Add in-memory heap storage implementation

- Implemented InMemoryHeapStorage using HashMap with Arc<RwLock>
- Added --in-memory CLI flag to use in-memory storage
- Provides thread-safe, zero-config storage for development and testing
- Added comprehensive unit tests for in-memory storage
- Added IN_MEMORY_STORAGE.md documentation
- Updated main.rs to support in-memory storage option
- InMemory variant added to AnyHeapStorage enum

Benefits:
- Fastest performance (no I/O overhead)
- No external dependencies
- Useful for testing, development, and ephemeral workloads
- Rich API with utility methods (len, keys, clear, contains_key, remove)

Limitations:
- Data lost on process termination
- Not suitable for production with persistent data needs
- Memory bounded by available RAM

Author: GitHub Actions

IN_MEMORY_STORAGE.md

@@ -0,0 +1,162 @@
+# In-Memory Heap Storage
+
+## Overview
+
+This repository now includes an in-memory heap storage implementation that stores V8 heap snapshots in RAM rather than persisting them to disk or cloud storage. This is useful for:
+
+- **Testing and Development**: Fast iteration without filesystem I/O overhead
+- **Temporary Sessions**: Sessions that don't require persistence beyond process lifetime
+- **Performance**: Faster read/write operations compared to disk or S3
+- **Simplicity**: No external dependencies or configuration required
+
+## Implementation Details
+
+### Architecture
+
+The `InMemoryHeapStorage` struct uses:
+- `HashMap<String, Vec<u8>>` to store heap snapshots keyed by heap name
+- `Arc<RwLock<...>>` for thread-safe concurrent access
+- Tokio's async RwLock for non-blocking operations
+
+### Features
+
+- **Thread-safe**: Multiple concurrent readers with exclusive writer access
+- **Clone-able**: Shares the same underlying storage across clones
+- **Zero-configuration**: Works out of the box with no setup
+- **Rich API**: Additional utility methods beyond the basic `put`/`get` interface
+
+### API
+
+Basic HeapStorage trait methods:
+- `put(name: &str, data: &[u8]) -> Result<(), String>` - Store heap snapshot
+- `get(name: &str) -> Result<Vec<u8>, String>` - Retrieve heap snapshot
+
+Additional utility methods:
+- `len() -> usize` - Get number of stored items
+- `is_empty() -> bool` - Check if storage is empty
+- `clear()` - Remove all stored data
+- `contains_key(name: &str) -> bool` - Check if key exists
+- `remove(name: &str) -> Option<Vec<u8>>` - Remove and return specific item
+- `keys() -> Vec<String>` - Get all stored keys
+
+## Usage
+
+### Command Line
+
+Run the server with in-memory storage:
+
+```bash
+# With stdio transport (default)
+cargo run --bin server -- --in-memory
+
+# With HTTP transport
+cargo run --bin server -- --in-memory --http-port 8080
+
+# With SSE transport
+cargo run --bin server -- --in-memory --sse-port 8080
+```
+
+### Programmatic Usage
+
+```rust
+use mcp::heap_storage::{InMemoryHeapStorage, HeapStorage};
+
+// Create new in-memory storage
+let storage = InMemoryHeapStorage::new();
+
+// Store data
+storage.put("heap1", b"snapshot data").await.unwrap();
+
+// Retrieve data
+let data = storage.get("heap1").await.unwrap();
+
+// Check existence
+if storage.contains_key("heap1").await {
+    println!("Found heap1");
+}
+
+// Get all keys
+let keys = storage.keys().await;
+println!("Stored heaps: {:?}", keys);
+
+// Clear all data
+storage.clear().await;
+```
+
+### Integration with AnyHeapStorage
+
+```rust
+use mcp::heap_storage::{AnyHeapStorage, InMemoryHeapStorage};
+
+let storage = AnyHeapStorage::InMemory(InMemoryHeapStorage::new());
+
+// Use through the HeapStorage trait
+storage.put("key", b"value").await.unwrap();
+let value = storage.get("key").await.unwrap();
+```
+
+## Comparison with Other Storage Backends
+
+| Feature | In-Memory | File | S3 |
+|---------|-----------|------|-----|
+| Persistence | Process lifetime only | Permanent | Permanent |
+| Performance | Fastest | Fast | Slower (network) |
+| Setup Required | None | Directory path | AWS credentials + bucket |
+| Memory Usage | High (all in RAM) | Low | Low |
+| Distributed Access | No | Shared filesystem only | Yes |
+| Best For | Testing, dev, temp sessions | Single server production | Multi-server production |
+
+## Configuration Options
+
+The in-memory storage conflicts with other storage options:
+- Cannot be used with `--s3-bucket`
+- Cannot be used with `--directory-path`
+- Cannot be used with `--stateless`
+
+## Limitations
+
+1. **No Persistence**: All data is lost when the process terminates
+2. **Memory Bounded**: Limited by available RAM
+3. **Single Process**: Cannot be shared across multiple server instances
+4. **No Backup**: No automatic snapshot or recovery mechanism
+
+## Testing
+
+The implementation includes comprehensive unit tests:
+
+```bash
+# Run all tests
+cargo test -p server
+
+# Run only heap_storage tests
+cargo test -p server heap_storage
+```
+
+Test coverage includes:
+- Basic put/get operations
+- Error handling for missing keys
+- Utility method functionality
+- Clone behavior (shared storage)
+- Integration with AnyHeapStorage enum
+
+## When to Use
+
+**Use in-memory storage when:**
+- Developing and testing locally
+- Running ephemeral workloads
+- Performance is critical and persistence is not
+- You want zero configuration overhead
+
+**Don't use in-memory storage when:**
+- You need data to survive process restarts
+- Running in production with important data
+- Memory is constrained
+- Multiple servers need to share state
+
+## Future Enhancements
+
+Possible improvements:
+- Memory usage limits with LRU eviction
+- Periodic snapshots to disk
+- Memory metrics and monitoring
+- TTL (time-to-live) for entries

