Add HTTP/2 support with h2c upgrade capability

examples/http2/.gitignore

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+*.beam
+*.ez
+/build
+erl_crash.dump
+*.crt
+*.key

examples/http2/README.md

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+# HTTP/2 Comprehensive Example for Mist
+
+This example demonstrates all HTTP/2 capabilities supported by the Mist web server, including **full H2C (HTTP/2 cleartext) upgrade support**.
+
+## Features Demonstrated
+
+### Core HTTP/2 Features
+- ✅ **H2C Upgrade**: Complete HTTP/1.1 → HTTP/2 upgrade mechanism
+- ✅ **Multiplexing**: Multiple requests/responses over a single connection
+- ✅ **Header Compression (HPACK)**: Efficient header encoding
+- ✅ **Flow Control**: Window-based flow control for streams
+- ✅ **Binary Framing**: Binary protocol instead of text-based HTTP/1.1
+- ✅ **Stream Prioritization**: Request prioritization (client-dependent)
+
+### Configuration Options
+- Custom max concurrent streams
+- Configurable initial window size
+- Adjustable max frame size
+- Optional max header list size
+
+## Running the Example
+
+### 1. Install Dependencies
+```bash
+cd examples/http2
+gleam deps download
+gleam build
+```
+
+### 2. Start the Server
+```bash
+gleam run
+```
+
+This starts two servers:
+- **HTTP/2 (h2c)** on http://localhost:9080 - HTTP/2 over cleartext with H2C upgrade
+- **HTTP/2 (TLS)** on https://localhost:8443 - HTTP/2 over TLS (requires certificates)
+
+### 3. Generate TLS Certificates (for HTTPS)
+```bash
+./generate_certs.sh
+```
+
+## Available Endpoints
+
+| Method | Path | Description | HTTP/2 Feature Tested |
+|--------|------|-------------|----------------------|
+| GET | `/` | Server info and capabilities | Basic connection |
+| GET/POST | `/echo` | Echo request details | Header inspection |
+| GET | `/stream` | Streaming response | Chunked data |
+| GET | `/large` | 100KB response | Flow control |
+| GET | `/headers` | Response with 50+ headers | HPACK compression |
+| GET | `/delay/{seconds}` | Delayed response (max 5s) | Multiplexing |
+| GET | `/status/{code}` | Return specific status | Status handling |
+| GET/POST | `/json` | JSON response/echo | Content types |
+| GET | `/binary` | Binary data download | Binary frames |
+| GET | `/metrics` | Server metrics | Monitoring |
+
+## Testing
+
+### Automated Test Suite
+
+**Unit Tests** (Gleam):
+```bash
+gleam test
+```
+
+**H2C Upgrade Integration Tests**:
+```bash
+./test_h2c_upgrade.sh
+```
+
+**Basic HTTP/2 Features Tests**:
+```bash
+./test_working_features.sh
+```
+
+### Manual Testing Examples
+
+#### 1. Basic HTTP/2 Request
+```bash
+# H2C upgrade (HTTP/1.1 → HTTP/2)
+curl --http2 -v http://localhost:9080/
+
+# Direct HTTP/2 (prior knowledge)
+curl --http2-prior-knowledge -v http://localhost:9080/
+
+# HTTP/2 over TLS (accept self-signed cert)
+curl --http2 -k -v https://localhost:8443/
+```
+
+#### 2. Test Multiplexing
+```bash
+# Send 5 parallel requests with different delays
+# Should complete in ~3 seconds (not 9 seconds sequentially)
+curl --http2-prior-knowledge --parallel --parallel-max 5 \
+  http://localhost:9080/delay/1 \
+  http://localhost:9080/delay/2 \
+  http://localhost:9080/delay/3 \
+  http://localhost:9080/delay/1 \
+  http://localhost:9080/delay/2
+```
+
+#### 3. Test Flow Control
+```bash
+# Download large response
+curl --http2-prior-knowledge -v http://localhost:9080/large > /dev/null
+
+# Watch for flow control frames in verbose output
+```
+
+#### 4. Test HPACK Compression
+```bash
+# Get response with many headers
+curl --http2-prior-knowledge -I http://localhost:9080/headers
+
+# Headers are compressed using HPACK
+```
+
+#### 5. Test Different Content Types
+```bash
+# JSON response
+curl --http2-prior-knowledge http://localhost:9080/json | jq .
+
+# Binary data
+curl --http2-prior-knowledge --output data.bin http://localhost:9080/binary
+
+# Server-sent events style
+curl --http2-prior-knowledge http://localhost:9080/stream
+```
+
+#### 6. POST Request with Data
+```bash
+# Echo POST data
+curl --http2-prior-knowledge -X POST -d '{"test": "data"}' \
