Update Algorithm & Flowchart.md
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## DNS Server Algorithm
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**1. Server Initialization**
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# DNS Server Algorithm & Flowchart
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```rust
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1.1 Load configuration from environment variables
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1.2 Initialize logging system
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1.3 Create SQLite database connection
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1.4 Initialize cache with NS records
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1.5 Start periodic cache cleanup task
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1.6 Bind UDP and TCP sockets on specified port
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```
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This document outlines the algorithm and flowchart for a DNS server implementation compliant with RFC 1035 (DNS) and RFC 4034 (DNSSEC).
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**2. Query Handling Flow**
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---
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## ✅ Server Algorithm
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### 1. Server Initialization
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1. Load configuration from environment variables.
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2. Initialize the logging system.
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3. Create SQLite database connection and initialize schema.
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4. Initialize cache with NS records.
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5. Start periodic cache cleanup task (every 5 minutes).
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6. Bind and listen on UDP and TCP sockets.
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### 2. Query Handling Flow
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#### Upon Receiving a DNS Query:
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1. Validate DNS query packet.
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2. Parse header and extract domain name and query type.
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3. If query type is `DNSKEY` or `DS`, return signed records.
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4. Check DNS cache:
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- If **hit**, build and return response.
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- If **miss**, lookup in database:
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- If found, respond and cache it.
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- If not found:
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- If authoritative, return `NXDOMAIN`.
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- Else, forward to upstream resolvers.
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5. Add DNSSEC signatures if applicable.
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6. Send response to the client.
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### 3. DNSSEC Signing Process
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1. Load DNSSEC key from configured file.
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2. For each relevant record:
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- Generate `RRSIG`.
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- Encode signature (Base64).
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- Calculate key tag and signature expiration.
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3. Add `RRSIG` to the answer section.
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4. Include `DNSKEY` in the authority section if needed.
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### 4. Response Generation Logic
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1. Construct response header:
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- Set QR flag and response code.
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- Include Authoritative Answer (AA) if authoritative.
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2. Attach original question section.
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3. Populate:
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- **Answer** section: with resolved records.
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- **Authority** section: with NS and DS records.
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- **Additional** section: with glue records, DNSKEY if required.
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---
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## 📊 Flowchart
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Below is the visual representation of the DNS query handling logic:
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```
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Start
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│
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▼
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Receive DNS Query
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│
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▼
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Parse Query Header/Question
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│
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▼
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Check Cache for Domain Record
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┌───────┴───────┐
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▼ ▼
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Cache Hit Cache Miss
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│ │
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▼ ▼
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Build Response Query Database
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│
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▼
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Check Authoritative Flag
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┌────────┴────────┐
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▼ ▼
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Record Found Record Not Found
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│ │
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▼ ▼
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Build Response Forward to Resolvers
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│ │
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▼ ▼
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Add DNSSEC ▼
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Signatures Receive Forwarded Response
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│ │
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▼ ▼
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Send Response to Client
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│
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▼
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End
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```
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**3. DNSSEC Signing Process**
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+---------------------+
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| Start DNS Server |
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+---------------------+
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v
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+---------------------+
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| Receive DNS Query |
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+---------------------+
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v
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+---------------------+
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| Parse Header and |
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| Extract Domain & |
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| Query Type |
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+---------------------+
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+---------------------+
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| |
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v v
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+---------------------+ +---------------------+
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| Is Query Type | | Use Cache |
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| DNSKEY/DS? | | |
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+---------------------+ +---------------------+
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| |
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Yes | |
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v v
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+---------------------+ +---------------------+
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| Return | | Lookup in SQLite DB |
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| DNSSEC Record | | |
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+---------------------+ +---------------------+
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v
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+---------------------+
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| Is Authoritative |
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| Zone? |
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+---------------------+
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No |
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v
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+---------------------+
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| Return NXDOMAIN |
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+---------------------+
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v
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+---------------------+
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| Add GSSEC |
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+---------------------+
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v
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+---------------------+
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| Send Response |
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+---------------------+
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v
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+---------------------+
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| End |
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+---------------------+
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```rust
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3.1 Load DNSSEC key from configured file
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3.2 For each relevant DNS record:
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3.2.1 Generate RRSIG record
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3.2.2 Encode signature using Base64
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3.2.3 Calculate key tag and signature expiration
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3.3 Add RRSIG records to DNS response
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3.4 Include DNSKEY records in authority section
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```
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**4. Response Generation Logic**
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```
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4.1 Create response header with:
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- Original query ID
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- QR flag set to response
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- Authoritative Answer flag
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- Appropriate response code (NOERROR/NXDOMAIN)
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4.2 Add original question section
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4.3 Populate answer section with:
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- Resource records from cache/database
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- TTL values from configuration
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4.4 Add authority section with:
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- NS records
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- DS records for DNSSEC
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4.5 Include additional section with:
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- A records for NS names
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- DNSKEY records when applicable
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```
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## Key Data Flow Components
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## 🧩 Key Components
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| Component | Purpose | Implementation Details |
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| :-- | :-- | :-- |
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| `DnsCache` | Response caching | Mutex-protected HashMap with TTL |
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| `ServerConfig` | Runtime configuration | Environment variables parsing |
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| `rusqlite` | Persistent storage | SQLite database with DNS records |
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| `tokio` | Async I/O handling | UDP/TCP listeners with task spawning |
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| `DNSSEC` | Response signing | RSA-SHA256 with preloaded keys |
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| Component | Purpose | Details |
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|----------------|----------------------------|------------------------------------------|
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| `DnsCache` | DNS Response Cache | Thread-safe HashMap with TTL |
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| `ServerConfig` | Server Configuration | Loaded via environment variables |
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| `rusqlite` | Record Storage | SQLite database backend |
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| `tokio` | Async I/O Runtime | UDP/TCP async handlers and tasks |
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| `DNSSEC` | Secure DNS Signing | RSA-SHA256 with Base64-encoded keys |
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## Error Handling Strategy
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---
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```rust
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- Use custom DnsError enum with thiserror crate
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- Graceful shutdown on SIGINT
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- Automatic cache cleanup every 5 minutes
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- Fallback to forwarding when local resolution fails
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- Comprehensive logging at all stages
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```
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## ⚠️ Error Handling Strategy
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The server implements RFC 1035 (DNS) and RFC 4034 (DNSSEC) specifications with a focus on:
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- Custom `DnsError` enum via `thiserror`
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- Graceful shutdown via `SIGINT`
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- Cache cleanup every 5 minutes
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- Fallback to resolver forwarding
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- Detailed logging at every stage
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1. Async I/O using Tokio runtime
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2. Thread-safe caching with atomic reference counting
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3. Configurable forwarding and fallback mechanisms
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4. DNSSEC signing capability for authoritative responses
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5. SQLite-based record storage with schema versioning
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<div style="text-align: center">⁂</div>
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---
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