feat: add NatsHeaderParser for MIME header parsing

2026-02-23 00:33:24 -05:00
parent 7cf6bb866e
commit e87d4c00d9
2 changed files with 152 additions and 0 deletions
--- a/src/NATS.Server/Protocol/NatsHeaderParser.cs
+++ b/src/NATS.Server/Protocol/NatsHeaderParser.cs
@@ -0,0 +1,101 @@
+using System.Text;
+
+namespace NATS.Server.Protocol;
+
+public readonly struct NatsHeaders
+{
+    public int Status { get; init; }
+    public string Description { get; init; }
+    public Dictionary<string, string[]> Headers { get; init; }
+
+    public static readonly NatsHeaders Invalid = new() { Status = -1, Description = string.Empty, Headers = new() };
+}
+
+public static class NatsHeaderParser
+{
+    private static readonly byte[] CrLf = "\r\n"u8.ToArray();
+    private static readonly byte[] Prefix = "NATS/1.0"u8.ToArray();
+
+    public static NatsHeaders Parse(ReadOnlySpan<byte> data)
+    {
+        if (data.Length < Prefix.Length)
+            return NatsHeaders.Invalid;
+
+        if (!data[..Prefix.Length].SequenceEqual(Prefix))
+            return NatsHeaders.Invalid;
+
+        int pos = Prefix.Length;
+        int status = 0;
+        string description = string.Empty;
+
+        // Parse status line: NATS/1.0[ status[ description]]\r\n
+        int lineEnd = data[pos..].IndexOf(CrLf);
+        if (lineEnd < 0)
+            return NatsHeaders.Invalid;
+
+        var statusLine = data[pos..(pos + lineEnd)];
+        pos += lineEnd + 2; // skip \r\n
+
+        if (statusLine.Length > 0)
+        {
+            int si = 0;
+            while (si < statusLine.Length && statusLine[si] == (byte)' ')
+                si++;
+
+            int numStart = si;
+            while (si < statusLine.Length && statusLine[si] >= (byte)'0' && statusLine[si] <= (byte)'9')
+                si++;
+
+            if (si > numStart)
+            {
+                status = int.Parse(Encoding.ASCII.GetString(statusLine[numStart..si]));
+
+                while (si < statusLine.Length && statusLine[si] == (byte)' ')
+                    si++;
+                if (si < statusLine.Length)
+                    description = Encoding.ASCII.GetString(statusLine[si..]);
+            }
+        }
+
+        // Parse key-value headers until empty line
+        var headers = new Dictionary<string, List<string>>(StringComparer.OrdinalIgnoreCase);
+        while (pos < data.Length)
+        {
+            var remaining = data[pos..];
+            if (remaining.Length >= 2 && remaining[0] == (byte)'\r' && remaining[1] == (byte)'\n')
+                break;
+
+            lineEnd = remaining.IndexOf(CrLf);
+            if (lineEnd < 0)
+                break;
+
+            var headerLine = remaining[..lineEnd];
+            pos += lineEnd + 2;
+
+            int colon = headerLine.IndexOf((byte)':');
+            if (colon < 0)
+                continue;
+
+            var key = Encoding.ASCII.GetString(headerLine[..colon]).Trim();
+            var value = Encoding.ASCII.GetString(headerLine[(colon + 1)..]).Trim();
+
+            if (!headers.TryGetValue(key, out var values))
+            {
+                values = [];
+                headers[key] = values;
+            }
+            values.Add(value);
+        }
+
+        var result = new Dictionary<string, string[]>(headers.Count, StringComparer.OrdinalIgnoreCase);
+        foreach (var (k, v) in headers)
+            result[k] = v.ToArray();
+
+        return new NatsHeaders
+        {
+            Status = status,
+            Description = description,
+            Headers = result,
+        };
+    }
+}