+  -H "Content-Type: application/json" \
+  http://localhost:9080/echo
+```
+
+## Advanced Testing with nghttp2
+
+If you have nghttp2 tools installed:
+
+### Installation
+```bash
+# macOS
+brew install nghttp2
+
+# Ubuntu/Debian
+apt-get install nghttp2-client
+
+# From source
+git clone https://github.com/nghttp2/nghttp2.git
+cd nghttp2
+./configure && make && sudo make install
+```
+
+### nghttp2 Testing Commands
+
+#### Detailed Protocol Information
+```bash
+# See detailed HTTP/2 frames
+nghttp -v http://localhost:9080/
+
+# With custom settings
+nghttp -v --window-bits=20 --max-concurrent-streams=100 \
+  http://localhost:9080/
+```
+
+#### Performance Testing with h2load
+```bash
+# Basic load test
+h2load -n 1000 -c 10 -m 100 http://localhost:9080/
+
+# Test with multiple URIs
+h2load -n 1000 -c 10 -m 50 \
+  http://localhost:9080/ \
+  http://localhost:9080/json \
+  http://localhost:9080/metrics
+
+# Extended test with timing
+h2load -n 10000 -c 100 -m 10 --duration=30 \
+  http://localhost:9080/
+```
+
+## Browser Testing
+
+Modern browsers automatically negotiate HTTP/2 when available.
+
+1. Open Chrome/Firefox/Safari
+2. Open Developer Tools (F12)
+3. Go to Network tab
+4. Visit http://localhost:9080/
+5. Check the "Protocol" column - should show "h2" for HTTP/2
+
+### Chrome Specific
+- chrome://net-internals/#http2 - View active HTTP/2 sessions
+- chrome://net-internals/#events - See detailed protocol events
+
+### Firefox Specific
+- about:networking#http2 - View HTTP/2 connections
+
+## Configuration Guide
+
+### Server Configuration
+```gleam
+handler
+|> mist.new()
+|> mist.with_http2()  // Enable with defaults
+|> mist.http2_max_concurrent_streams(1000)  // Max parallel streams
+|> mist.http2_initial_window_size(1_048_576)  // 1MB flow control window
+|> mist.http2_max_frame_size(32_768)  // 32KB max frame
+|> mist.http2_max_header_list_size(16_384)  // 16KB header limit
+|> mist.start
+```
+
+### Configuration Parameters
+
+| Parameter | Default | Description | Recommendation |
+|-----------|---------|-------------|----------------|
+| max_concurrent_streams | 100 | Max parallel requests | 100-1000 for typical servers |
+| initial_window_size | 65,535 | Flow control window (bytes) | 65KB-2MB depending on bandwidth |
+| max_frame_size | 16,384 | Max HTTP/2 frame size | 16KB-1MB (16KB is standard) |
+| max_header_list_size | None | Max header size | 8KB-16KB for most applications |
+
+## Monitoring and Debugging
+
+### Server Metrics Endpoint
+```bash
+curl --http2-prior-knowledge http://localhost:9080/metrics | jq .
+```
+
+### Logging
+The server logs HTTP/2 events. Set log level in your application:
+```gleam
+logging.configure()
+logging.set_level(logging.Debug)
+```
+
+### Common Issues
+
+1. **Connection not upgrading to HTTP/2**
+   - Ensure client supports HTTP/2
+   - Check with `curl --http2 -v` for protocol negotiation
+   - For h2c (cleartext), client must send upgrade header
+
+2. **TLS certificate errors**
+   - Generate certificates with `./generate_certs.sh`
+   - Use `-k` flag with curl to accept self-signed certs
+   - For production, use proper certificates
+
+3. **Performance issues**
+   - Adjust window sizes for your bandwidth
+   - Increase max_concurrent_streams for high load
+   - Monitor with h2load for bottlenecks
+
+## HTTP/2 vs HTTP/1.1 Comparison
+
+| Feature | HTTP/1.1 | HTTP/2 |
+|---------|----------|---------|
+| Protocol | Text | Binary |
+| Multiplexing | No (uses pipelining) | Yes |
+| Header Compression | No | Yes (HPACK) |
+| Server Push | No | Yes (disabled in this example) |
+| Flow Control | TCP only | Stream + Connection level |
+| Connections Needed | Multiple | Single |
+
+## Further Resources
+
+- [HTTP/2 RFC 7540](https://tools.ietf.org/html/rfc7540)
+- [HPACK RFC 7541](https://tools.ietf.org/html/rfc7541)
+- [nghttp2 Documentation](https://nghttp2.org/documentation/)
+- [Chrome HTTP/2 Debugging](https://developers.google.com/web/fundamentals/performance/http2)
+- [Mist Documentation](https://github.com/rawhat/mist)

