feat: Add automatic retry with exponential backoff and circuit breaker (#180)

* feat: Add automatic retry with exponential backoff and circuit breaker

Implements intelligent retry logic for improved reliability when the DeepSource API
experiences transient failures. This feature ensures high availability without user
intervention during API instability, rate limit spikes, or temporary network issues.

Key features:
- Exponential backoff with jitter to prevent thundering herd
- Per-endpoint circuit breaker pattern to prevent cascade failures
- Retry budget management to limit resource consumption
- Respect for Retry-After headers from the API
- Automatic handling of transient failures (network, 502, 503, 504)
- Rate-limited requests (429) are automatically retried

Configuration via environment variables:
- RETRY_MAX_ATTEMPTS (default: 3)
- RETRY_BASE_DELAY_MS (default: 1000ms)
- RETRY_MAX_DELAY_MS (default: 30000ms)
- RETRY_BUDGET_PER_MINUTE (default: 10)
- CIRCUIT_BREAKER_THRESHOLD (default: 5)
- CIRCUIT_BREAKER_TIMEOUT_MS (default: 30000ms)

Safety features:
- Only retries idempotent operations (queries/GET requests)
- Never retries mutations (update operations)
- Transparent to MCP clients - no user-visible errors during transient failures

Closes #153

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Co-Authored-By: Claude <[email protected]>

* fix: resolve DeepSource code quality issues

- Remove unused beforeEach import from test file
- Replace non-null assertions with proper error handling
- Fix lexical declaration scoping in switch statements
- Update test expectations to match corrected behavior
- Remove unused @playwright/test dev dependency

Fixes issues identified in PR #180 by DeepSource:
- JS-0356: Unused variables (1 major issue)
- JS-0339: Non-null assertions (2 major issues)
- JS-0054: Lexical declarations in case clauses (3 minor issues)

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

* fix: use ESLint disable comment for non-null assertions

The non-null assertions are safe because we just set the value in the Map
immediately before retrieving it. Using ESLint disable comments instead
of runtime checks avoids adding uncovered branches that would fail
coverage thresholds.

* fix: properly handle non-null assertions without suppression

Refactored getBreaker and getBudget methods to avoid non-null assertions
entirely by storing the created instance in a variable before setting it
in the Map. This eliminates the DeepSource JS-0339 issue while maintaining
the required test coverage thresholds.

* fix: resolve unhandled promise rejection in retry executor test

Fixed the test case 'should throw error when all retries fail' to properly
handle the promise rejection, preventing unhandled rejection warnings and
test failures in CI.

* fix: resolve remaining deepsource code quality issues

- JS-0105: Make isAxiosError method static as it doesn't use 'this'
- JS-0047: Add default cases to switch statements in recordSuccess and recordFailure
- JS-0045: Add explicit return statement in extractRetryAfter for consistency

All DeepSource issues have been resolved.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

* fix: resolve last deepsource issue js-0045

Remove async keyword from sleep function and ensure all code paths
return a Promise consistently.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

* Update src/utils/retry/retry-budget.ts

Co-authored-by: Copilot <[email protected]>

* Update src/utils/retry/circuit-breaker.ts

Co-authored-by: Copilot <[email protected]>

* test: improve test coverage for retry modules

- Add tests for circuit breaker default case handling (99.53% coverage)
- Add comprehensive tests for RetryBudget and RetryBudgetManager (100% coverage)
- Test getAllStats, resetAll, and clear methods
- Overall retry module coverage improved to 97.26%

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

* fix: add undefined check and deepsource skip comments

- Add undefined check when accessing retryTimestamps array element
- Add DeepSource skip comments for intentional any usage in tests
- Fix formatting in circuit-breaker.ts

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

---------

Co-authored-by: Claude <[email protected]>
Co-authored-by: Copilot <[email protected]>

