fix: add platform field and context_line extraction (#13)

Author: kashishhora

src/modules/exceptions.ts

@@ -1,4 +1,5 @@
 import { ErrorData, StackFrame, ChainedErrorData } from "../types.js";
+import { readFileSync } from "fs";
 
 // Maximum number of exceptions to capture in a cause chain
 const MAX_EXCEPTION_CHAIN_DEPTH = 10;
@@ -22,12 +23,14 @@ export function captureException(error: unknown): ErrorData {
     return {
       message: stringifyNonError(error),
       type: "NonError",
+      platform: "javascript",
     };
   }
 
   const errorData: ErrorData = {
     message: error.message || "",
     type: error.name || error.constructor?.name || "Error",
+    platform: "javascript",
   };
 
   // Capture stack trace if available
@@ -76,6 +79,7 @@ function parseV8StackTrace(stackTrace: string): StackFrame[] {
 
     const frame = parseV8StackFrame(line.trim());
     if (frame) {
+      addContextToFrame(frame);
       frames.push(frame);
     }
 
@@ -88,6 +92,40 @@ function parseV8StackTrace(stackTrace: string): StackFrame[] {
   return frames;
 }
 
+/**
+ * Adds context_line to a stack frame by reading the source file.
+ *
+ * This function extracts the line of code where the error occurred by:
+ * 1. Reading the source file using abs_path
+ * 2. Extracting the line at the specified line number
+ * 3. Setting the context_line field on the frame
+ *
+ * Only extracts context for user code (in_app: true)
+ * If the file cannot be read or the line number is invalid, context_line remains undefined.
+ *
+ * @param frame - The StackFrame to add context to (modified in place)
+ * @returns The modified StackFrame
+ */
+function addContextToFrame(frame: StackFrame): StackFrame {
+  if (!frame.in_app || !frame.abs_path || !frame.lineno) {
+    return frame;
+  }
+
+  try {
+    const source = readFileSync(frame.abs_path, "utf8");
+    const lines = source.split("\n");
+    const lineIndex = frame.lineno - 1; // Convert to 0-based index
+
+    if (lineIndex >= 0 && lineIndex < lines.length) {
+      frame.context_line = lines[lineIndex];
+    }
+  } catch {
+    // File not found or not readable - silently skip
+  }
+
+  return frame;
+}
+
 /**
  * Parses a location string from a V8 stack frame.
  *

src/tests/exceptions.test.ts

@@ -44,6 +44,19 @@ describe("captureException", () => {
       expect(result.message).toBe("Custom error message");
       expect(result.type).toBe("CustomError");
     });
+
+    it("should always set platform to 'javascript'", () => {
+      const error = new Error("Test error");
+      const result = captureException(error);
+
+      expect(result.platform).toBe("javascript");
+    });
+
+    it("should set platform to 'javascript' for non-Error objects", () => {
+      const result = captureException("string error");
+
+      expect(result.platform).toBe("javascript");
+    });
   });
 
   describe("stack trace parsing", () => {
@@ -161,6 +174,54 @@ describe("captureException", () => {
       expect(result.frames).toBeDefined();
       expect(result.frames!.length).toBeLessThanOrEqual(50);
     });
+
+    it("should capture context_line for in_app frames", () => {
+      // This test throws a real error, so context_line should be captured
+      const error = new Error("Test error");
+      const result = captureException(error);
+
+      expect(result.frames).toBeDefined();
+      const inAppFrames = result.frames!.filter((frame) => frame.in_app);
+      expect(inAppFrames.length).toBeGreaterThan(0);
+
+      // At least one in_app frame should have context_line
+      const hasContextLine = inAppFrames.some(
+        (frame) => frame.context_line !== undefined,
+      );
+      expect(hasContextLine).toBe(true);
+    });
+
+    it("should NOT capture context_line for library code (in_app: false)", () => {
+      // Create a mock stack trace with node_modules
+      const error = new Error("Test");
+      error.stack = `Error: Test
+    at libFunction (/app/node_modules/some-lib/index.js:42:10)
+    at internal (node:internal/process:123:45)`;
+
+      const result = captureException(error);
+
+      expect(result.frames).toBeDefined();
+      // All frames should be library code and should NOT have context_line
+      result.frames!.forEach((frame) => {
+        expect(frame.in_app).toBe(false);
+        expect(frame.context_line).toBeUndefined();
+      });
+    });
+
+    it("should handle missing files gracefully when extracting context_line", () => {
+      // Create a mock stack trace with a non-existent file
+      const error = new Error("Test");
+      error.stack = `Error: Test
+    at testFunction (/nonexistent/file/path.ts:10:5)`;
+
+      const result = captureException(error);
+
+      expect(result.frames).toBeDefined();
+      expect(result.frames!.length).toBe(1);
+      // Frame should be in_app but context_line should be undefined (file not found)
+      expect(result.frames![0].in_app).toBe(true);
+      expect(result.frames![0].context_line).toBeUndefined();
+    });
   });
 
   describe("Error.cause chain", () => {

src/types.ts

@@ -179,6 +179,7 @@ export interface StackFrame {
   colno?: number;
   in_app: boolean;
   abs_path?: string;
+  context_line?: string; // The line of code where the error occurred
 }
 
 export interface ChainedErrorData {
@@ -194,4 +195,5 @@ export interface ErrorData {
   stack?: string; // Full stack trace string
   frames?: StackFrame[]; // Parsed stack frames
   chained_errors?: ChainedErrorData[];
+  platform?: string; // Platform identifier (e.g., "javascript", "node")
 }