Add support for fetching container logs from a given time (#670)

docs/features/containers.md

@@ -527,3 +527,14 @@ const container = await new GenericContainer("alpine")
   })
   .start();
 ```
+
+You can specify a point in time as a UNIX timestamp from which you want the logs to start: 
+
+```javascript
+const msInSec = 1000;
+const tenSecondsAgoMs = new Date().getTime() - 10 * msInSec;
+const since = tenSecondsAgoMs / msInSec;
+
+(await container.logs({ since }))
+  .on("data", line => console.log(line))
+```

packages/testcontainers/src/generic-container/abstract-started-container.ts

@@ -83,7 +83,7 @@ export class AbstractStartedContainer implements StartedTestContainer {
     return this.startedTestContainer.exec(command);
   }
 
-  public logs(): Promise<Readable> {
-    return this.startedTestContainer.logs();
+  public logs(opts?: { since?: number }): Promise<Readable> {
+    return this.startedTestContainer.logs(opts);
   }
 }

packages/testcontainers/src/generic-container/generic-container-logs.test.ts

@@ -1,5 +1,6 @@
 import { GenericContainer } from "./generic-container";
 import { containerLog } from "../common";
+import { Wait } from "../wait-strategies/wait";
 
 describe("GenericContainer logs", () => {
   jest.setTimeout(180_000);
@@ -26,6 +27,32 @@ describe("GenericContainer logs", () => {
     await container.stop();
   });
 
+  it("should stream logs with since option from a started container", async () => {
+    const pauseMs = 5 * 1000;
+    const logBeforeSleep = "first";
+    const logAfterSleep = "second";
+    const container = await new GenericContainer("cristianrgreco/testcontainer:1.1.14")
+      .withEntrypoint([
+        "/bin/sh",
+        "-c",
+        `echo ${logBeforeSleep} && sleep ${pauseMs / 1000} && echo ${logAfterSleep} && sleep infinity`,
+      ])
+      .withWaitStrategy(Wait.forLogMessage(logBeforeSleep))
+      .start();
+
+    await new Promise((resolve) => setTimeout(resolve, pauseMs));
+
+    const inSleepTimestamp = new Date().getTime() - pauseMs + 1000;
+    const since = Math.floor(inSleepTimestamp / 1000);
+
+    const stream = await container.logs({ since });
+    const log: string = await new Promise((resolve) => stream.on("data", (line) => resolve(line.trim())));
+
+    expect(log).toBe(logAfterSleep);
+
+    await container.stop();
+  });
+
   it("should stream logs from a running container after restart", async () => {
     const containerLogTraceSpy = jest.spyOn(containerLog, "trace");
     const container = await new GenericContainer("cristianrgreco/testcontainer:1.1.14").withExposedPorts(8080).start();

packages/testcontainers/src/generic-container/started-generic-container.ts

@@ -181,8 +181,9 @@ export class StartedGenericContainer implements StartedTestContainer {
     return output;
   }
 
-  public async logs(): Promise<Readable> {
+  public async logs(opts?: { since?: number }): Promise<Readable> {
     const client = await getContainerRuntimeClient();
-    return client.container.logs(this.container);
+
+    return client.container.logs(this.container, opts);
   }
 }

packages/testcontainers/src/test-container.ts

@@ -74,7 +74,7 @@ export interface StartedTestContainer {
   copyFilesToContainer(filesToCopy: FileToCopy[]): Promise<void>;
   copyContentToContainer(contentsToCopy: ContentToCopy[]): Promise<void>;
   exec(command: string | string[]): Promise<ExecResult>;
-  logs(): Promise<Readable>;
+  logs(opts?: { since?: number }): Promise<Readable>;
 }
 
 export interface StoppedTestContainer {