Author: 3 people

.changeset/automatic-retry-circuit-breaker.md

@@ -0,0 +1,29 @@
+---
+'deepsource-mcp-server': minor
+---
+
+Add automatic retry with exponential backoff and circuit breaker
+
+Implements intelligent retry logic with the following features:
+
+- Exponential backoff with jitter to prevent thundering herd
+- Circuit breaker pattern per endpoint to prevent cascade failures
+- Retry budget management to limit resource consumption
+- Respect for Retry-After headers from the API
+- Automatic handling of transient failures (network, 502, 503, 504)
+- Rate-limited requests (429) are automatically retried with appropriate delays
+
+Configuration via environment variables:
+
+- `RETRY_MAX_ATTEMPTS`: Maximum retry attempts (default: 3)
+- `RETRY_BASE_DELAY_MS`: Base delay for exponential backoff (default: 1000ms)
+- `RETRY_MAX_DELAY_MS`: Maximum delay between retries (default: 30000ms)
+- `RETRY_BUDGET_PER_MINUTE`: Max retries per minute (default: 10)
+- `CIRCUIT_BREAKER_THRESHOLD`: Failures before opening circuit (default: 5)
+- `CIRCUIT_BREAKER_TIMEOUT_MS`: Recovery timeout (default: 30000ms)
+
+Safety features:
+
+- Only retries idempotent operations (queries/GET requests)
+- Never retries mutations (update operations)
+- Transparent to MCP clients - no user-visible errors during transient failures

.changeset/fix-deepsource-issues.md

@@ -0,0 +1,14 @@
+---
+'deepsource-mcp-server': patch
+---
+
+Fix all DeepSource code quality issues
+
+- JS-0356: Remove unused import in exponential-backoff test file
+- JS-0339: Replace non-null assertions with proper null checks and error handling in circuit-breaker and retry-budget modules
+- JS-0054: Fix lexical declaration scoping in switch case statements by adding block scope braces
+- JS-0105: Make isAxiosError method static in base-client.ts since it doesn't use 'this'
+- JS-0047: Add default cases to switch statements in recordSuccess and recordFailure methods
+- JS-0045: Add explicit return statement in extractRetryAfter arrow function for consistency
+- Update test expectations to match corrected circuit breaker behavior
+- Fix unhandled promise rejection in retry-executor test

.env.example

@@ -0,0 +1,28 @@
+# DeepSource MCP Server Environment Variables
+
+# Required: Your DeepSource API key for authentication
+DEEPSOURCE_API_KEY=your-deepsource-api-key
+
+# Optional: Logging configuration
+LOG_FILE=/tmp/deepsource-mcp.log
+LOG_LEVEL=INFO
+
+# Optional: Retry configuration (all have sensible defaults)
+# Maximum number of retry attempts for failed requests
+RETRY_MAX_ATTEMPTS=3
+
+# Base delay in milliseconds for exponential backoff
+RETRY_BASE_DELAY_MS=1000
+
+# Maximum delay in milliseconds between retries
+RETRY_MAX_DELAY_MS=30000
+
+# Maximum retries allowed per minute across all operations
+RETRY_BUDGET_PER_MINUTE=10
+
+# Optional: Circuit breaker configuration
+# Number of failures before circuit breaker opens
+CIRCUIT_BREAKER_THRESHOLD=5
+
+# Time in milliseconds before circuit breaker attempts recovery
+CIRCUIT_BREAKER_TIMEOUT_MS=30000

README.md

@@ -89,7 +89,13 @@ The simplest way to use the DeepSource MCP Server:
       "env": {
         "DEEPSOURCE_API_KEY": "your-deepsource-api-key",
         "LOG_FILE": "/tmp/deepsource-mcp.log",
-        "LOG_LEVEL": "INFO"
+        "LOG_LEVEL": "INFO",
+        "RETRY_MAX_ATTEMPTS": "3",
+        "RETRY_BASE_DELAY_MS": "1000",
+        "RETRY_MAX_DELAY_MS": "30000",
+        "RETRY_BUDGET_PER_MINUTE": "10",
+        "CIRCUIT_BREAKER_THRESHOLD": "5",
+        "CIRCUIT_BREAKER_TIMEOUT_MS": "30000"
       }
     }
   }
@@ -149,16 +155,28 @@ For development or customization:
 
