an embedded replica carries
     // its own sync state. Both are therefore single-connection databases.
+    // A concurrency of 0 means no limit, matching the remote clients, whose
+    // promise-limit semaphore treats a falsy limit as pass-through.
     const maxConnections =
-        isInMemory || config.syncUrl ? 1 : Math.max(1, config.concurrency);
+        isInMemory || config.syncUrl
+            ? 1
+            : Math.max(1, config.concurrency || Infinity);
 
     const options = {
         authToken: config.authToken,
diff --git a/packages/libsql-core/src/config.ts b/packages/libsql-core/src/config.ts
index 44dd7bf..cda770c 100644
--- a/packages/libsql-core/src/config.ts
+++ b/packages/libsql-core/src/config.ts
@@ -53,7 +53,7 @@ export function expandConfig(
 
     let { url, authToken, tls, intMode, concurrency } = config;
     // fill simple defaults right here
-    concurrency = Math.max(0, concurrency || 20);
+    concurrency = Math.max(0, concurrency ?? 20);
     intMode ??= "number";
 
     let connectionQueryParams: string[] = []; // recognized query parameters which we sanitize through white list of valid key-value pairs