server/src/main.rs

@@ -13,23 +13,27 @@ use tokio_util::sync::CancellationToken;
 
 mod mcp;
 use mcp::{StatelessService, StatefulService, initialize_v8};
-use mcp::heap_storage::{AnyHeapStorage, S3HeapStorage, FileHeapStorage};
+use mcp::heap_storage::{AnyHeapStorage, S3HeapStorage, FileHeapStorage, InMemoryHeapStorage};
 
 /// Command line arguments for configuring heap storage
 #[derive(Parser, Debug)]
 #[command(author, version, about, long_about = None)]
 struct Cli {
 
     /// S3 bucket name (required if --use-s3)
-    #[arg(long, conflicts_with_all = ["directory_path", "stateless"])]
+    #[arg(long, conflicts_with_all = ["directory_path", "stateless", "in_memory"])]
     s3_bucket: Option<String>,
 
     /// Directory path for filesystem storage (required if --use-filesystem)
-    #[arg(long, conflicts_with_all = ["s3_bucket", "stateless"])]
+    #[arg(long, conflicts_with_all = ["s3_bucket", "stateless", "in_memory"])]
     directory_path: Option<String>,
 
+    /// Use in-memory storage (heap state persists only during process lifetime)
+    #[arg(long, conflicts_with_all = ["s3_bucket", "directory_path", "stateless"])]
+    in_memory: bool,
+
     /// Run in stateless mode - no heap snapshots are saved or loaded
-    #[arg(long, conflicts_with_all = ["s3_bucket", "directory_path"])]
+    #[arg(long, conflicts_with_all = ["s3_bucket", "directory_path", "in_memory"])]
     stateless: bool,
 
     /// HTTP port to listen on (if not specified, uses stdio transport)
@@ -77,12 +81,18 @@ async fn main() -> Result<()> {
         }
     } else {
         // Stateful mode - with heap persistence
-        let heap_storage = if let Some(bucket) = cli.s3_bucket {
+        let heap_storage = if cli.in_memory {
+            tracing::info!("Using in-memory heap storage");
+            AnyHeapStorage::InMemory(InMemoryHeapStorage::new())
+        } else if let Some(bucket) = cli.s3_bucket {
+            tracing::info!("Using S3 heap storage with bucket: {}", bucket);
             AnyHeapStorage::S3(S3HeapStorage::new(bucket).await)
         } else if let Some(dir) = cli.directory_path {
+            tracing::info!("Using file heap storage with directory: {}", dir);
             AnyHeapStorage::File(FileHeapStorage::new(dir))
         } else {
             // default to file /tmp/mcp-v8-heaps
+            tracing::info!("Using default file heap storage: /tmp/mcp-v8-heaps");
             AnyHeapStorage::File(FileHeapStorage::new("/tmp/mcp-v8-heaps"))
         };