 ### Environment Variables
 
-| Variable             | Required | Default | Description                                         |
-| -------------------- | -------- | ------- | --------------------------------------------------- |
-| `DEEPSOURCE_API_KEY` | Yes      | -       | Your DeepSource API key for authentication          |
-| `LOG_FILE`           | No       | -       | Path to log file. If not set, no logs are written   |
-| `LOG_LEVEL`          | No       | `DEBUG` | Minimum log level: `DEBUG`, `INFO`, `WARN`, `ERROR` |
+| Variable                     | Required | Default | Description                                                   |
+| ---------------------------- | -------- | ------- | ------------------------------------------------------------- |
+| `DEEPSOURCE_API_KEY`         | Yes      | -       | Your DeepSource API key for authentication                    |
+| `LOG_FILE`                   | No       | -       | Path to log file. If not set, no logs are written             |
+| `LOG_LEVEL`                  | No       | `DEBUG` | Minimum log level: `DEBUG`, `INFO`, `WARN`, `ERROR`           |
+| `RETRY_MAX_ATTEMPTS`         | No       | `3`     | Maximum number of retry attempts for failed requests          |
+| `RETRY_BASE_DELAY_MS`        | No       | `1000`  | Base delay in milliseconds for exponential backoff            |
+| `RETRY_MAX_DELAY_MS`         | No       | `30000` | Maximum delay in milliseconds between retries                 |
+| `RETRY_BUDGET_PER_MINUTE`    | No       | `10`    | Maximum retries allowed per minute across all operations      |
+| `CIRCUIT_BREAKER_THRESHOLD`  | No       | `5`     | Number of failures before circuit breaker opens               |
+| `CIRCUIT_BREAKER_TIMEOUT_MS` | No       | `30000` | Time in milliseconds before circuit breaker attempts recovery |
 
 ### Performance Considerations
 
 - **Pagination**: Use appropriate page sizes (10-50 items) to balance response time and data completeness
-- **Rate Limits**: DeepSource API has rate limits. The server implements automatic retry with exponential backoff
+- **Automatic Retry**: The server implements intelligent retry logic with:
+  - Exponential backoff with jitter to prevent thundering herd
+  - Circuit breaker pattern to prevent cascade failures
+  - Retry budget to limit resource consumption
+  - Respect for Retry-After headers from the API
+- **Rate Limits**: Rate-limited requests (429) are automatically retried with appropriate delays
+- **Fault Tolerance**: Transient failures (network, 502, 503, 504) are handled gracefully
 - **Caching**: Results are not cached. Consider implementing caching for frequently accessed data
 
 ## Available Tools

src/__tests__/error-handlers.test.ts

@@ -380,12 +380,19 @@ describe('Error Handlers', () => {
     });
 
     it('should handle 500+ errors', () => {
-      const serverErrors = [500, 502, 503, 504, 520].map((status) => createMockAxiosError(status));
+      const serverErrors = [
+        { status: 500, expectedMessage: 'Server error' },
+        { status: 502, expectedMessage: 'Bad Gateway' },
+        { status: 503, expectedMessage: 'Service Unavailable' },
+        { status: 504, expectedMessage: 'Gateway Timeout' },
+        { status: 520, expectedMessage: 'Server error' },
+      ];
 
-      for (const error of serverErrors) {
+      for (const { status, expectedMessage } of serverErrors) {
+        const error = createMockAxiosError(status);
         const result = handleHttpStatusError(error);
         expect(result).not.toBeNull();
-        expect(result?.message).toContain('Server error');
+        expect(result?.message).toContain(expectedMessage);
         expect(result?.category).toBe(ErrorCategory.SERVER);
         expect(result?.originalError).toBe(error);
       }