examples/http2/generate_certs.sh

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+#!/bin/bash
+
+# Generate self-signed certificates for testing HTTP/2 over TLS
+
+echo "Generating self-signed certificates for localhost..."
+
+# Generate private key
+openssl genrsa -out localhost.key 4096
+
+# Generate certificate signing request
+openssl req -new -key localhost.key -out localhost.csr -subj "/C=US/ST=Test/L=Test/O=Test/CN=localhost"
+
+# Generate self-signed certificate
+openssl x509 -req -days 365 -in localhost.csr -signkey localhost.key -out localhost.crt
+
+# Clean up CSR
+rm localhost.csr
+
+echo "Certificates generated:"
+echo "  - localhost.key (private key)"
+echo "  - localhost.crt (certificate)"
+echo ""
+echo "These are self-signed certificates for testing only."
+echo "In production, use proper certificates from a trusted CA."

examples/http2/gleam.toml

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+name = "http2"
+version = "1.0.0"
+description = "Comprehensive HTTP/2 example for Mist"
+target = "erlang"
+
+[dependencies]
+gleam_stdlib = ">= 0.44.0 and < 2.0.0"
+mist = { path = "../.." }
+gleam_http = ">= 4.0.0 and < 5.0.0"
+gleam_erlang = ">= 1.0.0 and < 2.0.0"
+gleam_otp = ">= 1.0.0 and < 2.0.0"
+gleam_json = ">= 3.0.0 and < 4.0.0"
+
+[dev-dependencies]
+gleeunit = ">= 1.0.0 and < 2.0.0"

examples/http2/manifest.toml

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+# This file was generated by Gleam
+# You typically do not need to edit this file
+
+packages = [
+  { name = "exception", version = "2.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "exception", source = "hex", outer_checksum = "329D269D5C2A314F7364BD2711372B6F2C58FA6F39981572E5CA68624D291F8C" },
+  { name = "gleam_crypto", version = "1.5.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_crypto", source = "hex", outer_checksum = "50774BAFFF1144E7872814C566C5D653D83A3EBF23ACC3156B757A1B6819086E" },
+  { name = "gleam_erlang", version = "1.3.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_erlang", source = "hex", outer_checksum = "1124AD3AA21143E5AF0FC5CF3D9529F6DB8CA03E43A55711B60B6B7B3874375C" },
+  { name = "gleam_http", version = "4.1.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_http", source = "hex", outer_checksum = "DD0271B32C356FB684EC7E9F48B1E835D0480168848581F68983C0CC371405D4" },
+  { name = "gleam_json", version = "3.0.2", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_json", source = "hex", outer_checksum = "874FA3C3BB6E22DD2BB111966BD40B3759E9094E05257899A7C08F5DE77EC049" },
+  { name = "gleam_otp", version = "1.1.0", build_tools = ["gleam"], requirements = ["gleam_erlang", "gleam_stdlib"], otp_app = "gleam_otp", source = "hex", outer_checksum = "7987CBEBC8060B88F14575DEF546253F3116EBE2A5DA6FD82F38243FCE97C54B" },
+  { name = "gleam_stdlib", version = "0.62.1", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "0080706D3A5A9A36C40C68481D1D231D243AF602E6D2A2BE67BA8F8F4DFF45EC" },
+  { name = "gleam_yielder", version = "1.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_yielder", source = "hex", outer_checksum = "8E4E4ECFA7982859F430C57F549200C7749823C106759F4A19A78AEA6687717A" },
+  { name = "gleeunit", version = "1.6.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "FDC68A8C492B1E9B429249062CD9BAC9B5538C6FBF584817205D0998C42E1DAC" },
+  { name = "glisten", version = "8.0.1", build_tools = ["gleam"], requirements = ["gleam_erlang", "gleam_otp", "gleam_stdlib", "logging", "telemetry"], otp_app = "glisten", source = "hex", outer_checksum = "534BB27C71FB9E506345A767C0D76B17A9E9199934340C975DC003C710E3692D" },
+  { name = "gramps", version = "6.0.0", build_tools = ["gleam"], requirements = ["gleam_crypto", "gleam_erlang", "gleam_http", "gleam_stdlib"], otp_app = "gramps", source = "hex", outer_checksum = "8B7195978FBFD30B43DF791A8A272041B81E45D245314D7A41FC57237AA882A0" },
+  { name = "hpack_erl", version = "0.3.0", build_tools = ["rebar3"], requirements = [], otp_app = "hpack", source = "hex", outer_checksum = "D6137D7079169D8C485C6962DFE261AF5B9EF60FBC557344511C1E65E3D95FB0" },
+  { name = "logging", version = "1.3.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "logging", source = "hex", outer_checksum = "1098FBF10B54B44C2C7FDF0B01C1253CAFACDACABEFB4B0D027803246753E06D" },
+  { name = "mist", version = "5.0.3", build_tools = ["gleam"], requirements = ["exception", "gleam_erlang", "gleam_http", "gleam_json", "gleam_otp", "gleam_stdlib", "gleam_yielder", "glisten", "gramps", "hpack_erl", "logging"], source = "local", path = "../.." },
+  { name = "telemetry", version = "1.3.0", build_tools = ["rebar3"], requirements = [], otp_app = "telemetry", source = "hex", outer_checksum = "7015FC8919DBE63764F4B4B87A95B7C0996BD539E0D499BE6EC9D7F3875B79E6" },
+]
+
+[requirements]
+gleam_erlang = { version = ">= 1.0.0 and < 2.0.0" }
+gleam_http = { version = ">= 4.0.0 and < 5.0.0" }
+gleam_json = { version = ">= 3.0.0 and < 4.0.0" }
+gleam_otp = { version = ">= 1.0.0 and < 2.0.0" }
+gleam_stdlib = { version = ">= 0.44.0 and < 2.0.0" }
+gleeunit = { version = ">= 1.0.0 and < 2.0.0" }
+mist = { path = "../.." }